DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Building & Construction (
-   -   Why are crawl spaces vented? (

AllGoNoShow 11-09-2006 02:40 PM

Why are crawl spaces vented?
I have an old house with full basement that has an 13x24 addition put on the back of it a few years ago. This addition has a crawl space.

I just bought the house a few months ago and even when it gets colder, like in the low 40s, you can definetly feel the colder floor in the addition (even through the carpet). I live in upstate NY and am worried about how much worse they are gonna get when we get the inevitable 5 degree days here in a month or two. The crawlspace does have insulation although it is only R19-and there is a vapor barrier put on the ground. What purpose does venting the crawl space serve...would it be bad for me to close the vent for the winter?

Thanks for the replies!


MLO 11-09-2006 03:22 PM

Seems like the idea of "venting" the crawl space is very debate-able.

Obviously if there is moisture present occasionaly it does need to find a way out. But if the home is built according to sound building and perimeter drain methods, what purpose do the vents serve?

What if the air outside has a higher moisture content than the crawl space? Seems the vent would be a negative.

My brick home was built in the 50's with a concreted crawl space. I have no vents and the underside of the house is imaculate and well preserved. We are now doing a remodel and code sai's I have to install crawl space venting. I'm a little miffed being I have no current issues, and installing vents in the side of a brick wall is neither fun or asthetically pleasing to me.

Would love to hear from some experienced tradespeople on this topic as well...

majakdragon 11-09-2006 03:52 PM

I cannot give you an honest answer as to why vents are code, but I have had them on 3 houses from Ohio to Florida to Arkansas. I always close the vents in the Winter and open them in the Spring.

747 11-09-2006 04:00 PM

I have a crawl space and as stated above i open vents in summer and just closed them about a month ago.

Mike Swearingen 11-09-2006 04:02 PM

I'm a real estate broker, and have run into house inspections with "crawlspace vents not meeting code" (too high, too far apart, etc.).
I have been told that crawlspace vents are required to "vent excess moisture and drain floodwaters".
Well, duh, me.
Seems like that would allow it to run both as well as out.
The air moisture, coupled with the ground moisture, here on Albemarle Sound in northeastern NC is very high. To prevent constant condensation dripping from my crawlspace plumbing and HVAC ductwork, I had to install a 10" louvered exhaust fan in the crawlspace door that runs 24/7. Works like a charm.
I turn the fan off and close all vents for freezing winter weather season only. My problem solved.

Hammatime 11-09-2006 04:11 PM

In the winter you can close the vent. You are right about the debate going back and forth about crawl space venting. In my opinion if you put a 4 mil vapor barrier down and attach it to the foundation walls to be air tight there is no reason for a vent. But this is just my opinion and I don't write the code. The real problem arises later when someone goes into the crawl space and punctures the vapor barrier, by mistake.

The only way to omit the openings all together is by mechanical ventilation.

MLO 11-09-2006 04:18 PM

Hammatime, I would love not to have to punch holes in my brick walls for vents. Is there a mechanical system that is somewhat rationale to retrofit into a home, could you supply any details?

Hammatime 11-09-2006 04:33 PM

MLO, if you are adding an addition you will already be putting an access hole in your existing foundation to the new crawl space. Put the mechanical ventilation in the new crawlspace, so it draws from the old crawl space. The best thing to do would be to ask the building inspector what your options would be and tell him your concerns.

All times are GMT -5. The time now is 07:25 AM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1