Basement finishing Insulation question.

Basement Insulation Studies

Hi,
The two places I have seen studies of insulation in below grade interior basement insulation for perimeter walls are Building Sciences and a lesser known one, "The Challenges of Basement Insulation," by Aldrich and Zuluaga from 2006.

http://www.carb-swa.com/articles/in%20the%20news/HomeEnergy_The%20Challenges%20of%20Basement%20Insulation.pdf

As discussed many times on this forum, circulating air is the biggest culprit, i.e. air getting behind the insulation systems, and where FG fails. Both camps agree that rigid foam insulation is superior, however, Building Sciences advocates rigid foam to the floor, while the "A-Z" study advocates stopping short and leaving a 6 inch space before the floor. Their reasoning is a small leak will run down and have excess water quickly dry.

Has anyone had experience with the rigid foam to the floor, sealed, and then a leak develops? Does the water just continue to collect behind the sealed foam until the water finds a way out, maybe through a taped joint?

Then A-Z study mentioned how trapped moisture (not vapor) was a possible issue with rigid foam to the floor and they advocate leaving a 6 inch gap.

I am trying to reconcile these two studies, had anyone else examined both?

I know this has been covered ad nauseum on here but I haven't seen mention of this other study.

Thanks.

GBR in WA said:

"My question is with the rigid foam is it simply glued to the wall and floors with a construction adhesive approved for foam?"-------- Yes. The adhesive pattern is important against air movement; http://joneakes.com/jons-fixit-database/743

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That link doesn't describe adhesive patterns.....

GBR in WA said:

Hence the caulk/canned foam and tape, I recommend. F.b. on the rim joists, also; http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf

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Do I need to just glue it at the rafters in the same manner as the walls and then seal with spray foam?

GBR in WA;1082212The foamboard "expansion" gap is not required with f.b. as it shrinks over time said:

http://www.buildingscience.com/documents/published-articles/pa-foam-shrinks[/URL]

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Is that all foam board? Should I just get it as close to the wall as possible and then fill it with spray foam then?

GBR in WA;1082212ADA the drywall as a first defense against air to the concrete; [url said:

http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/[/url]

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I was planning on a drop ceiling.... That would make it difficult to seal at the top... Any other suggestion?


Thanks

I just wanted to point out my other thread which has this link

http://www.carb-swa.com/articles/in%...Insulation.pdf

which disagrees with ceiling to floor continuous rigid insulation...unless I'm reading it wrong.

If a leak develops....and we all know homes never spring a leak :whistling2: a sealed continuous rigid foam insulation method will damn up the excess water against the concrete wall with no escape other than vapor.

I was all set to do the Building Sciences method when I discovered this article done around Chicago....which is my zone.

Thanks

Thoughts?

It appears you are skipping some important steps in your reading. Foamboard installed air-tight to concrete will insulate and vapor retard any cold moisture coming through the concrete. If you air-seal the f.b. and glue as mentioned; with the "closed grid pattern" (horizontally and vertically) which limits the surface area of the air movement and wetness to diffuse through-- rather than drain-down to collect/pool at the bottom- possibly wetting wood framing (to mold, being organic) or cavity insulation from wicking- degrading it's R-value- if fiberglass; http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/90-controlling-heat.html

If you have a perimeter interior drainage system, the application would be different. Because it is an insulating sheathing board- it raises the dew-point of the cavity materials- wood framing/fiberglass or Roxul insulation- so you don't get condensation there. With plain f.g. batts, the dew-point would be the temperature of the concrete wall. For those locations with a deep frost-line and above-grade wall areas, foamboard is essential to control condensation because of the cold temperatures at those areas. Leaving a 6" gap at the bottom will create convective loops behind the drywall, warming the top of the wall/ceiling joists rim area 24/7 when the heat is on. The gap promotes air flow, much better to have dead-air (whole purpose/design of fiberglass insulation); https://docs.google.com/viewer?a=v&q=cache:M_ByAk5oMT4J:www.certainteed.com/resources/Use%2520of%2520Vapor%2520Retarders.pdf+water+resistant+gypsum+board+permeance+rating&hl=en&gl=us&pid=bl&srcid=ADGEESgt9RDzAXFRomDcEbQmwtyBGjayITUg0VINVFrtfPJ92PgXgKurYS55o3WmUhfYQVJ8lLEstHevvLyLOw_jzEBcxg8oPtfb6V8oA5PdgcXk_DFpAflg99BVUppB7X5bE6Foimib&sig=AHIEtbQYAZ0SWjnVJNXhfHFsk1RrK9G2HQ The foamboard is the vapor retarder mentioned on the first page of that link.

Compare the different basement insulation strategies listed on pp.7, and the moisture potentials of that wall throughout the article; http://www.buildingscience.com/docu...merica-high-r-foundations-case-study-analysis

Using your 3 yearly average low temperatures= 14* at 70* interior basement temperature, using R-5 f.b. and R-15 (3-1/2") cavity insulation, you would be safe at 23%RH and below. With R-10 XPS and R-15 cavity, above grade and to frost-line = safe at 48%RH, much better.

Gary
PS. I merged your other similar thread with this one.

Ok sorry for being difficult but I'm getting confused now because of the two threads merging :huh:


So my basement is mostly below ground. I got maybe 1.5-2 feet or so above ground.

http://www.carb-swa.com/articles/in the news/HomeEnergy_The Challenges of Basement Insulation.pdf

This link mentions stoping the insulation about 6 inches from the floor to let the moisture dry out.

https://docs.google.com/viewer?a=v&...Foimib&sig=AHIEtbQYAZ0SWjnVJNXhfHFsk1RrK9G2HQ

this one mentions that leaving any air space would lead to more moisture.


I was also talking to another friend and he was saying that in his reno he was just going to put dimple mat or another subfloor smiler down because if in the event you do get water their its not air tight and can dry out...

Let me know if this plan is good and if I'm on the right track

Would a better option be to use a Dri-Core subfloor? My lowest level of the basement which im working on is only 340 square feet +- so its not a huge space...

1)I'd lay the dri-core sub floor or some other .

2)then glue the R.F.B to the wall using a grid pattern (in order to not allow airflow on the walls and moisture to develop)

3) go from subfloor to the rafters and then glue a piece of a foam in between joist sealing it with caulk or spray foam.

4) Seal all the gaps with spray foam and tape all joints between boards and the floor

5) frame walls with 2x4's now and then fill bats with another form of insulation. Probably fiberglass at this point.

6) I don't put plastic sheeting on at this point I just drywall right over right?