Hello – Can I ask you guys a question:
We have a Bungalow with 2×4 roof line framing – a finished attic – and no insulation in the roof line. [Due to comfort issues] The 2nd floor is basically unusable for the owner (they recently bought it after a rehab).
We can get R49 across the top [attic] portion – as the span and height is wide enough. We can insulate along the roof line in the unfinished knee wall space with batts and foam board and bring into the space. So the span from top of knee wall to flat portion of attic is the tricky part of course. Slow rising foam is not practical for these owners or most owners.
So often the potential options can be viewed as:
-Dense Pack the 2×4 space with cellulose – no venting of course (potential moisture horror stories of dense packing a roof notwithstanding).
-Loose fill the 2×4 space will cellulose – no venting of course (while not dense packed we do come across many old homes with old insulation blown into these area that do not appear to have moisture issues in the roof line.
It Seems like retrofitting with spray foam is cost prohibitive [and the] above are the practical real life options for people.
Any thought and/or comments on these different approaches?
Clifford the Big Red Dog ____________________________________________________________________
This is an unfortunate circumstance for the homeowner… Your approach for the side attics and top portion are great and I suggest implementing those (is the attic portion vented?) Additionally, I suggest air-tight blocking between the stud bays of the knee wall where they meet the roof line.
Now, the tricky part: there is really no safe way to do this that I would feel 100% comfortable with using cellulose alone (dense or loose). For our climate zone and this roof type, the IRC says you must do one of three things:
1) Insulate entirely above the roof deck with rigid foam
2) Insulate with a combination of rigid foam above the roof deck and air impermeable insulation below
3) Air impermeable insulation below (with possibility of some loose fill in conjunction if the foam is thick enough)
That said, all of these are probably not an option for this project, so I would let the client be aware of the possible negative side effects before moving forward. If I had to choose one of the two options you had suggested, I would go with loose fill fiberglass instead of dense pack cellulose. Less dense fiberglass doesn’t hold as much water and will dry out easier. There will also be greater circulation of air through the insulation, which will help dry if moisture is accumulated.
I hope this helps! Good luck and let me know if you have additional questions!