Crawl space ventilation during construction
We are building a very very small studio cabin (16×24), with encapsulated conditioned crawl space with no wall vents. This is going to be off grid… and initially, having the crawl fully sealed and running a dehumidifier is not an option during most of the construction phase (until we eventually get solar.)
We are going to place foam board wall insulation and wall vapor barrier inside crawl prior to installing the floor joists and framing, and also install a temporary sacrificial vapor barrier on the ground eventually followed by a permanent ground vapor barrier once construction is complete.
Crawl will be accessed by an external door in a side wall.
What’s the best way to manage moisture etc during construction in this closed off space before we have the ability to run a dehumidifier?
Was thinking of making a temporary access door that has 1/8” hardware screen as the main door ‘panel’ … to keep critters out and allow for ventilation. Good idea? Bad idea?
We need a solution that doesn’t require any electricity until we get a solar system. We’re in a pretty humid environment.
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Replies
I assume your foundation is concrete or block.
I suggest doing the finish vapour barrier just the same on the floor before the framing, (as opposed to a temporary one), it'll be way more easier. Look at stego products, get a thick one like 15mil or 20mil so that it'll stand time, UV and walking/crawling on. Use the mastic or tape on the seams. Bathtub the whole crawlspace with continuous vapour barrier before you start rolling joists.
For the humidity part, You don't have to worry about it much, with the vapour barrier keeping the ground and sidewall vapour out, you won't get much vapour ingress. Any minor humidity will dry upward into the space. If you're concerned, You can buy a cheaper hygrometer from Amazon or a switchbot monitor and place it down there to monitor it.
Jamie
Thank you.
So are you saying you would also skip any type of vented temporary door? and if so would you A) leave the door opening completely open during construction and not put a door on until construction is complete or B) would you go ahead from the get go and close it up with a proper door?
Yes- CMU block wall filled with concrete and rebar.
LtB,
In the absence of mechanical ventilation or humidification I would definitely leave the crawlspace hatch open.
Have you considered how you will condition the space once construction is complete? In the absence of grid power your best bet is probably to connect the crawlspace with the rooms above with floor vents, so the temperature and humidity can equalize.
That's one of the options in our building code, and I've done it on a fairly large house with good results. The only downside is the crawlspace needs to be kept clean so any contaminants don't spread to the living space above.
Planning to use a dehumidifier eventually. That’s what is typically done around here.
No floor vents. It’s a very small studio cabin. Tiny house size.
Planning on a mini split and small wood stove.
I agree with Jberks - install the vapor barrier before the floor system...
ALSO be VERY careful about subsequent sequencing.
- DO NOT install the the floor system after a rain if there is moisture on the vapor barrier. Wait until things are very dried out.
- Consider how you are going to protect the floor system from getting wet until you are dried in, because once that gets wet, the moisture will migrate to the crawl and you will have a problem.
Seriously consider a portable battery powered generator (perhaps solar) to run a dehumidifeir in the crawl during construction. I think you will need it.
Make sure that the entire perimeter of the crawl CMU walls have the foundation drain and exterior side waterproofing installed before you install the interior crawl vapor barrier & floor system. I'd also consider an interior perimeter drain system that can sometimes also act in conjunction with a passive radon extraction system.
Thanks, this is helpful.
Right now we’re using propane powered generators as needed for other work…will consider your recommendation to also use generator to power a dehumidifier.