# sanity check....crawl space insulation



## JustinK (Oct 4, 2009)

Un less you have utilities in the space or need it for storage or are trying to do it cheap. I still prefer the old method of venting the crawl space and insulating the floor.


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## mmoses101-1 (Oct 16, 2012)

Justin, Thank for your input. Not sure I would call *conditioned crawlspace,* "cheap". I do think it is the right approach for my humid climit zone. Any thoughts on the type of SPF?


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## Windows on Wash (Aug 30, 2011)

I would not put CC SPF on the walls in this case. 

You do not want to prevent the brick from drying to either side and CC SPF can do that.

OC is fine and at enough of an applied thickness, it will provide you with the vapor permeance that you are looking for at the ribbon boards. If you are concerned, you can incorporate some rigid foam in the mix and shoot the foam over top.

Are you storing stuff down there? Do you have a conditioned air supply?


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## mmoses101-1 (Oct 16, 2012)

WoW, I've read this point before -that the foundation wall needs to be able to dry to the inside- from none other then Joe Lstiburek. But why? Is a high moister content going to affect the brick? Martin Holladay, over at GBA, has disgreed with Joe on this and apparently Joe has consided the point. In the 2012 Building America Report - 1108, ref (1) above, Joe leans heavly toward cc-SPF. But to be fair the report mostly says cc is less risky, not that using oc is a really bad idea.

There are no plan to use the space for storage. 
There is not a direct air supply to the crawlspace from the living area. The plan is that the negative pressure created by the installed exhaste fan (panasonic whisper) will pull conditioned air into the space through random cracks in the floor. If that doesn't work then I'll more to a dedicated supply.


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## mmoses101-1 (Oct 16, 2012)

Gary of WA, I would be very intrested in your comments on this topic as well. Your past post have been very helpful.

This is not to say I dont want others input b/c I do, only that I was hopping for one of those well researched and referanced post Gary is known for.


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## Windows on Wash (Aug 30, 2011)

Freeze thaw in this region are your concerns at the end of the day. 

If the brick has moisture in it and it has previously been able to dry to one side or the other, not allowing it to do so can damage the brick and create spalling. 

The brick hasn't failed previously, you need to be mindful of how you change its characteristics. 

I also don't care for cc SPF from a long term off gassing standpoint as there is mixed information on that. 

At the proper thickness, the OC SPF will give you a good enough vapor permeance to control any RH from getting to the brick.


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## JustinK (Oct 4, 2009)

I look it at like the less area you are heating and cooling the lower your costs are going to be. Insulating the floor and venting the crawl space just makes sense. I went with a conditioned crawl space because a roll of plastic and some foam board was alot cheaper than 1500sf of insulation. The hardwood floors are ice cold and it didnt solve the high humidity I have inside the house. I plan on adding insulation to floor when I get extra money.


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## Gary in WA (Mar 11, 2009)

Thank you for the summons, ;-) I've had a few liking the links, most don't comment so I'm left in the dark...

WoW, said most of it. I would make sure the crawl is getting conditioned air from above (if insulating the walls), this will remove any moisture build-up (and give less RH in the air as it goes through HVAC before coming down) and keep the wood warm- raising the dew-point- for less condensation. Your exhaust fan only may work now due to the rim joist gaps, but you need to meet code minimum; pp.6- 5 different ways; http://www.google.com/url?sa=t&rct=...cxhZUUbjb19gdOLGMmhxgpg&bvm=bv.59026428,d.cGU

Right now the RH is tracking the exterior but once you stop that supply air, just the gaps in floor sheathing above may not be enough to satisfy the exhaust pressure; http://www.smartvent.net/docs/crawlspacestudy.pdf

As the BSC link (first one) brought out on Fig.17, 20, 23- use a drainage mat/membrane rather than just SPF directly against the rubble to be safe against freezing (though your Zone may not have problems). This would ensure the water could drain rather than wet the wall and freeze. If extensive water, may require a trench/pump. When insulating the wall, leave 2 inches open at top for annual termite inspection.http://termites101.org/termite-basics/termites-by-region

May require radon control;http://energy.cr.usgs.gov/radon/rnus.html

IMHO, vent the crawlspace and just add foamboard to the joist bottoms (air-tight), R- value; depends on nearest large city-- ?, and depth of joist/cavity insulation; http://www.buildingscience.com/docu...ulating-sheathing-vapor-retarder-requirements

Fig.7: http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Leave an air space above the cavity fill or not; http://www.buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance

Gary


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## mmoses101-1 (Oct 16, 2012)

Gary, As always thanks for the input, very helpful.

