# Condition old vented crawlspace



## Windows on Wash (Aug 30, 2011)

Any moisture issues or infiltration noted in the crawl?


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## joecaption (Nov 30, 2011)

Any standing water?
Fungus on the floor joist?
Vapor barrier on the floor?
Floor joist insulated?


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## ryansdiydad (Aug 16, 2015)

No water issues. We have 2 sumps in there to make sure.

No insulation on the floor joists. Only insulation is the foundation walls in the new crawl spaces. Their is a vapor barrier under the slab for the new crawl sections. The 1955 section does not have a vapor barrier above the slab. 

There is no fungus or mold or anything. It's a pretty clean crawl.. Just dusty..


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## Windows on Wash (Aug 30, 2011)

I would make the shift to conditioned then. 

https://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces


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## ryansdiydad (Aug 16, 2015)

That link shows insulating the floor.. but I have also seen it recommended to do the walls instead.. also might have skipped it but don't I also need to open up a supply and return duck in the crawl?

In terms of the HVAC.. adding 900sgft to the system seems like a lot... do I need to be concerned with that?


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## Windows on Wash (Aug 30, 2011)

If the walls are sufficiently insulated and sealed, the amount of conditioned air is far less than inside of a normally inhabited space.


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## ryansdiydad (Aug 16, 2015)

So are the steps

- seal the vent and any other air gaps
- insulate walls
- open air supply and return in crawl 

?


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## Windows on Wash (Aug 30, 2011)

Yes.

Here is the good link: http://homeenergy.org/show/article/id/776/viewFull/

Be sure to cover the floor with a properly vapor barrier and seal at the wall if it is exposed earth. 

Seal and insulate the stem wall and ribbon boards properly and to code.

Supply conditioned air.


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## Gary in WA (Mar 11, 2009)

1. air seal the basement/crawlspace door, either way you decide to go.

2. Do a radon test (IF going with "closed") because the slab may need further attention to stop it if in a high area; https://www.epa.gov/sites/production/files/2015-07/documents/zonemapcolor.pdf

3. Insulate the rims with foil-faced foam board rather than fiberglass.

4. Closed crawls are great to limit moisture especially in the humid South. In a heating area, as yours, you would be heating the earth much more, causing an energy penalty. Though 900 sq.ft. may not be much money to heat, but you may not need the RH lowered if it is "There is no fungus or mold or anything. It's a pretty clean crawl.. Just* dusty..*" bold is mine.You didn't say how big the area is of the new addition- with insulated walls already- it may be cheaper to finish the other walls, and add air exchange vent*s *(plural) per code- and handle (after testing) the Radon- and possibly covering the foam board; check local Codes- eg. http://www2.iccsafe.org/cs/committeeArea/pdf_file/RE_06_64_07.pdf
Also, leave top 3" of FB off for termite inspections, if in high activity area; https://www.termites.com/information/statistics/tip-zone/ 

5. IF you decide to insulate the floor, add some foil-faced (same as on rims) foam board to the bottoms to stop thermal radiation or coupling; https://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

Gary


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## ryansdiydad (Aug 16, 2015)

Picture to maybe help. Its more like 1000sq after I checked the plans. 780 is original but most of those foundation walls face either the conditioned finished basement or the two new additions with insulated walls. 

Every crawl space section has an air supply run. But there is only one spot to tap in to a return. Pretty much right above the crawlspace access door in the finished basement. The return duct is not extended into any of the crawl space just goes up the wall into the living space above.

Radon hasn't been tested in 10 years but 10 years ago it was not an issue. 

Is foil faced foam board fire rated?

If I insulate the remaining walls then I wouldn't insulate the floors correct? It's one or the other.


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## Gary in WA (Mar 11, 2009)

To convert to a conditioned crawl will require a permit as you are under your own State Code, IBC, and IRC Code. 

This probably will entail them to either; accept foil-faced FB---- R-10 minimum (http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Illinois),--- OR ------ adding 1-1/2" of fiberglass (ignition barrier) in front of it- how?

Another problem is that rigid foam board (per code) requires a 24" vertically or horizontally portion below grade in the crawl.... cut up the slab, dig, dig, dig.... unless the footing is already exposed- page 36/66; https://www.energycodes.gov/sites/default/files/becu/2009_iecc_residential.pdf

Using just one exhaust (return air) may cause problems if not placed correctly for optimum air exchange under there- re-post new on our HVAC forum..... from code link; "
Crawlspaces must be mechanically vented (1 cfm exhaust per 50 square feet)
 or conditioned (heated and cooled as part of the building envelope)."

