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Foundation Vents In Addition

 
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Old 04-27-2019, 01:49 PM   #1
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Foundation Vents In Addition


We are doing this addition and I was hoping someone could advise me on foundation vent location.

If I'm interpreting the code right it would seem that I could put the two vents in without the question marks 3' from the outside corners.

What I'm not sure of is if I should also have the ones with question marks to allow cross ventilation vs just ventilation on the one end.
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Old 04-27-2019, 05:03 PM   #2
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Re: Foundation Vents In Addition


I always set mine to get cross ventilation as long as there wasn't going to be an obstruction down the road, like a deck being built.

Will you also have access to the existing basement or crawlspace?

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Old 04-27-2019, 08:12 PM   #3
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Re: Foundation Vents In Addition


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Originally Posted by TimNJ View Post
I always set mine to get cross ventilation as long as there wasn't going to be an obstruction down the road, like a deck being built.

Will you also have access to the existing basement or crawlspace?
Yes. There is a basement with exterior cellar type steps coming out of it that will come up into the new crawlspace.

Could you confirm we wouldn't need any on the 12' wall facing the yard since we would have adequate ventilation from the others?
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Old 04-27-2019, 08:28 PM   #4
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Re: Foundation Vents In Addition


I would vote for no vents. We haven't put vents in in years. Proper drain tile, proper vapor barrier with pea gravel on top, and proper insulation on foundation walls and on the box. You really want to go nuts, have an HVAC supply in there. Keeps some conditioned air moving in there and will slightly "pressurize" the crawl space.
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Old 04-27-2019, 08:52 PM   #5
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Re: Foundation Vents In Addition


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I would vote for no vents. We haven't put vents in in years. Proper drain tile, proper vapor barrier with pea gravel on top, and proper insulation on foundation walls and on the box. You really want to go nuts, have an HVAC supply in there. Keeps some conditioned air moving in there and will slightly "pressurize" the crawl space.
This approach is all well and good when the client has the budget for it. That wasn't the case here. I've read about that approach a good bit and would certainly do it at my own house.

This is that 100 year old house I was talking to you about the footing on by the way.
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Old 04-27-2019, 09:16 PM   #6
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Re: Foundation Vents In Addition


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Originally Posted by Xtrememtnbiker View Post
This approach is all well and good when the client has the budget for it. That wasn't the case here. I've read about that approach a good bit and would certainly do it at my own house.

This is that 100 year old house I was talking to you about the footing on by the way.
Everything I said should be done vented or not. I just skip the vents and add the supply. At least in my area R-10 is code minimum for foundation walls. We apply 2" Dow to the walls and tape the joints before we frame the deck and then have the box spray foamed with C.C. 1-1/2".
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Old 04-27-2019, 09:28 PM   #7
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Re: Foundation Vents In Addition


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Everything I said should be done vented or not. I just skip the vents and add the supply. At least in my area R-10 is code minimum for foundation walls. We apply 2" Dow to the walls and tape the joints before we frame the deck and then have the box spray foamed with C.C. 1-1/2".
Here it's just a vapor barrier (6 mil poly), no gravel on top, and no insulation on the walls, just R-19 in the floor.
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Old 04-27-2019, 09:34 PM   #8
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Re: Foundation Vents In Addition


Put in as many vents as you can.

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Old 04-28-2019, 07:53 AM   #9
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Re: Foundation Vents In Addition


Did a lot of crawl space additions with existing basements.
Always vapor barrier on ground and rat slab.
Connection from existing basement to new crawl with a good size accessible opening that I would try to locate in the center of the wall. Lets air move easier from entire basement and gives ho some extra storage space.
Also used the self closing foundation vents.
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Old 04-28-2019, 08:19 AM   #10
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Re: Foundation Vents In Addition


You need 1 SF of vent space for every 150 SF of space in the crawlspace. So let's say if your foundation size is 20X20 that's 400 SF/150 you will need vents that have combined square footage of 2.7 SF


Now if this is a new foundation and you have vapor-barrier (6 mil plastic) under the slab in that case you only need 1 SF of vent for every 1,500 square feet of space.

Per code, vents should be installed within 3' from each corner.
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Old 04-28-2019, 08:24 AM   #11
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Re: Foundation Vents In Addition


I installed two of these in a "damp" crawlspace a few years ago...older home...still going strong and works well.

You set the humidity level you want and it automatically shuts off if it reaches 32*.

Not necessarily on topic but may help someone with an inexpensive fix.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 04-28-2019, 04:08 PM   #12
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Re: Foundation Vents In Addition


Quote:
Originally Posted by Robie View Post
I installed two of these in a "damp" crawlspace a few years ago...older home...still going strong and works well.

You set the humidity level you want and it automatically shuts off if it reaches 32*.

Not necessarily on topic but may help someone with an inexpensive fix.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I just saw one of those at a job I did a few weeks ago.
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Old 04-28-2019, 04:11 PM   #13
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Re: Foundation Vents In Addition


Quote:
Originally Posted by TimNJ View Post
Did a lot of crawl space additions with existing basements.
Always vapor barrier on ground and rat slab.
Connection from existing basement to new crawl with a good size accessible opening that I would try to locate in the center of the wall. Lets air move easier from entire basement and gives ho some extra storage space.
Also used the self closing foundation vents.
No plans to pour a slab in this one. Although it does sound like a nice approach considering that there is already a stair case that walks up into the new crawl.

