ICS 13.220.40  
 
Reference number  
DRS 186 -2: 2023  
© RSB 2023  
  
 RWANDA 
STANDARD  DRS 
186-2  
 
Third  edition  
2023-mm-dd 
 
Fire safety for buildings — Code of 
practice  — 
Part 2: Details of construction  
   
DRS 186 -2: 2023  
©RSB 2023  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2023  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 186 -2: 2023  
iii                ©RSB 2023  - All rights reserved  
 Contents                                                                                                   Page 
Foreword  ................................ ................................ ................................ ................................ ...................  iv 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 Types of Construction  ................................ ................................ ................................ .................  2 
5 Walls  ................................ ................................ ................................ ................................ ..............  3 
6 Columns and beams  ................................ ................................ ................................ ....................  7 
7 Floors and roofs  ................................ ................................ ................................ ...........................  7 
8 Air-conditioning  ................................ ................................ ................................ ..........................  15 
9 Smoke and fire venting  ................................ ................................ ................................ ..............  16 
10 Service ducts  ................................ ................................ ................................ ..............................  17 
11 Basements  ................................ ................................ ................................ ................................ .. 17 
12 Chimneys  ................................ ................................ ................................ ................................ .... 18 
13 Staircases and lifts  ................................ ................................ ................................ .....................  18 
13.1  Staircases  ................................ ................................ ................................ ................................ .... 18 
13.2  Lifts  ................................ ................................ ................................ ................................ ..............  19 
14 Refuge area  ................................ ................................ ................................ ................................ . 20 
15 Refuse chutes  ................................ ................................ ................................ .............................  20 
16 Drainage  ................................ ................................ ................................ ................................ ...... 20 
17 Electrical services  ................................ ................................ ................................ ......................  20 
18 Finishes  ................................ ................................ ................................ ................................ ....... 21 
 DRS 186 -2: 2023  
©RSB 2023  - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by Rwanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adopted 
by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 186-2 was prepared by Technical Committee RSB/TC 28, Fire safety . 
In the preparation of this standard, reference was made to the following standard:  
IS 1641:1988 , Code of practice for Fire Safety of Buildings (General): General Principles of Fire Grading and 
Classification  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This third edition cancels and replaces the second edition (RS  186-2: 2018), clause 4, Table 1  and Table 3  
which have  been technically revised.  
DRS  186 consists of the following parts, under the general title Fire safety for buildings ― Code of practice : 
⎯ Part 1: General principles of fire grading and classification  
⎯ Part 2: Details of Construction  
⎯ Part 3: Fire safety in p ublic buildings  
⎯ Part 4: Selection, installation and maintenance of automatic fire detection and alarm system  
⎯ Part 5: Exit requirements and personal hazar d 
⎯ Committee membership  
The following organiz ations were represented on the Technical Committee on Fire safety  (RSB/TC 28) in the 
preparation of this standard.  
Bank of Kigali (BK)  
City of Kigali  
CrossTech  
Institution  of Engineers Rwanda (IER)  DRS 186 -2: 2023  
v                ©RSB 2023  - All rights reserved  
 Ministry of Infrastructure (MININFRA)  
PRIME Insurance  Ltd 
Rwanda Defence Force (RDF)  
Rwanda Energy Group (REG)  
Rwand a Environment Management Authority (REMA) 
Rwanda Housing Authority (RHA)  
Rwanda National Police (RNP)  
Rwanda Social Security Board (RSSB)  
Sanlam  
Société Rwandaise d’Assurance (SONARWA)  
University of Rwanda - College of Science and Technology  (UR - CST)  
Rwanda Standards Board (RSB) – Secretariat  
 DRS 186 -2: 2023  
1                ©RSB 2023  - All rights reserved  
 Fire safety of buildings — Code of pr actice — Part 2: Details of construction  
1 Scope  
This Draft Rwanda Standard specifies essential requirements for fire safety of buildings with respect to details of 
construction.  
2 Normative references  
The following referenced documents are indispensable for the application of this document. For dated references, only 
the edition cited applies. For undated references, the latest edition of the referenced document (including any 
amendments) applies.  
RS 186 -5, Fire Safety for buildings ― Code of practice ― Part 5: Exit requirements and personal hazards  
3 Terms and definitions  
For the purposes of this standard, the following terms and definitions apply.  
3.1 
Fire Resistance  
ability of an element of building construction, component for structure to fulfil, for a stated period of time, the required 
stability, fire integrity and/or thermal insulation and/or other expected duty in a standard fire resistance test  
3.2 
Fire Separation  
distance in metres measured from any other building on the site, or from other site or from the opposite side of street 
or other public space to the building for the purpose of preventing the spread of fire.  
3.3 
Fire resisting wall  
The wall that provides complete separation of one building from another or part of a building from another part of the 
same building to prevent any communicator of fire or any access or heat transmission to wall itself which may cause 
or assist in the comb ustion of materials of the side opposite to that portion which may be on fire.  
3.4 
venting fire   
©RSB 2023  - All rights reserved                  2 
 The process of inducting heat and smoke from building quickly by such parts that lateral spread of fire and heat is 
checked, firefighting operations are facilitated and minimum fire damage is caused.  
4 Types of Construction  
4.1 The design of any building and the type of materials used in its construction are important factors in making the 
building resistant to a complete burn -out and in preventing the rapid spread of fire, smoke or fumes, which may 
otherwise contribute to the lo ss of lives and property.  
4.2 The types of construction according to fire resistance are classified into four categories as defined in RS 186 -1. 
The fire resistance ratings for various types of construction for structural and non -structural members should be as 
given in Table 1.   
Table 1 — Fire Resistance Ratings of Structural Elements (in Hours)  
Structural Element  Type of Construction  
Type 1  Type 2  Type 3  Type 4  
 
