Kicking the skirting venting dead-horse, again

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mdnagel
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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
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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
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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
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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
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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.

VT Steve
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Sun Jul 28, 2019 8:39 am

Our double wide is now 10 years old, so time to catch up on normal maintenance items. This month is time to replace some of the automatic vents that have become undependable due to weather and time. I have some new ones to install, and now see that whomever installed the originals, cut to opening s a bit too large. Since we have vinyl skirting with 2" foam insulation, the screws that are used in the vents don't provide much snugness. A properly cut hole is supposed to do that.

My question is this. Can I use some silicone caulking around the inside of the vents to make these snug?

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Greg
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Sun Jul 28, 2019 8:47 am

should work fine. possibly cut a wood frame to fit the inside and screw into that.
"If I can't fix it, I can screw it up so bad no one else can either."

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

Sun Aug 11, 2019 11:21 am

As I was researching for some unrelated construction activities I ran across my county's code covering ventilation and this is what is says:

R408.1 Ventilation. The under-floor space between the
bottom of the floor joists and the earth under any building
(except space occupied by a basement) shall have
ventilation openings through foundation walls or exterior
walls. A ground cover of six mil (0.006 inch thick) black
polyethylene or approved equal shall be laid over the
ground within crawl spaces. The ground cover shall be
overlapped six inches minimum at the joints and shall
extend to the foundation wall.
Exception: The ground cover may be omitted in crawl
spaces if the crawl space has a concrete slab floor with a
minimum thickness of two inches.
R408.2 Openings for under-floor ventilation. The
minimum net area of ventilation openings shall not be less
than 1 square foot (0.0929 m 2 ) for each 300 square feet (28
m 2 ) of under-floor area. Required openings shall be evenly
placed to provide cross ventilation of the space except one
side of the building shall be permitted to have no ventilation
openings.

...

Exception: The total area of ventilation openings shall
be permitted to be reduced to 1/1,500 of the under-
floor area where the ground surface is covered with an
approved Class I vapor retarder material and the
required openings are placed to provide cross
ventilation of the space. The installation of operable
louvers shall not be prohibited. If the installed
ventilation is less than 1/300, or if operable louvers are
installed, a radon vent shall be installed to originate
from a point between the ground cover and soil. The
radon vent shall be installed in accordance with the
requirements of Appendix F (Radon) of this code.

--- End code snipit

I have a concrete pad (over 2" thick) with a vapor barrier on top (though barrier doesn't extend up the "walls"). At approximately 1375 sq-ft I would, if going with venting, need only about 4.6 sq-ft of venting.

As this all suggests: not ALL "solutions" are applicable universally- check with local, current, building codes.

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Greg
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Sun Aug 11, 2019 2:57 pm

I was working from NYS code that is supposed to mirror the fed. HUD code.

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

mdnagel
Posts: 176
Joined: Thu Jan 06, 2011 12:39 am

Sun Aug 11, 2019 3:47 pm

Code I referred to is from WA State, based on International code. It's not HUD, but I cannot see how physics could be different between standard home construction and HUD stuff.

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