43 Rules

HowHouses

Can BetterResist

HighWind

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

NBSIR 77-1197
Abstract

This guide presents to designers, builders,

government and private building authorities,

and building owners and occupants a series

of effective methods for improving the

resistance of new and existing buildings

against high winds. The methods described

may be applied to improving the

construction of new buildings as well as to increase the wind resistance of existing

buildings. This material offers guidelines for

selecting the location and orientation of

Introduction

These guidelines and illustrations are offered to help local government

housing authorities including builders,

designers, owners and occupants of low-rise

buildings in developing countries subject to extreme winds to improve the resistance of

their buildings to high winds.

Government and private building

officials are encouraged to use this information as a basis to stimulating awareness of bases for improved local building practices, and to translate the text of the report into the local language as needed.

A poster also has been developed that

illustrates several critical principles of windresistant design and construction practice

and identifies a local country point of contact

for additional information. The purpose of

this poster is to inform the general public of

the importance of better building design,

need for improved construction practices

and identifies where such information may

be found.

buildings and the building shapes, for

suggesting methods of construction, for

recommended building details, and for local production of connectors and fasteners. It covers two common types of construction

masonry and timber—as well as selected

details based on local materials such as bamboo and adobe.

Key Words: Architecture; buildings;

connectors; design criteria; fasteners; wind.

These findings stem from a project that

produced design criteria that would lead to improved performance of low-rise buildings

especially in developing countries subjected

to extreme winds. The project was

sponsored by the Agency for International

Development and carried through by the

National Bureau of Standards, Center for

Building Technology, in the belief that

additional research on wind was needed to reduce loss of life and property, human

suffering, disruption of productive capacity

and costs of disaster relief. This report is based in part on the

technical results contained in the National

Bureau of Standards Building Science Series

100: Building to Resist the Effect of Wind, Volume

3, "A Guide for Improved Masonry and

Timber Connections in Buildings." All five

volumes of BSS 100 together or separately

are available from the U.S. Government

Printing Office, Washington, D.C. 20402 or from AID Missions.
1. In locating a house take advantage of

natural windbreaks such as stands of trees,

small hills or hedges to reduce the impact of

prevailing winds.

2. Be especially careful of sites on or near tall hills. These can increase wind speeds by as much as 50 percent.

3. Valleys funnel winds; they can create abnormally high wind speeds. Consult an

engineer or weather station official before

building on such a site.

4. Buildings placed near one another can

affect wind speeds. Intense suction can

develop on the gable ends of pitched roofs. If the building is in the wake of another, expect

turbulence and some high local loading on

small elements such as cladding. Be sure these elements are securely fastened.

5. When building a windbreak

or shield, such as a row of trees or a wall, include small gaps to stabilize the flow on the lee side.
Suction decreases

6. Aim for roof pitches that approach 30

degrees (or about 1 m in 3). Wind loads are severe when roofs are pitched around five to ten degrees.

7. Avoid outside overhangs of more than

0.5 m, even if supported at the edge by

columns. If unavoidable, consider vents or

louvers to relieve the upward pressure.

8. A parapet around a roof can reduce high

suction along roof edges, but don't expect it to significantly reduce overall roof uplift.

9. Consider round or polygonal shapes as these often reduce wind pressures. Similarly,

certain structural systems, such as the Aframe, provide great stiffness.

10. Avoid openings that cannot be closed off during hurricanes. High winds penetrate the

building and create high outward pressures on walls and roof. If a broken window admits

high wind, arrange for openings on

opposite walls to relieve pressure build up.

11. Avoid large wall openings near the roof-line as this will weaken the

ability of roof to distribute loads to the rest of the structure.

12. Recessed building sections and courtyards may aggravate the effects

of high winds. Consult an engineer if possible.
Construction

13. Make sure that all elements of the house

are securely tied together, from foundation

to roof.

14. Place masonry blocks on a continuous

concrete footing in a trench. Avoid placing

masonry blocks directly on the ground, as

this will make your building settle unevenly,

causing wall cracks and openings for wind to penetrate. In extreme cases uneven

settlement may bring about building

collapse.

15. Whatever the structural materials, be

sure to anchor them solidly to the

foundation, using dowels, reinforcing bars,

tie-rods or other connectors suited to the

material. Embed anchors at least 25 cm into

the footing.

16. Anchor masonry walls and piers to the

foundation with 15 mm rods spaced (in case of

walls) not more than 2 m apart.
17. If a floor is raised off the ground and

supported on posts, piers, or pilings, anchor

the corners to the ground using galvanized

steel anchor pipe.

18. Tie corner columns or posts securely to adjacent walls, using tiebars and/or

horizontal reinforcement.