As you pointed out Gary, I don't think Freeze/thaw cycle is an issue in our region, note pg 9-12 in ref 1 (above). Anything South of the zone5/6 line is at a very low risk.

Your comment on drainage mat/membrane is well taken and I'll incluide that in my design. While I have not had any standing water issues the walls were wet in some areas when I installed the vapor barrier. But that could have been condistaion or a poor drange issue, which has been corrected. 

No radon issues, I've tested (short term test not long term) and results were acceptable. 

I am very surprised with your suggetion to simply vent. While venting is acceptable practice in some areas (warm dry climates) in the hot humid areas (which I'm in) I thought this discussion was settled. http://www.greenbuildingadvisor.com...paces-and-psychrometric-chart-are-not-friends
but irregardless, in my situation adding foamboard to the joist bottoms is not pratical due to hight limitation. 

Can I get you to comment on your thoughts of cc vs oc in this case.

Thanks.


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## Gary in WA (Mar 11, 2009)

"I am very surprised with your suggetion to simply vent. While venting is acceptable practice in some areas (warm dry climates) in the hot humid areas (which I'm in) I thought this discussion was settled."----------------- I am bias toward venting and warm floors.http://www.energy.wsu.edu/documents/AHT_Conditioned crawl spaces[1].pdf

I think you are in Zone 4, not a warm/humid zone (BELOW the white line); http://www.buildingscience.com/docu...heet-310-vapor-control-layer-recommendations/

Though conditioning the crawl is fine for your area (with no radon), similar to Princeville, NC where they tested both;heating/cooling degree days--- http://www.clrsearch.com/Princeville-Demographics/NC/Weather-Forecast-Temperature-Precipitation

https://www.clrsearch.com/Winchester-Demographics/VA/Weather-Forecast-Temperature-Precipitation

The test; http://www.google.com/url?sa=t&rct=...K96lanRIkEnCSKg&bvm=bv.56146854,d.cGE&cad=rja

Far as oc/vs/cc, your choice. May need an ignition barrier after the fact (check with local AHJ), and you will let in more moisture esp. on the south side from solar drive through rubble--- mute point with the membrane for either one... http://www2.iccsafe.org/cs/committeeArea/pdf_file/RE_06_64_07.pdf

I think your floors will be cold and watch the moisture build-up -- just sucking air from above with a fan below rather than dedicated (sized to meet MINIMUM code) supply...

Hope we helped!

Gary


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## Windows on Wash (Aug 30, 2011)

mmoses101-1 said:


> Gary, As always thanks for the input, very helpful.
> 
> *As you pointed out Gary, I don't think Freeze/thaw cycle is an issue in our region, note pg 9-12 in ref 1 (above). Anything South of the zone5/6 line is at a very low risk.
> *
> Your comment on drainage mat/membrane is well taken and I'll incluide that in my design. While I have not had any standing water issues the walls were wet in some areas when I installed the vapor barrier. But that could have been condistaion or a poor drange issue, which has been corrected.


Freeze thaw not an issue here...:whistling2:

I have looked at a bunch of busting brick this year so I will respectfully disagree with that assertion. If you are going to condition the crawl the risk is mitigated but if you insulate the wall effectively, you largely eliminate the heat sink to the outside wall and have a very cold wall.

If you aren't going to supply at least a little air to the crawl, I would insulated the floor and leave it vented.

If done right, there is no performance advantage to conditioning it and you will avoid all the other concerns of messing with a system that has worked already for decades.


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## mmoses101-1 (Oct 16, 2012)

WoW and Gary,

Thanks for your time and input. It was helpful and I'm glad I got some different perspectives.

When I started this I was under the impression that science had been settled, but I can see that there are a lot of people not convinced. And I think that's a good thing at the end of the day b/c it will create more discussions and research. However it sure does make it hard for the home owner to know which "right" method is the most right.

Until next time....my roof is next on the list.

-Mark


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## Windows on Wash (Aug 30, 2011)

The science is more settled when the conditions dictate different outcomes.

If you have ductwork, a means to get conditioned air into the crawl, plumbing, and other temperature sensitive items in the crawl, converting it to conditioned makes good sense.

If you have an older stem wall and nothing in there, getting the joists full of insulation and covering them with a good rigid foam works just as well.


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