Exterior walls  Fire separation less than 3.7m  Bearing  4 2 2 1 
Non-bearing  2 ½ 1 1 
Fire separation of 3.7 m or More but 
less than 9 m  Bearing  4 2 2 1 
Non-bearing  ½ 1 1 1 
Fire separation of 9 m or more  to be 
cheched  Bearing  4 2 2 1 
Non-bearing  1 1 1 1 
Fire walls  4 2 2 2 
Fire separation assemblies (like File check doors)  4 2 2 2 
Fire enclosures of exit ways, exit -Way hallways, stairways  and ramp  2 2 2 2 
Shaft other than exit way elevator Hoist ways  2 2 2 2 
Exit way access corridors  1 1 1 1 
Vertical separation of tenant spaces  1 1 1 1 
Dwelling unit separation  1 1 1 1 
Non-load bearing partitions  At least half an hour  
Interior hearing walls, bearing  Supporting more than one floor  
Partition, columns, girders, 
trusses (other than roof trusses)  4 2 2 2 
Supporting one and framing floor 
only 3 1½ 1 1 
Supporting a roof only  3 1½ 1 1 
Structural members support walls  3 1½ 1   1 DRS 186 -2: 2023  
3                ©RSB 2023  - All rights reserved  
 Floor construction including walls  3 1½ 1   1 
Roof construction  5 m or less in height to lowest 
member  2 1½ 1 1 
More than 5m but less than 6.7 m 
in height to lowest member  1 1 1 1 
6.7 m or more in height to lowest 
member  0 0 0 0 
4.3 Fire Resistance Ratings of Type 5 wooden frame should be based on fire rated coati ng or cover extends the 
fire resistance rating of structural members at least 1 h . 
4.4 For buildings above 15 m in height non -combustible materials should be used for construction and the internal 
walls of staircases should be of brick work or reinforced concrete or any other material of construction with minimum 
of 2 h rating. The walls for the chimney shall be of Typ e 1 or Type 2 construction depending upon whether the gas 
temperature is above 200 °C or less.  
4.5 When test is done according to relevant approved national or international standard, the fire resistance of an 
element of structure or combination of elements is determined from one of the following three methods:  
a) information as established by research data;  
b) direct application of the results of fire resistance test on an element of structures; and  
c) on the basis for calculating the fire resistance of a structural element; except for columns or walls  
5 Walls  
5.1 The fire ratings of some types of constructions for walls are given in Table 2 to Table 7.  
Table 2 — Masonry walls: Solid (required for resisting fire from one side at a time)  
Nature of Construction and Materials.  Minimum Thickness (mm), Excluding any Finish, for a fire Resistance (Hours) 
of : 
        Load Bearing           Non-Load Bearing  
1           1½          2          3            4       1           1½         2           3           4  
Reinforced a cement concrete  120       140        160       200       240  
(25)b      (25)b      (25)b    (25)b      (25)b  
 
Unreinforced cement concrete  150        175      -            -             -  
Non-fines concrete with:  
a) 13 mm cement/sand or 
gypsum/sand.  
b) 13 mm lightweight aggregate 
gypsum Plaster   
 
150        150       50         150       150  
 
150       150       150        150       150 
Bricks of clay:   
  
©RSB 2023  - All rights reserved                  4 
 a) Without finish.  
b) With 13mm  lightweight 
aggregate  Gypsum plaster  90       100        100       170      170  
90        90           90        100      100  75        90         100         170      170  
75        90          90          90         100  
Bricks of sand lime:  
a) Without finish  
b)  With 13 mm lightweight 
aggregate Gypsum plaster   
90       100         100       190     190  
90         90         90          100     100   
75        90         100         170       170  
75        90          90           90        100  
Blocks of concrete:  
a) Without finish  
b) With 13 mm lightweight 
aggregate Gypsum plaster  
c) With 13 mm cement/sand or 
gypsum/ Sand.   
90        100       100         —       — 
 
90        90         90         100      100   
75         90         100         140       150  
75         75         75            90        100  
 
75          90………90        100       140  
Blocks of lightweight concrete:  
a) Without finish  
b) With 13 mm lightweight 
aggregate Gypsum plaster  
a) c) With 13 mm cement/sand or 
gypsum/ Sand   
90        100        100       140       150  
90          90          90        100       100  
 
  
75          75          75         125        140  
50          63          75          75         75  
 
75         75           75          90         100  
Blocks of aerated concrete:  
a) Without finish  
b) With 13 mm lightweight 
aggregate Gypsum plaster   
90           100      100       140        180  
90           90       100…….100        150   
50          63          63         75         100 
a Walls containing at least 1 percent of vertical reinforcement  
b Minimum thickness of actual cover to reinforcement  
 
Table 3 — Masonry walls: Hollows (required for resisting fire from one side at a time)  
Nature of Construction and 
Materials  Minimum Thickness , Excluding any Finish, for a Fire Resistance (Hours) 
of: 
Load Bearing  Non-Load Bearing  
1  1½ 2 3 4 1½  1  1½  2  3  4  
Bricks of clay:  
a) Without finish  
 
b) With 13 mm lightweight 
aggregate Gypsum plaster  
c) Mudbricks (Refer on 
building regulation)   
170  
170  
170  
200  
200  
75  
100  
100  
170  
170  
200 
100 100 170 170 170 75 75 90 100 100 170 
           
Blocks of concrete:  
a) Without finish  
  
  
  
  
  
  
90   
125  
125  
140  
140  
150 
     90  125 125 140 140 140 DRS 186 -2: 2023  
5                ©RSB 2023  - All rights reserved  
 b) With 13 mm cement/sand or 
gypsum/ sand.  
 
c) With 13 mm lightweight 
aggregate gypsum plaster  190  200 200 ━ ━ 75  90 90 100 125 125 
Blocks of lightweight concrete:  
a) Without finish  
b) With 13 mm cement/sand or 
gypsum/ Sand  
c) With 13 mm lightweight 
aggregate Gypsum plaster   
100 
  
