# Insulation (floor underneath crawlspace)



## joecaption (Nov 30, 2011)

#1 go back and add your location to your profile.
#2 There needs to be a 6 mil. vaper barrier on the ground first.
#3 The rim joist needs 2" blue foam and air sealed with expanding foam.
#4 Any holes in the floors from plumbing or wiring also need to be air sealed with the foam.
Paper goes toward the conditioned surface.
Depending on your joist spacing you use 16 or 24" insulation hangers.
http://www.bing.com/images/search?q...372F12FDB474F60CA5FE5B53B9EC&selectedIndex=24


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## Albe (Mar 2, 2012)

How far are the floor joists off the ground? 

My suggestion: if you're laying on the ground looking up at the bottom of the floor, install fiberglass batts with the paper side TOWARDS the heated surface. In this case it would be plywood. At this point you will have exposed fiberglass to the elements. By elements I mean rodents who would love to rip the glass to shreds and make nests out of it. 

You can plastic over it but it's not recommended...this will trap moisture and create a huge mess. My suggestion is to use Dow board (foil faced ridgid foam board that come in 4' X 8' panels and in 1/2", 3/4" and 1" thicknesses) and install that over the joists to hold and cover up the fiberglass. Between every panel you just need to leave some gaps to allow for air flow. You may also want to drill a few air holes as well.

To secure the Dow board use button head or cap head nails! 

If you forget about the insulation, remember this: heat transfers from hot to cold. In the winter the outside wall is cold, your house is warm/hot and where the two meet, the air condenses! the paper facing on the insulation essentially "prevents" this condensation or keeps it on the warm side so it can then evaporate! 

Hope this helps!


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## Dave Sal (Dec 20, 2012)

DIYChick45 said:


> Hey guys,...My kitchen was an addition (Crawlspace underneath) and the floor gets cold as ice in the winter. I'm thinking of putting some batting between the joists in the crawlspace area. But what side would the paper be facing? My guess is the warm side but then I'd have raw fiberglass hanging down. Not sure how I would attach it too. Doesn't seem right. Any suggestions?


Google Building Science and then search for crawl space insulation. They recommend insulating the rim joists with foam boards, closing any vents, and treating the crawl space as part of the interior. That way you will reduce the chance of having condensation down there and your floors will be much more comfortable. I followed their recommendations and my crawl space now averages 63-65 degrees all year. Possibly no need to install insulation under floor either.


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## Gary in WA (Mar 11, 2009)

In Ohio, the paper facing goes toward the warm-in-winter= up. In a cooling climate,(eg. FL) warm-in-winter is down. If you go with PIC, the foil is the vapor barrier, tape the seams w. foil and don't put holes in it; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/ If the foam is thick enough for your location, you won't need asphalt paper-faced batts with old style floor boards for sub-floor. If they used plywood/OSB for sub-floor, it has a low vapor perm rating similar to paper-faced.
If you close it off by insulating the walls, then follow through and condition it with an air supply per code; http://www2.iccsafe.org/cs/committeeArea/pdf_file/RE_06_64_07.pdf

Gary


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## cbaur88 (Jan 25, 2011)

DIYChick45 said:


> Hey guys,...My kitchen was an addition (Crawlspace underneath) and the floor gets cold as ice in the winter. I'm thinking of putting some batting between the joists in the crawlspace area. But what side would the paper be facing? My guess is the warm side but then I'd have raw fiberglass hanging down. Not sure how I would attach it too. Doesn't seem right. Any suggestions?


I re-did my crawl space about two years ago. My Kitchen, Dinning, and Living room is over a crawl space and I felt the rooms were very cold. I added XPS Foam board to the crawl space foundation and sealed the seams with proper tape. Secured the board with a combination of adhesive and also bolts with large washers. I then added insulation between the joists. I used Roxul, I can't stand fiberglass, but that's just a personal preference. I spray foamed the sil ledge filling up gaps that were letting air in. I also sealed the rim joists which were a big culprit for letting air in. I cut the XPS foam board to fit and sealed edges with spray foam. I sealed up any electric, cable, etc.. holes with spray foam as well as any gaps around venting. I finally added a proper vapor barrier to the dirt floor and taped. I noticed a nice difference and I feel comfortable knowing what's down there is done right and the air I am breathing is much healthier. I keep a wireless temp and humidity gauge down there along with a dehumidifier which runs in the summer time. 

