View Full Version : Changing crawl space to conditioned space
04-27-2007, 01:15 PM
My home was built in 1889 and as such is rather loose and has a high air infiltration issue. It is built on a stone foundation with a short crawl space. At the present time, the crawl space is permanently open but only on one end with two relatively small openings. The openings are small and because they are on one end of the house there isn’t sufficient air movement through the crawl space. But, they are large enough to let a lot of cold air under the house in the winter.
At some point after the original construction, a small cellar was dug that is under the middle of the house. Because of it we have the high level of infiltration as there is no reasonable way to seal off the cellar from the crawl space around it or seal off the house from the cellar.
I have received an estimate from a specialty insulation company to use BioBased closed cell foam to insulate and air seal the foundation, seal plate, band board, and the immediate area of the joist pockets and under floor. They will not be spraying the full underside of the floor. The idea is to close and air seal the crawl and make it part of the conditioned space (they will also be correcting some missing vapor barrier and seal the vapor barrier seams).
Because the house will still be open to the crawl space, will there be enough natural air movement or will it be necessary to get supply air ducted down into the crawl space (not an easy thing to do). If it is necessary, how much air is needed?
Neither the insulation contractor nor numerous HVAC contractors have any idea if I need to duct air into the crawl or how much is needed. They all just shrug their shoulders and say it couldn’t hurt (I guess that must be a technical term).
Get them to spray floor, beams, joist and anything structural in the crawl and you will not need to condition it.
04-27-2007, 02:14 PM
That would add to the cost in a signigicant way. Plus, they were hesitant to do much spraying onto the vapor barrier. Is that a common practice?
04-27-2007, 06:00 PM
Try this link.
email me at koneill at sc dot rr dot com or post questions to this thread.
My phone number in the article is no longer valid.
I still do that type of work and have updated procedures but have moved.
Also check rlcengineering.com
also check buildingscience.com (.org?)
I'm trying to picture this deal in my head but, well, let's not go there.
Problem is cold air getting in through permanent openings.
Am I right to say the stone foundation goes all the way around the perimeter exept for those two openings?
Does the cellar get used and how do you get to it?
I think I would be doing what needs doing to isolate the cellar from crawl, and closing or restricting air into crawl.
Short crawl would be what in inches from dirt to subfloor?
Another measuring question of mine is the actual size of openings through the foundation?
In my mind adding insulation to an open to outside space is like storing insulation outside. Ducting heat to that space is forcing heat to go outside.
Having seen and working in all kinds of crawls makes me curious about yours. And, Oh, by the way crawls suck.
04-27-2007, 09:09 PM
Thanks for the links and I'll contact you once I have boned up on those sites.
your not spraying the VB just all the wood! RH will not be an issue after this.
04-27-2007, 09:31 PM
You are correct the foundation is continuous and the two openings are there for ventilation. They are each about 3” x 10” and each about five feet from the SE corner of the house one on the east wall and one on the south wall. There are no vents on any of the other foundations walls. The depth of the crawl space is about 12” max and many areas less.
Air is not only getting in through those two openings, but also through the generally loose construction of a house that is now 118 years old. Insulation batts that have been placed in the joist pockets are either so loose that air is able to get around them or they have fallen to the crawl floor. The inconsistency of the joist spacing makes it difficult to get batts insulation to stay in place even with tiger teeth.
The spray foam insulation is to provide complete (or nearly so) sealing of air infiltration around all the cracks and also those two openings. Since it is closed cell it will not be affected by moisture. Thus, it insulates and reduces infiltration.
04-27-2007, 09:40 PM
I mis-read your first post. Doing as you suggested was my first thought, but it does not isolate the cellar and thus the air in the crawl gets in the cellar, that then allows it into the house.
04-27-2007, 09:44 PM
Missed one of your questions:
The cellar does get used. We access it from the kitchen by stairs that are under the center hall stairs. This portion of the house (there is a newer addition that does not have these issues) is "T" shaped with the horizontal part of the "T" being the front of the house and the vertical part the kitchen. The house length is 39' with the kitchen in the center back as a 15' x 15' box. The crawl space in these areas are open to each other even thou they seem to have been built at different times.
04-27-2007, 10:28 PM
Read your article (very well written) and several on the RLC Engineering site. Many requirements in Craig's spec's for a sealed crawl we have. The one major one is the hieght of the soil in relationship to the top of the foundation wall. In most cases we are less than 12". We do have a sump pump and a de-humidifier in the cellar which has the access door to the crawl space in addition to not being sealed off from the crawl.
04-28-2007, 08:49 AM
put plastic over dirt
It may be easier to insulate the outside of the crawl stone walls
with Styrofoam, down at least 2ft below grade, then add cement layer, or bricks to hide --
this would be good time to add drain tile
another choice would be to foam the inside of the stone, after closing the 2 vent holes --
install a better door from outside
04-28-2007, 09:41 AM
The spray application you propose is the way to go if it is to complex to spray the floor.
But as cem-bsee says, at the very minimum you need to vapor isolate the floor with poly, place 3/8 crushed stone over poly for protection, lap poly 2' at seams on floor and up walls 6", have foamers spray foam over poly lap on walls.
Lastly, consider a rat slab, I know it's probably a ton of work, but worth it.
04-28-2007, 02:30 PM
What is a "rat slab"?
04-28-2007, 04:32 PM
be sure to leave 4inches of masonry exposed to inspect for insects!
rat slab probably = thin layer of concrete -- say at least 2inches = strong enuf for person, not for auto
04-28-2007, 09:00 PM
cem-bsee, you are right on , 2" of 3/8" stone mix concrete can be 2500# mix (5bag) small stone allows it to be pumped by tow behind grout pump
Only real way to seal a crawlspace floor
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