It is not possible to mix materials nor to install a new layer over slate or wood tiles.
Installing new roof over existing one.
Installing a new roof over an existing one can only be done if you have shingles because you can only put shingles over shingles.
Installing a new roof over shingles takes less time than tearing off the old 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.
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.
Installing a new roof over an existing one also called a layover or nailover is often possible although not always the best option.
Another reason is curling shingles as you can only install a new layer if the first one is completely flat and level.
Before you reshingle a roof read our step.
Beveled wood pieces called horsefeathers must be laid along the thick edges of the shakes to make a fairly flat surface.
You need a flat surface to install a new roof over existing shingles.
Looks just as good and lasts as long.
There s a lot of visible damage.
A properly installed layover roof can look and function as well.
Old shingles can curl over time.
Premade trusses will form the skeleton of your new roof above your old roof.
Use premade roof trusses premade roofing trusses will be easier and take less time than installing a stick built roof.
As long as it s done right and under the right conditions installing new shingles over old ones can last as long and look just as good as a complete re roof.
Asphalt shingles can be laid over cedar shakes or shingles however this is a roofing project best left to pros.
This provides added protection against ice dams.