air sealing rim joist area of older timber frame

[sesmiths]

Hi all,
A little off topic maybe...I live in an older (1840's vintage) timber framed house in central NY state. A recent energy a audit done on my somewhat leaky house recommended rim joist sealing as something I could do, though there weren't any real obvious problem areas found along the rim area. On the part of my house where there is a conventionally framed addition, I plan on sealing the rim joints with rigid insulation sealed in place with foam (great stuff) at the edges of the insulation. The rest of the house is where I need some advise. I'm worried that sealing in the 8"+ beams which are directly on the rubble foundation might be a recipe for rotting the sill as it won't be able to breathe on the interior side, and moisture may still wick up from the stone foundation. I have no desire to jack the house up and put a moisture barrier between the sill and foundation. My current plan is to just foam seal/caulk the joint between the sill and the sub-flooring above, and also the joints where the joists are rabbited into the beam, and skip covering the 8" sill beam. Is this the right way to approach this?
Scott

[beenthere]

Welcome to the forum.

What country do you live that someone is telling you to plug up the leaks in your home?
Ahhh! I see the state of NY

I would have the same concerns that you have, that it might lead to decay.

[Rooster]

What kind of wall system do you have?

What is covering the outside surface of the sill beams?  Decking? Siding?

How much of the foundation is covered by the siding?

I'm looking to see if you can address this issue from the outside without putting spray foam on a 170 year old frame.

Rooster

[sesmiths]

Thanks for the quick replies.  The frame has 2" plank exterior it with old split clapboard siding covered with asbestos shingle. Not all walls have the 2" plank.  The asbestos shingle siding extends down over the sill area and over the top of the foundation, so working on the exterior isn't really an option unless I wanted to replace a lot of shingles.    Also, that wouldn't really address the stack effect where air leaks at the cellar level cause air flow up through the walls and out of the building at roof level...from what I understand you mainly want to seal up leaks within the building envelope.   The stone foundation has a 1 or 2" skim coat of mortar over it on the interior and exterior on part of the house and just on the exterior on the oldest section of the house.  It's a typical older farmhouse in this part of the world...nothing fancy or a particularly wonderful example of timber frame construction...a strictly utilitarian building built by people with little money (but it's stood the test of time). The foundation goes up at least a few inches above ground level or more on all sides (full basement), so the sill beam is at least not below ground level.  Sub-flooring over the 1st floor joists is 1" rough floor boards covered by who knows how many layers of whatever

I've done a lot of interior remodeling over the 30 years we've owned it.  The walls were foam insulated before we bought it, with cellulose in the roof areas.  I've increased insulation in crawl space areas overhead as much as practical (cellulose), and replaced windows as I've remodeled rooms, and added interior vapor barriers where I could.  It's a lot tighter than when we bought it, but I'm always looking for any improvements and have no worries it'll ever get too tight .  I had a recent energy audit done, as NY has a program financed by NYSERDA, and I figured the blower door test would provide some helpful information for a new geothermal heating system we're planning on putting in.

The common practice for rim joist sealing these days is spray foaming the entire cavity near the foundation...the diy method is usually rigid foam sealed in place, however I have bad feelings of doing this to a timber framed building.  Hence the question.

[shinnlinger]

One thing that may also be an issue when sealing up an old cellar is radon.  This is less likely to be a concern where blasting was not done and I don't think there was too much home cellar blasting going on in 1840, and even if that did happen, most of the radon has probably worked it's way out by now, but, nonetheless your indoor air quality could be compromised some with all this sealing up. 

How about insulating the underside of the main floor instead? What do you use the current cellar for ?  Dirt floor?  If you can hang foam panels from the inside of the frame/sill down over the rocks a bit and then seal the foam to the rock with sprayfoam that might accomplish what you want but still allow some breathing.

[sesmiths]

One thing that may also be an issue when sealing up an old cellar is radon.  This is less likely to be a concern where blasting was not done and I don't think there was too much home cellar blasting going on in 1840, and even if that did happen, most of the radon has probably worked it's way out by now, but, nonetheless your indoor air quality could be compromised some with all this sealing up. 

How about insulating the underside of the main floor instead? What do you use the current cellar for ?  Dirt floor?  If you can hang foam panels from the inside of the frame/sill down over the rocks a bit and then seal the foam to the rock with sprayfoam that might accomplish what you want but still allow some breathing.

Hi,
Radon isn't an issue.  Previous test in the cellar (winter time w/ house closed up) showed extremely low levels.

Most of the cellar has a concrete floor w/ a 2nd area/room dirt where I put a plastic sheet and gravel over the dirt to cut down on some of the moisture.   Wood stove is in the cellar so we've never insulated the floors.  I did insulate the floor in the other area at one time, as it's cold and closed off from the main cellar in winter.  I used fiberglass...rodents liked it more than you can imagine, and I tore it back out.  With the new geo system in, I may revisit floor insulation again at some point, but the only thing I'd use in the future would be foam, and payback would be questionable.

Insulation's only part of the picture, air sealing being the more important part at this time (and the biggest bang for the buck).  Our house has close to 3x the air leakage that is recommended for new construction.  That's still not a bad # for old construction, and I doubt it could be brought down any where near the new construction #s without sealing the exterior with rigid insulation and residing (something I don't see in our future).  Anything easy I can do to reduce it some, I'm all for, though.  I doubt I could ever make it tight enough for air quality to be an issue.

FWIW, I also considered closed cell foam board over the sill beams initially, but thought that would be a real rot situation waiting to happen.  If it isn't sealed completely and moist air gets in, the water will condense on the cold side of the insulation and beam causing mold and rot to set in.   I could also seal rigid foam at the top of the top of the foundation/bottom of the sill, but wondered about moisture coming up from the foundation, unable to dry out.  The insulation/sealing guys don't seem to be concerned with this...just foam away...but they don't own the house.  That's why I was wondering if just foam sealing obvious air entry points would be the way to go.  It will also leave the beam exposed so you can see any problem areas, if they develop.  So I thought it might be a good idea to ask the guys who know timber framing about it.

Scott

[shinnlinger]

Usually the problem is interior moisture getting stuck in the walls, so sealing the inside face with panels or otherwise should be OK as long as the outside can still breath.  That said if you don't have decent drainage or your sill is sitting at grade you might have some other issues but as long as it can dry out I think you will be OK.