Crawl space vapor barrier, Zone 5 California, how high up the crawl space walls, vented vs unvented
Hello community,
I live in Northern California, Zone 5, in a dry climate, hot dry summers, and rain/snow in the winter.
Our basement and crawl space is not heated but the basement is a laundry room with a washer, dryer, and water heater (which generate their own heat).
We’re planning to put a vapor barrier on the dirt crawl space, as well as replacing siding on the lowest 4 feet of the house on 3 sides, and are considering exterior insulation where we replace siding (at the very least on the laundry room wall, but undecided about crawlspace wall).
The residents of the house are chemically sensitive and we wish to avoid a situation that would require us to connect the crawl space with the space above (we want to avoid installing a floor vent in between).
The house is heated and air conditioned with a ductless heat pump (plus some baseboard heaters). No central HVAC, no ducts.
Summers are always dry, and winters alternate between wet and dry depending on precipitation. Winter temps are 30’s to 50’s with rain and intermittent snow.
When installing a crawl space vapor barrier, how far up the crawl space walls is it best to go? I had been thinking that the vapor barriers usually go just up the concrete foundation walls, so that there’s a place for termite inspections and also to avoid plastic on wood (avoid allowing moisture from under the vapor barrier reaching the wood). Is that correct?
Is it accurate to say that the vapor barrier should only go up the concrete and not up to the wood?
Also, in this scenario, is vented good (with automatic vent that closes at 40 and opens at 70, which means it’d only be open in dry weather as we don’t get humid heat here). Or is unvented better? Did I interpret correctly that unvented crawl spaces require a vent between them and the living space above?
Also, is exterior insulation on the outside of the crawlspace wall (above-ground portion) a good idea? Or would subfloor insulation on the crawl space ceiling make more sense (since crawl space and basement are unheated)? Or both?
We are planning to have exterior insulation on the laundry room basement wall, since that was recommended by the mold clearance environmental hygienist who did our post-remediation mold clearance (he said insulation on the crawlspace wall, however, is not necessary). But there is likely air exchange between the crawl space and basement (there will only be cement and plywood between the two).
That entire lower level only has an entrance from outside (walk-in basement, which then has a door from the basement to crawlspace). That area only has an exterior entrance (one has to go outside to enter the basement).
We plan to insulate all the pipes. There is no heat in the basement/crawlspace besides the natural heat produced by the washer/dryer/water-heater in the basement laundry room.
Thanks!
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Replies
When I read the code book, I see a few options.
1 Vented the current situation and a poor choice for energy efficiency.
2 Conditioned connected to the interior space that you put off the table.
3 The other option is power vented this option could be less energy efficiency than option #1. The unstated intent is vented air is replaced by air pulled from the conditioned space and unconditioned air is pulled into the living space thru the gaps of the building’s envelope picking who knows what on it journey thru the mouse holes, cockroach trails ant farms.
Seems to me if one is truly chemically sensitive making any change would be very risky and best avoided. Seems like the energy penalty would be pretty small in that climate.
Walta
Thank you. Although I am for energy efficiently, safety for chemical sensitive residents and avoiding mold is a higher priority.
Questions:
Is it best to make sure that the vapor barrier we use attaches to the concrete foundation walls and not to the wood? What mil is best (10 mil)? We are going to need to do regular termite inspections because the people who will be living there wish to avoid using any pesticides, even borate-based ones.
Also, the dirt crawlspace and laundry room (basement) are not heated. We're planning to have exterior insulation on the outside of the laundry room basement wall as recommended by the mold inspector who did the clearance after remediation (since that area will have a washer/dryer/water-heater which will create some heat naturally, and we're going to leave the basement laundry room unfinished to be able to monitor mold). Does doing exterior insulation on the basement laundry room wall mean we should do the same for the crawlspace walls, or should we skip that for the crawlspace and just insulate the subfloor above the crawlspace? The crawlspace will not be used for any storage, so the only time someone will go in the crawlspace will be for maintenance/inspection. We plan to have a dehumidifier in the basement laundry room (which the residents will empty every day or two when they do laundry).
Thanks!