Old shingles can curl over time.
New rafters over existing roof.
Some roofers install a layer of waterproof shingle underlayment wsu over the existing shingles at the eave end as would be done for a roof laid on bare sheathing.
There s a lot of visible damage.
We are planning to frame the new roof over the existing roof.
To increase the strength of your new and existing rafters and to help eliminate the chances of sideways movement consider installing a support board across the rafter endings on both sides of the roof.
Dh is a very skilled carpenter and is confident that he can do this work.
Use premade roof trusses premade roofing trusses will be easier and take less time than installing a stick built roof.
This provides added protection against ice dams.
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You need a flat surface to install a new roof over existing shingles.
Installing a new roof over an existing one also called a layover or nailover is often possible although not always the best option.
Mold rot or other significant damage needs to be taken care of with a full replacement not hidden by new materials.
The cheapest option would be to leave the old roof in place and place the new rafters over the existing roof.
We simply slid the straightedge over until it hit the shed roof and then positioned a 2 by under the straightedge and marked the edge of the 2 by.
A properly installed layover roof can look and function as well.
To make the blind valleys we attached sleepers to the shed roof locating them by placing a 14 foot straightedge that is usually used for screeding concrete on top of the porch rafters to project the plane of the new porch roof over to the surface of the existing shed roof.
The roof sheathing on the old roof is not rotten just not up to the standards my dh thinks it should be.
We aren t planning on going up a floor so the roof would only be marginally higher than it is now.