100  
100  
—  
—  
75  
75 
 
63  
905 
75 
 
63  
90 
75 
 
75  
100 
100 
 
75  
140 
140 
 
90  
150 
140 
 
100 
 
Table 4 — Framed construction, load bearing (required for resisting fire from one side at a time)  
 Nature of Construction and Materials/  
Faced on Each Side with Timber Studs at Centres not exceeding 600 
mm Minimum Thickness (mm) of 
Protection  for a Fire Resistance 
of 1 h  
Plasterboard layers with joints staggered, joints in outer layer  taped and 
filled ━Total thickness for each face  25 
Lightweight aggregate gypsum plaster One layer of 12.7 mm plasterboard 
with a finish of  13 
Metal lath and plaster, thickness of plaster  Lightweight 
aggregate gypsum 
plaster :  22 
Sanded gypsum 
plaster (metal 
lathing grade)  13  
©RSB 2023  - All rights reserved                  6 
 Table 5 — Framed Construction, Non -Load Bearing (Required to Resist Fire from One Side at a Time)  
Nature of Construction and Materials/Steel or 
Timber Frame at Centres not Exceeding 600 mm, 
Facing on Both Sides of  
 Stud  
Construction  Minimum Thickness (mm) of  
Protection for a Fire  
Resistance of  
½ h         1h 1½ h         2h 
Dry lining with materials fixed direct  to studs (without plaster finish):  
One layer of plasterboard with taped and filled joints  Timber or steel  12.7    
Two layers of plasterboard with Joints staggered, 
joints in outer Thickness for each face Layer taped 
and filed — Total thickness for each face  Timber or steel  19 25   
One layer of wood wool slabs  Timber  25    
One layer of chipboard or of plywood  Timber or steel  18    
Lining with materials fixed direct to studs, with plaster finish  
Plasterboard of thickness:      
1) Finish With no less than 5 mm gypsum 
plaster  Timber or steel  
 9.5    
2) With not less than 13 m gypsum plaster 
finish   12.7   
Wet finish  
Metal lath and plaster, thickness of Plaster:      
1) plaster Sanded gypsum plaster  Timber or steel  13    
2) Lightweight aggregate gypsum  Timber   13 19 25 
steel   13   
 
Table 6 — Framed external walls load bearing (required for resisting fire from one side at a time)  
Nature of Construction and Materials  Minimum Thickness (mm) of Protection for a 
Fire Resistance of 1 h  
Timber studs at centres not exceeding 600 mm With internal 
linings of plasterboard layers with joints in outer layer taped 
and filled, total thickness  31 
5.2 The separating walls should be carried through the roof to a height of at least 60 cm above except in the case 
of reinforced brick/concrete slab roof where it should be bonded flash with a top level of the slab. At the time of 
designing openings, particular attention should be paid to all such factors as will limit fire spread through these 
openi ngs. Every opening in the wall should be protected by fire resisting doors having the fire rating of not less than 1 
h. Similar protection should also be done in other openings like rope races, motor alley ways, staircases, etc. of rating 
not less than 2 h . However, for Types 1, Type 2, Type 3 construction, a doorway or opening in a separating wall of 
any floor should be limited to 56 m2 in area with a maximum height of 2.75 m and maximum width of 2 m.  
5.3 When building(s) and /or compartment(s) are separated by separating wall(s) and there is a veranda on one or 
more sides of such building(s) and/or compartment(s), it is necessary that the separating wall should be built out DRS 186 -2: 2023  
7                ©RSB 2023  - All rights reserved  
 across the veranda and be carried through the roof of the same; otherwise the building(s) and/or compartment(s) 
should be regarded as having internal communication and, therefore, subject to danger of spread of fire.  
5.4 When openings in walls are provided to allow cable, etc, the space around cables and the wall should be 
protected in accordance with relevant Rwanda Standards . However, such space in case of openings provided to allow 
plumbing/gas/steam pipes and similar services should be scaled with filter material of fire rating not less than that of 
the walls in which these are situated.  
5.5 Where openings are permitted, they should not exceed three -fourths of the area of the wall in case of an external 
wall. 
5.6 A separating wall should be supported in a vertical line by a similar separating wall through all storeys below. 
The separating wall should be carried and bonded to the floor of appropriate fire -resisting construction.  
5.7 When a separating wall runs parallel to the axis of the north light opening or gabled roof, the screen wall should 
be carried through, and 60 cm above the top of the north light opening except in cases where the screen wall becomes 
of such a height that h orizontal distance between the north light opening and the roof of the adjoining building and/or 
compartment or between two sloping faces of the two consecutive roofs at the level of the top of the screen wall, is at 
least 6 m. If, however, the separati ng wall is at right angles to the axis of the north light opening or the gabled roof, the 
‘saw tooth’ gaps should be bricked up and screen wall extended above the ridge of the north light or the gabled roof.  
5.8 All separating walls should be built out to extend 15 cm beyond the eaves of the roof so as to effectively cut off 
the roofs of the parts so separated. The eaves should be cut away on each side of this extension of the separating 
wall. If there is an open ing on both sides of the separating within 3 m of the wall, those on one side should be 
bricked up to full thickness of wall, or an alternative should be provided with fire resisting doors of fire rating not 
less than of 2 h for walls of 4 h rating and 1 h for other rating.  
5.9 Common wooden roof members (trusses, joists and purlins) should not pass through the separating walls but 
they may be embedded there -in provided they do not extend more than 22.5 cm into wall and are separated from the 
similar roof member in the adjoining  building by at least 11 cm or solid wall material.  
5.10 Partition is used for separating sectors or rooms of a building but is not expected to have a fire resistance equal 
to any of the values. In fact, in practice it should not be considered otherwise than structure of light dimension and 
strength consistent with the purpose for which it is used. The minimum fire rating of the partition is given in Table 1.  
6 Columns and beams  
The fire ratings of some types of construction are given in Table 8, Table 9, Table 12 and Table 13. The specifications 
or materials should be so selected as to give ratings there -in. 
7 Floors and roofs  
7.1 The fire ratings of some types of construction is given in Table 10, Table 11, Table14, Table 15, and Table 16. 
This specifications of materials should be so selected so as to give these ratings.  
 
