To Insulate Crawl Space or Not?

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Old 02-11-10, 07:54 AM
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To Insulate Crawl Space or Not?

There seems to be a difference of opinion on whether or not to insulate the floor over a crawl space. From what I can gather these are the two sides:

My contractor and others say don't - it helps the house breathe.

The other side says do it - it helps retain heat and keeps moisture int he crawl space.

The crawl space walls are already insulated with insulation board and the dirt is covered with pea gravel and plastic sheeting.

So, should I run insulation between the floor joists or not?

Enlighten me!!!!
 
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Old 02-11-10, 02:08 PM
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If moisture gets trapped between the insulation & the wood above it, it could cause problems. Do you think you would save money by insulating? Do you have high heating bills?
 
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Old 02-11-10, 02:33 PM
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You can insulate the floor system if your crawlspace is properly ventilated and a vapor barrier is installed on the soil/gravel. Also be sure to check parameter drainage/soil slope and proper installation of downspout extensions. Soil must slope away from the home and downspout extensions should be routed 6' away from the foundation.

Remember to install the paper side towards the heated space.
 
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Old 02-11-10, 06:02 PM
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Old 02-13-10, 05:38 AM
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Originally Posted by Pulpo View Post
If moisture gets trapped between the insulation & the wood above it, it could cause problems. Do you think you would save money by insulating? Do you have high heating bills?
Its a new house - we've been in for a bit over 2 years, so we don't have a lot of experience here. That said, our winter heating bills seem very high. The floors over the crawl space, even the carpeted ones, seem pretty cold.

Is there insulation board I can put in under the floor that keeps the moisture in the crawl space?
 
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Old 02-13-10, 05:42 AM
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Originally Posted by GBR in WA View Post
Thanks, Gary. This looks like it answers my question. My reading of this tells me I should insulate under the floor and not the crawl space walls. The floor has plastic sheeting over pea gravel.

As I asked the other Pulpo, I'm assuming I should use some sort of insulation board - would you recommend one type over others?
 
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Old 02-13-10, 07:20 AM
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Hi Doc, I guess I have a different opinion, if you are interested. First, as an old timer and I hope professional and knowing the quality of many of the posters on this forum, it is a clear statement as to the complexity of this and many more issues where professional opinions go entirely in different directions. It's no wonder the home owners are left scratching their heads.

A common problem that people try to solve is cold floors and the cause of the problem is simple, heat rises. In homes with living space over an unheated garage, similar to an unheated crawl space, massive amounts of insulation and total air sealing are required to achieve warmer floors. The heat in the house simply goes up and the floors feel cold, not from the cold below, but from the cold windows, walls and air leaks. A little math for you. An ideally balanced home will lose it's entire volume of inside air every three hours. Less than that and you have to turn fans on to make up the difference, more than that and you have a typical leaky home and it can be brand new. But even at one air exchange every three hours, where does that incoming air go, right to your floors and it is cold air. So insulating the floors as opposed to insulating the crawl space may not give you the warm floors you are looking for.

As for their heat loss numbers, despite their professional approach, I would want more details, like how much air was being pulled from their sealed crawl? What other improvements were made or needed to be made, like sealing the rim joist, ie the house to foundation area?

With ducts and plumbing in a crawl space, water lines and drains, and a source of moisture that needs to be controlled in either case, I would seriously consider the sealed and insulated crawl. As for their assumption that extra heat is being lost through the uninsulated floor, heat loss calculations don't even consider that area as it is simply a huge thermal mass that stores heat rather than allowing it to blow away in the wind. The perimeter walls will lose heat, that is why they are insulated and you can go with more insulation if you choose.

A home with a full well insulated basement, with no intentional heat down there, will have 60 degree temps and a comfortable floor above. Introduce a bit of heat and that floor/ceiling will easily go to 70 degrees as the heat in the basement rises.

I could go on and on, but it is your call and my voice is only one so I wish you luck.

Bud
 
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Old 02-13-10, 07:36 AM
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I appreciate your opinion, Bud. It IS a complex issue - indeed, when we had the house built I had trouble making sense of the various considerations.

After I posted the last comment, I went down to look at the crawl space. I forgot - the walls have blueboard all the way up to the bottom of the joists.

