1947 Cape Cod Attic Insulation Advice Needed
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Lordoftheflies
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I was very surprised at how little weight the cellulose had bearing down on the drywall. I'm glad it was light. I scraped out the finer cracks and will build up thin layers of mud.
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At open-blow densities cellulose typically runs between 1-1.5lbs per cubic foot, so with ~18" of fluff you'd be looking at roughly 2lbs per square foot of ceiling, give or take. Looks like less than 2 square feet of patch, which wouldn't take a Schwarzenegger-esque physique to lift.
Lordoftheflies
Active Member
So today I found out where the mouse I just killed has been...........pooping.
Here is a good pic of how the insulation was installed on the kneewall incorrectly with the paper facing outwards. I think it wouldn't be too much trouble to just flip it around and have it facing the proper direction.
There was also no insulation on the hatch door minus that little pathetic attempt at insulating the gap. What people are thinking half the time I have no idea.
I used some fireblock foam on the gaps at the range hood vent. I also nailed down some of the floor boards that were rattling around a bit. Will tackle the PIC foamboard tomorrow.
I also basically threw everything out that was being stored in there. Haven't gone in there in a least 5 years so almost everything was completely useless.
Here is a good pic of how the insulation was installed on the kneewall incorrectly with the paper facing outwards. I think it wouldn't be too much trouble to just flip it around and have it facing the proper direction.
There was also no insulation on the hatch door minus that little pathetic attempt at insulating the gap. What people are thinking half the time I have no idea.
I used some fireblock foam on the gaps at the range hood vent. I also nailed down some of the floor boards that were rattling around a bit. Will tackle the PIC foamboard tomorrow.
I also basically threw everything out that was being stored in there. Haven't gone in there in a least 5 years so almost everything was completely useless.
Lordoftheflies
Active Member
The difference in temperature is amazing btw. Now the upstairs is the same as downstairs and you don't feel like you're walking straight into a sauna when you go up the stairs. Super happy with the results and even happier that I didn't listen to myself and instead listened to Dana and others. Thanks guys.
Lordoftheflies
Active Member
@Dana If I flip the kneewall insulation so the vapor barrier is on the warm side, is that safe? I thought it was bad form to have a double vapor barrier but typically I've seen that discussion regarding bathroom walls and/or basement walls with plastic sheets causing condensation and mold.
So should I............
1) Flip the kneewall insulation around
2) Remove the insulation completely?
3) Reinstall but remove the vapor barrier and support the fiberglass batting?
4) Leave it as is?
Regardless of the above I will install the PIC foam board on the rafters on top of the existing R-19 that is there. The board is R-4.4.
I will also install the foam board on the two side walls - one exterior, one facing the bathroom.
Here are some more pics.
So should I............
1) Flip the kneewall insulation around
2) Remove the insulation completely?
3) Reinstall but remove the vapor barrier and support the fiberglass batting?
4) Leave it as is?
Regardless of the above I will install the PIC foam board on the rafters on top of the existing R-19 that is there. The board is R-4.4.
I will also install the foam board on the two side walls - one exterior, one facing the bathroom.
Here are some more pics.
Lordoftheflies
Active Member
Got the first row done. I didn't even caulk between the boards after slitting it in half so it could fit the hatch - it's in there pretty darn tight.
Did the corner where the roof meets the side walls with the scrap I cut from the first now. Doing the second row now. Still deciding what to do with n eewall insulation. Leani g towards removing, dlipoing, and reinstalling.
Did the corner where the roof meets the side walls with the scrap I cut from the first now. Doing the second row now. Still deciding what to do with n eewall insulation. Leani g towards removing, dlipoing, and reinstalling.
Lordoftheflies
Active Member
That tape sticks really well. Thanks for the advice Dana.
Lordoftheflies
Active Member
Finished mine kneewall space today. Wasn't sure what to do when dealing the top edge of the foam board to the kneewall that has the insulation. Figured I would just foam it up on the heavy side but I think what is missing is a top plate.
I also had a few spots with the cap nails where I had to poke around a bit to find the rafters so I ended up putting a little piece of the foil tape over every cap nail. I had a couple of the caps pop off so at least this will prevent that from happening.
I also had a few spots with the cap nails where I had to poke around a bit to find the rafters so I ended up putting a little piece of the foil tape over every cap nail. I had a couple of the caps pop off so at least this will prevent that from happening.
Lordoftheflies
Active Member
More pics. You can see it's r-19 shoved into the 2x4 kneewall. I'd have to rip all that out and then out a top plate. Not sure if it is worth the expense or effort at this point. Any suggestions?
Lordoftheflies
Active Member
And having the paper facing away from the sheetrock....makes it a fire hazard, no? Is tht the main reason why faced Batts should be facing towards the sheetrock?
Kraft facers aren't true vapor barriers, and are not capable of preventing drying. It doesn't matter if it's on the cold-in-winter side of the assembly or the warm side.
Kraft facers are also impossible to make fully air tight, but are way better than an unfaced batt exposed to the attic space.
