Another Basement Thread

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camptappakeg69

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Hello everyone, longtime lurker, lots of great info on here!

Getting ready to redo the basement, was a mold farm previously with wood studs in contact with block wall and fiberglass insulation bats with vapor barrier on the walls. The floor had plastic vapor barrier and 2x2 sleepers then particle board sub floor then peel and stick tiles.Then add some ground water from the floor to block seam = stinky mess.

Basement gutted to block walls & bare concrete floor, drainage corrected, interior walls painted with drylock to a course above grade, only about 6~8 courses of 12 courses below grade. Upstate NY in zone five close to the border of zone 6.

My plans after reading almost all the threads on this subject in here is:

2" foam on floors and walls sealed on seams, with foam.
23/32 t&g osb subfloor with engineered hardwood floors,tile in the full bath
2x4 studded exterior walls with unfaced roxul or denim,then 1/2" sheetrock, then paint
Spray foam band joist area with spray foam sealed to top plate of new walls,then fill with roxul

My questions are:
Do I need a plastic vapor barrier under the foam in floor and behind foam under the grade with EPS foam?

I can find 250 xps foam cheaper than 2lb eps foam for the floors? Using 1lb eps on the walls, the company that i found recommended 2lb eps for the floor. Would the 250 xps on the floor require the plastic vapor barrier if I went that way?

Sound good so far?

Thanks in advance
 

Dana

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You don't need vapor barrier at the walls, but it's a good idea at the floor.

On the walls Roxul is preferable to denim, since the latter is hygroscopic, and can hang onto moisture a bit too long in a basement application.

You can use 1.5lb EPS (Type-II) everywhere if you like, and 1lb (Type-I) EPS would be fine on the walls. There is no need to go to 2lb EPS (Type-IX) on the floor. The ~15psi compression rating of Type-II EPS is lower than the 25psi for XPS or Type-IX EPS, but it's PLENTY of capacity under a 23/32 subfloor. How much flex do you think the subfloor will have when fully-supported by foam on concrete, as compared to mid-span between 16" o.c. joists? Just be sure to lap the seams of the subfloor with those of the foam by 12" or more to eliminate a weak seam that might get rockered over time. (That's important even if you're using 25psi goods as well.)

XPS is far less environmentally friendly than EPS due to the HFC blowing agents used. EPS is blown with pentane, and has outgassed 99% before it hits the distributor's loading dock. XPS is blown primarily with HFC134a, which gives it a higher R/inch for the first 20-50 years, after which it has the same performance as EPS.

Be sure to through-screw the subfloor to the slab at least 24" o.c. to control "potato chipping" curl or waves due to normal seasonal moisture cycling.
 

camptappakeg69

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Thanks Dana

They only recommended the type IX in case of me damaging it before the subfloor went down. I will see what the price difference is with the type II, seeing the IX was almost twice as much

Will go with the roxul instead of the denim for sure.

With the vapor barrier on the floor, would drilling through it render it ineffective? Was thinking of adhesive but wasn't sure if it would be affective if the vapor barrier was down first, but i guess maybe a blob of adhesive on the tapcon before sinking would work.

Also found this while searching for insulation...wasn't sure if I could use this instead or would it trap moisture against the floor and blocks....http://www.insulation4less.com
The prodex total 48" with r value 16 at 5mm thick seems pretty interesting.....
 

Dana

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Type-II EPS isn't as easy to bang up or break as Type-I. Type-IX is overkill.

Vapor diffusion is a vapor-pressure x surface area kind of deal. Given that the center of the hole you drill through it is more than 90% filled with a (low permeance) screw, how much total surface area are you exposing? I'll bet it's less than 3 square inches for the whole basement, maybe even less than one. Bottom line: The vapor barrier will still work about 99.99% as well with the TapCon holes as it would if it had no holes at all.

Radiant barriers need substantial air gaps on BOTH SIDES of the material to be effective, and work better at a high temperature difference than at the modest temperature differences you would see. If they have any applications at all that make sense (which isn't clearly the case for home construction) between slabs & subfloors (or under slabs) certainly isn't one of them. That is of course despite how they seem to market the stuff. Stapled to the rafters on an uninsulated barn to lower the solar gain might be "worth it".

Read the fine print on their R-16 claim which reads:

*Parameters of test: 24-inch on center 2" x 6" wood assembly. Roof application. Test method ASTM 1116. Airspace of 2.64 inch on each side of product. Heat-flow direction down. Interior side of product exposed.

That's how you were going to build it, with 2.64" of air between the Prodex and adjacent layers on each side, right? ;) That means you'd only be giving up about 6" of headroom in the basement!
 

camptappakeg69

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Thanks Dana, going with eps I on the walls and type II on the floor with the vapor barrier. I knew the r16 was too good to be true, but it sound's like it will be good for my pole barn when its time to insulate.
 

Dana

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If you're going to insulate the pole barn there are better things. The R16 is only valid for horizontal applications where the heat transfer is headed downward. It's better than nothing in the cooling season, but during the heating season it's performance would be roughly half that, in a dead-flat ceiling application. In a wall application it's performance is lower still due to the orientation allowing convection to sweep away the insulating air films near the material.

From bang/buck point of view it's really a bad deal, in almost any type of application except when there isn't sufficient space for "real" insulation. In the same 5.5" of space that it would take to meet the R16 spec you could install R23 rock wool, and it would have the same insulating effect no matter what the orientation, or the direction of heat flow.
 
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