GEA Golf Forum > Crawl space vents question

Full Version: Crawl space vents question

From: Larry (70445) [#1]
 9 Dec 2017
To: ALL

I have read numerous articles about the debate to leave craw space vents open or closed durning the winter. Some say to close durning winter, others say to leave open. Which is correct? Sounds like a 50/50 choice? Any opinions from builders? I live in SE Kansas, house has uncovered earth beneath the floor, in craw space, and floor is not insulated. OK builders give me direction! Thank you for any information or opinions.

EDITED: 10 Dec 2017 by 70445

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From: RedSoxNation [#2]
 9 Dec 2017
To: Larry (70445) [#1] 9 Dec 2017

No insulation close em.also u need vapor barrier on uncovered earth that wuold help

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From: Tom (TOM0956) [#3]
 9 Dec 2017
To: Larry (70445) [#1] 9 Dec 2017

My resume is substantial in the engineering/constructions industries beginning almost 40 years ago at the age of twelve when I realized what my architect father did for a living.

In the winter, you might want to close the vents to keep as much cold air from moving into your crawl space. The real issue though with crawl spaces is moisture and specifically vapor. You can get moisture from the ambient air conditions, from the soil of the floor of your crawl space, and through the walls of the space. Around here, (Atl) the new buzzword is encapsulation where you install a vapor barrier on the walls and floor and all of the edges of the barrier are sealed off as completely as possible. The vents are also closed off and positive, powered ventilation is also used to evacuate as much residual water vapor from the space. In theory, that is the best way to do it but anything involving a vapor barrier to mitigate the moisture migration is better than nothing.

But if your only concern is the vents in the winter...I'd close them. No question, for the reason stated above.

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From: glacier (DON BUCHAN) [#4]
 9 Dec 2017
To: Larry (70445) [#1] 9 Dec 2017

heated crawl space or not? Any exposed water pipes in crawl space?

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From: Larry (70445) [#5]
 9 Dec 2017
To: Tom (TOM0956) [#3] 9 Dec 2017

Thank You for you expert info, I appreciate it! Do you think it’s a good idea to insulate the floor?

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From: Saluki (SALUKI91) [#6]
 9 Dec 2017
To: Larry (70445) [#1] 9 Dec 2017

Free advice being worth what you paid... our crawl space was encapsulated several years ago (and after several thousands of dollars spent in mold remediation).

Moisture will never again be an issue for us, and an added bonus is that we can use the crawl space for storage. We have found no need to insulate the floor after encapsulation.

Given the cost of what could go wrong without it, the cost of encapsulation is a pretty cheap insurance policy.

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From: Tom (TOM0956) [#7]
 9 Dec 2017
To: Larry (70445) [#5] 9 Dec 2017

Your floor joists? By all means yes

Crawl space No

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From: badger boy (BIGBLAST) [#8]
 9 Dec 2017
To: ALL

You would only want to insulate the floor if if there was no ductwork/heat source in the crawlspace.
If there is a heat source, and probably water lines, insulate the outside crawlspace walls and close the vents so the heat from the ductwork keeps the water lines from freezing.
My crawlspace also has all the ductwork insulated which makes keeping whatever heat is available more critical, so I insulated all the outside walls and block the vents with insul-board. I cut the insul-board just slightly larger then the vent opening so I can wedge it in. I drive a long nail with a piece of wood on one side to be able to pull it out in the summer.

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From: HackerKayaker (BRIANC) [#9]
 9 Dec 2017
To: Tom (TOM0956) [#3] 9 Dec 2017

quote: Tom (TOM0956)
My resume is substantial in the engineering/constructions industries beginning almost 40 years ago at the age of twelve when I realized what my architect father did for a living.

In the winter, you might want to close the vents to keep as much cold air from moving into your crawl space. The real issue though with crawl spaces is moisture and specifically vapor. You can get moisture from the ambient air conditions, from the soil of the floor of your crawl space, and through the walls of the space. Around here, (Atl) the new buzzword is encapsulation where you install a vapor barrier on the walls and floor and all of the edges of the barrier are sealed off as completely as possible. The vents are also closed off and positive, powered ventilation is also used to evacuate as much residual water vapor from the space. In theory, that is the best way to do it but anything involving a vapor barrier to mitigate the moisture migration is better than nothing.