I think a place to start is adding some insulation between the joists and air sealing the crawlspace. Air sealing is probably best think you can do, stop that cold air from getting into your crawlspace will help allot. Good luck


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## asinsulation (Apr 11, 2011)

@ cbaur. Glad you see the difference in your project, but you probably did too much in foamboard on the walls and insulation in the joists as well as an airseal. If your vents are open, you are probably not seeing much ROI on the foamboard on the walls.

@ OP. Rim joists and airsealing are going to make a big difference in your climate control in the room, but your issue is with conduction, not convection. Now, you HAVE to airseal to see the full effect, but decide where first. if you want to do foamboard around the walls, seal any penetrations to the outside, along with the perimeter, and install at least a 6 mil vapor barrier that runs up behind the foamboard. No need to foamboard the wall that connects the addition to the basement. 

If you decide to address the floor directly, seal the perimeter, any penetrations in the floor, and any connections the crawlspace has to the basement. Apply your batts to the floor, and foamboard the connection wall to remove the crawlspace from the envelope. 

If you have ducts or water lines in this area(I would assume you do as its the kitchen) the first option is the way to go. If not, the second is your best bet. No sense in heating and cooling the extra footage for no purpose.


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## cbaur88 (Jan 25, 2011)

asinsulation said:


> @ cbaur. Glad you see the difference in your project, but you probably did too much in foamboard on the walls and insulation in the joists as well as an airseal. If your vents are open, you are probably not seeing much ROI on the foamboard on the walls.
> 
> @ OP. Rim joists and airsealing are going to make a big difference in your climate control in the room, but your issue is with conduction, not convection. Now, you HAVE to airseal to see the full effect, but decide where first. if you want to do foamboard around the walls, seal any penetrations to the outside, along with the perimeter, and install at least a 6 mil vapor barrier that runs up behind the foamboard. No need to foamboard the wall that connects the addition to the basement.
> 
> ...


@asinsulation, thanks for the info I appreciate it, however my crawl space has been converted to a conditional crawl. All vents have been sealed up and closed. I see small degree difference in the crawl space compared to my living space.


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## HomeSealed (Jan 3, 2008)

As mentioned above, you either insulate and seal the floor from the crawlspace, or the crawlspace from the exterior. You don't do both.


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## cbaur88 (Jan 25, 2011)

HomeSealed said:


> As mentioned above, you either insulate and seal the floor from the crawlspace, or the crawlspace from the exterior. You don't do both.


Unless it's a conditioned crawl :thumbsup:


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## HomeSealed (Jan 3, 2008)

cbaur88 said:


> Unless it's a conditioned crawl :thumbsup:


No cbaur, that is not correct. You would not insulate/seal a conditioned crawlspace from the other living space. That is what asinsulation was correcting you on as well. You would either insulate and seal the crawlspace walls, making it part of the building envelope, or you would seal and insulate the crawlspace FROM the other living space, making it outside of the envelope. 
Personally, I recommend the former. As they mention in the article, it should be treated as a "mini-basement".
http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation


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## cbaur88 (Jan 25, 2011)

HomeSealed said:


> No cbaur, that is not correct. You would not insulate/seal a conditioned crawlspace from the other living space. That is what asinsulation was correcting you on as well. You would either insulate and seal the crawlspace walls, making it part of the building envelope, or you would seal and insulate the crawlspace FROM the other living space, making it outside of the envelope.
> Personally, I recommend the former. As they mention in the article, it should be treated as a "mini-basement".
> http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation


I won't argue with you I've done allot of homework on the subject years ago and that's what I came up and implemented. Its working very well for me and I notice a nice difference in my home. :thumbsup:


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## asinsulation (Apr 11, 2011)

its good that you do see the difference. but with the vents sealed and the outside properly insulated with a vapor, you are pretty much just storing the batt insulation in your crawlspace


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## cbaur88 (Jan 25, 2011)

asinsulation said:


> its good that you do see the difference. but with the vents sealed and the outside properly insulated with a vapor, you are pretty much just storing the batt insulation in your crawlspace


I really don't think so as there is a noticable temp difference down in the crawl space and I don't want that colder air coming up through the floors making the room feel cold especially with no socks on :thumbsup::thumbsup:

No matter how much you insulate the walls it's going to still be a cold room. Not as cold as before but it's still going to be a cold space IMO.


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## asinsulation (Apr 11, 2011)

yes, but the reason you have a temperature difference is because you have stopped the circulation into the crawlspace. which is fine for now. just that it will leave alot of potential for moisture issues in the future, and drying out your floors. same principle as somebody who insulates both the attic floor and the roof rafters in the attic.


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## cbaur88 (Jan 25, 2011)

asinsulation said:


> yes, but the reason you have a temperature difference is because you have stopped the circulation into the crawlspace. which is fine for now. just that it will leave alot of potential for moisture issues in the future, and drying out your floors. same principle as somebody who insulates both the attic floor and the roof rafters in the attic.


So if I didn't stop the air ciculation in my crawl there wouldn't be a temp difference? Wouldn't it be colder had I not and the vents were open? I also put a dehumidifer down there to be safe with the moisture.


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## Gary in WA (Mar 11, 2009)

To condition a crawlspace requires insulating AND ventilating/changing the air; http://www2.iccsafe.org/cs/committeeArea/pdf_file/RE_06_64_07.pdf


http://www.buildingscience.com/docu...crawlspace-construction-performance-and-codes

If the radon and termites are allowed for....

Gary


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## cbaur88 (Jan 25, 2011)

Gary in WA said:


> To condition a crawlspace requires insulating AND ventilating/changing the air; http://www2.iccsafe.org/cs/committeeArea/pdf_file/RE_06_64_07.pdf
> 
> 
> http://www.buildingscience.com/docu...crawlspace-construction-performance-and-codes
> ...


I once read an article it was a few years ago I'll try and dig it up where it explained the vents in a crawlspace were not good and a technology implemented on houses year ago but have since changed. It basically said there was so real beneifit to them. I'll do my best to find this article and share..

I also have my ducts going through my crawl so my crawl gets some leakage to condition the air.


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## asinsulation (Apr 11, 2011)

venting is not good in some regions. trust me, here in new jersey, especially in central/south jersey and along the shore, it is highly recommended, and it does indeed work, as long as it is properly done just like anything else.


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## cbaur88 (Jan 25, 2011)

asinsulation said:


> venting is not good in some regions. trust me, here in new jersey, especially in central/south jersey and along the shore, it is highly recommended, and it does indeed work, as long as it is properly done just like anything else.


I hear you asinsulation and let me tell you I really appreciate all your info. This is the article I mostly followed along with some others great articles saying it was better to close em up so I got convinced to seal up my space. I am sure either way will work fine if you follow proper instructions for each environment. Thanks again! 


http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation


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## Gary in WA (Mar 11, 2009)

From your link; 

"Consult the resources listed below for specific guidance.
In cold climates or in very low-energy buildings, installing insulation below the ground cover is recommended. When a slab is poured over the ground in this application the temperature and humidity conditions in the crawlspace become very stable and essentially identical to the interior.
To remove any small incidental sources of moisture, it is important thatsome air circulate from the living space into the crawlspace.It is for this reason the approach is called a “conditioned crawlspace” not a “unvented crawlspace.” Flows of 50 cfm per 1000 sf when the mechanical system operates are recommended. From; http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation

We are not here to argue with you but help you and others build correctly and to minimum safety code. In NJ, you are under the IBC 2009; http://www.reedconstructiondata.com/building-codes/new-jersey/

From your prescriptive code on your situation; 

"1. Where warranted by climatic conditions, ventilation openings to the outdoors are not required if ventilation openings to the interior are provided.