 
  
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 Table 7.A — Framed external walls non -load bearing required to resist fire only from inside the building  
S/N Nature of Construction and 
Materials  Minimum Thickness (mm) of Protection for a 
Modified Fire Residence of  
 
   ½ h        1h   1½h          2h   3h   4h 
Steel frame with an external cladding of  
Non-combustible sheets (excluding sheet steel),  
With a steel supporting framework and internal  
lining of:   
 
1 Metal lath and plaster thickness  of 
plaster:  
a) Sanded gypsum plaster 
(metal lathing grade)  13 13     
b) Lightweight: aggregate 
gypsum plaster  10 13 15 15 15 19 
2 Two layer of plasterboard with joints 
staggered Joints in outer layer taped 
and filed -Total Thickness   
21  
32     
3 Plasterboard of thickness:        
a) With not less than 5 mm 
gypsum plaster finish  12.7      
b) With not less than 13 mm 
gypsum plaster finish  9.5      
c) With not less than 10 mm 
lightweight aggregate 
gypsum plaster.  9.5      
4 One layer of wood/wool slabs without 
finish   50     
5 One layer of compressed straw 
building slabs:        
a) Without finish  50      
b) With not less than 5 mm 
gypsum plaster finish   50     
6 Aerated concrete blocks  50 50 63 63 75 100 
7  Bricks of clay:        
a) Without finish  75 75 90 90 100 100 
b)  With not less than 13 m m 
lightweight Aggregate 
gypsum plaster    75 75 90 90 
 
 
 DRS 186 -2: 2023  
9                ©RSB 2023  - All rights reserved  
  
Table 7.B — Framed external walls non -load bearing required to resist fire only from inside the building  
S/N Nature of construction and materials  
 Maximum thickness (mm) of 
protection to provide sufficient 
insulation to achieve a modified 
fire resistance of up to 4 h.  
Steel frame with an external cladding of sheet steel fully lapped, steel bolted 
and fixed to steel sheeting rails, with timber or steel supporting framework and 
internal lining of:   
1 Metal lath and plaster thickness of plaster:   
a) Sanded gypsum plaster (metal lathing Grade)  13 
 
b) Lightweight aggregate gypsum plaster  10 
2 One layer of plasterboard with joints taped and filled.  12.7 
3 Plasterboard of thickness, with not less than 5 mm gypsum plaster 
finish  9.5 
4 One layer of wood/wool slabs  25 
5 One layer of compressed straw building slabs  50 
6 One layer of chipboard (fibreboard ) or of plywood  18 
7 Aerated concrete blocks  50 
8 Bricks of clay  75 
9 Any internal decorative lining with a cavity fill independently supported 
and retained in position of mineral fibre insulating material (excluding 
glass) or a density of 48 kg/m3 50 
 
Table 7.C — Framed Walls Non -Load Bearing Required to Resist Fire Only from Inside the Building  
S/N Nature of construction and materials  
Timber frame with external cladding of weather  
Baoding or external plywood, 9.5 mm with an  
Internal lining of:  Minimum thickness 
(mm) of protection for a 
fire resistance of 1½ h  
1 Plasterboard not less than 9.5 mm thick, finished With:   
c) Gypsum plaster   
d) Lightweight aggregate gypsum plaster  13 
10 
2 Plasterboard not less than 12.7 mm thick, finished With:   
a) Gypsum plaster  10  
©RSB 2023  - All rights reserved                  10 
 b) Lightweight aggregate gypsum plaster  10 
7.2 The reinforced concrete  of some types of construction  for walls are given in Table 8 to Table 11. 
Table 8 — Reinforced concrete columns  
S/N 
Nature of Construction and 
Materials  Minimum Dimension (m), Excluding any Finish, for a Fire 
Resistance of  
 ½ h 1 h 1½ 2h 3h 4h 
1 Full exposed  Width  150 200 250 300 400 450 
cover  20 25 30 35 35 35 
2 50 percent exposed  width  125 160 200 200 300 350 
cover  20 25 25 25 30 35 
3 One face exposed  Thickness  100 120 140 160 200 240 
cover  20 25 25 25 25 25 
Table 9 — Concrete Beams  
S/N 
Nature of Construction and 
Materials  Minimum Dimensions (mm), Excluding any Finish, For a 
Fire Resistance of  
 ½ h 1 h 1½ 2h 3h 4h 
1 Reinforced concrete (simply 
supported)  Width  80 120 150 200 240 280 
cover  20 30 40 60 70 80 
2 Reinforced concrete 
(continuous)  width  80 80 120 150 200 240 
cover  20 20 35 50 60 70 
3 Pre-stressed concrete (simply 
supported)  width  100 120 150 200 240 280 
cover  25 40 55 70 80 90 
4 Pre-stressed concrete 
(continuous)  width  80 100 120 150 200 240 
cover  20 30 40 55 70 80 
Table 1 0 — Concrete floors  
S/N 
Nature of Construction and 
Materials  Minimum Dimensions (mm), Excluding any Finish  
for a Fire Resistance of  
 ½ h 1 h 1½ 2h 3h 4h 
1 Reinforced concrete (simply 
supported)  Thickness  75 95 110 125 150 170 
cover  15 20 25 35 45 55 
2 Reinforced concrete 
(continuous)  Thickness  75 95 110 125 150 170 
cover  15 20 20 25 35 45 
  DRS 186 -2: 2023  
11                ©RSB 2023  - All rights reserved  
 Table 1 1 — Concrete floors: Ribbed open soffit  
S/N 
Nature of Construction and 
Materials  Minimum Dimension (mm), Excluding any finish, for a fire 
resistance of  
 ½ h 1 h 1½ 2h 3h 4h 
1 Reinforced concrete (simply 
supported)    Thickness  70 90 105 115 135 150 
Width  75 90 110 125 150 175 
cover  15 25 35 45 55 65 
2 Reinforced concrete 
(continuous)  Thickness  70 90 105 115 135 150 
Width  75 80 90 110 125 150 
cover  15 20 - 35 45 55 
7.3 Encased steel columns of some types of construction  for floors and roofs are given in t ables 12 and 13.  
Table 1 2 — Encased steel columns, 203 mm x 203 mm  (Protection applied on four sides)  
 
