Worth insulating unconditioned basement?
red1212
| Posted in Energy, Heating & Insulation on
Is there much benefit in insulating the concrete walls of an unconditioned basement? The basement will likely never turn into conditioned space due to low ceilings. I am debating putting 2″ rigid foam on the walls and rim joist since the floors above are always cold in the winter. The basement walls are about 6′ tall, house is in Maine, there is no rigid foam on the exterior of the foundation.
Is this worth doing, or just a waste of time since the space is unconditioned? Haven’t had any problems with frozen pipes that run through there, but it gets down to the high 30’s down there in the winter.
What about insulating the basement ceiling with some fiberglass bats?
Any thoughts? Appreciate any thoughts.
Replies
Unless there is a heat source in the basement, insulating the ceilings seems a bad idea, since you'll be preventing what head does reach the basement and maybe cause pipes to freeze.
One thing you can do that would cost a lot less and make a big difference is find any places where air is leaking in from the outside and seal them up. I'll let others chime in about insulating the walls.
~ Ted W ~
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It's particularly a bad idea when the OP was suggesting insulating the walls. :)
Copy pasted from the original post...
What about insulating the basement ceiling with some fiberglass bats?
But thanks, now I know I'm not the only one who does that.~ Ted W ~
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Just shows to go ya ... I sometimes can't read myself. :) duh If I could just read the words that were in front of me instead of skipping to the good parts.
I modified one of my favorite sayings to..
"A picture is worth 1000 words, but it's all jibberish if ya don't read the caption"~ Ted W ~
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What caption? :)
I can't support my statement with calculations, but insulating the basement walls will make a significant reduction in heat loss.
Exposed foam may be a fire issue, though.
What Ted said goes, but I'll add to it a bit. First tell us how much of the basement walls are below grade and whether you have a heating system down there.
If most of the basement walls are below grade, preferably a lot below frost line, then the ground may well keep the basement from freezing if you insulate the ceiling, unless you have a lot of outside air leaking into it under the sill, around other openings, etc. So you would want to seal up the space from air infiltration in any case.
If you have a heating system down there that needs combustion air, then beyond tightening up the basement you might think about ducting in the required air to right near the furnace, so the cold air isn't drawn through the whole basement space. This sounds like an older place, so there may well be enough air leakage into the floors above the basement and down into the basement air so that combustion air is conditioned from passage through the heated space above.
If you do tighten up that basement and insulate the walls, then the space will be a lot warmer just from heat loss from the heating system and the floor above will be that much warmer.
One final thought: if you have a heating system down there, then you are losing some heat through the uninsulated walls and the basement slab anyway. So if you insulate the ceiling, you still will be losing heat out the walls to ground if you don't add insulation to those walls.
1/2 the walls are about 80% below ground surface, the rest are about 50% concrete below ground surface and 50% wood frame/fiberglass batts above ground surface - I'd cover those with foam also.
No furnace in the basement, or anywhere else. There is ductwork partially run throughout the house that dead ends in the basement, but the people that built the place never finished it off or put in a furnace. We heat with a wood stove on the first floor- I'm going to install an outside air kit on that this year as well.
There are water pipes in the basement, but even with it currently poorly insulated, it only got down to 38 degrees in the coldest sub zero weather last winter.
I appreciate the comments. Sounds like the foam would make enough of a difference to be worth while even with no furnace or other heat source down there? Should I also put batts in the basement ceiling?
Edited 4/24/2009 8:48 am ET by red1212
Do you have any water supply or waste pipes in the basement? If so, insulating the floor might not be a good idea.
He was suggesting insulating the basement walls, not the ceiling.
I'm in southwestern Wisconsin, and it can get very cold here, to include minus twenties. Nonetheless, my uninsulated basement rarely gets below 55 degrees in the winter, even though it gets no heat. I insulate the pipes in the basement, specifically the hot water ones, but they don't take long to get hot water to the bathrooms above. I plan to turn the basement into a livable area soon, but I don't have a problem otherwise with hot water above. I'm surprised that your basement gets that cold. Where do you live?
Think of the floor and the basement and the basement walls as the envelope enclosing your heated space. You can enclose more space (i.e. insulate the walls) ... which will reduce your current energy use. You could insulate your floors which will enclose less space and require less heat, but then you don't have a buffer space for storage ... and the potential of freezing pipes as was suggested.
Don't forget ... can't leave the foam exposed ... it's a fire hazard (code violation). If you can afford it, do it. If you want a warmer floor, circulate air from the wood stove to the basement and temper it a bit more for warmer floors.
Insulate the part of the walls above grade and down to about three feet below grade for good measure. There's no point to insulating any deeper than that as the earth is such a massive heat sink; you might actually make it colder down there by doing so.
Do make very sure you don't have any air leaks into that space.
Once you have that done, you can put a small electric heater in there and its output won't be wasted but will trickle up through the ceiling and help keep your pipes and feets warm. I heat with a wood stove on the first floor, too, and unless there is always someone home to keep the stove stoked, there is a part of the daily heating cycle where the stove isn't doing much for you; having a thousand watts or so of electric baseboards set on 'low' in the basement can make a big difference at very little cost.
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foolish men call Justice....
I am in Maine too.
If warm floors are your primary concern use some batts immediately under the floor.
