I have a 2004 built 1.5 story in west michigan with an unfinished 1300sqft basement, 1300sqft main level and 500sqft 2nd level. I detect no comfort problems but with an ambient of 25f and set point of 69f the house consumes 24k/btuhr of fuel (93% natrual gas forced air). The above grade sections (not many) of the basement are insulated and drywalled, however the rim joist just has batts stuffed in it. Sidewalls are 2x6 with r20 and r30 in ceiling. The question is how much improvement would I see paying to have spray foam in the rims @ 3" / R20, or is it a waste of money for a noticable savings in energy?

Main Floor insulation? Basement is unfinished, but you stated the above grade walls are insulated and dry-walled, is the ceiling dry-walled? A rim joist is usually where the floor terminates as it typically runs perpendicular to and supports the floor joists. I would expect this to be located at the top of the basement wall, so I am not really tracking where these areas where the batts are stuffed into are located?

To what level is the basement heated? In general, unless you detect a cold spot in the area you are referring to, I doubt it will make all that much difference in the big picture.

Have you done a blower door test? As a guess I would think you may find a whole lot more BTU loss thru air infiltration than anything else. Setting up your own blower might be advantageous here as you can then take your time to look for and seal leaks. Sealing the "Rim" you are talking about may be a part of that...

main floor is not insulated, only the above grade sidewalls were insulated/drywalled in the basement per the builder. Currently the sill plate has pink foam laid on it and R19 batts stuffed in the boxes.

Basement air handler and ducting is in the basement, 2 vents open it's not unusually cold there.

Blower door test has not been performed yet, I was trying to resolve the glaringly obvious problems... ice and moisture behind those batts indicates a significant infiltration issue, no?

To install 3" of closed cell foam correctly would required two lifts of no more than 2" at a time. It's worth air sealing and insulating the band joist & foundation sill, but it only takes an inch to air seal, and R6+ of foam would be sufficient dew point control for R13-R15 batts on the interior side of that in your US zone 5 or 6 climate, for a cheaper and greener R20+. Anything more than that inch for air sealing and dew point control would be a waste.

The air sealing is the primary thermal benefit of spray-foaming the band joist and foundation sill. If you left it at that it's hard to estimate how much heat the air leakage was doing, but it's typically the single largest untreated air leak in most houses, more than all window & door air leakage combined. But if you stopped insulating at just the band joist & foundation sill you're missing the big picture (and the bigger savings.) If your load at 25F outdoor ambient is 24,000 BTU/hr, the load at your 99% outside design temp (something like 0F, give or take 5F depending on your ZIP code) would be about 36,000 BTU/hr, a ratio of 20 BTU/hr per foot of fully conditoined space which is really HIGH for a new-ish 1800' house with a 1300' basement. (My 2x4 framed sub-code-min 1920s vintage ~2400' house with ~ 1500' of insulated but unheated basement comes in at about 36,000 BTU/hr @ 0F !) An un-insulated foundation would likely account for more than 15% of your total number, and more than 15% of your annual fuel use. If you insulate the basement to current code min and the rest of the place is pretty tight your heat load should drop to under 30K @ 0F.

R15 continuous insulation would be current code-min, but 1.5" of foil faced polyiso (labeled R9-R10) with seams taped, trapped to the wall with a 2x4/R11-R15 studwall with NO interior side vapor retarder would meet or beat code min, and give you the option of finishing out that space later. If the furnace, ducts and plumbing are down there, this will make a sizeable difference on the heating bill, even if the ducts are insulated, despite the fact that the basement ceiling is insulated. If you installed the wall-foam first (glue it to the wall with blobs of foam board construction adhesive, then sprayed the inch or so fo closed cell polyurethane over the band joist and foundation sill and any foundation ledge over to seal the top of the wall foam you will have a continuous thermal break & non-susceptible first condensing surface.

Ice behind the batts is not an indication of outdoor infiltration, it's an indication that humid indoor air is infiltrating through the batts to the band joist. An inch of ccSPF covered with high-density R15s would not have that issue, and the vapor permeance of the foam would still offer a minimal drying path toward the interior for the band joist.

so basically it's not worth it unless i insulate the entire basement including the main level ceiling? starting looking other places for this "huge" BTU loss?

It's definitely "worth it" to air seal the band joist and foundation sill, always! It's usually THE SINGLE LARGEST AIR LEAK in most homes that haven't already undergone a round of serious air sealing.

Putting 3" of closed cell foam on the band joist & foundation sill is NOT "worth it", from an R-value point of view, or from a dew point control point of view. An inch is enough for both air sealing and dew point control- you can re-install the existing batts over it.

I thought you said the ceiling was already insulated???

If the basement ceiling is not insulated don't waste any money there- invest it in insulating the foundation walls.

well for $500 sprayed in and batts gone on a 32*40 basement why not just let them do the 3"? Ceiling is not insulated, only the ABOVE GRADE portions of the foundation walls (vertical) are insulated/drywall (per code i believe) and batts stuffed in the joist, pink foam between the joists and foundation walls. I should also mention in the rim area is a bump out for the direct vent fireplace, they would be sealing this up too...

Some of the basement is insulated - did you insulated the concrete foundation walls with fiberglass?

the condensing moisture you see actually represents exfiltration - not infiltration. It is moisture trying to escape from your house (on moving air) and condensing on a cold surface. If you truly want to decrease your heat loss, start with a blower door test, done by an independent energy auditor, and have him help you identify the air leakage spots in your house and then stop that infiltration. Once you've done that, start looking for areas to improve insulation. Working on insulation without knowing and repairing your infiltration is an excellent way to waste money. Kind of like talking you car to the garage and having them replace the spark plugs before you know if they are the cause of the problem.

