I am going to redo my crawlspace, which is a pier and beam foundation over a dirt floor, and got a quote from a local spray foam contractor. He wants to spray 3 inches of foam between the joists. I would rather have him spray 4 inches n the exterior walls ( 6 mil poly stapled to 1/2 ” pt plywood) and 1 inch between the joists. What do you think is the better solution?
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Replies
One thing that would make it easier to help you is if you fill in your profile, so we could tell what part of the country/planet you're in.
Why do you think you should insulate the crawlspace walls instead of the first floor?
Sorry, I'll fill out my profile right away. I live in Southern Vermont, but up on top of the hills, so it gets cold here, like minus 30 at least once a year. There are some heating lines (hydronic baseboard filled with anti freeze)as well as water supply and drain lines under the house. I had previously had 2 inches of foam wrapping the crawlspace with fiberglass between the joists. It worked ok, but the floor was always chilly. I thinks the heating lines kept the crawl above freezing, but If I insulate the walls well, ( my plan would give an r 35 rating to the walls) I shoud be able to save a bundle on propane while maintaining warmer floors.
I think the tricky part for you is that your insulation would only go down to grade level. Since the frost line there is probably 3-4' deep, the ground inside the crawl space is going to be cold at the bottom of the insulated wall.
It might be a good idea to do sort of a modified frost protected shallow foundation detail. Insulate your walls, but also run 2" of rigid foam down 2' and out 2' away from the wall. That will keep the cold and frost from getting too close to your crawlspace.
Even then, the ground won't want to get above 50 or 55 degrees in the winter, which means the air down there will be 50 or 55 degrees, and your toes will still feel cold. If you spring for 2" of foam over the whole dirt floor, and seal the walls to the foam floor, the air in the crawlspace will tend to be closer to the same temperature as the air in the house. That will make the toes happy.
Now the problem is during your hot humid summers, the moisture-laden outside air is going to want to get into your cool crawlspace and condense. That's bad. Adding vents, per code, only makes it easier for the outside air to get in and condense. Keeping it sealed up and running a dehumidifier in the summer would be one way of solving that problem.
Pretty involved, right? That's why your insulation contractor advised you to just insulate the floor.
Thanks for your reply. I was planning on sealing the crawl by running the poly up the walls and spraying them and the floor. I thought that 1 inch between the joists would provide an effective vapor barrier, and increasing it to 4 inches on the walls would keep the crawl above freezing. I will incorporate your idea of a modified frost protected foundation. Will 2 inch foam board do the trick?
If you're going through all this trouble, you might as well do it right and condition the crawl space--not just keep it above freezing, but heat it along with the house. That's what we do with regular basements and crawlspaces with frost walls, I don't see why your situation is different. If you're just keeping the crawlspace above freezing that means the floor is still going to be cold. That means your feet are cold, that means you're cold.
Instead of insulating the floor, just insulate the ground and heat the crawlspace. Make it part of the conditioned space in the house. That's the best way to avoid mold and musty smells, condensation and rot, and because your feet will be warm you can keep the thermostat lower. 4" of foam on the walls 2" of rigid foam 2' down and 2' out, and another 2" to 4" of rigid foam on the ground will make your house comfortable and rot-free.
Or just insulate the floor and the area where the mechanicals are and keep the thermostat a little higher. I don't know what the payback period will be for "my" system but it might cost $5K (don't know any specifics so that's about as WAG as you can get) which will take quite a while to pay for with the savings from your heat bill. Maybe you'll save $40 a month. That's a ten year payback. Is it worth it to you?
I think that the price you pay for comfort and not having things break or freeze outweighs the payback period. 5k is a lot of money, but 3" of spray foam just on the joists would cost almost 3K. BTW, the house is 24 X 40, so 960 sq ft too deal with.
I also prefer to insulate the walls. The square footage is usually less, less possibilty of frozen pipes (assuming crawl is heated), the floor is warmer when heated below, and you won't get the deeper frost penetration usually associated with ground that is not snow covered.
Mike, be careful here. I already suggested that a conditioned space is perhaps the best option. The response? Well, the suggestion was called snide. So be careful. IF someone disagrees with you, you are attacked. Just a fair warning.
OK, let me recap this for you nice and slowly.
The OP's got a PIER foundation in Vermont, with plywood walls, which presumably only go down to grade.
I asked why HE though he should insulate the floor. Asking questions is a way to get more information from someone, without rushing to an answer.
He provided more information, which allowed me to suggest two options. One is a better system but costs more. The other is not as good a system, but if costs are a concern it's a viable alternative.
