Help me Obi-Green Kenobi: an attic insulation problem
The house: built in the 1930s in Climate Zone 3C and in desperate need of a new roof.
The roof: mostly flat, with two smaller peaked sections, one of which is halfway covered in curved Spanish tile.
The attic: very small. There’s about 12-18″ of space between the ceiling and the roof deck. There’s physical access to maybe 5% of the attic via a tiny door in the split-level bedroom. Ventilation is provided by several circular holes around the roofline. There’s also some knob and tube wiring, which we can’t afford to replace at the moment.
The insulation: there isn’t any. And fixing that situation is has become a rock/hard place situation.
Recommendation #1 from ABC Insulation: when replacing the roof, lift up the roof deck and put down either R-19 or R-38 rigid fiberglass boards, leaving several inches around and above the K&T wiring.
Recommendation #2 from XYZ Insulation: no, no, Rec #1 is a terrible idea as the boards wouldn’t provide enough insulation. Instead, keep the roof deck in place, add a layer of insulation above the roof deck (which is a more complicated/expensive roofing job), then seal off the ventilated attic.
No, no, says ABC Insulation. Rec #2 is a terrible idea as it’s both more expensive and it would be very difficult to fully seal the attic since the edges can’t be insulated, nor can it be air sealed well since you physically can’t be inside the attic. A less-than-sealed attic will result in condensation and major problems down the road.
Please help. I’m at my wits end here as we very much need the insulation but also can’t afford to either a) invest in something that won’t actually help (e.g., insufficient insulation) or b) create a massive problem for us later (i.e., the condensation).
Much appreciated!
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Replies
It's hard to judge without pictures/diagrams and I am not a pro but this sounds like an awful lot of fooling around to maintain some K&T wiring that you really should replace. And once you do either of these options, you are then not going to want to touch that attic for a very long time - locking yourself into continuing to use that wiring for the long haul. If you are going so far as to remove the entire roof deck, the limited amount of K&T wiring in your attic should be simple to replace and then you have simpler/cheaper/easier/safer options for how to you deal with your insulation.
What is the construction of the roof? Is it trusses?
I'd probably opt for:
1) Remove as much roof deck as needed to gain access for the required work. You may be able to leave large sections in place and take a more surgical approach.
2) Replace all K&T wiring
3) Air seal any holes into the ceiling cavity from your conditioned space (can lights, etc.)
4) Insulate the ceiling cavity using a combination of blown in insulation and batts, being sure that you leave a few inches below the roof deck for air flow and that your soffit vents are not blocked.
5) Install your roof. You may want to consider active ventilation given how flat the roof is. They make little solar powered roof vents that may work well in your climate.
There is probably a third option:
1) Cut holes in your ceiling to gain required access to the attic from below
2) Replace all K&T wiring
3) Block off all vents in the soffit
4) Use spray foam from below to fully insulate and seal off the attic space
5) Repair ceiling drywall
6) Replace roof (leaving roof deck in place)
Thank you, CD! I appreciate the brainstorming.
I think you have to surrender to the reality of replacing that wiring before doing anything
Most electricians around here won't work on it, so if anything goes wrong, or you want to add on something, it has to be replaced anyway.
It is not unsafe per se, other than lack of a ground, but it really is the first thing before insulation.
Sigh. Thanks, gus. I appreciate the perspective (even if I don't like the price tag).
My preference would be to insulate on top of the roof deck using rigid foam, which is usually polyiso. This is the normal way to insulate a commercial building's flat roof, so there is nothing unusual about it. This is likely have fewer potential problems down the road than trying to do anything to insulate the interior of the attic. Open a strip of roof deck around the perimeter to air seal the edges as needed, that shouldn't be that big of a deal to do if you're doing a full reroof project anyway.
I agree with the other posters that it's a good idea to replace the old knob and tube wiring regardless. You could potentially open up more of the roof deck to allow access to do that electrical work, so this would be a good time to consider a full rewire of the areas using K&T right now.
Bill
Thank you, Bill! Helpful to hear.