I guess that's a start. What else would I need to do? Should I cover the 4 vents in the crawlspace wall - at least in the wintertime?

jack
 
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Old 02-13-10, 07:50 AM
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You are in a green grass state so no vents should be used. I would insulate the floor joist.
 
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Old 02-13-10, 08:43 AM
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Since you already have the wall insulation and the plastic on the floor, I would check to be sure the plastic is sealed at the walls and other penetrations, then try it with those vents closed. Put one of the remote temp devices down there and see where the temperature goes. Place it high so it somewhat represents how it will help or hurt the cold floor above. A radon test would be advisable at some point, once you decide which way to go.

If you can see in somewhere determine if anyone sealed around the perimeter of the floor to foundation, gaps, seals and wood to concrete. That may just be hidden behind that blue board.

What else is down there? Furnace, exposed pipes, water line, heat ducts, other? Does your furnace have a dedicated air source? You say it is a new house, ranch, two story, ?, but you are concerned about heating costs, how bad are they? Just having those vents open in the winter could be a big chunk of the problem.

Now I'll add to your list. I know it is a new house, but the high energy costs tell an energy auditor that something is wrong. Once we see how high and the size/style of the home, we can judge the performance, at least from a distance. Let us know, close those vents and see if those floors warm up.

Airman and I and others may not agree, but we all work towards the same solution, a warm affordable home. Besides, if we all had the same opinion, the forum would only need one professional, boring.

Bud
 
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Old 02-13-10, 09:03 AM
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Doc, I think we're getting side tracked. Do you think there is money to be saved if you insulate the floor? If so, do you have an estimate in dollars?

If there is little no money to be saved, do you think the house will feel more comfortable?

Those are the only two reasons I can see that make it worthwhile.
 
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Old 02-13-10, 12:21 PM
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Indeed - if there was a single answer to everything how boring would life be

Our house is a ranch - about 2400 square feet; half basement and half crawl space. Our main heat is electric heat pump backed up with LP. Between December and March (or so) our electric bills are around $250 or so. This past month it was $300, but it was REAL cold.

No mechanicals in the crawlspace - they're all in the basement. The furnace draws from the outside on the other side of the house. Pretty much the only things in there are water pipes (pex for what its worth), electrical wires, and insluated HVAC runs to floor vents.

I've estimated that putting in kraft-faced fiberglass would cost around $300, but I haven't measured the square footage yet. I guess I'd use that or maybe extruded foam boards and glue them to the subfloor? Either way, I'd do this myself, so only materials cost.

As for the vents - I thought I closed them last fall - from the outside - but when I looked at them this morning from the inside I could see light through them. Odd. Perhaps I should crawl up in there and check that out. Maybe they're closed but still letting in a bunch of cold air - maybe I should put pieces of foam board in them?

I really appreciate the advice from you all. Doing research via this forum is great fun!
 
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Old 02-13-10, 01:22 PM
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My only concern on your thinking would be the exposed foam board. Different code departments have different opinions as to whether it must be covered with a fire barrier or not. Some will accept the foil facing, but there is a commercial version from DOW that all should accept, except the HO ?cost?

Insulation on ducts is probably minimal, so a extra layer would help. Enjoy

Bud
 
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Old 02-13-10, 01:59 PM
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I'll check on code for the board if I decide to go that route.

The ducts are those round insulated ones. Any ideas how I might put insulation around those?
 
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Old 02-13-10, 02:28 PM
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Personally, I don't think you'll save any money by installing insulation there. What type of attic do you have? Are there soffit &/or ridge vents?
 
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Old 02-13-10, 04:44 PM
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we have both. Also - 2X6 exterior walls with that I think is a pretty good insulation package.
 
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Old 02-13-10, 04:53 PM
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Since you have the proper venting in the attic, you can insulate it using fan fold between the insulation & the ceiling. If anything is going to save money, that will do it.
 
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Old 02-13-10, 05:30 PM
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We need to get back on track! Insulating the attic and walls will do nothing for his floor!!!!! I would insulate the floor.
 
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Old 02-13-10, 06:23 PM
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Hey, Airman - what's a green grass state????
 
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Old 02-13-10, 06:45 PM
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airman, Insulation is usually used to prevent heat loss & save money. I guarantee that he won't save 10 cents by insulating that floor but there is a good chance that he'll will if he insulates the attic.
 
