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· Grand Poobah
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Discussion Starter · #1 ·
I have a large crawlspace about 3300 square foot floor. Walls are 4 foot high and total about 1000sf.
The floor is poured concrete and the walls are cement.
I want to seal it to reduce humidity, put in a dehumidifier that pumps water out side and then cover the walls with closed cell insulation boards.
As anyone does this?
Was it worth it?

Good sealers are expensive. Looking at using Ghost shield 9500 which will cost somewhere around $800 in material.
Insulation boards like super tuff from Homer Depot R 3.3 and I'd need about 30 boards.
I guess I'd glue it with whatever caulking glue they make for that stuff.

Thoughts?
 

· Premium Member
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656 Posts
Why do you want to insulate the crawl space, are you going to store anything in there? If you are not storing anything in there and you do not plan to heat it then only insulate the floor above the space and use the rigid insulation to seal the underside of the floor beams. Tape all the seams to keep out drafts. You should only insulate heated spaces the unheated spaces, attic and crawl space, are for air circulation that keeps the humidity in the house down. Always make sure if you start adding insulation that your roof is properly vented, you don't want condensation problems.
 
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· Premium Member
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I just had my crawl space sealed (encapsulated), but it was a dirt not concrete floor.

It went from a damp, musty smelling cave to a dry clean smelling storage space overnight.

I added a dehumidifier to the space, and in addition to keeping it dry, I expect the hot air to semi heat the space in the winter.

Not having cold floors would be a plus. I didn't insulate the walls.

I used Healthy Basement Systems after checking out a few others. I thought it was expensive, but necessary.

Around $5000 for 1400 Sq Ft. It took a crew of four 1 day to do it.

All in all, I'm happy with the results.

If my crawl space were all concrete, I would have just put in the proper sized dehumidifier and left it at that.

I just got tired of the musty smell. The only reason to insulate is if you have cold floors above it.

Try the proper sized and type dehumidifier first (not the room type, but one made for a crawl space) and save a headache.
 

· Giraffe Hunter
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3,727 Posts
I did my reloading room in my basement and the foam board, though expensive is really the only option. Its mold proof which is all that matters in a damp basement and it gives you an excellent R value for the thickness. I used 2 inch foam fastened with wood strips screwed and glued into the concrete walls. Worth every penny IMO.
 

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how far out of the ground are the foundation walls? Enough room for a few vents? I suggest UGL dry lock just roll it on. Insulate the floor joist (if 2x10 use r-30 ) paper face toward the living space. As far as insulating the walls probably over kill, the earth around foundation is about the best insulation you can get.
 

· Grand Poobah
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21,090 Posts
Discussion Starter · #9 ·
Thanks for responses guys.

I do wish to use it to store seasonal stuff. Christmas decorations, hunting gear maybe

The foundation walls are not very high and the old school way of venting the crawlspace has fallen out of favor.
I read a bit about why and it seems to make sense to me.

Concrete is porous and while certainly better than dirt moisture still comes through so I want to seal it.
That will cut any humidity more than anything else.
The best thing i read to do is insulate the walls after sealing the concrete and put vents so the air is part of the whole house.
so it's airconditioned and heated.
I don't want to put registers in the floors to the crawlspace though.

My pipes run in the crawlspace so it gets heat from the house because they never froze.
The main water line actually comes up from below the concrete.

I was always against putting insulation between the floor joists because of humidity causing mold and that's a bad thing.
But if i seal it and put a good dehumidifier in that's not an issue.

But if i insulate the walls it's about 1000 sf
if I insulate the ceiling it's about 3000 sf and I have to be concerned with the pipes that are exposed like the main.
 

· King Coal and Lord of the Blue Ladies
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2,148 Posts
I just had my crawl space sealed (encapsulated), but it was a dirt not concrete floor.

It went from a damp, musty smelling cave to a dry clean smelling storage space overnight.

I added a dehumidifier to the space, and in addition to keeping it dry, I expect the hot air to semi heat the space in the winter.

Not having cold floors would be a plus. I didn't insulate the walls.

I used Healthy Basement Systems after checking out a few others. I thought it was expensive, but necessary.

Around $5000 for 1400 Sq Ft. It took a crew of four 1 day to do it.

All in all, I'm happy with the results.

