basement wall insulation - help me avoid a mistake

i may be misremembering (been reading a lot about a lot of different subjects of late), but seem to recall something iffy about foil and concrete. i could be wrong.

here's info on the polyiso r-value: http://www.energyvanguard.com/blog-...s-The-R-Value-of-Insulation-Is-Not-a-Constant

well, so far i'm 80% done with the floor using 1.5" foam and 3/4" advantec subfloor. i've been using spray foam cans to attach the foam boards to the concrete. weight it down for 20 mins while i work on something else (mostly the subfloor), then put on subfloor using more spray foam and weights. so far so good. no tapcons. no anything. no break in the vapor barrier.

to get the tongue and groove sheathing fully seated, i've used a 12lb maul to bang things together and haven't budged the spray-foamed foam or sheathing, so i think i'm good. hopefully it doesn't loosen up over time, but if it does, it's not like things will shift anyway.

i will eventually post some pics.

velvetfoot said:

A lot easier than gluing it to the walls, for sure.

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yep, but i have a decent idea in mind for the walls. plus, flat doesn't matter as much for the walls since i'm building a 2x4 wall in front of the foam once it's done. i just need to worry about the air seal.

one other question:

for my fireplace upstairs, it sits in an alcove (though flush on the finished surface). the basement has the same arrangement geometrically, but with no fireplace/stove. we are planning to finish it off with drywall and put the TV there.

i want to know if it's okay for me to put foam insulation on the underside of the upstairs fireplace floor. see pic. i cannot imagine it would be an issue, but wanted to see if you could see any pitfalls.

gzecc said:

For fire code the ceiling drywall need to extend past the wall top plate to the foundation sill. Easy to do prior to building the wall. Not so much after.

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question for you on this item:

are you saying that my ceiling drywall should run all the way from the inside of the room to the top plate of the cripple wall (which is supporting the upstairs rim/joists) and then i butt my XPS into it? essentially, i would have a 5/8" discontinuous area in my XPS insulation for the entire perimeter of the house???

i read some other articles where people mentioned this firecode requirement. some seem to say yes, the drywall goes to the wall. others say that the foam should run all the way up and create a continuous insulation layer, and then drywall can butt into it before you frame your wall.

i also read that you would probably also need a horizontal fireblock every 10ft horizontal (same thing - it would be a break in the insulation). and, you need fireblock at all vertical and horizontal chases.

seems like a lot of work!

also, general question for anyone still paying attention: one of my floor joists is very close to the exterior wall. there's about a 3-4" gap between the joist and rim board. it's going to be nearly impossible for me to jam up a piece of XPS and spray foam it. is it okay if i just caulk the edges along the rim board and then stuff full of batt insulation? it'll still be a PITA, but probably easier and less messy. thoughts?

vinny11950 said:

So the rim board and the joist are running parallel? If so, your solution should work. As long as you close air gaps and insulate you should be fine.

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correct, they are parallel for about 40' with a 3-4" gap

vinny11950 said:

Okay... I imagine it will be tough aiming the spray foam straw at the bottom of the rim board where it meets the sill plate. Maybe something like this:

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yeah, i've been using a hose on other areas - though plastic tubing, not electrical wire sheathing. it sucks too. maybe the electrical wire works better...

i found the insulation process to be very tedious and annoying. issues i ha d:
1. the step between my foundation wall (concrete) and exterior timber wall (2x4) was such that i had to cut all my pieces at that location and create a joint/step in the insulation. doubled/tripled the effort there
2. insulating the rim joist was a serious PITA for my case b/c one end had a 1ft cantilevered floor overhead and the other end had all my electrical and plumbing running right next to the rim board. really tough to get into those spots
3. there's still an air gap between the foam and the wood due to imperfect framing and typical irregularities. i ended up "air sealing" this using silver foil tape. definitely made a difference.

in the long run, i'm sure it'll be a good investment. but, it definitely dragged on for me. demoing the basement, doing a seismic retrofit, and framing new interior walls has been enjoyable. the foam part, not so much. cost-wise, i probably saved $400 (20%) versus closed cell spray foam. however, due to concerns about off-gassing from the CCF, and having a newborn in the house, i opted for the XPS approach.

for the floors, i used 1.5" XPS with 3/4" T&G advantech OSB sheathing. both are great. i glued foam to concrete and OSB to foam using spray foam.

for the walls, i used 3" XPS. in the 2x4 walls, i reinstalled the r11 fiberglass insulation that was previously in the walls i demoed.

i am a few weeks away from drywalling. i plan to toss in some roxul into certain areas (mainly the rimboard area since i only got 1.5" foam in there)

trimming out the windows and doors will be interesting. with the wall thickness and foam thickness plus the offset of the interior walls, i'm looking at perhaps 12-14" of casing.

lml999 said:

Looks like some tidy work. Did you ever go with an HRV? I just had one installed last week, happy to talk about it..

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sure, tell me about it. i haven't done anything to the HVAC yet. i posted another thread about moving my thermostat to the basement to help with regulating temps between upstairs and downstairs, but haven't gotten much feedback yet.

lml999 said:

Moving the thermostat won't change the temp balance between upstairs and downstairs. If you can change the heat delivery (opening/closing vents, etc) that's a better way to do it...or create an additional zone. In our old house we separated the basement from the main and upper zones, that was much better. In our new house, we've got one zone for the basement and two zones on each of the two other floors. Makes it much easier to dial in temps or to not heat a particular part of the house.

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thanks for the feedback.

given the layout of our ductwork (one main trunk from the furnace that branches all throughout the house (up and downstairs)), there's no way it could be converted to a zoned system.

the reason i think the temp balance will change is that the downstairs currently gets no warm air directly from the fireplace. it gets no air from anywhere. if i put the thermostat in the basement and set it to 66, the furnace will kick on and start heating (up and downstairs) until the basement reaches that temp. in the process of doing that, it will be using a good amount of the really warm air from the superheated living room with the fireplace as its source. essentially, we'll circulate and mix the air in the house.

if the thermostat stays upstairs, i can't just program it to be 74 degrees (to overcome the natural 73 degrees from the fireplace) and have it try to raise the upstairs temp to that level constantly. even then, the downstairs likely wouldn't be the temp we want.

does that make sense?