1947 Cape Cod Attic Insulation Advice Needed

Discussion in 'HVAC Heating & Cooling' started by lordoftheflies, Jun 29, 2019.

  1. lordoftheflies

    lordoftheflies Active Member

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    Yeah no active equipment in any of the crawl space.

    I started blocking off the joist bays with the 2" xps foam. Fun times as I had to rip up one of the floorboards - no access to get the spray foam can in there. I will have to remove two rows of floorboards on the other side.

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  2. lordoftheflies

    lordoftheflies Active Member

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    Did the third knee wall crawl space today.

    I'm concerned about the missing top plate in the knee wall itself. On the other two I the faced insulation (faced the wrong way) kind of lent itself to making it easy to just spray foam where the foam board meets the knee wall. On this one there was only unfaced insulation that's thicker than r-19 that was way too thick and kept falling over and was held in place with cardboard and spare foam pieces (all done by my contractor buddy who obviously doesn't know what he is doing).

    So, I think my plan of action now is:

    1. Remove all the knee wall insulation
    2. Install blocking in each knee wall stud bay with 2x4s.
    3. Buy some R-15 rockwool for the 2x4 stud bays
    4. Buy some more foil faced foam board

    How does that sound @Dana?

    The only "active" thing in any of the knee walls are the pull chain light fixtures. Actually, on the one I was working on today the traditional incandescent bulb was touching the faced paper of the insulation and it was all black around the bulb. I can't believe I never noticed that before. I moved it lower (needless to say I know).

    On the other side of the rockwool is the bathtub.

    2019-08-13 15.15.39.jpg

    Below you can see how much the existing batts are sticking out of the 2x4 studs.

    2019-08-13 15.15.47.jpg
    Installed more 2" xps foam board in the joist bays to air seal.

    2019-08-13 17.30.25.jpg

    What a mess.

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    I can't tell what it is but it's quite a bit thicker than R-19 (you can see the R-19 that's faced and it doesn't stick out that much)

    2019-08-13 17.30.42.jpg
     
  3. lordoftheflies

    lordoftheflies Active Member

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    Actually I only had to remove one row of flooring from the 1st knee wall space.

    Now all 3 spaces have the joist bays blocked off and foamed. I will have to remove 2 built in drawers in the remaining section of knee wall space in order to insulate.

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  4. lordoftheflies

    lordoftheflies Active Member

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    Regarding 4.

    I was thinking maybe 2" xps foam board would be nice...but at $34 a sheet............compared to $12 for 1/2" sheetrock.....But then the foam board is R-10 vs R-0.5.

    The foil faced 3/4" foam board is $16.24 a sheet........

    Hm............
     
  5. Dana

    Dana In the trades

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    If most of the R-value is at the roof deck there isn't much benefit to adding foam board to an R13-R15 insulated kneewall. XPS is about the worst thing you could do for it, since it has the highest enviromental cost and highest $/R.

    The batts do need an air barrier on the attic space side, but that could be drywall. If you wanted to bump up the R value with continuous foam that's OK, but if you're not going to also install drywall over it don't use polystyrene (EPS or XPS), since it has worse characteristics from a fire.smoke hazard point of view. Foil faced polyiso (any thickness) is somewhat safer, but polyiso with a true fire rating is best. Since there is probably wiring in that kneewall (?) with at least some potential for starting a fire it's in a different category than using it on the rafters.

    With the batts that are too thick for the framing it's fine to leave them in place and just trim them almost-flush with the stud edges with a batt knife, leaving a half-inch to an inch of batt proud of the stud edges to guarantee a compression fit. I suspect they're R25s (8' nominal loft) designed to fit into 2x8 framing bays (7.25" deep), which when fully compressed into a 2x8 bay perform at about R24. If you leave fully an inch of compressible excess it'll be about R15 when compressed to 3.5" in a 2x4 bay.
     
  6. lordoftheflies

    lordoftheflies Active Member

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    The roof deck has R-19 batts and the R-4.4 foil faced polyiso....so not quite enough for the climate zone.....So if I do what you say with the existing batts and 1/2 drywall that will leave 19 + 4.4 + 15 + .5 roughly = R-39.

    For fireproofness then wouldn't using rockwool be the ideal choice? I'd rather just rip out everything that's there only because it's install the wrong way anyways and I won't need a vapor barrier with the rockwool either. I think two bags of the thermal batt will be sufficient and it's easier to work with than fussing around with the batts.

    There is only one outlet on the kneewall of one of the spaces. The other two don't have any outlets and the only wiring is for the pull chain light fixture. Also, I do have AFCI breakers at the panel for all living space homeruns......

    What about adding top plates to the knee wall stud bays? Worthy of the effort and cost?

    Thanks Dana.
     
