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How to Tie Roofing from an Addition to Your Home’s Existing Roof

If you are adding an addition to your home, it’s important that the roofing of the new structure be tied firmly to your existing home.

The first thing you need to do is have the engineer who designed your addition determine whether the trusses of your home can support the weight of the new roof. Once the engineer signs off on it, the next priority is to keep your home weather-tight during construction.

Building the New Roof

The first step is to set the new rafters or trusses on the addition’s walls up to the point of the eave of the house. Then snap the chalk lines on the shingles to mark the center of what will be the new valley.

You can either strip the shingles from that area or simply leave them in place and frame over them.

Next you want to install a valley board over the old shingles to create the solid nailing surface you will need to install jack rafters. Once these two boards are nailed down, apply roofing cement on the nails and along the outside edge to prevent possible leaks.

Tying in the Shingles

Use a cut valley to tie in the new shingles with the old. Once the addition’s roof has been framed and sheathed, you want to snap a line on the existing roof shingles about two inches above the center of the valley.

Then cut through the shingles and underlayment, unseal the shingle tabs and pop the nails of the overlying course. Then you want to remove two shingles on each side of the new valleys until you reach the bottom. Save and number these because you will be replacing them later.

Almost There

Lifting the underlayment out of the way, lay the waterproof shingle rule underlayment over the valley, then shingle the addition to the roof, allowing the new shingles to fold through the center of the valley and onto the existing roof deck by at least 12 inches.

Re-lay the shingles you removed earlier, bed the end of each shingle with a 2-inch ribbon of roofing cement placed about 4 inches up from the center of the valley, and you’re done!


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