Quote:
Originally Posted by greg24k View Post
You need 1 SF of vent space for every 150 SF of space in the crawlspace. So let's say if your foundation size is 20X20 that's 400 SF/150 you will need vents that have combined square footage of 2.7 SF


Now if this is a new foundation and you have vapor-barrier (6 mil plastic) under the slab in that case you only need 1 SF of vent for every 1,500 square feet of space.

Per code, vents should be installed within 3' from each corner.
Is the inside corner that is created by the addition joining the house considered a corner?

Also the way I read that corner rule is that I wouldn't need one on each face at a corner. Is that correct?
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Old 04-28-2019, 08:25 PM   #14
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Re: Foundation Vents In Addition


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No plans to pour a slab in this one. Although it does sound like a nice approach considering that there is already a stair case that walks up into the new crawl.



Is the inside corner that is created by the addition joining the house considered a corner?

Also the way I read that corner rule is that I wouldn't need one on each face at a corner. Is that correct?
If possible foundation vents should be placed on all sides of the foundation. This will create a steady flow of air and air exchange. One way to look at it is 1 vent should be installed for each 8 to 10 feet of the foundation wall. Most of the time and most architects will specify 2 vents only on one foundation wall, no matter which one for as long as they installed not more than 3' from the corners.
Last addition I did I just installed 2 vents and there are no issues.
What did the architect specified on the plans?
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Old 04-28-2019, 10:22 PM   #15
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Re: Foundation Vents In Addition


Quote:
Originally Posted by greg24k View Post
If possible foundation vents should be placed on all sides of the foundation. This will create a steady flow of air and air exchange. One way to look at it is 1 vent should be installed for each 8 to 10 feet of the foundation wall. Most of the time and most architects will specify 2 vents only on one foundation wall, no matter which one for as long as they installed not more than 3' from the corners.
Last addition I did I just installed 2 vents and there are no issues.
What did the architect specified on the plans?
In this case with it being an addition I was figuring that the ones opposite the basement foundation wouldn't be needed since there aren't any vents in the basement foundation for cross ventilation.

I drew the plans. No foundation vent details.
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Old 04-28-2019, 11:28 PM   #16
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Re: Foundation Vents In Addition


Sometimes it's hard to get them properly spaced or enough of them. Although it's not optimal it's okay, at least out here, to count the crawlspace access from the outside in the vent area calcs.

Also the vent area is NFVA (Net Free Ventilation Area) which is quite a bit less then the actual vent size. Most vents now have that difference called out on a cut sheet or on the website.
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Old 04-28-2019, 11:38 PM   #17
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Re: Foundation Vents In Addition


Any living space that might accumulate heating gas or even ground generated or DVW Naturual gas needs to be vented.....

Especially L.P. using homes=L.P. sinks and blows house off foundations and crawl spaces....


I'd install a 2-3" Faux DVW stack/plastic pipe chimney to draw the damp/and boom-boom gases out with closing valve for winter time. < less then 100$.

Another value added feature is a low voltage Sewer/conduit pipe for misc. wiring from basement to crawl space to new attic space. Very handy for the I forgot cables etc, spy wiring.
both ends plugged/caulked to prevent air/vermin movement on the conduit...

The air chimney needs a vermin screen of galvanized or stainless rat proof mesh at each end, and a rain half-bend on the high out of -doors end.
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Old 04-29-2019, 07:31 AM   #18
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Re: Foundation Vents In Addition


Quote:
Originally Posted by overanalyze View Post
I would vote for no vents. We haven't put vents in in years. Proper drain tile, proper vapor barrier with pea gravel on top, and proper insulation on foundation walls and on the box. You really want to go nuts, have an HVAC supply in there. Keeps some conditioned air moving in there and will slightly "pressurize" the crawl space.
What we do for the most part.

We put down visqueen, then pour concrete in all crawlspaces. We only pour it about 3" thick and it only gets a bull float finish.
Then spray foam the walls. Lately they also get a layer of fiberglass blanket over the top, due to code.
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Old 04-29-2019, 07:55 AM   #19
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Re: Foundation Vents In Addition


You could do a crawl space liner and no vents. I had a crawl space liner installed under my whole house and took out the foundation vents.

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Old 04-29-2019, 08:18 AM   #20
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Re: Foundation Vents In Addition


If you take out the foundation vents you need mechanical ventilation.

R408.3 Unvented crawl space.
Ventilation openings in under-floor spaces specified in Sections R408.1 and R408.2
shall not be required where the following items are provided:
1. Exposed earth is covered with a continuous Class I vapor retarder. Joints of the vapor retarder shall overlap by 6 inches (152 mm) and shall be sealed or taped. The edges of the vapor retarder shall extend not less than 6 inches (152 mm) up the stem wall and shall be attached and sealed to the stem wall or insulation.

2. One of the following is provided for the under-floor space:

2.1. Continuously operated mechanical exhaust ventilation at a rate equal to 1 cubic
foot per minute (0.47 L/s) for each 50 square feet (4.7 m2) of crawl space floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.11 of this code.

2.2. Conditioned air supply sized to deliver at a rate equal to 1 cubic foot per minute
(0.47 L/s) for each 50 square feet (4.7 m2) of under-floor area, including a return air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.11 of this code.

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