  7. Dana

    Dana In the trades

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    From a code compliance point of view you can't just add the kneewall R to the roof deck R- in fact only the roof deck R counts, even though an air tight insulated kneewall is still doing something.

    Yes, rock wool is considerably more fireproof than fiberglass.

    You don't need a vapor barrier with either fiberglass or rock wool, but both need an air barrier to perform fully to spec. That air barrier could be housewrap, drywall, foam board, masonite, MDF or any number of materials as long as it's sealed.

    Installing blocking to prevent air from moving through the kneewall attic is important for overall thermal and moisture performance. That blocking could be made of foam board, if you like. Even cut-up corrugated cardboard sealed in place would work- the idea is to prevent convection or wind currents from becoming a thermal bypass through the kneewall attic that is insulated at both the roof deck and kneewall. I'm not sure if fire codes would require a 2x4 blocking there, but using high denstity rock wool batts does a pretty good job as as a fireblock in stud cavities, even if not fully addressed by code.
     
  8. lordoftheflies

    lordoftheflies Active Member

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    Well, I think solid blocking (foam board or wood) will be the way I'm going to go. Along with removing the batts and installing rockwool.

    Today I took out one of the built in drawers/dressers in the kneewall. Let me tell you, whoever built this should be shot. Nothing was sealed. The floor of the dresser was completely exposed to the attic...which is why the drawers always smelled terrible......because I found about 800lbs of mouse droppings in the space.

    The rockwool insulation was pitiful. In two of the rafter bays the insulation had just fallen down.

    What a disaster and I'm glad I decided to open it up...because just like everything else in this house, it was done horribly quick, cheap, and lame.

    Here it is with the drawers removed. Look at the floor. What is THAT?? There was some kind of paper faced foil.

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    No sealing done in between the drawers and the wall.

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    Look at the base of the dresser! WADUHECK?

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    This is what it looked like when I pulled the frame out.

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  9. lordoftheflies

    lordoftheflies Active Member

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    Here I'm looking sideways towards the center of the house and there's a dormer on the other side of the wall.....The roof extends past the dormer and I won't be able to get in there to do anything.

    2019-08-15 17.30.28.jpg

    Just to the right of this picture is brick where the chimney goes up on the outside of the house.

    I AIN'T NO EXPERT BUT I DON'T THINK I'M SUPPOSED TO BE ABLE TO SEE THE BLUE SKY FROM INSIDE OF A SEALED WALL NOW AM I??

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    Oh and what have we got here? A nice buried junction box. What an absolute joke.

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    Almost all cleaned up. Will remove the rest of the poop infested insulation next time. Tacked down a piece of plywood. Not sure why they tacked down such a skinny piece of wood (they actually doubled it up on top of each other smh).

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  10. Dana

    Dana In the trades

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    Aluminized kraft facers on batt insulation was pretty common in the very late 1950s into the mid-'60s, but fell out of favor in cooler climates since they sometimes created moisture traps and mold conditions due to the extremely low vapor permeance of the thin foil. They are still sometimes used in the cooling dominated regions of the US, giving a low-E/radiant-barrier affect when facing an air gap (such as an open attic.)

    I'm also pretty sure you shouldn't be seeing blue sky through the wall. Perhaps you should only go in there at night or when it's cloudy. :)
     
  11. lordoftheflies

    lordoftheflies Active Member

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    It wasn't batts underneath the foil - it was literally just paper + foil for some reason. Anyways, all that old insulation is gone. I got some DAP Dynaflex caulk to fill in that hole to the blue sky. Boy, that stuff is super soft. Slathered it all over where the brick met the sheathing. Installed two pieces of 14" wide rafter vents per rafter. I decided to skip the skinny one because it was too skinny. I think I'll just use a can or 2 of spray foam and call that a day.

    I must have vacuumed up about 10 lbs of mouse droppings. All clean now.

    2019-08-26 16.54.11.jpg

    Unbelievably it looks like there is blocking between the joists. But it was not sealed so I hit it with the foam.

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    Here if you zoom in and look hard you can see the plastic rafter vent and the proper gap between the roof deck on the sloped portion of the kneewall. Yay!

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    After caulking I just decided to foam it up on the brick. Not sure why it was just exposed brick there in the first place.

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  12. Dana

    Dana In the trades

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    Aluminized paper with foil on one side is just a cheaper version of radiant barrier than most of what is currently in the market.

    The low-emissivity/high-reflectivity of the aluminum has some affect on cooling loads when the foil side is next to a film of air 0.1" or greater (such as a whole attic), but it's hardly the same as "real" insulation, even if it's a product with shiny aluminum facing an air gap on both sides.
     
  13. lordoftheflies

    lordoftheflies Active Member

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    Installed the baffle vents, new insulation (R-19 for the rafters, R-13 for the walls) that I had lying around extra from the bathroom. In fact it was JUST enough. Perfect!

