Report 2 (of 6): A Strapping Solution - Jamaica

Introduction

Home owners in the lower income bracket in Jamaica are most at risk during a storm or hurricane because many live in wooden houses that are generally in a state of disrepair and are not structurally sound. The houses are not attached to the foundations and they do not have roof ties or hurricane clamps which make a building structure more resistant to strong winds.

When Hurricane Gilbert hit Jamaica just over a decade ago, it caused millions of dollars of damage. For those living in informal settlements and poor housing the devastation was catastrophic.

The Construction Resource and Development Centre

A retrofit programme was set out by the Construction Resource and Development Centre (CRDC) and work was carried out with local roof builders who learned the principals of hurricane resistant roofing. Ten years later, safer roofs are still being installed.

Specifications for a Roof

Roofs are held together by five major connections:

- the wall plate and the walls
- the rafters and the wall plate
- the ridgeboard and the rafters
- the laths and the rafters
- the zinc sheets and the laths

If these connections are not installed properly, it will result in partial damage or complete loss of the roof during a hurricane.

Wall plate and Walls

The wall plate is the first connection between the walls and the rest of the roof and it forms a frame on which the other sections of the roof sit. It must therefore be securely fastened to the rest of the building or the entire roof will lift in a hurricane.

To strengthen an existing roof, rawl bolts should be drilled into the belt beam and placed four feet apart. Metal straps made from steel sheeting (1 inch x 3/16th) can be placed over the wall plate and fastened to the block work.

Rafters and Wall Plate

Rafters are usually made from 2 inch by 4 inch deep timber that runs from the eaves to the ridgeboard. The rafter is connected to the wall plate and the ridge. Twisted hurricane straps should be installed where the rafters join the wall plate. They should be nailed or screwed to both the wall plate and the rafter, thereby preventing the rafters lifting off the wall plate. Old zinc sheeting cut into strips can be used instead of straps. The sheeting should be cut into 1 inch wide strips and nailed over the rafter and into the wall plate.

By raising the roof to increase the slope, the pressure on the rafters is reduced and by reducing the overhang to less than 18 inches, the roof is more likely to remain intact.

Rafters and the Ridgeboard

To prevent this damage, a collar tie should be placed between every second or third pair of rafters which will stop the force of the wind pulling apart the two sides of the roof. Alternatively, a steel strap over the top of the rafter can be used.

Lath to Rafters

The laths should be placed no more than two feet six inches apart and where possible, 1 inch x 4 inch timber should be used. The laths should be held to each of the rafters with either one screw or two nail fixings (2.5 or 3 inches long).

If the laths are too widely spaced on an existing roof, more can be added by lifting the zinc sheeting.

Zinc Sheets and Laths

Zinc sheets protect the roof from wind and rain. It should be properly nailed down, particularly at the edge of the roof, using zinc nails or screws and fillets to hold the zinc sheeting (wire nails should not be used). A recommended nailing pattern is one nail at every other corrugation along the eaves and ridges, and one nail at every third corrugation in the centre of the roof. Where there is unboxed gable overhang, there should be a nail or screw at every corrugation.

It is important to use the correct gauge zinc and the zinc sheets should be of 26 gauge (28 or 30 gauge is too thin).

Eaves and Gable Ends

Damage to the eaves and gable ends often starts because these areas are exposed. Overhangs should be kept as short as possible (less than 18 inches) and board edges and cover strips should be used. Patio roofs should be separate from the main roof or they may blow off together. Boxed eaves will also help prevent the loss of the roof.

1 inch = 25.4 millimetres

Cost

The cost of the hurricane resistant roof is US$1,000 but there is credit available at affordable interest rates through the Credit Union or the National Housing Trust in Jamaica, to help people restore their roofs. The cost of upgrading and strenghtening a roof is a fraction of the cost of replacing the entire roof after it has been damaged by a hurricane. Using hurricane straps will prevent some storm damage if the cost of a retrofit roof is too much initially.

