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Crawl space insulation technique?


chrisprickett
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OK guys, I'm from the land of slab on grade, so bear with me. I was looking at a cabin up "North" for an investment. It's a new build (two years old). The area gets cold in the winter, and has a fair amount of that white stuff you guys call snow.

Upon checking it out, I saw that there was no insulation under the floor. It's a 30" deep crawl, with 3" styrofoam insulation on the inside walls. The floor is dirt, and had about an inch or so of water in it. We had pretty good rains the last month.

What I'd like to know is what is the best type of insulation/vapor barrier to put under the floor,(I was thinking batt and poly) and is the water in the bottom of the crawl going to be a long term headache? BTW it is well ventilated.

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Originally posted by chrisprickett

OK guys, I'm from the land of slab on grade, so bear with me. I was looking at a cabin up "North" for an investment. It's a new build (two years old). The area gets cold in the winter, and has a fair amount of that white stuff you guys call snow.

Upon checking it out, I saw that there was no insulation under the floor. It's a 30" deep crawl, with 3" styrofoam insulation on the inside walls. The floor is dirt, and had about an inch or so of water in it. We had pretty good rains the last month.

What I'd like to know is what is the best type of insulation/vapor barrier to put under the floor,(I was thinking batt and poly) and is the water in the bottom of the crawl going to be a long term headache? BTW it is well ventilated.

Ok, first of all, standing water in the crawlspace is bad. Don't allow it to continue. There should be zero standing water down there, no exceptions. If you want, I can tell you how to get rid of it.

Next, even if you get rid of it, the crawlspace is still going to be damp and you'll probably need that ventilation year round. So the 3" of foam insuation at the perimeter isn't going to do squat for saving energy or keeping your floor warm.

I'd just stuff the joist bays with unfaced batts. Don't use any vapor barrier; it'll probably cause more problems than it'll solve. If the subfloor is plywood, it'll be enough of a vapor retarder for the floor plane.

Where is the house?

- Jim Katen, Oregon

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Hi Chris,

You didn't say whether the crawl was ventilated or sealed. I'm guessing it's not ventilated or what would be the point of having insulation on the side walls.

If it is sealed, I'm with Jim 100% - water under the house is bad. Fix the source of the infiltration and then do a super good job of applying your poly. Then you can insulate it like Jim says. If you'd like, I can shoot you one of Jeff Tooley's articles about how to 100% seal a crawlspace so that you can turn that into conditioned space and won't have to lose any sleep about it any more.

ONE TEAM - ONE FIGHT!!!

Mike

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Hi,

The bottoms of crawls here are anywhere from 12 inches to 8ft. below grade and we keep water out all the time. A crawl isn't anything more than a basement with a dirt floor. It isn't hard to keep water out of a basement, you've just gotta think like water. [:D]

Make sure all roof runoff is conveyed to a point at least six feet from the foundation view downspout extensions or bubbler pots and that you've got the lot around the home graded so that there's about 1" fall for every foot for the first six feet (6"). As long as you don't have a high water table, you're not at the bottom of a draw or in direct line of flow down a slope it will stay dry.

That said, if a barrier is done right. Even if you get some infiltration the barrier will float up on top of the soil stay intact and then return to it's proper position when the water recedes.

That's a lot of vents, which is good if you don't have a hot/humid summer climate, but what's the point of insulating the foundation walls with vents, unless of course they are closing them up in winter?

OT - OF!!!

M.

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Is the area you are looking in a heated climate?

As others have said, get rid of the water first. Knowing that the majority of your heat loss is out the roof, insulating the floor may not give you the results you are after, especially if the walls are insulated.

If you do want to insulate, I say insulate with no vapor barrier.

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Oh, I didn't say it wouldn't help. 10% sounds about right, though on the high side (the walls are insulated). Also, one of those documents states "up to 10%" loss through the floors. The best would be if the floor was insulated. However, If you can insulate the floor and decrease the maximum 10% down to say 5%, that would save you $5 per month on a $100 heating bill. Is that worth it? Well, maybe. All I'm saying is that it may not give you the results you want. Personally, I'd only insulate it if my feet were cold (which I did in my old house).

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I'm not sure why the builder would have insulated the walls and then ventilated the space.

I'm repeating there should be no standing water.

I'd spray the floor with poly spray foam to create a vapor barrier and to insulate the floor. Creating an effective vapor barrier using other means is tedious and to be effective it must be directly against the floor. Here is one instance where the foam would be cost effective.

If the owner is a DYI, you can buy 50cu ft kits for about 440.00 bucks and chances are that would suffice for a couple inches. Other, cheaper materials could be used in addition to up R values if wanted, but that'd make a darn nice vapor barrier.

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Chris,

What I see here is a two fold problem.

1. Moisture

2. Building Science Design

To repeat what everyone has said because it's most IMPORTANT.

Get rid of the H2O.

If you have a round hole in the ground it's called a well. It's supposed to have water

If it's square it's called a basement/crawlspace and it's met to be DRY.

I'd say almost everyone here can help you with that.

Here is something you may wish to add to your design if you so desire.

Download Attachment: icon_photo.gif FdnSeepageTroughs_M.JPG

93 KB

Adding leaders is a good idea providing they are effective.

Notice the drainage tile around the perimeter of the footing. That may be something to consider if conditions demand it.

On the bigger picture.

Download Attachment: icon_photo.gif Swales_M.JPG

138.04 KB

There is more but you get the idea.

Now comes the difficult part of the remedial process and something I would not attempt to solve without further information.

Here's a GREAT resource from my library.

Builder's Guide to Cold Climates

Details for design and construction

by Joseph Lstiburek

And lastly, I would drive around the hood and check out crawls that are working and copy their designs - no cost.

Now, if it's a high water problem .......and you really want to see snow, have I got a deal for you.

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You have too much money, if you are looking at a second home. Buy it then wait six months and start coughing and claim mold damage and sue 'em.

Seriously, get rid of water, consider the insulation and let us know where it is so we can visit. Desicated mice, with hot sauce are tasty.

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Originally posted by RobC

Chris,

What I see here is a two fold problem.

1. Moisture

2. Building Science Design

To repeat what everyone has said because it's most IMPORTANT.

Get rid of the H2O.

If you have a round hole in the ground it's called a well. It's supposed to have water

If it's square it's called a basement/crawlspace and it's met to be DRY.

I'd say almost everyone here can help you with that.

Here is something you may wish to add to your design if you so desire.

Download Attachment: icon_photo.gif FdnSeepageTroughs_M.JPG

93 KB

Adding leaders is a good idea providing they are effective.

Notice the drainage tile around the perimeter of the footing. That may be something to consider if conditions demand it.

On the bigger picture.

Download Attachment: icon_photo.gif Swales_M.JPG

138.04 KB

There is more but you get the idea.

Now comes the difficult part of the remedial process and something I would not attempt to solve without further information.

Here's a GREAT resource from my library.

Builder's Guide to Cold Climates

Details for design and construction

by Joseph Lstiburek

And lastly, I would drive around the hood and check out crawls that are working and copy their designs - no cost.

Now, if it's a high water problem .......and you really want to see snow, have I got a deal for you.

Rob,

The builder's done about 150 of the same design, and they all are built exactly the same. All have water. I'm getting cold feet (pun intended).

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Originally posted by chrisprickett

Originally posted by Corners

Do you have any pics of the property?

Here's a few...

That water is unacceptable in a crawlspace.

Ducts that have been in the water should be removed, discarded and replaced.

I live, eat & breathe crawlspaces on a daily basis. What you have there is a big problem.

- Jim Katen, Oregon

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