Yes, kraft facers are a fire hazard, and in locations used for storage fire codes would usually require covering them with a timed thermal barrier against ignition, such as wallboard. Wallboard would qualify, and can make a fairly robust air barrier when caulked to the framing, seams taped.
Kraft facers are also impossible to make fully air tight, but are way better than an unfaced batt exposed to the attic space.
Yes, kraft facers are a fire hazard, and in locations used for storage fire codes would usually require covering them with a timed thermal barrier against ignition, such as wallboard. Wallboard would qualify, and can make a fairly robust air barrier when caulked to the framing, seams taped.
Lordoftheflies
Active Member
Should I install more foam board against the kneewall then? I'd have to replace the insulation since it's r-19 that's sticking out a lot.......
Also, on my wife's side of the house I noticed the floorboard was missing for the area where the roof meets the joists. I think I need to put foam blocking and spray foam the gap on each bay. I'll have to pull up the floor on the side I did already to do as well. However, I don't have soffit vents so maybe it's overkill?
Also put a 2" piece of XPS foam on the hatch door. Will add weatherstripping next time I go to homedepot.
Found some weird note cards written with a fountain pen and a weird doll made in Japan......
Also, on my wife's side of the house I noticed the floorboard was missing for the area where the roof meets the joists. I think I need to put foam blocking and spray foam the gap on each bay. I'll have to pull up the floor on the side I did already to do as well. However, I don't have soffit vents so maybe it's overkill?
Also put a 2" piece of XPS foam on the hatch door. Will add weatherstripping next time I go to homedepot.
Found some weird note cards written with a fountain pen and a weird doll made in Japan......
It's fine to use foil faced polyiso as the air barrier for the kneewall. Codes still require a thermal barrier against ignition unless it has a fire rated facer, but even unrated polyiso is a LOT harder to light-off and spreads fire more slowly than kraft paper.
Glad to hear the upstairs & downstairs temperatures are starting to even-out, just in time for another heat wave!
Glad to hear the upstairs & downstairs temperatures are starting to even-out, just in time for another heat wave!
Lordoftheflies
Active Member
I never had that Corona. I settled instead for an A&W Root Beer + Haagen-Daaz vanilla float. That was amazing. Unfortunately the picture doesn't do the drink justice. It was AMAZING.
Ok I'll put up some more foil faced foam board. I suppose I should have the foil facing the attic side, yes?
When asked if the product was fireproof a Johns Manville rep replied:
So......should I cover the foil faced foam board that I just did in the crawl space with 1/2" sheetrock now?
Unfortunately the picture doesn't do the drink justice. It was AMAZING. Ok I'll put up some more foil faced foam board. I suppose I should have the foil facing the attic side, yes?
When asked if the product was fireproof a Johns Manville rep replied:
Hello, The AP foil faced foam product is not fire proof. The product is typically covered with either an exterior wall covering such as siding or an interior wall covering such as drywall. The product can not be left exposed as it will generate a great of smoke if exposed to a flame or heat source of sufficient temperature. Best regards, Doug Fast
So......should I cover the foil faced foam board that I just did in the crawl space with 1/2" sheetrock now?
Lordoftheflies
Active Member
And do you think putting the foam blocking in the joist bays is a worthwhile effort?
Blocking the joist bays is absolutely the right thing to do.
I'd just go ahead with sheet rock for covering the knee walls. The additional R value of doing it with foam board isn't buying you very much, given that there is an insulated roof between the kneewall and the great outdoors.
It's true that the toxic smoke is the bigger issue than flame spread when it comes to polyiso. As long as there aren't open ventilation or heating/cooling ducts in those kneewall attics the smoke would stay pretty local. Fire codes usually take that into account, but I haven't read up on your local code.
A root beer float seems about right!
I'd just go ahead with sheet rock for covering the knee walls. The additional R value of doing it with foam board isn't buying you very much, given that there is an insulated roof between the kneewall and the great outdoors.
It's true that the toxic smoke is the bigger issue than flame spread when it comes to polyiso. As long as there aren't open ventilation or heating/cooling ducts in those kneewall attics the smoke would stay pretty local. Fire codes usually take that into account, but I haven't read up on your local code.
A root beer float seems about right!
Lordoftheflies
Active Member
And just leave the foam board I already installed on the rafters and the sides exposed? Or to be on the safe side just cover that with sheetrock as well?
Lordoftheflies
Active Member
I have no ducting in the crawl spaces or the attic.
By some local codes the conditioned space side wallboard would be considered a sufficient thermal barrier when there is no ducts or ignition sources in the kneewall-attic space. Under some other local codes there would be a lesser ignition barrier requirement that could be met with something less than half-inch wallboard, especially if the space is used for (or could be used for) storage space.
To be 100% code-compliant in every ZIP code you'd be covering the foam on the rafters with half inch wallboard too. By losing the low-E facer it would knock about R1 off the "whole assembly" performance value, but the half-inch wallboard adds another R0.5 (and measurable thermal mass), so any efficiency hit from covering the shiny facer is miniscule.
Whatever your local codes are, the risks of exposed foam are still quite low for kneewall attic spaces that don't have ducts, water heaters or other active equipment in them.
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