----------------------------- One OR the other is correct, but read this report from tried both ways and it cost more to condition in a heating climate; http://aceee.org/files/proceedings/2010/data/papers/1929.pdf

A lot drier in Flagstaff, (like your "dusty" crawl) though your temps are close to the same; 
https://www.currentresults.com/Weather/Arizona/Places/flagstaff-temperatures-by-month-average.php

--------- https://www.currentresults.com/Weather/Illinois/average-annual-temperatures.php

AND both had a 90% furnace and ducts below.... stands to reason that both would get an energy penalty. 

Are all the code required vents in the crawl through the walls?

Is there poly plastic vapor barrier under all the slabs, or do you need that also- on top?

Gary


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## speedstick15 (Jan 17, 2017)

What's the temperature like for you? I'd seal all vents and close any air gaps before doing anything else.


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## Dave Sal (Dec 20, 2012)

I live in the Chicago area. I have a tri-level home with a concrete crawl space about 4 feet high. Had two air vents, one on each side, and after many years of cold floors above, decided to seal off the two air vents and seal the rim joists using R10 rigid foam. The air temps in the crawl space now stay an average of 63 degrees all year round, based on a remote thermometer probe that I mounted down there. It used to get close to freezing during the winter and I'm surprised that the water lines didn't freeze. I have an HVAC duct running in the crawlspace but no supply vent.


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## Windows on Wash (Aug 30, 2011)

Dave Sal said:


> I live in the Chicago area. I have a tri-level home with a concrete crawl space about 4 feet high. Had two air vents, one on each side, and after many years of cold floors above, decided to seal off the two air vents and seal the rim joists using R10 rigid foam. The air temps in the crawl space now stay an average of 63 degrees all year round, based on a remote thermometer probe that I mounted down there. It used to get close to freezing during the winter and I'm surprised that the water lines didn't freeze. I have an HVAC duct running in the crawlspace but no supply vent.


Perfect post.

The fact you aren't actively/purposefully circulating air shows how much heat/energy communication there is between the floors. 

The real benefit to air circulation in many cases is to make sure the area is scrubbed of excess moisture.


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## Gary in WA (Mar 11, 2009)

That's great, Dave. Did you check with a radon test before closing the vents that diluted the gas before closing them? The map shows you may need a continuous running fan or a passive pipe through the roof, check locally, as you are under your State Code, IBC and locally IRC; http://www.constructconnect.com/building-codes/?search=Illinois

Radon map; https://www.epa.gov/radon/find-info...-zones-and-state-contact-information#radonmap

Did you air seal the subfloor first because now that you pressurized the crawlspace and it has to get out somewhere- possibly to the roof via a plumbing chase- same as a fire- wiring holes to interior/exterior walls many times lead to attic space above. Could have been doing that passively before but now doing it mechanically- forcing it up. Did you seal all joints in the HVAC ducting to get maximum air flow to the individual rooms, opening a calculated airflow hole in supply duct to get only what you need to meet code. Sounds like just a temp fix, since you didn't insulated the walls or 2' below grade with rigid insulation... or the exhaust vent to air communicate with the house, was that it?

Gary


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## Dave Sal (Dec 20, 2012)

Gary in WA said:


> That's great, Dave. Did you check with a radon test before closing the vents that diluted the gas before closing them? The map shows you may need a continuous running fan or a passive pipe through the roof, check locally, as you are under your State Code, IBC and locally IRC; http://www.constructconnect.com/building-codes/?search=Illinois
> 
> Radon map; https://www.epa.gov/radon/find-info...-zones-and-state-contact-information#radonmap
> 
> ...


Thanks for the info and the links. I did a radon test about 10 years ago, prior to the sealing of the crawl space. It showed no radon issues at the time. I have sealed the HVAC ducting throughout the crawlspace as well as at the furnace. It sounds like it would be a good idea to get another radon test and use it in the crawl space. I should mention that the utility room, where the furnace, water heater, and washer and dryer are located, has a small opening to the crawlspace probably measuring around 2'x1', but not accessible to anyone other than a cat.


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## Gary in WA (Mar 11, 2009)

So that would be a back crawl entrance to the utility room, OR is that the access door to the crawl- either way- weatherstrip/insulate it from the conditioned utility room. 

If you didn't want to go to the extra expense of foil-faced foam board on the joist bottoms (last link in post #10) ---- leaving the vents open to ventilate for moisture control--- you could install Tyvek housewrap to the joist bottoms for air sealing, then the cavity fiberglass insulation could have the (existing) gap (inherent with FG as it compresses due to gravity) between it and the floor to be more effective as you are stopping the air movement through the fibrous batt; http://www.buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance

This way, you are stopping; the thermal loss, the crawl from supplying air to attic to encourage ice dams, and any possible gas from permeating the floor to living space above, yet any moisture can leave through it at 58 perms. Then you wouldn't need to finish changing to a conditioned crawl or disclose it when selling yet reap the benefits now.

Gary


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