But if your only concern is the vents in the winter...I'd close them. No question, for the reason stated above.


I am having our crawl space encapsulated the end of January.......kinda pricey but it will have so many benefits. No more cold floors or musty smelling when the weather is damp. Should help in selling if and when we do that........

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From: HackerKayaker (BRIANC) [#10]
 9 Dec 2017
To: Saluki (SALUKI91) [#6] 9 Dec 2017

quote: Saluki (SALUKI91)
Free advice being worth what you paid... our crawl space was encapsulated several years ago (and after several thousands of dollars spent in mold remediation).

Moisture will never again be an issue for us, and an added bonus is that we can use the crawl space for storage. We have found no need to insulate the floor after encapsulation.

Given the cost of what could go wrong without it, the cost of encapsulation is a pretty cheap insurance policy.


Having ours encapsulated this coming January. Looking forward to it.

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From: Charlie (CHARLIED6) [#11]
 9 Dec 2017
To: ALL

Our house in Tennessee has a very tall "crawl space". You can stand up in about 1/3 of it and have to stoop over a little in the remaining 2/3 of the crawl space. The ground has plastic sheeting covering it and the walls are insulated with foam board.

Even with the plastic sheeting and foam board, I noticed that in mid-summer, the humidity in the crawl space got high (about 75% to 80%). Therefore, I closed off all the vent openings and insulated them with fiberglass insulation and foam board. Then I installed a dehumidifier in the crawl space. In less than 24 hours, the humidity in the crawl space dropped from about 80% to about 45%.

I now leave the humidistat set on 50% and it is very comfortable in the crawl space. Additionally, the musty odor/smell has been eliminated.

When warm outside air is drawn into a cool crawl space, the humidity of the air increases. If you don't use a dehumidifier to reduce the humidity, you will end up with damp, moldy conditions in the crawl space. Some of that damp, moldy air will end up in your living space. It doesn't cost much to encapsulate the crawl space if you do it yourself. A dehumidifier is inexpensive. All you need is an electric outlet to plug the dehumidifier into and a drain to drain the condensate into.

Charlie-----------------------------------------------------------

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From: Tom (TOM0956) [#12]
 9 Dec 2017
To: HackerKayaker (BRIANC) [#9] 9 Dec 2017

Yes I believe you are correct about the benefits vs costs. Good luck with yours. Over the years I've undertaken an encapsulation of my crawl space but only with the heaviest of PE sheeting. By this summer I'll have the dehumidification component taken care of.

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From: HackerKayaker (BRIANC) [#13]
 9 Dec 2017
To: Tom (TOM0956) [#12] 9 Dec 2017

It will be 120 mills thick, sealed and taped. Walls will be insulated and a new sump pump. We don't havemuch mold so we are going to do it ourselves. The salesman said it was easy enough to do with a couple bombs.

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From: Tom (TOM0956) [#14]
 9 Dec 2017
To: HackerKayaker (BRIANC) [#13] 9 Dec 2017

Are you only taping the edges or is there a cement that seals your material?

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From: HackerKayaker (BRIANC) [#15]
 9 Dec 2017
To: Tom (TOM0956) [#14] 9 Dec 2017

They use adhesive and then tape

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From: Tom (TOM0956) [#16]
 9 Dec 2017
To: HackerKayaker (BRIANC) [#15] 9 Dec 2017

You’re doing it yourself? Where are you buying your materials from?

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From: Southside [#17]
 9 Dec 2017
To: ALL

There are crawl spaces with vents and crawl spaces with no vents. As such there are two different and distinct approaches to insulating. Just give this article a quick read.

http://www.hgtv.com/remodel/interior-remodel/crawl-space-insulation-what-you-should-know

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From: HackerKayaker (BRIANC) [#18]
 9 Dec 2017
To: Tom (TOM0956) [#16] 10 Dec 2017

I am not doing it...... Perhaps if I wasn't 70 I might

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From: Tom (TOM0956) [#19]
 10 Dec 2017
To: HackerKayaker (BRIANC) [#18] 10 Dec 2017

Ops I misread one of your earlier replies. :-)

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From: RedSoxNation [#20]
 12 Dec 2017
To: Charlie (CHARLIED6) [#11] 12 Dec 2017

I did the same thing in Knoxville late in 2015. Put the house on the market June of 2016, it sold in less than 24 hours for more than asking price

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