What are my options to replace fiberglass insulation in vaulted ceiling?
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| Posted in Energy Efficiency and Durability on
The vaulted ceiling is scissor truss construction with a 6/12 ceiling and 9/12 roof pitch. I’ve been in the attic and have very limited access, but I can see wires running through the insulation, gaps, and no insulation on top of the ridge peak. In order to replace the insulation I figure I will have to remove sections of the drywall for access from below. When I gain access from below I could rake out the fiberglass insulation and then use some type of blowin insulation. What insulation could I have blown into this space with a 6/12 pitch?
Thanks for the advice.
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Are there insulation baffles in place in each rafter bay at the eaves?
Only one side of the scissor truss is on a outside wall. The other side joins into the attic that has a flat ceiling. The outside soffits are enclosed and there is a baffle on every third rafter bay. I presume you might have a concern with ventilation and moisture. The entire roof has a ridge vent and the portion of the house with a flat ceiling has gable vents plus the small round soffit vents. I live in Northern California below the Oregon border where relative humidity is low. The local energy consultant is not concerned if the soffit ventilation is closed off with new insulation as this would only happen one side of the house.
We just completed a scissor truss job. Because the space was tight at the eaves and we couldn't get the cellulose thickness we wanted at the eaves, we sprayed the lower ~4 feet down to the eaves with about 8" of closed cell foam Above that, we blew in about 20" of cellulose. This was new construction, to retrofit (your case), all the drywall at the eaves would obviously have to be removed for access. Not easy, but doable and cheap to repair.
Thanks Jim,
Using closed cell foam at the eaves to attain a higher R-value is a great recommendation which I now plan on using. The local insulation contractor says blow in cellulose can't be used because the vaulted ceiling is 6/12 which results in sagging. They recommend removing most of the drywall and doing a proper job of installing the fiberglass insulation. I don't understand the theory of using fiberglass insulation in a vented area since fiberglass batts are open cell and would allow air circulation lowering the actual R-value performance especially on the nights when it gets below freezing. Is there blow in insulation that has a binding agent that would address the sagging? The contractor tells me any blow in insulation with a binding agent has to be applied perpendicular to the surface which they say can't be done in my situation.
Brad, remove all drywall, strap ceiling at desired spacing 16" or even 12" if really concerned, then the drywall will hold a tank.
Brad,
1. If you choose fiberglass insulation (whether batts or blown-in) or cellulose insulation, you MUST ventilate each rafter bay. For more information on this issue, see How to Build an Insulated Cathedral Ceiling.
2. The best insulation in this situation is probably spray polyurethane foam. If you choose spray foam, you don't need to ventilate.
Hi Martin,
I agree the best solution is removing the drywall/fiberglass insulation and spraying with polyurethane foam. What are my options to create a 8-10" deep surface between the scissor truss? I need a surface to spray the foam against from inside the room. My next question is: Since I have to redrywall is there a insulating sheathing product for the ceiing to replace the drywall? I plan on paneling the ceiling with tongue and groove wood. This insulating sheathing would also give the benefit of creating a thermal break from the scissor truss.
Thanks so much,
Brad