S/N Nature of Construction and Materials  Minimum Thickness (mm) of 
Protection for a Modified Fire 
Residence of  
 1 h       1½h         2h        3h         4h       
Hollow protection (without an air cavity over the flanges) :       
1 aMetal lathing with towelled light weight  aggregate gypsum 
plaster   13 
 15 20 32  
2 Plasterboard with 1*6 mm wire binding at 100 mm pitch, finished 
with Lightweight aggregate gypsum plaster not less than the 
thickness Specified:  10 13 15 15 15 
 a) 9.5 mm plasterboard  10 15    
 b) 19 mm plasterboard  10 13 20   
3 Solid bricks of clay, composition sand  lime, reinforced in every  
Horizontal joint, unplastered  50 
 50 
 50 
 75 
 100 
 
5 aerated concrete blocks  60 60 60   
6 Solid blocks of lightweight concrete hollow protections (with an 
air cavity over the flanges)  50 50 50 60 75 
Solid protection       
1 Concrete, not leaner than 1:2: 4 mix (unplastered):       
a) Concrete not assumed to be load bearing, reinforced)   
25  
25  
25  
40  
60 
b) Concrete assumed to be load bearing  50 50 50 75 75 
2 bLightweight concrete § not learner than 1:2:4 (mix) 
(unplastered) concrete not assumed to be load bearing, 
reinforced  25 25 25 40 60  
©RSB 2023  - All rights reserved                  12 
 a So fixed, or designed, as to allow full penetration for mechanical bond.  
b Reinforcement shall consist of steel binding wire not less than 2*3 mm in thickness or a steel mesh weighing not less than 0*5  
kg/m ². In concrete protection, the spacing of that reinforcement shall not exceed 200 mm in any direction  
 
Table 1 3 — Encased Steel Beams, 406 mm x 176 mm  (Protection applied on three sides)  
S/N Nature of Construction and Materials  Minimum Thickness (mm) of Protection for a 
fire resistance of  
  ½ h        1 h           1½         2 h         3 h        4 h  
Hollow protection (without an air cavity beneath the 
lower flange).   
 1 * Metal lathing with trowelled lightweight aggregate  
Gypsum plaster (metal lathing grade)  Plasterboard 
with  
1*6 mm wire binding at 100 mm pitch, finished with 
lightweight aggregate gypsum  plaster not less than 
the thickness specified:   13 13 15 20 25  
9*5 mm  plasterboard  10 10 15    
19 mm plasterboard  10 10 13 20   
Solid protection        
1 Concrete, not leaner than 1:2 : 4 mix (unplastered):   
  
  
  
  
  
 
a) Concrete not assumed to be load bearing, 
reinforced  25 25 25 25 50 75 
b) Concrete assumed to be load bearing  50 50 50 50 75 75 
2 Lightweight concrete 4not learner than 1 : 2 : 4 (mix) 
Unplastered  25 25 25 25 40 60 
1 So fixed, or designed, as to allow full penetration for mechanical bond.  
2 Where wire binding cannot be used, expert advice should be south regarding alternative methods of support to enable the lower  edges of the 
plasterboard to be fixed together and to the lower flange, and for the top edge of the plasterboard to be held in po sition.  
3 Reinforcement shall consist of steel binding wire not less than 2.3 mm in thickness or a steel mesh weighing not less than 0. 5 kg/m ². In concrete 
protection, the spacing of that reinforcement shall not exceed 200 mm in any direction.  
4 Concrete not assumed to be load bearing, reinforced 
7.4 Timber floors of some types of construction for floors and roofs are given in tables 14, 15 and 16. 
Table 1 4 — Timber floors ━ tongued and grooved boarding, or sheets of tongued and grooved plywood or 
wood chipboard, of not less than 21 mm finished thickness  
S/N Nature of Construction and Materials  
 Minimum Thickness (mm) of 
Protection for a Fire Resistance of:  
½ h         1 h        2 h  
37 mm (minimum) timber joists with a ceiling of:   
1 Timber lathing and plaster, plaster of thickness  15   
2 Metal lathing and plaster, thickness of plaster:     
Sanded gypsum plaster (metal lathing grade)  15   DRS 186 -2: 2023  
13                ©RSB 2023  - All rights reserved  
 Lightweight aggregate gypsum plaster  13 13 25 
3 One layer of plasterboard with taped and filled 
joints  12.7   
4 Two layers of plasterboard with joints staggered, 
joints in outer layer taped and filled total thickness   
19  
31  
5 One layer of plasterboard not less than 9.5 mm 
thick, finished with:     
Gypsum plaster  5   
Sanded gypsum plaster  13   
Lightweight aggregate gypsum plaster  13   
6 One layer of plasterboard not less than 12*7 mm 
thick, finished with:     
Gypsum plaster  5   
Lightweight aggregate gypsum plaster  10   
7 One layer of asbestos insulating board with any 
transverse joints backed by fillets of asbestos 
insulating board not less than 9 mm thick, or by 
timber  9 12  
Table 1 5 — Timber floors ━ Tongued and grooved boarding, or sheets of tongued and grooved plywood or 
wood chipboard, of not less than 15 mm finished thickness  
 
S/N Nature of construction and materials  Minimum Thickness 
(mm) of Protection for fire 
resistance of  
1½ 1 h 2 h 
37 mm (minimum) timber joists with a ceiling of :     
1 Timber lathing and plaster, plaster of thickness  15   
2 Metal lathing and plaster, thickness of plaster for     
Sanded gypsum plaster (metal lathing grade)  15   
Lightweight aggregate gypsum plaster  13 13 25 
3 One layer of plasterboard with joints taped and filled and 
backed by timber  12.7   
4 Two layers of plasterboard with joints staggered, joints in outer 
layer taped and filled total thickness  22 31  
5 One layer of plasterboard not less than 9*5mm thick, finish 
with:     
6 Gypsum plaster  5   
Sanded gypsum plaster  15 
    
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 Lightweight aggregate gypsum plaster  13   
7 One layer of plasterboard not less than 9*5 mm thick,  
Finish with:   
   