Oh, and my skin is not thin. Plenty thick, crusty even. Yours?
Case in point, Horse's.
Hey, life's too short to argue. We both know the right way. Beers all around!
This is true. What time is beer-O-clock?
It's beer o'clock now! Today's my Friday, so I might have two.
Thinking about working in ANOTHER dirt floor crawlspace would make me want to drink! Too much of my life spent with the Morlocks already.
I'd stay away from them, go topside and hang out with the Eloi especially if they are as cute as Samantha Mumba.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Best advice I've got on this site yet!
Your so right about the mustiness and ventilation issues. I've never found a solution for that which was totally satisfactory (ie fast, cheap, simple and no hassle, LOL). Most of the crawlspaces we were in were sloped and often had lots of exposed bedrock. What is the best way to insulate the floor? How does insulating the floor affect subsequent movement in the crawlspace?
Why do you think you should insulate the crawlspace walls instead of the first floor?
Because it is a far better option, perhaps?
Because it is a far better option, perhaps?
Perhaps, perhaps not. He's got a pier foundation, not the typical concrete frost wall that makes it a no-brainer. In order for it to perform well he's got to do some additional work.
Or did you miss that in your rush to post a snide comment?
Nothing snide about it. Sorry if you are thin skinned or something.
I beleive he is converting to a crawlspace, or perhaps it is you who falls to read posts?
No, Mike has it right. I had the previously had the crawl insulated on just the walls with 2" rigid foam. Since I did an addition this summer, I figured that I may as well get thing right and insulate the space the way it should have been done in the first place. I really appreciate Mike's well thought out comments, and am looking forward to a more comfortable house.
NO what? I said insulate it correctly. So if by NO you mean you wish to do it wrong, then knock yourself out. Bizzare.
If you read your previous post, you said that you believed that I was converting to a crawlspace. NO, I am fixing a poorly done insulation job in an existing crawlspace. That is what no. In the future please refrain from insulting others who are using this forum to share and gain knowledge. No one enjoys it.
tsell, I never insult anyone who has not made snide nasty comments. There clearly are alot of additudes on this board.
Perhaps you might to send your post ot Mike. Your mistake, but it is ok. I understand now.
tsell, as for the confusion of pier conversion or crawlspace updating. You know if you were not so quick to bash and attack you might take a moment to realize that there are dozens of very similar threads on this board. ANd those threads run over several day if not weeks. It is quite excusable unless you are a messerable personality type to find a bit of confusion once in awhile.
And tsell, if you don't think YOUR initial statement, and I quote "I am going to redo my crawlspace, which is a pier and beam foundation over a dirt floor, . . ." is a bit confusing, ie "IS A PIER AND BEAM ..." then I am not sure what to tell you. So excuse me.
Doright, I obviously hit a nerve, and I am sorry. I was pretty darn tired at the end of a s****y day, and misread your post, particularly your first one which was in agreement of my initial concern of just insulating between the joists. I think Mike hit the nail on the head when he said "beers all around". I do appreciate all the input from the members of this board. As for my first post being confusing, it may well have been. It is difficult sometimes to describe an unusual situation. I do have a pier and beam foundation, which has been enclosed to create a crawlspace. It is easy to miscommunicate when you are not face to face, and sometimes the intent of your words is not correctly interpreted. At the end of the day we are all here to gain knowledge, and I have certainly learned quite a bit here.
There are some good articles in Fine Homebuilding about crawl spaces. We have a crawl space in our cabin in NW Wisconsin. We do not have piers, however. We have concrete block with vents. I liked the recent article that said that a crawl space is a basement for trolls, and should be treated as such. One of our neighbors insulated both walls and floors, and he had such condensation problems that he rotted out his main floor joist! He noticed it when the cedar siding on the walls started sagging. So, you've really got to be careful what you do, here. Whatever you choose to do, monitor it so if you have a problem you can fix it! The rule of thumb here in Muskie country is that you either insulate the walls or the floor, but not both. Additionally, most of us have started to close off our vents all year. Poly on the ground is a must - get heavy stuff. We have seen both duct tape on the seams, and no duct tape on the seams as recommendations.
One of the problems with an insulated floor is that only 5% of the heat goes down, so it's hard to get the floor warm by virtue of how it heats up in the first place. Ours is always cold, at first, when we arrive, but then warms up when the house is thoroughly warm.
Good luck with your decisions - if it weren't for crawl spaces I don't know what we'd find to talk about with the neighbors some days. By the way, the guy with the rotten main floor beam had his crawl space filled with cement.