A late reply to Vince G2’s 3/15/10 post RE: Crawlspace insulation, etc…
I’ve read your posts and the replies with great interest, and I’ve even been to the BSC site and read until my brain got a little numb. I have a client who wants to replace the skirting around her sunroom, as the wood used was in contact with the ground and has finally begun to rot. In several ways her situation is similar to yours: the room (12′ x 20′) is attached to the house on one 20′ side; the opposite 20′ side is supported by three piers. The street side was skirted with a nice-looking wood (the stuff that’s rotting), the 20′ side just has plywood, and the backyard side has no skirting but is shielded from view (but not wind) by an attached deck. The space is 20″ – 24″ high. The main complaint I am dealing with besides unsightly wood is a cold sunroom. The client has recently reinsulated between the floor joists with blown-in cellulose held in place by a fabric that resembles a housewrap, though not one I’m familiar with if it is. Last year when I first looked at the project (which had to be rescheduled to this fall) and the cellulose was not there, but some clearly ineffective old fiberglass, I had proposed sealing the three sides with PT plywood attached to a short PT stud wall. The plywood would have been covered with blueboard and one of the stucco-like products that brush on and stick to extruded polystyrene. The whole assembly would have extended a few inches below grade and been firmly attached and braced to the underside of the floor framing, and, yes was to have included vents. And I planned on uprgrading whatever vapor barrier was lying on the dirt, probably with a single, appropriately sized, woven plastic tarp . Now it’s time to do the job, but nagging doubts about the building science issues led me to the forum here. The BSC website was all about “treating the crawl space like a short basement: insulate the perimeter, not the floors.” The floor has been recently re-insulated, so I don’t want to mess with that. Enclosing the perimeter and installing vents, after what I’ve read, seems self-defeating. Not sealing the perimeter leaves a lot of cold winter wind for the cellulose to deal with. (We’re in western Massachusetts). It seems my choices are: ~seal and insulate 3 perimeter edges, install very good vapor retarder on the ground (is a single large tarp good enough?), and no vents, or ~leave the 3 perimeter edges porous (lattice is an option), and hope the cellulose does the trick, or ~lattices edges, and add polyiso taped at the seams to the underside of the cellulose-filled joists. The BSC website detailed an option like this third one for an open, pier foundation situation, with one difference: there was an air space in the joist cavity above the joist insulation. I’m not sure what the airspace was for, and whether having it was critical (they were talking about fiberglass, not cellulose, between the joists). I guess I would go with the third plan if I knew the airspace didn’t matter with cellulose. Sealing the perimeter makes me worry about any moisture that does get through–I don’t think conditioning the space is an option. I am hoping your experience may help. Your posts were about six months ago. Did you reach enlightenment? Did you do the work, and if so, what did you end up doing?
Replies
Paragraphs are your friend.
Breaking your posts, especially long posts, into paragraphs makes them much easier to read; and much more likely that they will be read. That, in turn, makes it more likely that you will recieve answers to your questions.
Trying to get thru your huge block of text is painful.
Thanks.
Yep, I gave up about the 4th line.
fitz
Use this link to get to Vince's profile page . http://forums.finehomebuilding.com/members/vince-g2 There you will find a highlighted thing about sending him a message.
Send him one and include the link to your post here.
If the stars are aligned right, you might get a response.
could've sworn there were paragraphs...
Thanks for the advice. I really did put paragraphs in the post, which is too wordy, I agree. I don't know what happened after I clicked on "post" . I did send a message to Vince G2; we'll see how the stars are configured on that.
When I get another moment I'll try rephrasing the question-- with paragraphs.
If you don't click on the source button, you can type as you see fit to write a paragraph-no need for HTML, just hit enter b/4 starting a new paragraph. (I JUST HIT ENTER)
and there she be.
Screw HTML, this isn't a computer class.
Yeah, don't click on "Source"
Yeah, don't click on "Source" -- just type. And hit "Enter" for a new paragraph.
Unfortunately there's no "Preview" option with this "new, improved" (cough, cough) software, so you kinda need to know how to do it in advance.
Back again, with repost (but not riposte)
I had clicked on "source" because that seemed to be the only way to copy and paste my post from where I typed it originally. So much for avoiding retyping. Here's my "repost", with paragraphs:
Basically it boils down to a 12' x 20' sunroom that has brand-new cellulose blown in between the 2x8 floor joists. Two of the 3 unattached sides need skirting for aesthetics (lattice would work), but in that case, would the cellulose, held in place by what looks to be housewrap, by itself be enough to keep the floors warm? The new insulation job hasn't seen a winter yet. This is in the westernmost part of Massachusetts.
My original inclination was to seal the perimeter with a short, PT wall assembly faced with stuccoed blueboard, a solution similar to what "clewless" proposed in a discussion on this site 6 months ago. I agree that the ground vapor retarder and and all other sealing would have to be impeccable with first-rate materials. Not that I couldn't achieve this, it does raise the stress (and expense) level.
Back to the porous skirting option, I liked the detail outlined at the following location I can't seem to make it a link):
http://buildingscience.com/document/insights/bsi-009-new-light-in-crawlspaces/?searchterm=insulated floor
The detail is in Figure 7 (scroll to the end), but I couldn't figure out why there was an airspace underneath the floor. I could add foil faced rigid insulation to my client's floor, but I can't create an airspace, and the insulation is cellulose, not fiberglass. But the article does mention that this detail works for buildings on piers with no skirting.
trying again with the link
http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/?searchterm=insulated floor
3rd time's the charm
Okay, I just tested the second try at the link, and it works. I also reread the part of the article that I thought said Figure 7 was suitable for open, pier foundations, but it does not say that it is or that it isn't. Still, I'm inclined to use lattice, with or without the polyiso. Would a foil-faced insulation create moisture problems within th floor cavity? My client does not have a vinyl floor (an issue in the BSI article).