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Old 02-13-10, 06:52 PM
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Pulpo

I might mention that I have something like 18 inches of blown insulation in the attic.
 
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Old 02-13-10, 08:14 PM
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Originally Posted by Pulpo View Post
airman, Insulation is usually used to prevent heat loss & save money. I guarantee that he won't save 10 cents by insulating that floor but there is a good chance that he'll will if he insulates the attic.
Original post was about a cold floor! How is insulating the attic going to help the floor? If the floor was insulated it would stay warmer.
 
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Old 02-13-10, 08:17 PM
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Originally Posted by doc View Post
Hey, Airman - what's a green grass state????
Any area of the country were warm season grass will grow without watering. Green grass states usually will mean that they will have high RH in the summer.
 
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Old 02-14-10, 04:35 AM
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Originally Posted by airman.1994 View Post
Any area of the country were warm season grass will grow without watering. Green grass states usually will mean that they will have high RH in the summer.
Ah, makes sense. Thanks.
 
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Old 02-14-10, 04:53 AM
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I've been wanting to ask that question for the past few years myself.
 
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Old 02-14-10, 07:25 AM
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If he insulates the attic the entire house will be warmer, including the floor. That's how.
 
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Old 02-14-10, 07:39 AM
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You don't think 18 inches up there is enough?
 
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Old 02-14-10, 09:19 AM
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I do think the 18 inches is enough, but I also agree with Pulpo in that the high heating costs and comfort issues are telling you there is something wrong. It may be the floor/crawl issue you are addressing, or it maybe elsewhere. I have audited a number of new homes where the owners were astonished at the problems that were uncovered. Quality homes built by quality contractors where by oversight, time restraints, or lack of knowledge, the work wasn't done correctly. And the one test that every home owner can apply to know if something is wrong or not, is their energy costs and comfort. Step by step, when your bills come down and that floor feels warmer, you will know you fixed something.

I always feel like my hands are tied as I want to pull out the blower door and infrared camera and go hunting .

Bud
 
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Old 02-14-10, 09:36 AM
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Bud -

that makes perfect sense. Our contractor, from all we can tell, is a quality contractor and from all I can tell the walls are well insulated as is the attic. The crawl walls have 1 1/2 or 2 inches of blue board and the rim joist has fiberglass stuffed inbetween the joists. Looks like he did all the right stuff, but floors are cold and our bills are high. Maybe the floor is supposed to be cold - especially the tile - and maybe our bills aren't THAT high......
 
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Old 02-14-10, 10:26 PM
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If your zip is 473, you need R-49 in the attic- with 18” of cellulose = R-63 Fiberglass = R-45. Insulation Fact Sheet R-25 required on the crawlspace walls--- 5” of pink or blue without the floor insulated…. Fiberglass on the rim does little to stop air infiltration: Insulate Basement Rim Joists | thefamilyhandyman.com | DIY Projects | Reader's Digest

But if you want warm floors: BSI-009: New Light In Crawlspaces —

Be safe, Gary
 
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Old 02-15-10, 06:05 AM
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Your comment that your bills may not be THAT high, is appropriate. Take your off season bills, like fall or spring when no heat or ac is in use and those represent a base line, say $100 per month. That would mean your heating costs are approximately $150 to $200 per month. However, some folks have very low electric rates so that can still be more than it should be. To make you feel better, I have audited homes in my area (northeast) that use over 2,000 gallons of fuel oil and last year, prices were close to $5.00 per gallon. Yes, some people paid close to $10,000 for the year. When I talked to my local oil co, trying to enlist their support for promoting energy efficiency, I asked if it wasn't difficult to make some deliveries. She said, when the temps are low, they have to make two deliveries per week to some homes. ie, 400 gallons a week. Oil is currently $2.50 to $3.00 per gallon, but still an awful lot of money.

Do you feel any better .

Bud
 
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Old 02-16-10, 05:52 PM
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Gary - thanks for the links. Good info.

Bud - yes, that does make me feel a bit better about the heating bills. Reminded me of spring and fall, as you said, with no heat/ac and when we keep the windows open. I suppose when its 10 degrees outside I should expect to pay.....

All in all, you've all given me lots to consider. I appreciate the time and the opinions!

thanks!

jack
 
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