We recently remodeled (more accurately, mostly rebuilt) our house.  The new house uses the old foundation with a few bump-outs and a newly poured foundations/slabs in the garage, shop, and 2nd entry.  The garage and shop are slab-on-grade, while the second entry has a crawlspace underneath.  The old foundation was wall-on-grade, which was quite common around here when the original house was built.  The engineer recommended that we do the same for the new area, even though it is not a common approach to foundations these days.

The 2nd entry has had a cold floor this winter, so I went down in the crawlspace to take a look and see why it is this way.  While down there, I discovered a few problems that I hope I can fix.  See the attached pictures for what is there today and an idea to fix it.  This area is a bit unique in that the floor, while being over a crawlspace, is only about 6 inches above the exterior grade.  In order to accomplish this, the floor joists are hung on ledgers on the face of the foundation wall, as shown in the picture, rather than sitting on the foundation wall.  The exterior framed walls do sit directly on top of the foundation walls.  There is a forced air supply vent down in the crawlspace, and a "return" which allows air to re-enter the living space above the crawlspace.  The crawlspace is about 70 square feet in size.

Anyway, this is what I found and my concerns:

1)  I think the main source of the cold floor is the ledgers, which are near the top of the foundation walls, which are not insulated at all.   The exterior side of the ledger portion of the wall is at least partially above-grade, so I have a very low R-value here.

2)  I noticed that that the builder placed poly on the floor, but it is not sealed at all around the edges, so I don't know if it is of much value for keeping radon out of the living space.  Radon is commonly a problem around here.

3)  While the sill plate is definitely pressure treated, the ledger appears to not be pressure treated.  It is possible that it is a different type of pressure-treating (the builder used "Wolmanized" lumber some places, which has a somewhat red tint to it... I need to look again -- I'm hoping it is this type rather than plain lumber).

4)  There is quite a bit of moisture condensing on the bottom of the poly.

I paid a lot of close attention to air sealing, moisture control, and insulating techniques during the construction process, but I missed this crawlspace until now and I unfortunately need to fix it myself or get my builder to fix it.

My first inclination was to spray foam the ledger to 3 or 4 inches of thickness, letting the thickness taper off until I have just the XPS at a few feet below grade.  Also, I was thinking of replacing the polyethylene and having it extend six inches up the walls, sealing and attaching it on the walls.  My concern, then is moisture passing through the concrete to the ledger -- especially if the ledger is not pressure treated.  I need to have some place into which the foundation wall can dry.  If the XPS extends all the way to the the poly, then there is nowhere for the wall to shed moisture wicked up from the structural fill.

Thanks for any thoughts or input!

Jeff

Uhoh, lost the attachments... Trying again:

What I have now:



Proposed fix:



Jeff

I found this stamped on the ledger lumber:

SPIB No 1 KD 19
HT 861

I was able to track down the meaning of the first line:

"Southern Pine Inspection Bureau" No 1 Grade, Kiln Dried to 19% or lesser moisture content

I guess HT is "heat treated"; don't know what the 861 means.

I guess the ledger is not pressure treated unless this stamp was placed on the lumber before pressure treating.

Re the PT lumber, as you suspect PT lumber starts out as KD lumber that is then pressure treated so it will have the stamps on if from before it was PTed. BTW - Wolmanized is just a brand of PT.

I live on the east cost so admittedly our PT lumber is different, still I believe the above pertains.

I would not recommend cutting the XPS; if you have moist soils (you obviously have moisture under the poly) you'll get additional moisture coming in through the concrete. Have you looked at the possibility that the cold floors result from air infiltration - possibly at the top of the foundation?

PS - they sell radon test kits at the big box store for around $10 to $15 bucks. Might be good to try one.

It's possible that there is a small amount of air infiltration, but I think I did a pretty good job of sealing between the top of the foundation wall and the bottom of the framed wall, which would be the only place for air to leak in.  Overall, the house measured very tight with a blower-door test.  With that said, it's still possible that some air is leaking past the sill gasket and down around the ledgers.  I'll seal all around the ledgers with gap-filling foam before I cover the ledgers with closed-cell poly foam.

