# Project: Basement Insulating



## Colbyt (Jan 27, 2014)

Don't know their names. Basement is a hole in the ground that sooner or later will get some water. Closed cell foam does not absorb whatever comes in. That is why it is the proper choice.


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## Windows on Wash (Aug 30, 2011)

2 years on the payback...that is Awesome!!!



Polyiso is still available and just make sure you have the right facing on it for the perm rate that you need. 

If you don't currently have moisture issue through the basement walls, you should be good. 

BSC has several briefs on basement walls. 

Get your tea and reading glasses!!

:thumbsup::thumbsup:


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## Gary in WA (Mar 11, 2009)

If the basement is dry, either or. Faced polyiso will stop any horizontal vapor diffusion to the interior, only allowing vertical diffusion- drying the wall above grade, risky with flowerbeds/downspouts/water source nearby. Sending moisture toward the sill plate, hope there is a sill sealer under it to prevent wicking; http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code

Unfaced polyiso will allow horizontal difussion/drying through it, though if wet it loses +60% of R-value in a year, Fig.7; http://commercial.owenscorning.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf

Many basements appear dry as the moisture is immediately evaporated away as it forms, make sure it is dry...after all that work. So, you are aware of; air sealing the drywall, FB under the plate, glue grid pattern on FB, fireblocking, required R-value per location, adding cavity insulation lowers FB temp for condensation there, etc....

Gary


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## Ocelaris (Oct 9, 2012)

Thanks, we don't have any actual water, but after taking the old furring strips out, the bottom of the concrete definetly had rusted some of the nails. The house is 60 years old and the gutters were not properly maintained, so I hate to base my decision on the previous owner's lack of maintenance. But it seems that XPS being semi moisture permeable would be the "safer" choice. However it kills me to pay $40 for a 4' section of XPS at R10 @ 2" thick vs. PolyIso at 2" and R13 for $32. We need about 44, 4' sections, so that's roughly 300-400$ more for XPS! 

There does not appear to have been any actual water entry, but where the downspouts came down there definitely was some evaporation as there are mineral deposits on the wall. We addressed most of these issues with a new roof, gutters, downspouts etc.. and I put in gutter guards which have done well so far. I also graded some areas around the house, but that doesn't mean it's completely resolved, it's just mitigated as much as is reasonably possible. The house is 60 years old, and had not been maintained, and I hate to base our future decisions (perm rating) on the past, but we haven't had the paneling down long enough to know whether that's mitigated. The panels were moldy at the bottom, and the nails in the walls at the bottom had rusted a bit; so XPS seems like a safer bet, but I'm going to do some more research.


This is my favorite article so far, fairly straight forward for home owners, but I've read a dozen so far.

http://www.buildingscience.com/documents/bareports/ba-0309-renovating-your-basment

We made a door to the basement from the garage puncturing the envelope and although the garage was insulated heavily (and heated by a space heater to keep it from freezing), I could tell immediately the change. We'll hopefully get that sealed up this weekend.


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## Ocelaris (Oct 9, 2012)

So the main question is whether the foam attached to the concrete needs to be vapor permeable to some degree. A lot of articles suggest having XPS so it can dry to the interior, but I've run across a few articles which rebutt the claim that any concrete needs to dry to the interior. 

We've been in this house 2 years, and 4 months was without gutters (long story, but the roofers didn't finish before it got cold), in which time we've never had any actual water, just moisture at the bottom and corners, which I'm perfectly fine to constrain to behind aluminum faced polyiso. 

This one in particular rebutts any requirement to "dry to the interior"

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall



> Does interior basement insulation need to be vapor-permeable? No. The idea that a damp concrete wall should be able to dry towards the interior — in other words, that any insulation on the interior of a basement wall should be vapor-permeable — is mistaken. In fact, you don’t want to encourage any moisture to enter your home. Your concrete wall can stay damp for a century; that dampness won’t hurt the concrete.


Clarified a bit here by the same author:

http://www.greenbuildingadvisor.com/blogs/dept/musings/joe-lstiburek-discusses-basement-insulation-and-vapor-retarders

Other articles say it must dry to the interior:

http://www.buildingscience.com/documents/bareports/ba-0202-basement-insulation-systems


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## Gary in WA (Mar 11, 2009)

I've read a lot of basement insulating links.... lol, each basement is different, just as each wall is different. Many tests are by computer, the real-life ones; I believe more. 
If worried about water, use XPS in the lower 1/2 of concrete wall, PIC in the upper 1/2; then it could dry- if wet through the soil- without rot in the sill plate or frame wall. Green-Build.... parrots BSC, mostly. 

If following code, you may be able to mix the different types insulation for total R-value (2012 allows this); http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=New%20Jersey Then you can use only R-5 XPS and R-15 cavity fill for; 68*F room temp, based on coldest 3 months average temps; http://climate.rutgers.edu/stateclim_v1/data/north_njhisttemp.html 
The fb temp behind cavity ins. (first condensing surface) is at 48*F with safety up to 49% Relative Humidity of room air without condensation there, above that would require using a dehumidifier. 

Gary


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## Ocelaris (Oct 9, 2012)

Thanks for all the advice; I went down to home depot to put in the order and indeed they no longer carry the 2" Poly ISO, It looks like they had some 1.5" at another store, but basically could only provide 1", so I went with 2" XPS and called it a day. Delivery will be this friday and we're hoping to start installing this weekend.

I have a question about the sil plate area. We have a steel sheet on top of the block, and then the joists rest on top of that. I was just going to pull the steel down to the concrete and glue it behind the insulation, fastening it with the 1x3 boards to the concrete. But I know the block is hollow all the way throughout, as there were 2 BX cable runs from the top to the block. Is there a better way to go about sealing the block on top? The walls are about 7.5" tall, so I have another 6" of 2" xps that I could place on top, but I was planning on using that for the sil plate. I still plan on foam insulating the whole thing when it's warmer out; but is it fine to just try and tap down the steel plate around the block?

Also is it a good/ok idea to seal the bottom of the foam board? It sometimes curves up at the end so even if I cut the foam board it may have a gap, and I don't wait air escaping at the bottom. Is it ok to use regular foam gun or cans to seal the bottom? Or will that melt the XPS, in which case I would use caulk. 

Thanks as always!




















Top of the block


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## Gary in WA (Mar 11, 2009)

Pretty fuzzy pic, if there is room, I would fill the CMU cells with a pour-in insulation before adding FB over the cavities. IMO, the metal does nothing but give a surface for condensation if not insulated. So , if easily done, remove the exposed (- outside of plate) aluminum for recycle ($) and caulk the joint at/under the wood plate, add the fill, add the rigid FB- air seal with caulking/sealant. http://www.masonrymagazine.com/1-03/pourpump.html

Gary


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## Ocelaris (Oct 9, 2012)

Well, didn't get that response in time, but I think it would have been difficult as there is a ton of space back there. Anyways, made some progress, most of the basement is now covered. I'll spray foam the sil plate and steel sheathing, I tucked it in behind the insulation, glued it down; so hopefully no air will be going, and it will have spray foam over it eventually. But we have a long way to go before we can close up the sil plate. The hot water radiator connections are in that space and I have to repipe all of them, so can't exactly sweat copper pipe with insulation sprayed back in there!

That was a real PITA screwing down the boards through 2" of foam; had to get 4" long 1/4" tap con screws and in some places had to use 4 1/2"! The new Makita rotary hammer made short work of the concrete drilling though


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