How to Replace a Garage Roof Rafter

What You'll Need
4x4-inch posts

When you have a problem with a roof rafter in the garage, it’s important that you immediately take care of it to keep the roof secure. This can seem like a huge job, but in fact, it’s not too difficult. In face, you won’t be replacing the rafter but adding a support on the side along its length, a process known as sistering. This will give you all the strength you need. Follow the simple steps below to replace a roof rafter in your garage.

Step 1 - Wood

The sister rafter need to be as wide and as deep as the original rafter. It also needs to be only slightly shorter on each end. The longer the sister, the better support it will give. Measure your rafter and select a piece of wood that’s straight, of the proper dimensions, and cut it to the length you need to be a sister rafter.

You’ll also need a pair of long 4x4-inch posts. These need to be of an adequate length to support the original rafter above and below the problem area. Measure the height and cut the post appropriately.

Step 2 - Support

Stand up the post that will be below the problem area and hammer into place so that it gives firm support to the rafter, keeping a straight. Now take the longer post and hammer into place so it gives support above the problem area. These will also act a supports for the sister rafter when you’re fixing it in place.

Step 3 - Rot

If the problem with the rafter is rot, once the rafter is supported above and below the rotten area, you’ll need to take out the wood that’s rotted. Do this with a saw, being certain you remove all the rotted area. On the side opposite where you’ll place the sister rafter, have a piece of wood the same width and depth as the rafter, but 12 inches longer in each direction than the rotted area. Nail in place to offer extra support.

Step 4 - Sister Rafter

You’ll need help to put the sister rafter in place. One person should be at the top, where the rafter joins the roof peak, and the other where the rafter meets the wall. Once it’s in place, start by nailing the top of the sister in place while the other person nails the bottom in place.

Use nails that are long and strong enough to go deep into the original rafter. The nails should go along the top, bottom and middle of the sister and be spaced 6 inches apart. This will give a very firm bond and keep the original rafter straight. Once you’re satisfied that the sister rafter is firm in place and giving good support to the roof, it’s time to remove the supports. To do this, knock at the top of the posts with the hammer. Start with the longer support, and hammer toward the center of the garage. Have a friend to hold the support so it doesn’t fall. Repeat with the other support.