As for radon levels, the old house measured 7 before we did the rebuild, so I had the  builder put an active radon system in the basement.  This system does not extend to this crawl space, so I suspect there is some radon emerging there.  The house as a whole measures under 2 now with the electronic radon meter from Amazon, but I'd rather at least do this space correctly with the poly than leave it as-is.

Thanks,

Jeff

Is there a way that this CS area could be connected to the newly installed radon mitigation system? I'm assuming the system consists of some piping and a 24x7 blower to create a vacuum under the basement slab? I wonder if the small amount of air movement would help to exhaust some humidity from below the CS plastic? I do think your plan for the plastic is a good one. And you need some kind of gap to make sure that moisture from under the plastic isn't being directly channeled behind the existing rigid foam and up into the framing.

A radon reading of 7 is kinda high. I think the limit used to be 6 but the EPA lowered it to 4. Or is that state controlled? You probably know way more about that than a lot of folks. Anyway, I built a house a few years back and the home buyer had it tested. The real estate agent tells me "The radon levels are way up". I talked to the guy who did the testing and the reading was 4.5! Typical for a RE agent to make make a big deal out of something that isn't. None the less I had a radon mitigation system installed to the tune of $1800. I kinda felt that part of the expense is just that they are so uncommon here - although it did come with additional periodic testing and a performance warranty.

Matt G,

I thought about connecting the crawlspace to the radon mitigation system, but I don't know if it would be worth it since the whole house reading is pretty low now with the basement mitigation measures.  I think the effort is worth it, though, to at least make sure that the crawlspace floor is properly covered with poly sheeting.

Radon is definitely a problem where we are... Many homes have mitigation systems, but not all.  Some people aren't aware of the issue, some homes have very low numbers even though a neighbor may have high numbers, and some people just ignore the danger. 

Jeff

If the ledger is near or below grade, as depicted, you need to keep the vapor permeabilty of any insulating treatment on the high side, or ground moisture will destroy the ledger.

If you can dig down on the exterior to the frost line and insulate from the outside, that would be better. Sealing the above-grade exterior with semi-permeable silane or acrylic sealers also keeps the foundation from absorbing weather-related moisture, reducing the necessary interior-drying capacity.  Any dampproofing above grade needs to be at least semi-permmeable to allow the foundation to dry to the exterior when conditions allow, while reducing capillary draw from rain/snow splash.

If  insulated on the interior, insulating the ledger with open cell foam or Type I/Type II EPS (sealed at the edges with any density foam) would maximize the inward drying capacity.

At floor, lapping the poly up to the XPS and sealing it to the XPS with duct-mastic (or  furring) would be better. If a termite-inspection channel is required, cut it just below the ledger.  If termites are an issue in your area, insert copper Z-flashing between the XPS and the concrete at the bottom, and mastic-seal the ground vapor barrier to the copper. With that sort of treatment you may be able to get a variance on any code requirements for inspection channels.

Dana1,

For now I will install fiberglass over the ledger, since it sounds like closed-cell foam is a bad idea (someone else made the same comment on another forum).  That will allow me to keep an eye on the ledger and make sure there is not a moisture issue; maybe I'll replace with open-cell down the road. 

Also, I like your idea about insulating on the outside.... This is definitely doable as only one wall of the crawlspace is on the exterior of the structure; the other three walls are either adjacent to the garage or the basement of the house.  Those walls could still wick moisture from the structural fill (it's pretty damp), but they aren't exposed to rain/snow.  The other thing that just occurred to me is that the "exterior" of the two garage-facing walls are already insulated below grade with XPS on the garage side, down about 18 inches I think.  Heat loss, then is an issue for only the six inches of exposed foundation in the garage.  This will become less of an issue once I heat the garage.

As for the damp-proofing on the exterior foundation walls, I don't know what the builder used.  It is grey in color and looks like it is not vapor-permeable, but I suppose one can't know only by looking.

