How to handle this insulation situation
mculik5
| Posted in Energy, Heating & Insulation on
I will be having my attic sealed and insulated with closed-cell spray foam. For various reasons, and after a TON of research, I’ve concluded that this is the best approach for my situation.
However, there are two related complicating factors:
1. My house DOES NOT have eaves/soffits. The roof does not overhang the sides of the house at all. The only venting in the attic right now is two gable vents, and three roof vents (not ridge vents). There are no soffit vents.
2. My roof cuts into the second-story ceilings at the front and rear edges of the house (will make more sense if you look at the attached pics). These small sections of ceiling are effectively cathedral ceilings.
These sloped ceiling areas are basically inaccessible, and the spray foam contractor said he can’t spray foam into them because that would require a long wand on the gun, and the foam would cure in the wand.
Presently, there is some very old fiberglass batt in these areas (estimated R-8).
As shown in the attached pics, the spray foam contractor suggested building up the spray foam to form a sort of mini-knee wall where the roof meets the ceiling, separating the attic from the space above the sloped ceiling.
This approach makes me very nervous because:
– In the summer, warm, most air will enter the space and condense behind the ceiling because it will be cooler from the air conditioning.
– In the winter, the warmth going through the ceiling and limited insulation will heat the roof deck and cause ice dams when it snows.
The house is in climate zone 5A.
The folks on Green Building Advisor have said that they only solution is to tear down the sloped part of the ceiling, spray foam from the inside, and put the ceiling back up. This is a major project that I really don’t want to do if I can help it. They also said that filling the space with cellulose or rock wool might rot my roof deck.
Are their points valid? Are there alternative solutions?
Thanks.
Replies
As I was reading of your situation and before I got to the part about what the folks at GBA said, I told myself that, "... he needs to tear off that ceiling sheetrock and spray foam into the rafters." So that's what I think.
I also think you should stay away from that particular spray foam contractor. Because it seems to me that all he wants to do is score the easy part of the job and leave the rest to rot.
Darn...
Thanks for the reply.
OK - so everyone seems to agree that the only right way to do this is to tear the ceiling down. That's a much larger project that I'm interested in taking on. I also don't want to take a chance filling the cavities with cellulose or leaving them as-is, because if (or more likely, when) water gets in there, I'll have an even bigger project on my hands.
Here's my list-ditch idea:
Spray foam the attic as planned, BUT leave the gable vents/roof vents open, and DON'T build up the mini-knee wall.
My thought is that this approach won't change the current ventilation setup of the attic, but the insulation in the rafters will reduce the amount the attic heats up because of the sun.
For what it's worth, when it's mid-80s and sunny outside, the attic temp is 120+ (I put a data logging thermometer up there to determine this). My main goal is to reduce the attic temp, as this will reduce radiant heating through the ceiling upstairs, and help the HVAC equipment in the attic.
Then, when we put a new roof on in a few years, we can pull the decking off, spray the back of the ceiling, and fully seal the attic.
Any issues with this approach?
Heat arriving in home by radiation and conduction.
It is quite easy to pull the sloping part of the ceiling down.
I imagine it is drywall, this is easy to pull down, and easy to replace.
Placing spray foam in the gaps between the rafters will not attenuate the heat arriving in your home.
An better alternative, is to fix three inch thick sheets of polystyrene below the joists, and to cover these with drywall.
If it gets so hot every summer in your loft, the timbers there will be very dry and there is no possiblity of rot or mold.
If you are concerned about heat from the sun, radiating through the roof then:
You must realize that the roofs set up, sun shining on one side, heat transfering through the roof, by radiation and conduction via the rafters, will show very little improvement using the system you propose.
Alternative ideas, paint the outside of the roof white.
Grow some trees for shade.
Fix sheets of polystyrene below the rafters across the whole ceiling.
Consider that a lot of the suns heat arrives in your home by conduction and to fix sheets of polystyrne below all the joists.