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Draft Template:Part 12 (Waterproofing Roofs - SBS) - RCABC Roofing Practices Manual
Draft Template:Part 12 (Waterproofing Roofs - SBS)
1 Protected and Modified Protected Membrane Roof Assemblies
This Part pertains to the design and installation of roofs that are designed and constructed as Protected Membrane Roof Systems or Modified Protected Membrane Systems; in these systems, gravel ballast or pavers are used to secure the system materials against wind uplift and floatation in water. For roofs designed with accessible coverings, refer to Part 14 THE ROOF as a PLATFORM: Coverings, Living Spaces and Structures.
When a roof is designed as a Protected Membrane Roof System or as a Modified Protected Membrane System, it must be secured in keeping with the design standards and ballast weight requirements in Part 3 SECURING the ROOF ASSEMBLY. In addition, the roof must be designed to incorporate
gravel ballast guards around drains
a drainage layer beneath XPS insulation.
filter fabric installed over XPS insulation, in order to
contain the insulation and thereby prevent ‘insulation stacking’ (displacement) when insulation boards become buoyant in water.
prevent fines from settling at the membrane level and filling the voids between insulation board joints.
Where membranes installed on vertical surfaces may be damaged from foot traffic or shifting coverings, they must be protected as, for example, with base metal flashings.
Every Protected Membrane Roof System or Modified Protected Membrane System designed with gravel ballast must conform to the securement requirements set out in 3.3.2 Ballasted Roof Assemblies and specify ballast conforming to the minimum requirements shown in the table below.
Table 12.1 RGC Ballast Guide
Stone Ballast Required Weight
Ballast Depth
Up to 50 mm (2") 60 Kg/M2 (12 lb./sf) 40 mm (1 ¾")
75 mm (3") 8r Kg/M2 (17 lb./sf) 60 mm (2 ¼")
100 mm (4") 108 Kg/M2 (22 lb./sf) 75 mm (3")
125 mm (5") 132 Kg/M2 (27 lb./sf) 90 mm (3 ½")
150 mm (6") 156 Kg/M2 (32 lb./sf) 105 mm (4 ¼")
175 mm (7") 180 Kg/M2 (37 lb./sf) 125 mm (5")
200 mm (8") 204 Kg/M2 (42 lb./sf) 140 mm (5 ½")
See also 3.2.2 Gravel Ballast in Part 3 SECURING the ROOF ASSEMBLY.
Membranes must conform to the material requirements set out in 9.2.1 Composition, Thickness and Selection.
Insulation must be Type IV XPS and must be supplied by the Contractor. Refer to 7.2 Materials.
Drainage mats and filter fabrics must conform to the Standards set out for Overburdens in 14.2.4 Components for Vegetated Systems and Other Roof Coverings.
Pavers that are partially supported (i.e. with pedestals) should be capable of resisting anticipated loads (consider, for example, hydraulically pressed concrete pavers).
should be adjustable, when a level surface is required.
must be proprietary (purpose-made) and include an integral spacer rib measuring at least a 3mm (⅛”), to uniformly separate pavers.
Gravel ballast used to secure a Protected Membrane Roof System or Modified Protected Membrane System must be clean, washed, round or crushed stone, falling within the following gradations:
35 mm (1 ½") - 100 % Passing
25 mm (1") 70 - 100 % Passing
20 mm (¾") 5 - 20 % Passing
12.7 mm (½") 0 - 6 % Passing
5 mm (3/16") 0 - 2 % Passing
All components of a Protected Membrane Roof System or Modified Protected Membrane System, including the gravel or paver ballast, must be supplied and installed by the Contractor. Where a Vegetated System (VRS) is used as ballast, the VRS may be installed by others but
the work must be coordinated with the Contractor.
the VRS installed immediately upon completion of the Contractor’s work, to ensure the roof system is held in place.
See also 12.1.3.5 Filter Fabric and 14.1.2.2 Roof Coverings.
1.3.2 Membranes
Membranes, membrane flashing and insulation must be installed in keeping with the Standards found elsewhere in this Manual.
No UV-sensitive membrane may be left exposed to UV radiation and must be fully protected by a granulated cap membrane, metal flashing or Overburden.
3)	The second ply in a Protected Membrane Roof System may be a base membrane that is acceptable to the membrane manufacturer for that application, and must meet the membrane requirements in 9.2.1 Composition, Thickness and Selection for puncture resistance and thickness.