Termites are a non-issue here... I guess it's just too cold for them.  I plan to seal the poly to the concrete with something (mastic is probably the right product to use), and also use furring to hold it nice and tight.

Thanks,

Jeff

Posted By JeffInCO on 18 Jan 2011 07:31 PM
Dana1,

For now I will install fiberglass over the ledger, since it sounds like closed-cell foam is a bad idea (someone else made the same comment on another forum).  That will allow me to keep an eye on the ledger and make sure there is not a moisture issue; maybe I'll replace with open-cell down the road. 

Also, I like your idea about insulating on the outside.... This is definitely doable as only one wall of the crawlspace is on the exterior of the structure; the other three walls are either adjacent to the garage or the basement of the house.  Those walls could still wick moisture from the structural fill (it's pretty damp), but they aren't exposed to rain/snow.  The other thing that just occurred to me is that the "exterior" of the two garage-facing walls are already insulated below grade with XPS on the garage side, down about 18 inches I think.  Heat loss, then is an issue for only the six inches of exposed foundation in the garage.  This will become less of an issue once I heat the garage.

As for the damp-proofing on the exterior foundation walls, I don't know what the builder used.  It is grey in color and looks like it is not vapor-permeable, but I suppose one can't know only by looking.

Termites are a non-issue here... I guess it's just too cold for them.  I plan to seal the poly to the concrete with something (mastic is probably the right product to use), and also use furring to hold it nice and tight.

Thanks,

Jeff

Fiberglass over the ledger may be WORSE than closed cell foam in climates where it can stay below 35F for days/weeks on end.  Convection of crawlspace air through the air-permeable fiberglass will deposit frost/condensation on the (now much colder in winter) ledger, and it's moisture content will rise, putting it at higher risk.  It's nearly impossible to make a perfect air-barrier over the fiberglass to prevent this from happening, whereas with spray foam or rigid foam + foam sealants it can be pretty easy.

Open cell foam or unfaced rigid EPS would be preferable.  If cost is an issue, with better climate data (where is this house located?) it's possible to design a stackup where you cobble in 0.5-1" of XPS tight to the ledger and foam-seal around it to eliminate even the tiniest air flow around it, and finish out the R using unfaced batting + water-vapor permeable air barrier. 

Any interior fiberglass needs to have an interior air-barrier to prevent convection currents from robbing it of R-value at the temperature extremes, whether you've protected the ledger with foam or not.  Kraft facers on batts are too vapor-retardent, and foil facers even more so.  Using semi or highly-permeable housewrap as the air-barrier installed snugly against the batting works though.  Sometimes it's easier/better to use low-density R19 batts and compress it to ~4-4.5" with the air-barrier sheeting, to reduced voids and convection bypasses within the insulation layer.  Compressed to 4" you'll get ~R14.5-R15 out of it, compressed to 3.5" it'll be ~R13. Keeping the air-barrier tight to the fiber is key.  With out the  interior air barrier an R19 batt will perform  at
Insulating on the exterior would be preferable, since it raises the temperature/lowers the humidity of the ledger, protecting it from wintertime moisture drives from the interior.  A combination if exterior foam/interior fiber for higher-R has pretty much the same design constraints as with an interior-foam + fiber solution.

The foundation may be coated with an asphalt based foundation waterproofing which is non compatible with XPS (Styrofoam), meaning it will cause the foam to disintegrate. You have some kind of coating on the wall so it should be sandblasted off prior to installing the XPS.

The house is located in Colorado, east of the Rockies by a few miles, about halfway between Denver and Fort Collins.  Known as the "Front Range" around here.  The elevation is about 5000 feet.

I can do exactly what you said... To repeat: 1" of XPS, foam sealed around the XPS and ledger.  Fibreglass over the XPS.  I have some leftover Tyvec that I can use to cover the fibreglass.  Cost of materials is a non-issue since this is such a small space.

Thanks,

Jeff

The old portion of the foundation is coated with asphalt; the new is coated with something that looks more like gray paint.  It has a semi-gloss sheen.  I don't think it contains asphalt.

Jeff