How to Convert a Flat Garage Roof to a Pitched Roof

What You'll Need
Prefabricated roof trusses

A flat garage roof isn’t the best thing to have on a structure as it’s subject to pooling water and snow. Changing the garage to a pitched roof takes work but brings greater protection as well as more room in the garage. It’s not an easy job, and requires at least two people, but the results are worthwhile, and you don’t need extensive knowledge of carpentry to do it.

Step 1 - Remove Flat Roof

Before you can properly measure for you pitched roof you need to remove the old flat roof. Take off any shingles and covering, followed by the plywood of the roof and discard. Inspect the structure that remains for any rot in the wood. If all is fine then you can proceed. Pay attention to the spacing of the joists and be certain they can hold weight.

Step 2 - Trusses

The simplest way to replace the flat garage roof with a pitched roof is to use prefabricated roof trusses. Measure the width of the garage to know how long you need them to be, and count how many joists there are along the length. You should put a truss over every second joist.

Start by putting a truss at the front end of the garage. You’ll need to connect it to the wall structure and joists with base plates that have been bolted in place. After this put more another roof truss on two joists away, using the same method. Connect the two at the ridge for strength. Continue to add trusses until you reach the other end of the garage. If you need to leave the work overnight, cover the entire roof area with tarps.

Step 3 - Plywood

Before covering the roof with plywood you will need to measure and cut plywood for the gable ends. Attach the screws to the sides of the roof trusses. Once you’ve done this, cover the roof with plywood, cutting the sheets where needed and hammering into place on the roof trusses. At this point your flat garage roof has taken on an entirely new shape.

Step 4 - Roof Covering

With the pitched roof in place, now you need to cover it. Start with tarpaper, running it in rolls along the length of garage and working up toward the peak. Making sure it's flat, nail in place. This will create waterproofing for the plywood. Over this you’ll need to place the shingles, again working up toward the peak and finishing with ridge shingles to ensure water doesn’t enter from the top.

Step 5 - Gable Ends

The pitch roof is now covered, but the raised gable ends are still bare plywood. To finish them off you’ll need to cover them in the same way that the rest of the garage is covered, typically with siding. This is easily installed directly over plywood. Complete by priming and painting the siding and the flat garage roof has been transformed.