Garage Roofing Part 3 – Building the Roof

In the previous two installments of our garage roofing series, we have looked at how to plan the work, whether repairing an existing roof or building a new one. We have also looked at the process of choosing garage roofing materials depending on your needs and budget. In this last part, we will finally get to the building itself. You will get tips on how to approach the work, along with some do's and don'ts. Let us begin.

If you are building a garage from scratch, you may already have started on the roof at this point. Some people like to construct the roof trusses as part of the wall structure – where each truss stands on two vertical pillars, and each of these sets of trusses and pillars make up one cross-section of the whole building structure. This can be a bit cumbersome to work with in some cases, so to do it in a way that is a bit more manageable, I would erect the wall structure first, stabilize it, and then put up the trusses. When you are ready to begin work above head-height, you should strongly consider putting up scaffolding to stand on. It is not only safer to work from than a ladder, but also easier, as you have both hands free to work.

Erecting the trusses
This is a job for two to three people. First thing to do, is mark the position of each truss on the top of the walls, where the trusses will eventually be fastened. The distance between trusses is dictated by the needs of your chose roofing material. Heavy materials need a lot of support, meaning less distance between trusses. The first truss is then lifted onto the top of the walls, so that it straddles what will become the floor of the garage. The truss is then erected by tying a long rafter to the very top of the truss with a bit of line – and then pushing it to an upright position. Two people are ready to position the lower chord of the truss on its precise locations on both walls, while a third person stands on the ground between the walls and pushes the truss upwards with the rafter. The truss is then secured diagonally at first – a rafter can be nailed to the truss and the wall, holding it in its upright position.

Now you can anchor it to the wall. When the next truss is erected, it can then be temporarily anchored to the first one, stabilizing them both. Keep going this way until all of the trusses are up. Once all the trusses are in the right place, with the right distance between them and centered over the walls, it is time to do a little extra stabilization – especially if the roof is a pitched roof. First, you want to secure the roof against wind forces hitting the gables. Think of it like this: What you want to do, is prevent the trusses from keeling over like a house of cards. What you do, is install some form of bracing running diagonally across each side of the roof. These could be rafters, but even better is to use steel straps specially made for this. You should also anchor each side of each truss to some point at least half-way down the walls – preferably as far down as the foundation. This helps protect against wind-forces that might otherwise rip the entire roof off completely.

Adding rafters or decking
Before laying the your chosen garage roofing material, you need to put up rafters or decking, depending on the material. Plywood decking is pretty much only used with asphalt roof products such as roofing felt or asphalt shingles. Most other products use rafters. To figure out the dimensions and density of the rafters you should consult the documentation supplied with the roofing material – or better yet, talk to an engineer. The easiest way to attach rafters and decking is to use a pneumatic nail-gun. They can be quite expensive, but are often available to rent. It takes a lot of nails to build a roof, so going at it with a hammer is really a lot of work – probably too much. If you decide you need to add extra rain water protection, you could add a plastic barrier right between the trusses and the rafters. It will then be nailed down along with the rafters. Just be careful not to tear it anywhere, as that any holes will defeat its purpose.

Laying the roof
Now it is time to finish your garage roof. If you have chose roofing shingles of the sort that must be laid on rafters, it is a good idea to start out by making a number of small stacks of shingles evenly on the rafters. That will allow you to do the actual laying out in a much more even flow, than if you had to climb down to the scaffold to get each shingle. Whatever the material, be careful if you have to walk on it. Some types, such as slate roofing and clay tile will not like it if you walk straight on them, so try to avoid that. If you are laying asphalt shingles, they will also need to be nailed down, in this case to a plywood deck. Again – we're talking a lot of nails here, so that nail-gun is pretty much a necessity.

This was the final chapter of our little garage roofing series, so I hope you can take away some useful information to use in your next roofing project. Do not forget safety comes first!