Gypsum plaster  5   
Lightweight aggregate gypsum plaster  10   
Table 1 6 — Timber floors ━ Any structurally suitable flooring of timber or particle boards  
S/N Nature of Construction and Materials  Minimum thickness 
(mm) of protection 
for a fire resistance 
of: 
½ h 1 h 
37 mm  (minimum) timber joists with a ceiling of :    
1 Timber lathing and plaster, plaster of thickness.  15  
2 Metal lathing and plaster, thickness of plaster for:  
   
 a) Sanded gypsum plaster (metal lathing grade)  15  
 b) Lightweight aggregate gypsum plaster  13 19 
3 One layer of plasterboard with joints taped and filled and 
backed by timber  2*7  
4 Two layers of plasterboard with joints staggered, joints in 
outer layer taped  
and filled total thickness  25  
5 Two layers of plasterboard, each not less than 9*5 mm thick, 
joints between Boards staggered and outer layer finished with 
gypsum plaster  5  
6 One layer of plasterboard not less than 9.5 mm thick, finished 
with:   
 a) Sanded gypsum plaster  13  
 b) Lightweight aggregate gypsum plaster  15 
7 One layer of plasterboard not less than 12*7 mm thick, 
finished with:    
 a) Sanded gypsum plaster  15  
 
  b) Lightweight aggregate gypsum plaster  13 
7.5 In case of a building of more than 15 m in height, all floors should be compartmented with area not exceeding 750 
m2 by a separation wall with 2 h fire rating. For floors having provision of sprinklers, the area may be increased by 50 %. 
In long buildings, the fire separation walls should be at distance not exceeding 40 m. For departmental stores, shopping 
centres and similar occupancies, the area may be reduced to 500 m2. Where this is not possible provision of the 
sprinklers should be kept with appropriate spacing.  DRS 186 -2: 2023  
15                ©RSB 2023  - All rights reserved  
 7.6 A surface covering of non -combustible and non -toxic material should be laid directly on the incombustible floor. 
Wood flooring may be laid directly on such surface covering or directly on such floor provided that in either case there 
is no intervening spa ce and that any wood fillets for affixing such flooring is bedded not more than 2.5 cm thickness in 
the non -combustible floor.  
7.7 In the case of building used for storage purposes, the floor surface should conform to the above, in addition, it 
should be at least 15 cm above the ground level or the level of the door sills whichever is higher, and should slant 
towards the doors. An op ening through a floor should comply with the following:  
a) at the time of designing openings particular attention should be paid to all such factors which will limit fire spread 
through these openings.  
b) when opening in floors are provided to allow cable, etc, the space around cable and the floor should be protected 
according to the provision of relevant national or international standard ; However,  such space in case of openings 
provided to allow plumbing/gas/steam pipes and similar services should be sealed with filler material of fire rating 
not less than 1 h.  
c) openings for steam, gas and/or water pipes and electrical conduits, whether of iron or earthenware, should have 
a radial clearance, to allow for any heat expansion, not greater than 3 mm.  
d) the enclosure for staircases and hoists should be constructed entirely of brick, concrete or of reinforced concrete 
or similar material of construction having 2 h rating. Every opening from the enclosure on to a roof used as floor 
or to any other part of t he building should be fitted with a fire resistant door of rating not less than 1 h.  
e) if any staircase or hoist extends to the top storey of a building the roof of which is not a roof used as a floor, the 
enclosing walls should be carried through and at least 45 cm above the roof of the building and a skylight or 
window glazed should be pro vided above the roof of the building. Alternatively, if the roof of the building is used 
as a floor; it should comply with (d), and this should also apply for any furnace or motor chamber communicating 
with the staircase or hoist enclosure.  
7.8 Linings or false ceilings should not be permissible in buildings and in situations where permitted, such additions 
should not detract in any way from minimum fire rating of half an hour. In some cases, requiring provision of skylights, 
monitor lights or n orth lights in the roofs and where these are necessary, the glazing should be of glass in metal frames 
for fire rating of half an hour minimum.  
7.9 Composite roofs may be used over as addition to the roofs of buildings as a weather proofing, but should not 
be considered as a roof in itself that is, without the support of a non -combustible construction beneath, unless it is of 
not less than half an ho ur fire resistance.  
8 Air-conditioning  
8.1 Air-conditioning systems should be so installed and maintained as to minimize the danger of spread of fire, 
smoke or fumes thereby from one floor or fire area to another, or from outside into any occupied building or structure.  
8.2 Air-conditioning systems circulating air to more than one floor area should be provided with dampers designed 
to close automatically in case of fire and thereby prevent spread of fire or smoke. Such a system should also be 
provided with automatic controls to stop fans in case of i n which case these should be designed to remain in operation.  
8.3 Air–conditioning systems serving large places of assembly (over 1 000 persons), large depart -mental stores or 
hotels with over 100 rooms in a single block should be provided with effective means for preventing circulation of 
smoke through the system in th e case of fire in air filters or from other sources drawn into the system even though  
©RSB 2023  - All rights reserved                  16 
 there is insufficient heat to actuate heat sensitive devices controlling fans or dampers. Such means should consist of 
approved effective smoke detectors.  
8.4 Air-conditioning should conform to the following:  
a) escape routes like staircases, common corridors, lift lobbies, etc, should not be used as return air passage;  
b) the ducting should be constructed of metal in accordance with relevant Rwanda standard ; 
c) wherever the ducts pass through fire walls or floors, the opening around the ducts should be sealed with fire 
resisting materials of same rating as of walls/floors;  
d) as far as possible, metallic ducts should be used even for the return air instead of space above the false 
ceiling;  
e) the material used for insulating the duct system (inside or outside) should be of flame resistant and non -
conductor of heat;  
f) area more than 750 m2 on individual floor should be segregated by a fire wall and automatic fire dampers for 
isolation should be provided; and  
g) in case of more than one floor, automatic fire dampers arrangement should be providing by ducting on each 
floor for isolation purposes. Where plenums used for return air passage, ceiling and its fixtures and air filters 
of the air handling units should be flame resistant [(see 8.4 (e)]. Inspection panels should be provided in the 
main trucking. No combustible material should be fixed nearer than 15 cm to any duct unless such ducting is 
properly enclosed and protected with flame resistant material.  