If my crawl space were all concrete, I would have just put in the proper sized dehumidifier and left it at that.

I just got tired of the musty smell. The only reason to insulate is if you have cold floors above it.

Try the proper sized and type dehumidifier first (not the room type, but one made for a crawl space) and save a headache.
wow awesome I was just talking to my wife about this today. I need to get this done! Thanks for the info
 

· Registered
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Crawlspaces are supposed to be vented. Per code is 1 square inch of vent area per 1 sf of crawlspace area for proper ventilation.
Usually use 16" wide by 8" high vent louvers with screens.
Crawlspaces are supposed to have a 2" rat slab as well.
Following those standards should give you usable storage without condensation problems.
If you seal everything up you will have to condition the air or provide mechanical ventilation to prevent condensation and humidity issues that others have mentioned.
 

· Grand Poobah
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21,090 Posts
Discussion Starter · #14 ·
Crawlspaces are supposed to be vented. Per code is 1 square inch of vent area per 1 sf of crawlspace area for proper ventilation.
Usually use 16" wide by 8" high vent louvers with screens.
Crawlspaces are supposed to have a 2" rat slab as well.
Following those standards should give you usable storage without condensation problems.
If you seal everything up you will have to condition the air or provide mechanical ventilation to prevent condensation and humidity issues that others have mentioned.
I think that's behind the times. Passive ventilation to the outside cause more problems than it solves.
I'm considering mechanical ventilaltion in that I want to seal & insulate it and run a dehumidifier.
 

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I usually up grade the interior of a foundation like so : Two coats of Dry lock on the walls and floor . I frame out walls an inch and a half or so from the concrete . Then I install encapsulated insulation between the studs , not touching the walls . Then plywood hung vertically . Have done quite a few basements with no problems. You could fir it out and put rigid over the firring strips but it should have some air flow bottom to top.
 

· Banned
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I had a crawl space spray foamed with open cell.... Great investment!
Every evening/night that addition would heat up. That concrete slab crawl space was next to my driveway and worked as a heat sink.... At night it would radiate that heat back up through the floor.

Sprayed 6" on side walls and under floor.
 

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Is that why people mount firing strips against the wall to nail the insulation too?
I thought if you seal the concrete you can glue the insulation directly onto it?

I think that's behind the times. Passive ventilation to the outside cause more problems than it solves.
I'm considering mechanical ventilaltion in that I want to seal & insulate it and run a dehumidifier.
Behind the times maybe, but current code if you build a new crawlspace and it gets reviewed by an examiner and inspected by a building inspector. Do anything outside of this and you have to have a licensed professional prove and sign off on that it works and assume liability if it doesn't work and creates condensation or mold as a result.
 

· Not a participant of the LIF circle jerk.
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I have a large crawlspace about 3300 square foot floor. Walls are 4 foot high and total about 1000sf.
The floor is poured concrete and the walls are cement.
I want to seal it to reduce humidity, put in a dehumidifier that pumps water out side and then cover the walls with closed cell insulation boards.
As anyone does this?
Was it worth it?

Good sealers are expensive. Looking at using Ghost shield 9500 which will cost somewhere around $800 in material.
Insulation boards like super tuff from Homer Depot R 3.3 and I'd need about 30 boards.
I guess I'd glue it with whatever caulking glue they make for that stuff.

Thoughts?
You'll also need fire protection for that rigid foam. (i.e. drywall,)
 

· Premium Member
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1,281 Posts
Is that why people mount firing strips against the wall to nail the insulation too?
I thought if you seal the concrete you can glue the insulation directly onto it?

I think that's behind the times. Passive ventilation to the outside cause more problems than it solves.
I'm considering mechanical ventilaltion in that I want to seal & insulate it and run a dehumidifier.
There are as many different types of crawl spaces that get lumped into the term.

My crawl space had dirt floors and concrete walls. The only thing furring strips nail or glued to the walls would do for me is give the termites a highway to the floor joists. As for insulation, you need a certain type that resists termites, otherwise they can nest in there.

1 sq in per 1 sq ft space would mean I need a 10 sq ft vent for my 1400 crawl space. Maybe for a house built on slab open under it, but for crawl spaces completely enclosed inside a concrete foundation?

The best way to get rid of the moisture is with a proper dehumidifier. Not the room kind. A crawl space dehumidifier cost about $1200
 
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