The National Housing Trust

The National Housing Trust (NHT) is a unique Jamaican Institution formed in 1976 in response to the urgent need for an agency which would generate additional funding for housing finance and provide shelter solutions for those in need. Through a unique worker/employer partnership, 2% of the gross wages of workers and 3% of employer's wage bills are channelled into the NHT. The combination of corporate and personal savings created a pool of funds enabling the Trust to provide affordable housing to the lower income groups, based solely on local funding.

Maintenance

Many roofs fail in a hurricane because they become weak from the rusting of nails or sheeting, the rotting of roof timbers and facia boards, as a result of unrepaired leaks or simply old age. Termites and woodworm also attack untreated or unprotected timbers. The regular maintenance of roofs keeps them strong, leak-free and prevents costly repairs or replacement.

Tips for Keeping Roofs Safe

- Inspect the roof after heavy rain and fix leaks as soon as they occur.
- Replace defective timbers and rusted sheeting.
- Paint facia and edge details to lengthen their lives.
- Check for termite trails or dust piles from the roof and ceiling timbers. Treat thoroughly and quickly if infestation is found.
- Do not use untreated lumber in buildings, unless it is termite resistant, for example, cedar.
- Galvanised sheeting tends to rust in areas subject to sea spray and so a thick gauge aluminium sheeting should be used in these areas, or the roof should be kept painted to resist the corrosive effects of salt.

Innovative Solutions for Landslides

When a hurricane strikes, heavy rains follow. Whole hillsides can crumble taking houses with them. An innovative solution to prevent landslides has been developed using rubber tyres to help stabilise the soil.

First, the hillside needs to be dug out. The tyres are then stacked together and filled with earth to weight them down. Eventually, plants will begin to root between the tyres which provides a strong hold against landslides. Tyres do not deteriorate in condition and they will not fall down the hillside, providing that they are packed properly initially. They are an easy resource to obtain and last for years.

Intermediate Technology would like to thank the Construction Resource and Development Centre in Jamaica for providing the original material on the Retrofit Programme and the National Housing Trust.

For further information, please contact:

Construction Resource and Development Centre,
11 Lady Musgrave Avenue,
Kingston 10,
JAMAICA.

Tel: +809 978 4061 2
Tel: +809 982 1763

Further reading available from ITDG Development Bookshop

Developing Building for Safety Programmes: Guidelines for organizing safe building programmes in disaster-prone areas.
Yasemin Aysan, Andrew Clayton, Alistair Cory, Ian Davis and David Sanderson
Summarizes the basic principles to be considered in the planning and implementation of community-based building improvement programmes for small dwellings in disaster prone areas and includes case studies illustrating suggestions made.
120pp ISBN 1 85339 184 0 Paperback 1995 (ITP) £8.95

Building for Safety Compendium: An annotated bibliography and information directory for safe building.
Andrew Clayton and Ian Davis
Compendium of key publications, organizations, information sources and funding agencies for building improvement programmes. Over 100 selected publications and institutions.
56pp ISBN 1 85339 181 6 Paperback 1994 (ITP) £8.95

Technical Principles of Building for Safety
Andrew Coburn, Richard Hughes, Robin Spence and Antonois Pomonis
Details the basic principles to be considered in the planning and implementation of community-based building improvement programmes for small dwellings in disaster-prone areas. Includes section on earthquakes, flood and wind resistant construction.
120pp ISBN 1 85339 182 4 Paperback 1995 (ITP) £8.95

Communicating Building for Safety: Guidelines for communicating technical information to local builders and householders.
Eric Dudley and Ane Haaland
Presents the principles of communicating the information needed for building improvement. Covers the uses of different media to convey information and describes the use of graphic design for education.
80pp ISBN 1 85339 183 2 Paperback 1994 (ITP) £8.95

Appropriate Building Materials: Third edition
Roland Stulz and Kiran Mukerji
The third and latest edition of this standard building materials sourcebook. Summarizes technical data and practical information and identifies appropriate solutions to any given problem in low-cost construction. Completely revised and updated.
420pp ISBN 1 85339 225 1 Paperback (ITO) £16.95

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TVE/ Practical Action gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.