2. The total area of ventilation openings is permitted to be reduced to 1/1,500 of the under-floor area where the ground surface is covered with a Class I vapor retarder material and the required openings are placed so as to provide cross ventilation of the space. The installation of operable louvers shall not be prohibited.

3. Ventilation openings are not required where continuously operated mechanical ventilation is provided at a rate of 1.0 cubic foot per minute (cfm) for each 50 square feet (1.02 L/s for each 10 m2) of crawl space floor area and the ground surface is covered with a Class I vapor retarder." From: http://publicecodes.cyberregs.com/icod/ibc/2009/icod_ibc_2009_12_par008.htm

The duct leakage alone may be enough to provide the supply (if really bad), but you need to figure the cfm's supplied, page #6 here, 5 different ways to condition your crawl; http://www.buildingscience.com/docu...crawlspace-construction-performance-and-codes check with your local AHJ. 

You may have read this; http://dirt-crawl-spaces.com/crawlspace-venting.html

They give one some possible ways to condition a crawlspace on another page, probably posted in 2007 as the code links in right hand corner are no longer valid; 

"There are other possibilities for conditioning your crawl space. For example, a fan blowing 30-40 cubic feet per minute of air from upstairs (conditioned space) into the crawl space provides air exchange and drying, while pressurizing the crawl space. To get the air back upstairs, install several transfer grilles in the floor. This is a good approach if the crawl space is clean, but if it's moldy, you'll need a different approach.
There is way to both condition the crawl space and ventilate the entire house in line with the new ASHRAE 62.2 ventilation standard. That is to install a fan to continuously exhaust air out of the crawl space to the outside and install two or more transfer grilles in the floor so new conditioned air can enter the crawl space from up stairs.
The new ventilation standard says to add fresh air to the building envelope at the rate of .01 cfm per square foot of the house and 7.5 cfm per occupant. The number of occupants is defined as the number of bedrooms plus one. Therefore a 2000 square-foot home (2000 x .01 = 20 cfm) with three bedrooms (3 + 1 x 7.5 = 30 cfm) will need a 50 cfm fan." 


Gary


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## cbaur88 (Jan 25, 2011)

Think were beating a dead horse here, thanks for the info. As I mentioned I have leakage from my ducts going through my crawl space. Thanks for the great "Bolded" info :thumbsup:


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## Gary in WA (Mar 11, 2009)

It did look silly, fixed it, sorry... lol. Point is, without anywhere for the air supply to exhaust to, it will rise and deposit moisture on the framing if the temp differences are great enough. Vented crawls are radiation coupled at the joists/ground; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

You will/may probably not have that, or if there is moisture present and you see the colder framing start to spot/discolor, (back in the corners of crawl due to insufficient air flow movement), add some exhaust vents to the house. If the leaks are great and the crawl is pressurized, but warm all over, you may be fine. "Tis a fine line..... hope it works for you.

Gary


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## cbaur88 (Jan 25, 2011)

Gary in WA said:


> It did look silly, fixed it, sorry... lol. Point is, without anywhere for the air supply to exhaust to, it will rise and deposit moisture on the framing if the temp differences are great enough. Vented crawls are radiation coupled at the joists/ground; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/
> 
> You will/may probably not have that, or if there is moisture present and you see the colder framing start to spot/discolor, (back in the corners of crawl due to insufficient air flow movement), add some exhaust vents to the house. If the leaks are great and the crawl is pressurized, but warm all over, you may be fine. "Tis a fine line..... hope it works for you.
> 
> Gary


I basically followed what the articles mentioned. Only thing I did which might be over kill is add insulation between the joists. Numerous articles recommend to close the vents up and condition the crawl, which I did. I added a dehumidifier for moisture issues if there are any. I felt that the crawl temps were still too cool didn't want that seeping through the floors. :thumbsup:


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## HomeSealed (Jan 3, 2008)

Right. So you _were_ on the right track (sealing the vents and conditioning the space is a legitimate option), but what we have been saying is that the duct leakage may not be adequate down there and your point about it being too cold is proof of that. You then went _against_ the theory behind making it conditioned space by insulating the floor joists. You made it even LESS "conditioned" by doing that. Do you see what we are saying? Either treat it as conditioned space or don't. You can't combine the two methods without creating the potential for issues. Seal it in or seal it out.... The very first line of the bs.com link that you posted says to treat the CS as a "mini-basement". You would not rectify a cold basement by insulating the floor above it would you?


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## cbaur88 (Jan 25, 2011)

HomeSealed said:


> Right. So you _were_ on the right track (sealing the vents and conditioning the space is a legitimate option), but what we have been saying is that the duct leakage is not adequate down there and your point about it being too cold is proof of that. You then went _against_ the theory behind making it conditioned space by insulating the floor joists. Do you see what we are saying? Either treat it as conditioned space or don't. You can't combine the two methods without creating the potential for issues.


 
Beating a dead horse, let's just let it go guys please. The duct leakage is for conditioning the air not to make it warm or cold like the rest of the house that's a waste of energy and $$.

I do see all your points based on going by the book, I really do and I appreciate it and hear it. Let's just let it go, I am not trying to argue, thanks so much guys!!!


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## asinsulation (Apr 11, 2011)

cbaur88 said:


> The duct leakage is for conditioning the air not to make it warm or cold like the rest of the house that's a waste of energy and $$.


I am over the crawlspace issue, as I think the point is there. But I have a serious question now. If conditioning the crawlspace does not mean heating it and cooling it along with the rest of the home, what exactly does it mean???:confused1:


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## cbaur88 (Jan 25, 2011)

asinsulation said:


> I am over the crawlspace issue, as I think the point is there. But I have a serious question now. If conditioning the crawlspace does not mean heating it and cooling it along with the rest of the home, what exactly does it mean???:confused1:


I thought I asked to let it go but since you want to continue it :thumbup: why don't you google it and find out for yourself? 

Some of the articles I've read mentioned that leakage from your ducts can sometimes be enought to condition your crawl space DEPENDING ON HOW BIG IT IS. So that's the route I took, I personally felt the leakage from my ducts and felt the warm air and cool air leaking into the crawl :thumbsup:

If if you makes you feel better you guys are so right I am so wrong, lol:thumbsup: BTW if your over it why are you still asking questions? 

Thanks all!


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## HomeSealed (Jan 3, 2008)

cbaur, no argument here. Obviously I can't speak for all, but the primary reason that most of us who are professionals post here is simply to help folks out. At the end of the day you can certainly take our advice or leave it, but our only interest is providing you and the other DIY'ers that may view this thread with accurate information. It really is not about who is right or wrong, just making sure that other people get good advice.


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## cbaur88 (Jan 25, 2011)

HomeSealed said:


> cbaur, no argument here. Obviously I can't speak for all, but the primary reason that most of us who are professionals post here is simply to help folks out. At the end of the day you can certainly take our advice or leave it, but our only interest is providing you and the other DIY'ers that may view this thread with accurate information. It really is not about who is right or wrong, just making sure that other people get good advice.


HomeSealed I couldn't agree with you more and I thank you for sharing the above. I can't tell you how many times I come to the forum and ask questions and get wonderful information and knowledge. Last think I want to do is rub people the wrong way. People on here have helped me a TON over the years as I am no professional. I just did some homework, on here and other place and went with what I thought was best. In my case little over kill and should have insulated the floors but it's done and so far no issues and good ROI. 

My appologies if I came off defensive to you and others on here about the work I did. I spent hours upon hours down there and was maticulous. Again thank you for the information and I learned a thing or two. Thank you


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