    Installed the foil faced foam board, taped, 2" xps foam blocking for the joist bays (not 16" on center btw of course), taped, and spray foamed.

    Also started putting in the framing so I can just close up that wall.

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  14. lordoftheflies

    lordoftheflies Active Member

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  15. lordoftheflies

    lordoftheflies Active Member

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  16. lordoftheflies

    lordoftheflies Active Member

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    I was thinking of insulating the floor joists with the leftover blown-in insulation....but instead of getting the machine I figured I'd just crumble it up by hand. I won't be installing any built in drawers. Need to throw stuff out, not store more stuff.
     
  17. Dana

    Dana In the trades

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    If the framing isn't 16" or 24" o.c. it's more difficult to fit batts to a high quality standard.

    R19s are arguably the crummiest insulation material in common use today. When compressed to 5.5" (a 2x6 framing bay) it only performs at R18. When compressed to 3.5" (a 2x4 framing bay) it performs at R13. In effect it's just a "fluffed" R13 batt- it even weighs the same per square foot, exactly the same amount of material, but sold at a higher price than R13s. The low density of R19s also makes it more of an air filter than an air-retarder, barely slowing down the rate of any air leaks moving through it.

    If it's not too late, R21 fiberglass or R23 rock wool are both far superior products, easier to sculpt-to-perfect-fit using a batt knife than squishy-spoogey R19s.

    With non-standard width framing cutting chunks of batt 1/2" longer than the stud bay width (say, if it's 19" edge to edge between studs, not on-center, cut it 19.5") it can fit pretty well with the chunks butted up, and little waste. Cutting them length-wise a half-inch wider than the cavity space works too and it sometimes quicker, but makes more waste. (But putting the shreds between the floor joists and burying them in cellulose works.)

    Cellulose is compressed to a fairly high density in the bags it's shipped in. Crumbling by hand doesn't necessarily fluff it up enough to meet spec on R-value (it's well beyond optimal density.) Agitating it in a heavy-duty plastic 5 gallon bucket with a mud-mixer on a low speed drill can get you there. It's not a super-quick process, but quicker than breaking it up finely by hand. If you have the cover/lid for the bucket (or make one) and drill a hole in a cover/top for the 5 gallon bucket to accommodate the shaft of the drill you can spin it up a bit faster, without filling the whole room with fluff & dust.

    Five gallons is about 0.67 cubic feet. Optimal open-blown cellulose is about 1.5 lbs per cubic foot, so it only takes about a pound of chunks fluffed up enough to fill the bucket to hit the right range. Estimate the size of the starting chunk by looking at weigh numbers on the bag using a bit of 5th grade arithmetic and at tape measure, and just slice off chunks according, crudely breaking it into chunks small enough to fit into the bucket. Precision doesn't matter too much, but err to the high side. If it's only 1.2lbs per cubic foot it may settle a bit in the first couple of years, if it's 2lbs per cubic foot it won't settle much at all, and will still perform north of R3.5/inch if thoroughly fluffed.
     
  18. lordoftheflies

    lordoftheflies Active Member

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    Well, I had the extra R-19 from way back as well as from the bathroom so I just used it instead of throwing it away.

    That said, I haven't put anything down on the floor joists yet. Those are 2x8 and it's 71" across. 5 joists in the middle so that's 71 - (5 x 1.5) = 63.5" of bay space to fill.

    R-23 rockwool is only 5.5" high. Shouldn't I get the R-30 version at least? That's 7.25" tall. Then it would be flush against the 2x8 and I could even install the foam board on top of that too, no?

    I don't know if that plan is overkill. Plus the fact that I didn't lift up the floorboards in the main kneewall spaces to redo the insulation there. Hm.
     
  19. lordoftheflies

    lordoftheflies Active Member

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    Thanks for the tip on the bucket. I saw some videos on YT of that as well.

    Maybe I'm overthinking it a bit. I think I'll just use what I have (cellulose) and break it up as you suggested and call it a day. If I need more than I can pickup a few bags for $14 a piece.
     
  20. Dana

    Dana In the trades

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    Probably are, but everybody needs a hobby, eh? ;)

    Eventually all air-sealing and insulation projects wind down to the rat-killing stage, where you're sniffing out those last few pesky leaks and gaps. If you're a gadget guy with a couple hundred USD to spare, the (comparatively) inexpensive IR cameras that use a smart-phone or tablet computer for the display can be quite useful for finding and eventually fixing those too. The "Pro" version has higher resolution and a wider temperature range, but the cheaper version is perfect for debugging heat leaks in houses & home heating/cooling systems, or find missing pets. :rolleyes:

    I don't keep one at home (where it would be mostly just a toy) but we keep one in my company's lab for use on a variety of problems. When it gets cold enough I'll be borrowing it to chase down a few things at my house.
     
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