With a full basement freezing puipes are generally not a concern here, since the earth temperature at 5' below surface averages over fifty degrees. That would keep the cellar warm enbough to not worry about pipes IF there is no draft but you do have a lot of wall surface above ground to lose heat out there.
So I would insulate both the walls and the floor.
I would not worry about covering foam down there since you have no heat/flame source and it is not a living space.
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That's a good point Piffin. I'm not worried about the pipes freezing - it would have happened last winter if it was going to, but it only got down to 38 in the basement.
I'm more hoping to keep it at about 50 degrees - I hope that with the walls fully insulated, the huge mass of the uninsulated concrete floor should keep it at 50 since it is below the frost line. I hadn't thought to put any foam on the floor. Since the ceiling is only about 6'3" now (they hit ledge and didn't blast), I end up losing precious head room, although it's really just a storage space. I guess I could put down an inch of XPS and some plywood over that? Is that really worth doing?
Are kraft faced batts an acceptable way to insulate the ceiling and it that worth doing?
Edited 4/24/2009 8:59 am ET by red1212
Red,Insulating the walls and leaving the floor alone should raise your winter temps a lot, especially if you do all the air leakage detailing first.Kraft faced batts will help some to keep the floor warmer when you are running the woodstove, but it is hard to say how much. If it were mine, I'd focus first on the air leaks and the walls, and then monitor it next winter. You would then have the info you need to see if more work is warranted, and in which direction you ought to go.Another issue is humidity. Below grade spaces that are well air-sealed can get very musty from rising damp. It might be better to allow air and heat to circulate between the conditioned space above and the insulated basement below, to forestall mildew and the resulting musty odors.Is the floor slab poured over a vapor barrier?Bill
There is no vapor barrier, but also no issues with bulk water intrusion (flooding, seepage etc.) It does get damp in the summer and I run a dehumidifier to keep the cold water pipes from sweating and any mildew from taking hold. Never any mildew smells. The house is about 20 years old and I'm hopeful that it stays leak free.
I think it is a good idea to do it a bit at a time to see what kind of results I get and tweak things from there. I'm leaning toward air sealing and foam on the walls/band this year and leaving the floor and ceiling alone.
Red,That all sounds good to me. After you do the air-sealing, you could possibly have less condensation on the cold pipes in the summer, since outdoor humid air cannot get in, or not as much of it.This assumes that not a lot of vapor is rising invisibly through the slab. My house in Colorado had a crawlspace that was very sealed and it had zero bulk water intrusion, but very high humidity from transpiration through the concrete. It was a bit musty, but no huge problem, either.BillEdited to add: By the way, I agree that fireproofing the foam in your particular crawlspace is a waste of time.
Edited 4/24/2009 4:13 pm by BillBrennen
"I'm leaning toward air sealing and foam on the walls/band this year and leaving the floor and ceiling alone."I think that's the right place to start
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make sure what ever you do you air seal and insulate you rim/band joist. use un faced fiberglass to fill each bay 2 inches shy of the inside edge of your top plate andthen put a pice of 2 inch polyisocyceurinate (foil faced R-MAX)in flush with the inside of the top plate (your building envilope) and then seal it with silicone. This acts as a vapor barrier and along with all the other air sealing you do thats a good first step. If you dont want to pay to insulate the whole of the basement you could always use some XPS (blue foam) and insulate on the outside of your foundation 2 feet below grade. Coverthis with flashing or some AWW. You should aslo in this case put a "wing" sloped away from the foundation 2 feet down. Quite effective and less cost probibitive.
But truth is, "if you're not going to do something right, why do it?" If you're gonna dig, dig to your footer and wing out there...continue your thermal boundry over the entirety, as it should have been done in the first place...Good call on the rim/band joist though...what do we use? about 1 tube of silicon per four joist bays??? Makes a difference at test out time though, tell ya' what...All I ever wanted in life was an unfair advantage...
I duno as AKwarm would advise the "break even cost" says that doing so is not cost effective. if anything digging that deep would only make sence if you had some serious moisure issues from diffusion. go with a new drainige plain/ capillary break and wing out like I said."A small leak can sink a great ship."
-Benjamin Franklin-
you wouldn't have insulated that wall in a new construction scenario????AKwarm is for conformists.......and nerds:)All I ever wanted in life was an unfair advantage...
sure in a new build, but its hard enough to get you guys to dig the 2 feet in a retro deal.and you might say that AKwarm is my unfair advantage in this case. but yes here in alaska deffinetly on a new build it would be fully wraped and draining properly from under the slab, around the footer and up to grade."A small leak can sink a great ship."
-Benjamin Franklin-
I would insulate the walls with foam, and the floor, too. Tape all joints with Tyvek tape or an approved tape. This will prevent a lot of humidity from entering your home and keep your home warmer in the winter. See http://www.buildingscience.com
These panels might work for you:
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Billy
I think you could treat it the same way as you would a conditioned crawlspace. Buildingscience.com has a lot of good information about them.
I think there's a lot of benefit. I always added extra heat into my basements so the floors would be toasty warm . Heat rises so it's not wasted heat.
Heat doesn't rise any more than it goes sideways or down. Radiation occours 360°.Hot AIR rises.if you insulate the walls, most heat does stay in untill it rises, but I see some people do what you say with un-insulated cellar and they have the crocuses blooming in Feb. and the soil never freezes along the foundation.
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