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The easiest and probably cheapest way to roof a garage, is to build a flat roof. Flat roof construction has a number of advantages, in that it uses less building materials than a pitched roof, is very easy to build – even if you are doing it alone, and because it may allow you to build a garage where local building codes prohibit buildings over a certain height.

Of course a flat roof is not really flat. In reality it is a gently sloping roof, with just enough angle to allow rainwater to drain off. There may be a single slope, which usually makes for the simplest possible construction, or there may be two slopes, draining the water to a single corner of the roof. This is usually seen where the constructor wishes to maintain the illusion of a completely flat roof. This is done by adding parapets around the entire roof, penning the water in. What is seen as a flat roof, is then actually a sloping roof hidden behind a horizontal parapet. Usually, this is only done with roofing felt as the roofing material, as it is pretty much the only material that can be made sufficiently watertight when used to cover the inside of what is essentially a rooftop water basin. The water is drained directly into a downspout in this sort of construction. This type of flat roof can be built by the determined and experienced do-it-yourself’er, but it does require some knowledge to do correctly. A much easier and safer project would be to build a flat roof with a one-way slope. The water will drain down the roof and into a rain gutter, and from there into the downspout. With this sort of design, there are much fewer elements in the roof, much fewer steps to take and much less risk of building something too prone to failure. It is also much easier to detect leaks and faults, since the construction is much more open and inspection-friendly.

To get started building a flat garage roof, first determine what sort of roofing material you wan to use. Most one-way sloping roofs seem to use corrugated roofing sheets of either plastic or metal, but roofing felt is also very commonly used. Roofing shingles are not often used, since there is a greater risk that water could be blown in between them. For the same reason, clay roof tiles are never used for flat roofs, and in fact are not designed for the purpose. Plastic sheets can be used on slopes of only a few degrees, because they can be made very watertight where they overlap. Roofing felt is even better, as it has no overlaps when newly laid. Over time though, overlapping seams may lift and allow water to enter. This is why the roof should still slope a few degrees.

When you have decided on your material, you can start designing the trusses. Find out which way you want the slope to go over your garage. That is also going to be the direction of the trusses. The shorter the span of the trusses, the easier they are going to be to make, and the less heavy-duty they need to be. To determine the distance between trusses and thus also the number of them, you should consult the user instructions for your chosen roofing material. It is usually somewhere around 2-3 feet. Flat roof trusses are easy to place on top of the loadbearing walls and you will quickly find the best way to secure them to the wall, as you lay them out. Next, nail or screw the the rafters on if you are using roofing sheets – or plywood decking, if you use roofing felt. Again, refer to the instructions for attaching the roofing material itself. Sheets are easy enough, while roofing felt requires some extra  equipment like a propane burner and some roofing asphalt. The last step is the finishing of the roof. This entails doing the overhangs, eaves, gables, etc. Basically, all openings must be closed or covered in such a way, that rain water or snow can not enter the roof counstruction no matter what. There are many products on the market for doing exactly that – no matter what your roof is made of.

A flat garage roof can be an easy and cheap way to get the job done, provided you see the pitfalls and do a proper job.

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Category: Garage Roofing

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