Deep Energy Retrofits , Energy Efficient Stuff , Indoor Air Quality , Stuff that makes me crazy
Damp basement season. It’s coming
What are you going to do about it? Hopefully not install an exhaust only system to pull more humid air into your humid basement.
Don’t. Do. It.
I’ve been discouraging these systems forever, here in Nova Scotia. They don’t reduce humidity levels in basements, but that’s what the marketing infers. What they do is exhaust the humid air from the basement while bringing in humid air from the outside. There is no way to reduce relative humidity levels and stop condensation without a) increasing the ambient air temperature so that it can carry more moisture while at the same time increasing the temperature of all exposed (or first condensing) surfaces or b) stripping moisture out of the ambient air (that’s what a dehumidifier does — oh, wait, that’s the market these exhaust only systems are muscling in on). In reality, the best way to deal with humid basements is to #1 Find the moisture source(s), and #2 Eliminate them. That’s the straight up, bottom line, end of story.
Moisture sources like open sumps are the problem — sealing this off before doing anything else will go a long way to reducing the moisture level in your basement or crawlspace. Note the white efflorescence on the wall — that’s salt crystals left behind from moisture migrating through the wall.
Open sumps, cracks in concrete that allow bulk water into the basement, these are pretty obvious sources. Less obvious sources include crappy drainage at the foundation, damaged or non-existent drainpipe leaders, high water tables.
Then there’s the fact that cooler surfaces cause moisture to condense out of warm, humid air. Concrete or masonry, present in most basements, are terrific first condensing surfaces. Insulating concrete and masonry can help to reduce the extent of condensation. But only if all moisture sources are dealt with so there’s trapping of more moisture in the basement…so back to #1 above.
Read this blog post by Allison Bailes at Energy Vanguard if you want more details about the pitfalls of exhaust-only systems and a fantastic in-depth explanation of why they won’t, don’t, can’t work in basements. Although he references New Orleans specifically, the physics that lead to problems with humid air and cold surfaces, along with the need to eliminate moisture sources in basements and crawlspaces are the same everywhere. The severity of the problem is related to the climate zone and the condition of the basement.
Just had a convo with a cold climate builder who said he has had concerns about the viability of the continuity of the air/vapour barrier created by using high-density foam in frame walls where budget dictates non-kiln-dried framing materials. Once the foam has set, and the wood starts to dry out, he has seen the studs twist and cup and significant cracks develop at the junction between the studs and the foam, and in some cases throughout the foam itself.
Although he didn’t tell me if he’d done a before/after blower door test to see what the delta, his concern was enough to make him change products. He now uses high density foam on all non-framed walls where there is no issue with movement or shrinkage and the more flexible low density foam on framed walls. He’s willing to take the hit on the lower insulation value and the additional vapour barrier requirement.
I hadn’t bumped into this issue before and wonder if there are more people who have experienced this problem, and if so, is there any documentation, and if not, do you think there should be?
edit to original post:
…apart from installation issues, I mean. Have asked a few questions of one Net Zero builder who is using high-density foam and he pointed to installation QA/QC problems with +2″ layers being sprayed, or layers are being sprayed without enough setting time between them if pulling and cracking are issues. He noted one incidence where a crap installation at the rim joists resulted in shrinkage and pulling that left gaps of 1 to 1.5 inches!
He didn’t see much of an issue with air barrier being compromised, because spray foam would be in contact with sheathing and that is stable. I have a few phone calls with other Net Zero/Low Energy builders this week that are unrelated to this topic, but I know they have experience with high density foam, so I’ll ask some more questions and report back on what I find.
Energy Efficient Stuff , Stuff that makes me crazy
Sir, Ma’am: Step Away From the Foil Faced Bubble Wrap!
So Martin Holladay at Green Building Advisor blogged about foil faced bubble wrap last week. Will that stuff and the ridiculous claims around it in regards to insulation ever ever ever go away?
And here’s a recent 4-pager from NAIMA
I see that Allison Bailes at Energy Vanguard also blogged about it back in 201o.
And here’s a bunch of info I posted in October 2007. Note that even then, I couldn’t believe that it was **still** something that had such bandwidth. This was posted on the old Green Building Listserve…but the whole article is available as a pdf here.
There’s a good discussion going on in the LinkedIN RESNET BPI – Energy Audit & Home Performance Group, instigated by Chris Laumer-Giddens.
One comment sums it up: “The fact that Mr. Holladay felt compelled to write this article is troublesome because it just goes to show how many unqualified, willfully ignorant contractors are out there. Not only do these people offer their clients little return on their investment, it’s likely they diverge from code and protocol, causing property damage and potentially endangering lives.”
The stuff of nightmares…litigation and very unhappy householders.
More excellent discussion has come up today, courtesy Arlene Zavocki Stewart in regards to the issue of ‘effective’ R-values. R-value, U-factor = measurement of conduction. Building envelope materials all have properties that impact heat transfer via convection and radiation as well as conduction, but mere mortals using standard issue energy modelling software acceptable to home performance, DSM, and other incentive/funding programs, can only measure or model the conduction portion with any vigor. Engineers, physicists and fans of complex spreadsheet building (she raises her hand sheepishly) may be able to do otherwise, but it doesn’t count for your client if you can’t plug it into the modelling program and have it make sense with what’s already being calculated. I have bumped into this challenge in terms of modelling thermal mass for cold climate passive solar design, but it’s the same issue: how much heat gain does a material or assembly absorb or reflect from a radiant source, and how much does that contribute to the heating or cooling regime of the building?
Arlene brings a great point to the discussion: “Codes allow ‘cutting edge’ products but our ways of measurement and communication on their features often can’t be quantified in existing conventions. Developing accurate ones is very expensive and takes years for widespread adoption, a funding line item that investors just don’t seem to account for.”
In the meantime, we have ‘snake foil’ salespeople out there, talking up effective R-values that defy all the laws of thermodynamics. I will stop short of banging my head against the wall now.
Blue House Energy , Energy Efficient Stuff
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