# Crawl space insulation



## wkndwrnch (Oct 7, 2012)

Kitchen floor is cold! Our new to us house, 120 year old farmhouse with one addition 25 years ago.1500 sq ft on crawl space, 1 1/2 story converted attic.I removed fiberglass insulation from floor joists,I packed rim joist with fiberglass insulation,covered floor joists with foil bubble insulation. Much cleaner,fiberglass insulation needed replacing! One room of original house gets cold to walk on in winter.I have not seen any evidence of insulation in original walls of house, what else can I do to warm up floor of the kitchen


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## fishhead (Jul 19, 2006)

It might help to insulate your foundation down to a foot or so. My house had exposed blocks around the crawl space so I put 2" of foam on the blocks and covered it with facing cement.

I also insulated one floor by putting down 1" blue foam covered with stained particle board and put 4 coats of polyurethane on it. That made a huge difference.


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## terapin (Sep 7, 2013)

If you have the skills or money, I would recommend a rat slab in the crawl space. Once thats poured put the foam insulation on the inside of the blocks, like fishhead suggested. 


What is a rat slab? _ A "Rat Slab", is a placement of concrete in the crawl space of a house. A rat slab is sometimes required by local codes, but not always. It helps to resist burrowing rodents and can when placed over a vapor barier, help reduce groundwater invasion. As a bonus it makes for a clean underfloor and a better crawling space for sub contractors.

The concrete is generally placed 2" in thickness without steel reinforcement. It is a good idea to add fiber to the mix to reduce cracking. The finish is not as fine as a floor slab. Usually only a bull float is used with sometimes minor trowelling._


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## wkndwrnch (Oct 7, 2012)

Thanks for the replies,still some time to get under the house before cold weather.
I have 2 1/2" foam panels from "basement finish systems", bought them as seconds. Worked excellent in my polebarn on rafters and walls. I will apply to the crawl space inside walls, under the kitchen area.


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## wharton (Oct 9, 2011)

I build new places on crawls. No choice here, the water table seems to start right under the leaves. :grump: I do a sealed conditioned space with a rat slab, foam on the walls, no vents, a large dehumidifier, and an indoor/ outdoor temp. and humidity gauge with the remote sensor located in the crawl. We just moved into a new one in June, house sits on a flat lot, in the woods, and on top of 60' of clay (per well driller) Crawl is dryer than anything in the area, less that 45% humidity, and a few degrees cooler than the rooms above. 

Keep a close eye on the joists, now that they are covered in bubble wrap. This may be a potential issue with trapping moisture in the floor system, and could lead to mold or rot issues. Then again, it may work great, but it needs to be monitored. Most crawls in this area are a disaster for a few reasons including, poor grading and gutter issues. lack of rat slab with stone and plastic under. Lack of footer drains that exit to daylight, or a pumped drywell. Fiberglass batts between the joists, and the biggest one....... the failed delusion that you can effectively control moisture and humidity in a mixed climate using foundation vents. I don't know about other areas of this continent, but here in the northeast, vents simply do not work. Given that, the local code enforcement bureaucracy go with what they know. If vents don't work, then you need more of them. I gave up on those idiots when they told me that I didn't need to build an expensive conditioned crawl, but if I did it the same old way, I would need 16 vents on a 26'x36' foundation. LOL, you can't fix stupid.


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## TrexTrev (Sep 12, 2013)

One thing to note is that fiberglass does NOT insulate in a open space. If you have it on your band board exposed to the open basement it isn't doing anything except filtering the dust out of the air, fiberglass requires static air to act as a thermal barrier to create its r value which in most installations in modern building it does get so its r value is always lower than advertised. In general fiberglass is a horrible insulator. For example the R13 rating on a 2x4 wall is only in a lab setting and only at low temp differences, fiberglass becomes less efficient as the differences between temps becomes greater. At a 70 degree difference it loses fifty percent of its r value. Fiberglass is also very prone to mold, both because of its paper backing and its open lattice structure that catches organic matter out of the air as it moves through it. It is a very poor choice for a crawl and I would never recommend its use in that environment or just in general if it can be helped. 

Closed cell Foam cut to fit in your band and glued to the wall of your foundation is a much better choice. It is water proof and will resist mold growth. Its R value is better and overall performance in all most all applications is superior. If you are not going to condition your crawl and are looking for way to warm your floor i would suggest 2 part spray foam. You can apply directly to the rafter and floor and will seal air tight and water tight. It come in tanks similar to propane tanks and once the 2 are combined in the nozzle it will expand about 300%. So spraying on a 1 in layer will give you 3in of foam and has a r value of about 8 per inch. It is more expensive, but it hands down will seal up better and create a very warm floor with zero bridging, you can also spray your ducts and water pipes at the same time and save on your water, and heating bill too. These are small things i learned in 15 years owing a construction company. I have spent a lot of time and research on the topic of insulation, hydro-scopic wall systems, and antique building materials such as lime mortars and plasters.


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## wkndwrnch (Oct 7, 2012)

Thanks for the information. I read about spray foam two part kit. Thinking long term, this seems like the most beneficial, and something we need to consider!I will go with "blue foam" on the walls for now.


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## wharton (Oct 9, 2011)

TrexTrev said:


> One thing to note is that fiberglass does NOT insulate in a open space. If you have it on your band board exposed to the open basement it isn't doing anything except filtering the dust out of the air,
> 
> Sorry, but this dog won't hunt. There is minimal air movement in the joist bay area, and your claim that is doing nothing is a bit extreme. Yes, there are better options, but fiberglass is far from worthless.
> 
> ...


I would personally avoid spraying any mechanical system with foam. These systems are mean to be serviced, upgraded and maintained. tough to do when you have to chip and scrape foam off to do the job correctly. A better approach is to seal, insulate and condition the crawl or basement. Lots of info. available on this technique. It has a long history of success, and is far better than trying to coat floor structures and mechanicals, which can create additional issues.


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## wkndwrnch (Oct 7, 2012)

Thanks all for the input. I decided not to do 2 part spray foam application. Cost is a big factor,and not much room to work with in some parts of the house. I am considering "Great Stuff" on the rim joist,because I can do a few cans at a time.I am working on installing 6mil clear on the dirt floor this month, (paid retail price on a box from Lowes).I lost a deal on some 2" insulation board for the walls, but another deal will come up!


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## wharton (Oct 9, 2011)

Give great stuff a try, but it can be frustrating, and very difficult to use in that manner. I would take rough measurements of each band joist space and cut 1" foam to fit. Make each piece about 3/4" small both ways, leaving a 3/8" caulking space. Then used the great stuff to caulk the panels in place. Cheaper, easier, and very effective. Good luck. BTW, if you have to regularly access this space, old pieces of carpet, placed upside-down on the poly floor covering, do a great job of protecting the plastic, and your knees. Have fun, glad it isn't me under there, LOL


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