h) the fire dampers should be located in and return air ducts passages at the following points automatically 
operate and simultaneously switch off air handling fans:  
1) at the fire separation wall,  
2) where ducts/passages enter the central vertical shaft,  
3) where the ducts pass through floor, and  
4) at the inlet of supply air duct and the return  air duct of each compartment on every floor.  
8.5 In case of buildings more than 24 m in height in non -ventilated lobbics corridors, smoke extraction shaft should 
be provided. The automatic fire damper should be so arranged so as to close by gravity in a direction of movement 
and to remain tightly closed  upon operation.  
9 Smoke and fire venting  
9.1 Provision has to be made for venting fire which allows escape of hot gases and smoke release by accidental 
burning of combustible material stored or are being processed inside a building, and will give ample time for all the 
inmates to escape before the roof collapses either in part or wholly in the eve nt of fire.  
9.1.1  Provisions in this regard are essential for industrial buildings; details of which are covered in a separate 
standard. The form of vent should be a ventilator -cum-exhaust which in addition to the requisite grading of fire rating 
is easily openable.  DRS 186 -2: 2023  
17                ©RSB 2023  - All rights reserved  
 9.2 Smoke venting facilities, where required for safe use of exits in windowless buildings, underground structures, 
large area factories, departmental store, domestic dwelling, theatres, cinemas, le cture halls, and where required 
should be automatic in action.  
9.3 Natural draft smoke venting should utilize roof vents or vents in walls at or near the ceiling level; such vents should 
be normally open, or if closed, should be designed for automatic opening in case of fire, by release of heat smoke 
sensitive elements, breakage of glass, or melting of plastic under the influence of heat; or by other approved methods.  
9.4 Where smoke venting facilities are installed for purposes of exit safety, these should be adequate to prevent 
dangerous accumulation of smoke during the period of time necessary to evacuate the area served, using available 
exit facilities with a margin of  safety to allow for unforeseen contingencies.  
9.5 The discharge apertures of all natural draft smoke vents should be so arranged as to be readily susceptible to 
opening by fire service personnel.  
9.6 Power operated smoke exhausting systems may be substituted for natural draft vents  
9.7 In case of buildings more than 15 m in height the staircase should be ventilated to the atmosphere at each landing 
and a vent at the top, the vent openings should be 0.5 m in the external wall and top.  
10 Service ducts  
10.1 Service ducts should be enclosed by walls and doors (if any) of 2 h fire rat ing; if ducts are larger than 1m ³ the 
floor should seal than, but provide suitable openings for the pipes to pass through, with the gaps sealed.  
10.2 A vent opening at the top of the service shaft should be provided between one -fourth and one -half of the area 
of the shaft.  
11 Basements  
11.1 Each basement should be separately ventilated. Vents with cross -sectional area not less than 2.5 % of the floor 
area, spread evenly round the perimeter of the basement, should be provided in the form of grills or breakable stall 
board lights or pavem ent lights or by way of shafts.  
11.2 Alternatively, a system of air inlets should be provided at basement floor level and smoke outle ts at basement 
ceiling level.  
11.3 Inlets and extractors may be terminated at ground level with stall board or pavement lights as before, but ducts 
to convey fresh air to the baseme nt floor level have to be laid.  
11.4 Stall board and pavement lights should be in positions easily accessible to the fire brigade and clearly marked 
“SMOKE OUTLET”, or “AIR INLET” with an indication of area served at or near the opening.  
11.5 The staircase of basements should be of enclosed type having fire resistance of not less than 2 h and should 
be situated at the periphery of the basement to be entered at ground level only from the open air and in such positions 
that smoke from any fire in  the basement should not obstruct and exit serving the ground and upper storeys of the 
building and should communicate with basement through a lobby provided with fire resisting self -closing doors of 1 h 
fire resistance. If the travel distance exceeds  18.50 m, additional star cases should be provided at proper places.   
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 11.6 In multi -level basements, intake ducts may serve all basement levels, but each basement and basement 
compartment should have separ ate smoke outlet duct or ducts.  
11.7 Mechanical extractors for smoke venting from low basement levels should also be provided, with provision of 
automatic and manual operation of system actuation of heat /smoke detectors or sprinklers.  
11.8 Mechanical extractors shall have an inter -locking arrangement, such that extractors continue to operate and 
supply fans stop automatically with the actuation of fire detectors.  
11.9 Mechanical extractors shall have an alternative source of supply. Ventilating ducts should be integrated with the 
structure and made out of brick masonry or RCC as far as possible and when this duct crosses the transformer area 
or electrical switch board, fire dampers should be provided.  
11.10 Basement:/sub -basement should not be used for storage, cooking purposes, garage and shop unless provision 
is made for sprinkler system. If cut out, openings in the basements should be protected by automatic spray in the event 
of a fire.  
12 Chimneys  
Over and above the provisions given in 4.2, the following provisions should be followed:  
a) a clearance of at least 4 cm between the outer surface of the chimney and any adjacent combustible material 
forming part of a wall lining enclosing the chimney;  
b) the fire resistance of any structure surrounding a flew or flew pipe should be not less than that for external walls. 
In the case of flew pipe there should be an air space between it and the surrounding structure of sufficient width 
to permit access to the  pipe for inspection and repair;  
c) when a flue pipe passes through  any other room or an enclosed roof space it should be protected by structure 
having a fire resistance equal to the external walls;  
d) the chimney excluding the pot should be carried to a minimum height of 1 m above the highest point of its junction 
with the roof;  
e) the outlet of a flue from domestic appliance having a roof covering should be at least 2.5 m in a horizontal  plain 
from the roof of any structure built upon the roof or at least 0.6 m higher than any ridge within 2.5 m;  
f) if the roof covering is not fire resistant, no flue outlet should be lower than the ridge for the highest point of the 
roof or less than 1 m above any ridge within 2.5 m; and  
g) where a metal chimney passes through a roof covering which is not fire resistant, it shall be guarded by a      
suitable iron or metal thimble extending not less than 22.5 cm above and below roof construction and of a size to 
provide not less than 15 cm clearance on all sides of chimneys.  
13 Staircases and lifts  
13.1 Staircases  