2" of of 2# foam is common practice and would be my second choice, ahead of the wall, after the ceiling insulation.

Next a minimum of 1" of Thermax will make your comfort go up and your fuel bill go down. You can do this without finishing the basement.

http://building.dow.com/en-us/products/thermax-white-finish-insulation/?sc_itemid=33672786-e964-4c3f-a3eb-7bf6634d13a0

Frost and moisture behind the bats in the rim pockets? You should have led with that You have to fix that, as it supports the rest of the house and is a very bad place to introduce moisture. 3" of spray is probably overkill. What is the cost difference between 1" and 3" sprayed? 1" sprayed mainly for it's sealing properties and enough R value to get it's surface above the dew point to stop condensing moisture at the rim, then put the batts back, or replace them with sheet foam. This would probably save you a few bucks, but it's your money and time.

You are probably still wasting more heat thru air infiltration than anywhere else, so if it were me, I would look for air leakage house-wide once the rim moisture issue is addressed. As Dana mentioned, that moisture at the rim is coming from inside your house. Since stack effect usually causes air to be drawn in at the bottom of the wall and pushed out at the top as warm air rises in the home, your furnace system may also be unbalanced, and you may be positively pressurizing the basement forcing air out to and thru the rim and condensing it's moisture there.

Once you take air infiltration off of the table, heat transfer is about R value, temp difference and surface area. You have 1300SF of probably un-insulated concrete floor and X amount of SF of concrete walls below the stud walls also probably un-insulated. Lots of surface area with a direct path to earth temp... Only way to deal with that is to insulate it. That is a lot of area to cover, at quite a bit of cost so I would definitely look at air leakage first

Posted By ls3c6 on 16 Feb 2016 11:25 AM
well for $500 sprayed in and batts gone on a 32*40 basement why not just let them do the 3"? Ceiling is not insulated, only the ABOVE GRADE portions of the foundation walls (vertical) are insulated/drywall (per code i believe) and batts stuffed in the joist, pink foam between the joists and foundation walls. I should also mention in the rim area is a bump out for the direct vent fireplace, they would be sealing this up too...

You don't want to let them do the 3" because 3" is simply the wrong number. Spraying 3" in a single lift is a fire hazard while curing and would be a crappy job due to shrinkage/cracking and adhesion issues. All 2lb foam application sheets I've read to date specify no more than 50mm/2" per lift. It must be installed in 2 lifts of less than 2", separated in time with a cooling/curing period. It's very unlikely to happen that way if they're only quoting $500.

I suspect they quoted 3" in order to hit a code-min R20. But R20 of closed cell foam underperforms R20 of a lower R/inch foam due to the dramatically higher thermal bridging of the shorter path through the framing. A typical framing species runs about R1.2/inch so the framing fraction with 3" foam is only R3.5-ish, whereas if it takes 5.5-6" for the cavity to hit R20 the framing fraction is R6.5-R7, or roughly half the heat loss you get through the framing with 3" of foam. This is more than a simply academic difference. Even if you went with 3" of foam, it's worth adding 3.5" batts to limit the thermal bridging.

You could do a single pass of 2", but that wouldn't get you to code min. It's overkill for dew point control on any fiber fluffage you'd add over it, but that's fine. At least the risk of setting your house on fire is low, and it won't shrink and pull away from the structural wood at the edges.

The cheap foamy sill gaskets are much leakier than they look. The only sill gaskets that really seem to do the job are the pricier EPDM sill gaskets.

I'm sure there is exposed above-grade concrete on your foundations. Without insulation a square foot of that exposed concrete loses about ten times as much heat as square foot of code-min studwall. In other words, if you have 1' of concrete showing around the perimeter of your house, that foot of exposed concrete is losing about as much heat as the full first floor walls above it (!). And that's just the above-grade foundation losses. It's highly unlikely that your foundation sills are all less than a foot above grade (or are they?)

Good info, so my goal should be finding someone that will accurately seal and spray 1", seal sill and replace fiberglass when finished.

Overall what btu/hr at 25f 69f set point should I be shooting for?

Posted By ls3c6 on 16 Feb 2016 09:21 PM
Good info, so my goal should be finding someone that will accurately seal and spray 1", seal sill and replace fiberglass when finished.

Overall what btu/hr at 25f 69f set point should I be shooting for?

As low as possible, of course! :-)

Realistically, with some blower door directed air sealing and fixing any glaring insulation gaps such as the lack of foundation insulation you should be able to get the heat load under 18,000 BTU/hr @ +25F, maybe even ~15K depending on the particulars.

note that the blower door is an inherent part of the job. Trying to insulate and seal leaks without that is akin to diagnosing an engine problem without starting the engine - IOW, a guess.

Yabbut, some of the guesses are nearly always right, such as band joists & foundation sills always leak substantial air unless sealed, and bare concrete foundation walls are monster heat leaks. There's no down side to fixing those first, even if there are other sizable defects still to discover.

Short of a blower door, you can still do a lot with a decent sized reversible window fan and a smoke pencil. Spotting the gaps in the insulation sometimes takes infra-red imaging cameras, but with patience, observation, and some good hunches you can do a lot with a $50 pistol grip IR thermometer too. It takes longer to sort it all out with lesser tools, but when you're living in the place you have more time to ponder & poke than an air-sealing contractor does.

well I peeled off some of the joist insulation last night and every. single. penetration. they made is a gaping blow my hand off air leak (15f ambient at the time). I'm going to start with great stuff sealing those and ordering an energy audit.