How best to insulate my attic
Hello everybody. I’m new here, have been reading for about a month. Really great stuff.
I’m looking for some advice on how best to insulate my attic.
Here is my situation: This is my first house, and hopefully my last. It’s a circa 1900 Edwardian 3 storey (3rd storey is attic) in Ottawa, Ontario, Canada. The attic is roughly 1000 sq feet. It currently has about 2 inches of rock wool batting under the mostly intact rough floor boards. The floor joists are 24 inches apart and there is a 7 inch gap between the attic floor and the 2nd floor ceillings. I don’t plan on using the attic (or atleast, not in the next 15-20 years). The attic is vented well (according to home inspection). The reccomended insulation level in my area is R40, however R50 is ideal. The door leading to the attic will also be insulated, caulked, etc.
Ok – here are my ideas:
1. pull up the floor boards, remove old insulation, add a vapour barrier (caulk barrier to joists) and replace with R24 under the floor and R30 on top of the floor running perpendicular to the joists.
If I add a vapour barrier, do I need to worry more about moisture?
2. pull up floor boards, remove old, add new to R50 without vapour barrier.
3. Forget about old under floor insulation, add vapour barrier on top of existing floor baords, lay R30-R40 insulation on top of vapour barrier.
Will this cause moisture below the floor? Is this a viable solution? Is it worth doing yourself ( I know it’s a sucky job!), or should I consider having a pro spray foam into the wallks and ceilings up there.
Any responses would be greatly appreciated. Thanks in advance.
Replies
My comments:
1. pull up the floor boards, remove old insulation, add a vapour barrier (caulk barrier to joists) and replace with R24 under the floor and R30 on top of the floor running perpendicular to the joists.
If I add a vapour barrier, do I need to worry more about moisture?
Leave old insulation in place if not contaminated with rodent/batt droppings. Do not lift up all boards to install vapour barrier. Lift at appropriate locations to airseal attic penetrations and install blown cellulose under boards and over boards if you don't need the space or you could added fiberglass bats over the boards. Forget about the other methods.
Consider drop in weatherstripped, insulated hatch cover for the stairwell. Eliminates having to insulate stairwell wall cavities and under stair treads, back of door plus weatherstrip door.
If the house is not damp from basement, stored firewood, etc , the kitchens/ baths have good ventilation to the outdoors, and you do your airsealing well, then moisture should not be a problem. In the coldest weather you may see a bit of frost on nail points sticking through roof boards or a slight skim coat of frost on boards, but these should not cause problems. Researchers have said that it is impossible to prevent all frost/condenstaion and, in fact, may not be necessary to do so. That would be perfection and do we need it? or will we drive ourselves crazy looking for it?
pierre... i'd do it exactly the same way as experienced...
all cellulose... about 24" , assuming a settled depth of 20"..calculate the bag count ... section it off and have at it..
the prep work is most important... air seal with gun foam... dams at the plate lines
if ou can... have the house tested with a blower door before & afterMike Smith Rhode Island : Design / Build / Repair / Restore
That's funny. I'd have said, "Leave old insulation in place particularly if contaminated with rodent/batt droppings."
All kidding aside, rodent and bat droppings can be bad stuff. Think hantavirus and airborn rabies. If there's a lot of such detritus, it might be worth hiring a pro. If just a little, I'd blow right over it. Andy Engel
Senior editor, Fine Woodworking magazine
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None of this matters in geological time.
Ok - that sounds like a better fit, and seems to agree with what I've been reading. I actually had my blower door test yesterday, but the inspector couldn't give me a straight answer about how best to insulate up there.
Thanks again guys.
A little finer call, Andy, but makes sense. I should have mentioned the pros if cleanup was necessary but I just assume most people would not attempt to clean a serious contamination by themselves.
Be careful with flooring or sheathing over insulation in the attic. I installed flooring over loose-fill cellulose. Moisture was migrating from the rooms below and condensing out on the bottom side of the floor above. I have since done two things.
1. Applied two coats of Zinsser BIN on the interior side as a vapor barrier.
2. Elevated the floor sheathing about 3 inches to allow air to circulate and evacuate the moisture. Problem is gone.
Had you done "comprehensive" airsealing at all attic penetrations??