The details with regard to the provisions of staircases have been given in DRS 186 -5. DRS 186 -2: 2023  
19                ©RSB 2023  - All rights reserved  
 13.2 Lifts  
13.2.1  The general requirements for the provision of lifts should be as follows:  
a) walls of lifts and enclosures should have a fire rating of 2 h; lift shaft should have a vent at the top of area not less 
than 0.2 m ²; 
b) lift motor room should be located preferably on top of the shaft and separated from the shaft by the floor of the 
room;  
c) landing doors in lifts and enclosures should have a fire resistance of not less than 1 h;  
d) the number of lifts in one lift tank should not exceed 4. Individual shafts in a bank (of two rows) should be separated 
by a wall of 2 h fire rating;  
e) lift care door should have a fire resistance rating of not less than 1 h;  
f) collapsible gates should not be used for lifts and if used should have doors with fire resistance of at least 1 h;  
g) in opening other than the lift job by door in the lobby enclosure wall should also have the minimum fire resistance 
of one hour;  
h) exit from the lift lobby, if located in the core of the building should be to a self -closing stop door of minimum 1 h 
fire rating;  
i) lifts should not normally communicate to the basement;  
j) suitable arrangements, such as providing slope in the floor of lift lobby should be made to prevent water used 
during firefighting on any landing from entering the lift shaft; and  
k) sign should be posted and maintained at every floor at or near the lift indicting that in case of fire occupants, 
should use the stairs unless instructed otherwise. The sign should also contain a plan for each floor showing the 
location of staircase.  
l) Communication system  (cfr building code)  
13.2.2  Where applicable, fire lifts should be provided with a minimum capacity for 8 passengers with floor area of 
not less than 1.4 m2 and fully automated with emergency switch on the ground level. In general, building over 15 m in 
height should be provided with fire lifts. Each fire lift s hould be equipped with suitable inter -communication equipment 
communicating with the control room on the ground floor of the building. The number and location of fire lifts in a 
building should be decided after taking into consideration various factors lik e building, population, floor, areas, section 
of building, etc. The words ‘fire lift’ should be conspicuously displayed in illuminous paint on the lift landing door at 
each floor level.   
©RSB 2023  - All rights reserved                  20 
 14 Refuge area  
h) In case of buildings more than 24 m in height, refuge ar ea of 15m ² or an area equal to 0.25 m ² per person to 
accommodate the occupants of two consecutive floors, whichever is higher, should be provided as under. Refuge 
area should be provided on the periphery of the floor and open to air at least on one side protected with suitable 
railings, for:  
a) floors above 24 m and up to 39 m ━ one refuse area on the floor immediately above 24 m; and  
b) floor above 39 m one refuse area on the floor immediately above 39 m and soon after every 15 m.  
15 Refuse chutes  
Refuse chutes should have an enclosure wall of non -combustible material with fire resistance of not less than 2 h. 
They shall not be located within the staircase enclosure or service shafts, or air -conditioning shafts. Inspection panel 
and doors should be tight fitting with 1 h fire resistance; the chutes should be as far away as possible form exits.  
16 Drainage  
16.1 It is essential to make provision for drainage of any such water on all floors to prevent or minimize water damage 
of the contents.  
16.2 The drain pipe should be provided on the external wall for drainage of water from all floors. On large area floors 
several such pipes may be necessary which should be spaced 30 m apart. The pipe should conform to relevant 
Rwanda Standards.  
17 Electrical services  
17.1 electric distribution cables/wiring should be laid in a separate duct. The duct should be sealed at every 
alternative floor with non -combustible materials having the same fire resistance as that of the duct. Low and medium 
voltage wiring running in shaft a nd above false ceiling should run in separate conduits.  
17.2 Water mains, telephones lines, inter -comeliness, gas pipes or any other service line should not be laid in the 
duct for electric cables.  
17.3 Inspection panel doors and any other opening in the shaft should be provided with fire doors having fire 
resistance of not less than 1 h.  
17.4 Medium and low voltage wiring running in shafts and within false ceiling should run in metal conduit; the false 
ceiling including all fixtures used for its suspension should be of non -combustible material.  
17.5 An independent and well -ventilated service room of a 2 -h minimum fire resistance should be provided on the 
ground floor with direct access from outside or from the corridor for the purpose of termination of electric supply . 
17.6 Transformer bays H.T. and L.T.  supply rooms, air -conditioning plant systems and boiler rooms shall be in 
separate fire resisting rooms and shall conform to RS 186 -2 and relevant national regulations.  DRS 186 -2: 2023  
21                ©RSB 2023  - All rights reserved  
 18 Finishes  
18.1 The use of flammable surface finishes on walls (including external façade of the building) and ceilings affects 
the safety of the occupants of a building. Such finishes tend to spread the fire and even through the structural elements 
may be adequately fir e resistant, serious danger to life may result. It is, therefore, essential to have adequate 
precautions to minimize spread of flame of wall, facade of building and ceiling surfaces. Any materials used for various 
surfaces and décor should be such that  the flame spread rating should not be more than the recommended values 
and in addition should not generate toxic smoke/fumes.  
18.2 Susceptibility to fire of various types of wall surfaces is determined in terms of flame spread . 
18.3 Based on the rate of spread of flame, four classes are determined as follows:  
a) Class 1: Surfaces of very low flame spread ; 
b) Class 2: Surfaces of low flame spread ; 
c) Class 3: Surfaces of medium flame spread ; and  
d) Class 4; Surfaces of rapid flame spread . 
18.4 In case of buildings more than 15 m in height, the interior finish material should not have rating exceeding 
Class 1.  
18.5 The situation under which materials falling into various classes should be used in building construction is given 
below:  
a) Class 1 may be used in any situation ; 
b) Class 2  may be used in any situation except on walls facade of the building, and ceilings of staircases, walls 
and partitions, and corridors;  and 
c) Class 3  should be used only in living rooms, and bedrooms (but not in rooms on the roof) and only as a lining 
to solid not on staircases or façade of the building.  
NOTE Panelling  (lining) should be permitted in a limited area. It should not be permitted in a vestibule.  
18.6 When frames, walls, partitions or floors are lined with combustible materials the surfaces on both sides of the 
material should c onform to the appropriate class .  
 
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©RSB 2023  - All right s reserved