19. Make intersecting walls continuous by means of tiebars and/or horizontal

reinforcement that extends into neighboring

walls and partitions.

20. Keep wall openings small at corners so as not to weaken the structure.

21. Protect glass with louvers or other means to avoid breakage by flying

debris.

22. When using infill wall construction, be sure to tie vertical and

horizontal reinforcement securely into the adjacent structure and

foundation. Use 8 mm bars with end hooks.

23. Use running rather than stacked bond

when building with masonry.

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Running bond Stacked bond

24. To control cracking, reinforce brick,

concrete block, adobe or other masonry

block construction internally using metal

rods, split cane, bamboo or other ties embedded in grout. Be sure to maintain a tight bond between the reinforcement and

the surrounding material.
25. Ensure positive connections between

door and window sills, posts and lintels and the walls in which

they are placed.

26. Near the ocean or other corrosive

atmospheres, protect metal reinforcing bars, ties and other connectors

from corrosion by covering over with a waterproof material.

27. To resist twisting of timber joints, use connectors in pairs, one on either side of the

members being joined or tie with a metal

strap.

28. Avoid flexible joints as they are subject to large displacements under lateral or uplift loads.

29. Avoid using mortar alone to fill small uneven wall openings. It is better to cut masonry units to fit these openings.

30. Insist on high quality masonry. For

example, adobe may be made to better resist abrasion, heat and water by

stabilizing it with rapid curing road-oil or an asphalt emulsion.

31. When building with masonry, use bond

beams to connect all load bearing elements.
32. Be sure to tie the roof securely to its supporting walls or posts.

Ignoring this caution is the single greatest cause of destruction due to high winds.

33. Consider ventilation slots placed at the

ridge. These are very effective in reducing

the internal pressure and thus decreasing

total uplift on the roof.

34. When connecting a timber roof to a masonry wall, extend the fastener strap over and around the roof joist. Nail it to the joist

and embed the ends in the concrete or masonry to a depth of 25 cm.

35. Tie roof-framing to timber walls with

sheet metal straps or brackets or wood

cleats. Nail straps to members, being sure to drive nails laterally, not in direct pull.

Galvanized

strap anchor
36. When using screws to attach a corrugated iron roof to wood purlins, use

self-drilling screws if possible, spaced no more than three corrugations apart, with a screw head or washer of at least 20 mm in diameter. For regions of intense uplift

pressure, the screws should be placed no more than two corrugations apart. If sheet

metal straps and rivets are used, wrap the

straps completely around the purlins. —wrnmmr

36b.

. Purlin

Sheet metal straps

37. For extra bracing against racking and

uplift of a wood frame wall and roof,

consider a continuous diagonal timber brace

nailed to wall studs, joist and rafter.

38. Choose and attach the roof cladding with

great care. Cladding dislodged by wind can set off a chain reaction that

will quickly destroy the roof's stabilizing function. Protect perishable

cladding such as thatch, and replace damaged portions.
Hints febr

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^ 39. Sheet metal straps may be easily fabricated with few tools. Use a minimum thickness (20-gauge) galvanized sheet metal. A width of 30 mm

and a length of .5m suits many applications.

40. A multipurpose bracket can be fabricated

from 20-gauge galvanized steel sheet.

Dimensions can vary. Slits cut in the sheet

metal permit forming the bracket for a variety of uses.

41. Split-ring connectors for roof trusses may be fabricated by cutting 20 mm wide

sections from 75 mm diameter steel pipe, and

then cutting the ring at an angle.

42. Metal plate connectors for truss joints

may be fabricated locally, usually from 20-

gauge galvanized sheet metal. The sheet

metal is punched in a way that produces

barbs or teeth at right angles to the plate.
43. These additional connection details may be used with variations as needed for the requirements of each case.BAMBOO JOINTS

1 cm x 60-100 cm lashing Use twisted bamboo, rattan or

galvanized iron wire

DETAIL A DETAIL B DETAIL C

Bamboo details drawn

from the free publication “The Use

of Bamboo and Reeds

in Building

Construction,"

Department of Economic and Social Affairs, United

Nations, New York,

NY, Catalogue No. ST/SOA/113.
Stephen A. Kliment, AIA

663 Fifth Avenue New York, New York 10022

and

Noel J. Raufaste

Richard D. Marshall Center for Building Technology

Institute for Applied Technology

National Bureau of Standards Washington, D.C. 20234

Sponsored by: The Office of Science and Technology

Agency for International Development

Department of State Washington, D.C. 20523

Under a Participating Agency

Service Agreement (PASA)

No. TA(CE)04-73

MAY 1977