Assuming your roofing contractor is using standard 36 wide 15 roofing felt double coverage means that each layer of felt put down across the roof laps 19 over the upper half of the previous course.
2 layers of roof sheathing.
Poor ventilation from a past roof along with 3 ply equals that delamination.
It got nailed over 2 x 12 joists 24 o c.
Based on the pictures alone i don t know what to say.
Nailing new shingles over existing ones is less expensive and faster requiring less labor but it also means you lose the chance to assess the sheathing for signs of water damage.
Wood shakes minimum 3 4 sheathing wood shakes nail type minimum length.
Most building codes allow for two layers of asphalt shingles on a house so stripping off everything down to the plywood sheathing may not be your only choice.
So anywhere along the gable end that you can see the felt you ll see two layers.
The first course starts with an extra 1 2 wide run.
Plywood is layers of wood.
I am replacing a roof right now built in 1982 and the 3 ply is delaminated pretty heavily.
Skinning over old sheathing does occur but i have never seen someone skin over plywood in that condition.
I think there are better ways to design an unvented roof for example by using rigid foam above the roof sheathing instead of closed cell spray foam on the underside of the roof sheathing.
On a 2 12 pitch roof.
Water shield is the next roofing layer that creates a water proof barrier where ice or water can buildup near the roof eaves.
Roof sheathing materials plywood.
If you re in search of quotes for a roof sheathing job improvenet can put you in touch with up to four local contractors for free.
It s up to you.
And if you re still wondering what roof sheathing is and what materials are typically used read on and satisfy your curiosity.
Plywood used for roof decking is typically called sheathing and carries a grade stamp indicating its load and span ratings and other performance factors.
It s usually a peel and stick product that adheres directly to the roof deck.
Roof deck is the roofing material that sits on top of the roof trusses.
Most roof decking is made from sheets of plywood.
Dimensional comp shingles over 3 tab 1 1 4 1 1 2 1 1 2 1 1 2 more than 1 layer of roofing not recommended over 3 8 sheathing.
Should you sandwich roof sheathing between two impermeable layers.