I am working, doing audits, with a contractor who tends to make basements, crawlspaces into conditioned space. Especially when all or most of the duct work is in the crawlspace. He does this by covering the floor, side walls and piers with heavy plastic. He then uses rigid foam insulation on the walls, foams the joints and above and seals the vents and access hatches. Then we duct seal and re-insulate.

Has anyone been doing this for a while? Any unentended consquences?

Views: 6529

Reply to This

Replies to This Discussion

I'll be looking forward to your results.  There is a guy in Raleigh you can probably get a few minutees with.  His name is Cyrus Dastur and he is one of the principle engineers on the Flagstaff project.  I suspect you're misinterpreting the 53% number.  That just sounds way too high.  Cyrus can be reached on 919-857-9005.

No, the 53% penalty is exactly what they state, but their conclusion is wrong, or at least misrepresented.  I made it through the article, the Flagstaff side, and that number is excessive because they removed the R-30 floor insulation of the control design and then tested the crawl with just R-13 on most (but not all) of the wall area and then ignored the thermal loss through the ground perimeter.  IMO, they should have just left the back door open and made the numbers look really good or bad, whichever they wanted.  To say the least, I was not impressed with their testing and when you read the full report, neither were they.  Terminated testing, unknown occupant activity, and controls that were changed so that one has to guess at what was lost to judge what was gained. 

From their diagrams, they have entirely exposed foundations on the outside, and the wall insulation on the inside is not going below grade, an absolute must when insulating a basement or crawl wall.  The net result would of course be an increase in heat loss.

I had many questions, but I have seen enough to dispute their conclusions should someone reference this report and re-working an 09 report at this time is rather low on my reading list.  For anyone who thinks otherwise, read the full report, the authors state their own doubts in their results.  The sad part is that this misleading conclusion is out there under the guise of science and will be confusing people for many years.

In cold climates, it may indeed be beneficial to insulate the floor above the crawl, but it would still be beneficial to follow good practices and insulate those walls.  One does not have to be exclusive of the other and one can calculate the savings in all configurations.  If the software can't, go back to the basic equations and do it the old fashioned way.


Not scientific, but I live in a house I built in 1984 that has a basement.  the basement was never insulated.  It has 30 inches of poured cement wall above grade in a 6800 HDD  climate, and it is 28x36.  I heat with an oil fired boiler & baseboard heat.  in 2006 we changed out the boiler to a 'low mass' unit.  The basement temps in the ceramic & hardwood first floor finishes dropped  from reasonable to damn cold.  In the summer of 2007 I sprayed an inch & a half of closed cell foam on the basement walls and the following winter those same floors were (and still are) more comfortable than ever.  Oh yeah, the oil budget went down nealy 100 gallons too.

I spray foam for a living, so I have been suggesting sealed crawl spaces and insulated basement walls at every opportunity since.  The general reaction has been 'does it really have to cost that much?' followed by 'wow, I can't believe how much that changed my house', and 'I just gave your number to my friend_________'

I have discovered through observation and non scientific attention to client feedback that clients we spray under the floor for are comonly less satisfied than those where we created a heated crawl space or heated basement under their living space. 

We heat our domestic hot water in an indirect tank off the boiler.  In 2010 we put in a solar water heater and that saved about the same amount of oil as insulating the basement did.

I have found that spray foam doesn't stick to poly, so we don't use poly for this.  We use EPDM roofing membrane instead.  that works well. 

Hi Pat,

Replying to the post above this one, but I began energy consulting before all of the software was available and still do most of my work by hand.  What that has taught me is identifying where the heat is going.  When I have a high confidence in the home owner's use, then it is my responsibility to match that number.  Foundation heat loss, be it a crawl or basement, be it incidental or intentional heat, is a major contributor.  The good news is that in many cases these spaces are easily accessed and either a rigid or spray foam applied.  I have one customer with an 1800 something home with an old stone foundation.  Between the wind, cold, and critters he had had enough and found a spray foam guy and did a number on the whole perimeter.  His comment was, it's a new house.  And I've seen others.  Done right, people won't need to insulate the floors, which is exactly the reason the above report seemed so off base.


2 days ago I did a nieghbors house.The blower door was 4300@50 on a small 1200sq.ft.wood frame cape..All I did was 2' foam bd.on the foundation vents and foamed them in.I did another door just to see.It came in at 3200@50.1 hr.s work and redused building leakage by 25% with one sheet of 2" and a can of foam...Shhhhh....... dont tell anyone.  

I read that some are using foam or foam board on crawlspace walls or to close off the vents.  Code requires an ignition barrier on many of these products and where storage is used a thermal barrier also.  What are  you all doing to address this?



The most commonly used rigid foam board used on crawlsapce walls is probably Thermax Sheathing and it has passed FM 4880 which means it does not require ignition barrier protection.  You can look it up by going to dowbuildingsolutions.com or sending me an E-mail and I can get you the documentation,

Scott Cummings


Be careful when you refer to Thermal Barriers and Ignition Barriers on foam.  Many closed cell foam manufacturers have passed testing that shows their materials do not require an Ignition Barrier in applications where an Ignition Barrier is required because those materials pass the ignition barrier test without any protection and comply with AC377 Apendix X.  An ignition barrier is the only protection required in many interstitial space applications of foam chracterized by limited or no access, containing wires, pipes, ducts, or mechanical devices, air from this space cannot communicate with other spaces, and the space is separated from the rest of the building by a Thermal Barrier.  Please feel free to look at this document from teh Spray Polyurethane Foam Alliance.  It is a newly published revision of their Thermal Barrier document.



Works great, when it's done RIGHT!

Familiarize yourself with your state code. if you convert to a sealed crawl space you'll need to do something to condition the space and control moisture/humidity.  We use a dehum. down here, but most codes specify hvac air be used.

The "State Code" comment is dead on.  In North Carolina, they terminate the crawlspace wall insulation above grade.  In the IRC, it is required to go 2' into the ground or 2' out along the ground like you do with a frost protected footer.  The need for this penetraton is really dependent upon where you are building the crawlspace.  In either event, knowing your code is the key.

Scott Cummings

Dow Building Solutions


Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Alfie Davis posted a blog post

Rent to Own Companies Montana

Montana is a great place where you definitely feel at home especially if you own your own home,…See More
10 hours ago
Colin Genge posted an event

Home Efficiency Forum at Courtyard Portland City Center

October 21, 2015 at 8am to October 23, 2015 at 5pm
Home Efficiency Forum (formerly known as Boot Camp) brings Northwest Raters, Verifiers, builders…See More
19 hours ago
MCX posted a blog post

Good HVAC in Arlington, Texas

Arlington is a city in the U.S. state of Texas, within the Dallas–Fort Worth–Arlington metropolitan…See More
19 hours ago
Profile IconRichard L. Sanderson and Diane Jackson joined Diane Chojnowski's group

Home Energy Pros on Twitter

We've created a twitter list of members of Home Energy Pros who tweet!See More
20 hours ago
Diane Jackson commented on Diane Chojnowski's group Home Energy Pros on Twitter
"@addisonhomes "
21 hours ago
Diane Jackson posted a blog post
21 hours ago
John Gillis replied to John Gillis's discussion Energy Savings of Whole House Fans vs. Air Conditioners in SoCal Featured on New 'Ask This Old House' Season in the group News & Announcements
"Hi Eric. Thanks for the response. If you wouldn't mind calling/e-mailing Nelson Warner or…"
Profile IconShandi Whited, Noah Sanders, Edward G Fahrenkrug Jr and 2 more joined Home Energy Pros

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service