ODPEM Government of Jamaica
Office of Disaster Preparedness and Emergency Management
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Be Prepared
 
Build It Right


Start with the Right Site

If you have a choice, it is important to select the safest site. Large exposed level areas, whether high or low, are less protected than hill slopes.


 

Although the top of a hill may have the best view, it is the least protected. Is it better to build into the slope.

 

 

River valleys or other sloped valleys should always be avoided. These act as funnels for the wind and build up its speed. You must, therefore, be particularly careful not to build in places where your house will be exposed to floods or fast flowing water, or where the foundation of your house can be washed away by storm water.

 

 

Once you have selected your site, it should be made level. If the site is on a slight slope you must do whatever excavation and filling is needed to make it completely level. If the slope is steeper, then you must build an earth ramp. Make an earth ramp by filling with enough earth to get a flat surface. If the slope is even steeper, you must build a wooden or concrete platform.

 

 

For a wooden platform, the posts must be at least 4" x 4". They must be firmly fixed in concrete. This makes the support rigid and strong. If these supporting posts are long, they must be braced by other boards, at least 2" x 4" in size. The house may then be built on this support.

 

 

Although a site on the slope is safer from flooding you should also make sure that water flows around and not into the house. The best way to do this is to dig a storm drain. A storm drain is a trench dug on the uphill side of the house. This will collect the water coming down the hill, and take it around the house.

 

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The Shape of the House

 

The shape of the house you choose will affect how storm-proof it is.

A square shape is best, since it provides least wind resistance and requires the least material for building.

 

 

The second best shape is a rectangular house.

 

 

However, as you can see, this shape provides a longer face to the wind. This means that the house will be exposed to more wind pressure.
 
The worst shapes that can be built are like these:

 

 

In a storm, the winds get trapped by the shaded sides of the house. This means that they cannot flow as easily around these as for the square house. The house therefore gets the full force of the wind.


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Strap Down the Roof to Make it Storm-Proof


A good house without a roof is not of much value, so it is important to have a strong roof. If care is taken and the right connections made, your roof should survive the strongest of hurricanes.

The slope of the roof will affect how well it stand up to the wind. A slope of 30 degrees is best, since at this slope, the uplift of the wind is balanced by its downward pressure.

A slope of 1 in 2 is a little below 30 degrees, but will do. 1 in 2 means for every 2 ft. across, you go up 1 ft.

 

 

The first step in making your roof is the gable ends. These are triangular (three cornered) sections that extend up to the roof at both ends of the house. They help to support and secure the roof. They are made of 2" x 4" board and strengthened, using braces and gussets. Gussets are flat pieces of wood, nailed to joints to strengthen them.

 

 

The slant edges of the gable ends should be sloped at 1 in 2.

Once the gable ends are in place, the ridge board should then be put on. This the board at the centre of the roof, to which the upper ends of the rafters are attached. The ridge board must be firmly connected to the gable ends, using fasteners and straps.

 

 

After the ridge board is firmly in position, the rafters are attached. They must be notched to fit neatly onto the wall plate, fastened and strapped firmly to them.

They must be attached to the ridge board and the bottom lip of the rafters must be fitted underneath. The rafters should also be strapped to the ridge board and the ridge board to the rafters.

 

 

The rafters should not overhang the wall by more than 1’ 6". If the overlap is longer, too much of the roof will be exposed to the wind. This will make it easier for the roof to lift.

Once the rafters are in position, the frame of the gable end must be covered with some sheathing. This should be screwed or bolted on.

After the rafters, gable ends and ridge board are in firmly, the laths should be fastened to the rafters by straps or cleats. Nailing is not enough, since the nails will pull up easily.

 

 

A common form of failure in roofs is the removal of the sheeting. To make sure that the sheeting stays in place, it should be bolted or screwed down, instead of nailed.

Every crest of the sheeting near to the eave and ridge board should be screwed or bolted. For the rows in between, at least every other crest should be screwed or bolted.

For sheeting, no gauge thinner than 26 gauge should be used for roofs. For 26 gauge sheeting, the spacing between the lath should not be more than 2’ 6’. For stronger sheeting, fewer laths are needed. For 22 gauge, the spacing should not be more than 4 ft.

 

 

The corrugated sheeting should be properly over-lapped to prevent water from blowing under the seam.

 

 

The roof capping is the part of the sheeting that runs over the top of the roof. It should be made from material as strong as the sheeting itself. It should be bolted or screwed down to the lath on either side of the ridge board or hip rafter.

The eave should not be more than 1’6" wide. The space between the sheeting and the wall plate should be closed up to prevent the wind from getting under the sheeting and lifting it. This can be done by nailing a board called the facia board onto the wall plate and using cleats to connect this facia board tot he rafters as well.

A facia board is a flat board, usually about 1" x 6". It is nailed with the fact outwards. This is why it is called a face or facia board.

 

 

A better way to seal the eave is to use a box eave. In the box eave, all sheeting in the overhang is enclosed with wood (both underneath and at the sides). In a box eave, a facia board is nailed to the outer edge of the rafter and boards are nailed under the overhang section of the rafter. This completely encloses the overhang and takes all of the uplift force of the wind off the overhang sheeting. It also prevents wind from blowing between the sheeting and the wall plate into the house.

 

 

 



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