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Old 11-30-2011, 09:01 AM   #16
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Insulation 'Great Stuff' by DOW Chem.


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Originally Posted by Windows on Wash View Post
The vapor barrier in your crawl space should be across the floor and sealed to the step wall.
Thanks Windows, I think I may have used the wrong choice of words. I understand the vapor barrier being on the floor, I currently have one, it's older but its there. Maybe the word I should have used is vapor retardant? For instance facing of fiberglass batts as I understand is installed toward the warm part of the house creating a vapor barrier or vapor retardant. That is what I meant when talking about the rigid foam, etc...

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Old 11-30-2011, 10:37 AM   #17
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Insulation 'Great Stuff' by DOW Chem.


Vapor retarder is correct.

What is the floor above the crawlspace covered with? If it is vinyl or another vapor impermeable substrate, you don't, nor should you, have one.

If you apply a good layer of rigid foam across the rafters, you can skip the vapor retarder altogether as the plywood is providing a Class 3 retarder already.
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Old 11-30-2011, 11:09 AM   #18
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Insulation 'Great Stuff' by DOW Chem.


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Vapor retarder is correct.

What is the floor above the crawlspace covered with? If it is vinyl or another vapor impermeable substrate, you don't, nor should you, have one.

If you apply a good layer of rigid foam across the rafters, you can skip the vapor retarder altogether as the plywood is providing a Class 3 retarder already.
The living space above the crawlspace is the dinning room, living room, and also the kitchen. The kitchen is floor is ceramic tile with vinyl underneath. The living room and dinning as of right now are covered in your basic carpet.

This is an older home and I believe the correct name for the type of flooring in my home is plank so I am not sure if that provides retarder.

With that said Windows on Wash what would you do or advise? What I am thinking is cutting to size and putting in rigid foam flush against the bottom of the plank flooring between the joists & sealing it with great stuff and then adding some unfaced batt fiber over it. Some of the rigid foam i am seeing online like HD is saying it's got moisture-resistant facers and has radiant-barrier-quality reflective foil, not sure I want that or not. That's where I need some advice as well, thanks again you've been very helpful.
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Old 12-01-2011, 12:06 PM   #19
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Insulation 'Great Stuff' by DOW Chem.


You have a vapor barrier (less than 0.1 perm) on the warm side with the vinyl floor tile at this point so you want to make sure you don't use a vapor barrier on the underfloor insulation. If you do, you will be creating a double vapor barrier which is not ideal and will just trap moisture in the cavity.

Make sure the poly on the floor is continuous and sealed to the block wall holding down ground source moisture.

In a perfect world, I would spray 2-3" of closed cell foam on the under floor. This will give you and R-12-18 and still leave a permeability rating of about 1 or so. This will reduce the surface temperature of the underfloor considerably so you should not have any condensation issues in the summer months.

After that, I would either put up Roxul or unfaced batts and install a rigid EPS foam over the joists to interrupt the thermal bridging of the floor.

If you go the exposed foam route, you will need some sort of ignition barrier (assuming the crawlspace if just for utilities and not storage) over the foam.

You could also roxul across the joists in lieu of the foam and they you don't need an ignition barrier.
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Old 12-01-2011, 01:52 PM   #20
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Quote:
Originally Posted by Windows on Wash View Post
You have a vapor barrier (less than 0.1 perm) on the warm side with the vinyl floor tile at this point so you want to make sure you don't use a vapor barrier on the underfloor insulation. If you do, you will be creating a double vapor barrier which is not ideal and will just trap moisture in the cavity.

Thanks Wash, only the kitchen which makes up less then half the living space above the crawl space has the vinyl and tile. The rest of the space in question to my knowledge only has the plank floor, carpet cushion, & then carpet. Not sure if this is huge concern and I need to vapor barrier the rest of the living space while avoiding creating a double v. barrier below the kitchen area.

Make sure the poly on the floor is continuous and sealed to the block wall holding down ground source moisture.

The poly or vapor barrier on the floor is black and is not sealed to the block wall. That's something I'll have to address as well.

In a perfect world, I would spray 2-3" of closed cell foam on the under floor. This will give you and R-12-18 and still leave a permeability rating of about 1 or so. This will reduce the surface temperature of the underfloor considerably so you should not have any condensation issues in the summer months.

I would like to use Foam it Green DIY, however to get 2" of coating is for my approx 600 sq ft is approx $1,400, ouch + you factor in the time of year. From reading foam don't work to well in cold weather. Gotta heat it up, gotta heat up the surface area. Sounds like a real pain in the a$$ but I know it's the best solution. I also kicked around doing a hybrid of 1" of foam and then unfaced fiber over top.

After that, I would either put up Roxul or unfaced batts and install a rigid EPS foam over the joists to interrupt the thermal bridging of the floor.

Excellent idea and something to consider.

If you go the exposed foam route, you will need some sort of ignition barrier (assuming the crawlspace if just for utilities and not storage) over the foam.

When you mention exposed foam do you mean the spray foam or the rigid foam going across the joists? What would be an ignition barrier?

You could also roxul across the joists in lieu of the foam and they you don't need an ignition barrier.
Thanks again for all your help!
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Old 12-01-2011, 03:03 PM   #21
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Insulation 'Great Stuff' by DOW Chem.


No need to worry about the vapor barrier question in the other locations.

You don't need to supply one but you just need to take special care not to install one where you already have one in place (i.e. vinyl floor tile).

Just go ahead and install a duplicate vapor barrier across the floor. You existing one is probably torn in some locations already. No need to remove the existing one. Just go over the top and seal it to the wall and any penetrations in it (i.e. pillars, support beams, etc).

The foam can be kept at room temperature for a will and will dispense just fine. The surface temperature of the floor from the underside will be somewhat close to room temperature so you are okay on that end of things too.

You can put rigid foam up there as well but you want to stay near that perm rating of 1-2 on the kitchen section. Fiber faced iso is usually about 1 perm, unfaced XPS will be about 1.2 at 1", unfaced EPS (Type-I) will be about 1 perm at 5". Make sure if you go the rigid route that it is all taped and sealed up well.

The rigid foam across the joists. The spray foam would be covered by the cavity insulation.

Thanks to my buddy Dana for most of the perm ratings.
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Old 12-01-2011, 03:12 PM   #22
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Thanks a bunch again Wash I sincerely appreciate it.

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