Replacing insulation for 4/12 pitch scissor truss roof with Vaulted Ceiling
Question: How to best remove and replace insulation on existing 4/12 pitch scissor truss roof with vaulted ceiling? We are in the Pacific Northwest near Seattle, WA.
We recently discover a sag which sits over a portion of the roof ridgeline composed of Scissor Trusses (see picture). The remainder of the large gable roof is composed of Fink Trusses with “W” webbing. I discovered that the metal gang nail connector plate connecting the center post on the truss and the lower chord of the scissor trusses were separating on four of the scissor trusses. The metal connector plates were also separating on much of the Fink Trusses as well.
In any case, it was concluded by insurance forensic investigation that the cause of failure on the scissor trusses were due to long term moisture variation from insufficient attic ventilation.
We have plenty of intake soffit vents but 5 years ago we had new blown-in insulation added on top of the old batt insulation in the scissor truss attic space. Unbeknownst to me, the insulation installer had also blocked the gable vents and the knee wall separating the scissor truss attic space from the fink truss attic space with cardboard.
As we proceed forward to do the necessary repair, we are intending to remove all the insulation in order to get access to all the metal connector plates. I am concerned about how to appropriately insulate the vaulted area of the scissor truss attic space. You will see from the photo that for the forensic investigation a portion of the drywall was removed from the vaulted room. The cellulose blown-in insulation is pile high above the batt insulation and blocking the soffit vents.
Our scope is as follow for the repair:
a) Structural Engineer to design plywood gusset to repair the separated metal connector plates on each of the trusses.
b) Remove all the insulation from the attic in order to inspect and repair the metal connector plates.
c) Truss repair with plywood gusset
d) Replace asphalt roofing and remove all wood sheathing with new wood sheathing for entire roof. Keep existing screen soffit vents but add new ridge vent.
e) Complete insulation installation during roof replacement from top of roof.
Per the scope of work, I am wondering how to best install the insulation necessary in the very confined scissor truss attic space and still get the correct “Attic Ventilation” so we don’t have condensation issues, or future issues with the trusses due to “insufficient attic ventilation”. The pitch of the roof is 4/12 pitch so near the eave it is nearly impossible to get at from the attic. However, the wood sheathing will be replaced during the reroofing. Is there a way that the installer can add baffles on the wood sheathing from the soffit to the ridge vent? Will the baffles be adequate as lack of ventilation in our attic has been a huge nightmare.
What type of insulation is best for this scope of work? Will loose cellulose blown-in insulation be appropriate.
Is there a better method for ventilation on this type of vaulted roof system besides soffit vents with baffles (which gets completely blocked by insulation) and ridge vent?
Any precautionary measures that I should take?
I read of rigid foam insulation on top of the wood sheathing but how will that work when the remainder of the gable roof is made of fink trusses? Would you rigid foam the entire roof and the attic space would be without any insulation? I’m a little confused regarding the rigid foam? I don’t know if there are any installers of rigid foam in our area. I like to avoid using spray foam because of the chemicals used and issues with potential smells if it is incorrectly applied.
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