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Old 01-26-2019, 06:21 AM   #16
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Re: Does foam board trap moisture?


Just that I would not agree with the spray foam. Spray foam makes a total mess. I cut XPS to snug fit, then put acrylic caulk around it.
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Old 01-26-2019, 07:21 AM   #17
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Re: Does foam board trap moisture?


unfaced FOAMULAR XPS 250, 1 thick, has a rating of 1.1 perm. 2 thick has a rating of 0.70 perm, or, about equal to that of 15/32 oriented strand board sheathing (OSB).

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Old 01-26-2019, 07:58 AM   #18
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Re: Does foam board trap moisture?


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Originally Posted by SPS-1 View Post
Just that I would not agree with the spray foam. Spray foam makes a total mess. I cut XPS to snug fit, then put acrylic caulk around it.

Agreed. Just tough to reach in some spots.

If they are doing all the bands, invest in a decent foam gun and use window and door foam (Closed Cell Variety) for the perimeters. You will make less of a mess.

Foam is a must in the case of I-joists as nobody is cutting them to fit flush to the top and bottom chords in those cases.

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Old 01-28-2019, 12:58 PM   #19
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Re: Does foam board trap moisture?


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Foam is a must in the case of I-joists as nobody is cutting them to fit flush to the top and bottom chords in those cases.
Exactly. I have I joists which would make cutting the foam boards much more work - possible but much more work. However, I'm really leaning towards the foam board because I'm not convinced of the safety of sprayfoam. I have a 3 year old and a newborn on the way in March. I don't want to put my family at risk.

If I do end up having the courage of cutting each board to size around the I-joists, I'm still confused with which product to use to sealing the gaps. Caulking doesn't last forever and doesnt the canned sprayfoam have the same potential toxic considerations?
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Old 01-28-2019, 01:00 PM   #20
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Re: Does foam board trap moisture?


Frothpak. Most new construction is foamed now

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Old 01-28-2019, 01:13 PM   #21
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Re: Does foam board trap moisture?


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Exactly. I have I joists which would make cutting the foam boards much more work - possible but much more work. However, I'm really leaning towards the foam board because I'm not convinced of the safety of sprayfoam. I have a 3 year old and a newborn on the way in March. I don't want to put my family at risk.

If I do end up having the courage of cutting each board to size around the I-joists, I'm still confused with which product to use to sealing the gaps. Caulking doesn't last forever and doesnt the canned sprayfoam have the same potential toxic considerations?

The potential for off-gassing and poor mixtures (i.e. the biggest issues with rig spray foaming) do not exist with canned foam.



Get a gun, extension straw, and use window and door foam (closed cell) and it should be great.
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Old 01-28-2019, 02:46 PM   #22
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Re: Does foam board trap moisture?


To cut the foam board a tip from the forum was to sharpen the edge of a 3" drywall knife and use that to cut. I had an old one with a angled blade so gave it a shot. Much easier as it can cut deeper than any utility knife and being wider it draws a straight line easily.

As for the i-joist you might cut some pieces of foam to fill out each side so the fill piece becomes just a rectangle.

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Old 01-28-2019, 03:26 PM   #23
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Re: Does foam board trap moisture?


Thanks for info everyone!

Bud, that's smart thinking. Probably better than trying to cut each fill peice to fit snug between the I-joists.

Cheers to all
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Old 01-28-2019, 03:28 PM   #24
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Re: Does foam board trap moisture?


You would be notching the 4 corners which isn't that hard once you figure the size that you need if you want a really tight fit. I always default back to just getting the largest one that I can in there and foam gun the rest.
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Old 01-28-2019, 05:00 PM   #25
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Re: Does foam board trap moisture?


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To cut the foam board a tip from the forum was to sharpen the edge of a 3" drywall knife and use that to cut. I had an old one with a angled blade so gave it a shot. Much easier as it can cut deeper than any utility knife and being wider it draws a straight line easily.

As for the i-joist you might cut some pieces of foam to fill out each side so the fill piece becomes just a rectangle.

Bud
What I do is use a razor knife with a sharp blade and either a framing square or a drywall square depending on cut size. Run it down quick tight to the square, then remove teh square and push hard as you score it down. Then you break it at the cut by holding the board down and banging down on the piece quick and it snaps, essentially like drywall. Sounds hard, but it goes quick. This works especially well on long cuts on big pieces. cutting off more than a couple of inches.

i've used a Japanese saw on the stuff and it works great when the razor doesn't. finer teeth cuts through quick and makes less of a mess.

https://www.amazon.com/Stanley-20-33...oding=UTF8&me=

IMHO, measure rough and spray foam it. honestly very little to be gained by getting it perfect if you have the foam.
for the I joists I haven't done it, but I'd measure the tallest and widest parts subtract 1-2"s then just cut each corner triangle off and foam.
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Old 01-28-2019, 05:42 PM   #26
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Re: Does foam board trap moisture?


If they are all the same size, and you have a bunch of them, I would set up a table saw jig. We do that and it makes much shorter work of the cutting if you have more than a handful to do.
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