All membrane flashing must be carried up the vertical surface at least 200mm (8”) higher than the top of the ballast.
Before any roof covering, structure or equipment is installed, roof membranes must be
scanned for leaks when an integrity scan is specified.
free of deficiencies.
Insulation must be installed by the Contractor.
1.3.4 Drainage and Penetrations
A drainage mat must be installed below the XPS insulation. A second drainage layer may be installed above the insulation but is at the discretion of the Design Authority.
Specialized proprietary drainage products must be acceptable to the membrane manufacturer.
Ballast guards must be installed around all roof drains. See 11.2.2 Roof Drains & Scuppers.
For drains and penetrations, refer to the Standards in Part 11 DRAINS and PENETRATIONS.
1.3.5 Filter Fabric
Fabric filter mats must be
installed loose-laid (un-bonded) over the insulation and below any type of ballast or roof covering.
overlapped at all edges a minimum of 300mm (12").
at least 2.5 m x 2.5 m (8’ x 8’) in size.
slit to fit over roof penetrations, and cut out around roof drains and other openings.
Filter fabric must extend up perimeter edges and curbs, and placed loose (unattached) under metal counter flashings or wall finishes. See also 13.3.4 (6) concerning Linear Metal Flashings.
1.3.6 Gravel and Paver Ballast
Gravel or pavers used as ballast on a Protected Membrane Roof System constitute part of the roof system and therefore each kind of ballast must
conform to the minimum requirements set out in Part 3 SECURING the ROOF ASSEMBLY.
be evenly distributed or installed over the insulation, drainage layer and filter fabric assembly.
be supplied and installed by the Contractor, not by another trade.
Pavers and unit-type masonry, such as brick or stone, must be supported by
proprietary (purpose-made) pedestals with at least a 3mm (⅛”) integral spacer ribs for uniform spacing of pavers.
a proprietary drainage layer overlaid with a filter fabric mat.
a drainage layer of loose aggregate (such as pea gravel) measuring at least 25 mm (1") in depth, installed over a filter fabric.
Pedestals or a drainage layer must permit at least 12.7 mm (½″) of vertical separation between the paver and the underlying substrate, to provide airflow for drying surfaces and assist in leveling. Pedestals should not impede the flow of water or air, and should uniformly distribute the dead load of pavers, and other unit masonry products, as well as predicted live loads.
2 Built-in Membrane Gutters
When a built in membrane gutter adjoins a RoofStar-guaranteed Water-shedding System, the gutter waterproofing must be constructed by the Contractor to be included by the RoofStar Guarantee. Built-in membrane gutters that drain a roof not covered by a RoofStar Guarantee are not eligible for a RoofStar Guarantee.
Conventionally Insulated Systems that drain into a built-in gutter must abut solid blocking at the gutter edge that provides
When a Waterproofing System transitions to a Water-shedding System by way of a common built-in gutter, the gutter membrane must be carried up the Water-shedding System slope (when measured vertically from the maximum water level)
To qualify for a RoofStar Guarantee, existing gutters should be redesigned if their capacity is undersized, but they must nevertheless incorporate an overflow drain in keeping with the Standards in this Part. Where the primary drain in an existing gutter is undersized for the capacity of the gutter, the primary drain must be replaced with a properly sized drain.
For transitions between the built-in gutter and steep roof assemblies, refer to Part 10 in any of the Water-shedding Systems Standards.
carried up an adjoining Water-shedding System (measured vertically from the maximum water level)
Gutter membranes must be mechanically secured at their terminations, both on the outside of the gutter edge and on the field:
Fasteners securing the membrane on the field must be placed at least 150 mm (6”) above the maximum water level.
Securement fastener spacing shall be no more than 300 mm (12”) O.C.
Gutter drains and overflows must be installed in keeping with the Design requirements outlined in Design above. Drain flanges that are bent to accommodate the side walls of the gutter must be mechanically fastened to the gutter wall before membrane application. Refer to the RoofStar Guarantee Standards for roof drains in any of the Standards for Waterproofing Systems.
When an adjoining Water-shedding System is insulated (typically ASM only), the transition from gutter to the Water-shedding System may require the use of tapered insulation incorporating a drainage plane between layers of tapered insulation. See Construction Detail ASM 12.1.2 Built-in Gutter Assembly for an illustrated example.
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