Kicking the skirting venting dead-horse, again

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mdnagel
Posts: 135
Joined: Thu Jan 06, 2011 12:39 am

Sun Jul 07, 2019 1:37 pm

I am continuing to research venting requirements as I try to complete my planning for skirting (and other) work.

I recently learned that I need to keep my interior humidity levels at no more than 50%. I'd thought that it was OK to be slightly higher, but apparently not... Anyway, the reason I'm mentioning this is because I am struggling to drop interior humidity levels: I just replaced my bathroom fans with 75 cfm from 50 cfm, and have a couple of small (too small?) dehumidifiers running. Belly wrap has several openings (damage) that I will be repairing, so, hopefully, that'll help. Humidity levels inside fluctuate quite a bit because outside humidity levels fluctuate a LOT: it's really wet here!

I've noticed that, obviously, if I have windows open (to help cool things down- summer months) when outside humidity levels are high that interior humidity levels shoot up. It is this obvious situation that got me to once again think about venting on skirting...

By having venting in my skirting I am allowing the outside air to bring in humidity, similar to the affects of inside humidity levels when when opening windows.

Based on the following readings it appears that I should look to close off venting during the cooling months (summer up here) and open up during the heating months (winter):

https://inspectapedia.com/ventilation/C ... ndards.php
https://www.buellinspections.com/vented ... northwest/
https://www.buellinspections.com/rainin ... he-winter/
https://www.gcienergyconsultants.com/to ... -question/

I am tempted to have swapable access doors on either end of the building, ones that are solid (metal) to be installed during the summer months, and ones that are fully screened to be installed during the winter months. We have a wood stove, which brings in air from under the house, so for sure venting is required (in order to allow a pull of air) for that. With these two access doors I figure roughly 12 ft-sq of venting, which willll pretty much come close to matching the existing venting that's been in place: difference, however, will be that venting will ONLY be at the ends, rather than spread around the perimeter; I'd think that, however, the larger openings would create a pretty good flow.


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Greg
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Sun Jul 07, 2019 3:23 pm

What do you have for a ground moisture barrier? Code requires a minimum of 6 mil plastic if not a full concrete pad. During warm months ground moisture is trapped by the skirting and with no vents enters into the home through the floor. 1sq/ft of vent pre every 150 /ft of floor space. Trust me, I've been where you are at.

Greg
"If I can't fix it, I can screw it up so bad no one else can either."

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Jim from Canada
Posts: 550
Joined: Mon Mar 05, 2007 10:39 am
Location: Seaforth, ON

Mon Jul 08, 2019 7:24 am

This is how I am doing mine. Vented in summer, closed in winter.

https://www.youtube.com/watch?v=O_ppdFS-VlM&t=193s
Remember, minimum code requirement is just that....MINIMUM

mdnagel
Posts: 135
Joined: Thu Jan 06, 2011 12:39 am

Mon Jul 08, 2019 9:38 am

Greg, I've got a vapor barrier on concrete slab.

Have a high water table. I've been working on perimeter drainage for quiet a while: could do more yet; I need to do a bit more grading (will be doing some when I do my skirting and other work).

Jim, if you read those links you'll find that, for me (and as stated from some home inspectors here in the PNW), closing in summer and opening up during the winter is the right way to do it. Warm air can contain more moisture. But at any rate, I think that having the ability to close off and to vent is the way to go. And, while there are "code requirements" that don't mean they are based on sound scientific data: the links I provided above use actual, hard data- suggestion is that there really wasn't a comprehensive study of the entire picture when all the "codes" were established: venting was promoted as a solution before we figured to use vapor barriers and once we started using vapor barriers we didn't revisit the venting issues in combination. That said, there are different conditions in different locations: there's radon to consider in some places, so for there you HAVE to vent.

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Jim from Canada
Posts: 550
Joined: Mon Mar 05, 2007 10:39 am
Location: Seaforth, ON

Mon Jul 08, 2019 5:39 pm

Well, I'm in Canada, so if we had the skirting open in the winter we'd freeze to death right after all the plumbing froze. We have humid summers so keeping it vented during those times makes more sense as you don't want the humidity trapped under there causing rot and such. The moving air helps with that.
Remember, minimum code requirement is just that....MINIMUM


mdnagel
Posts: 135
Joined: Thu Jan 06, 2011 12:39 am

Sat Jul 13, 2019 9:30 pm

Yeah, freezing. Understand. Here isn't not a big concern.

If one is moving moist air that isn't lower moisture content than the existing air then you end up with more moisture. The velocity of the moving air will modify this, though I am not sure it's a significant difference unless it's very high velocity.

I've got a temperature and humidity data logger that I'm thinking about deploying. Not sure if I can formulate a good enough set of testing parameters to get meaningful data.

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