Unfortunately, my county (Boulder County, CO) requires me to vent the crawl space under my addition. I am looking for some vents that will work in the rim board (too late to put them in the concrete, would have created grade issues anyway). I have a 600 sq.ft. crawl space and they require 1 sq.ft. of vent per 1500 sq.ft. (since I will have a vapor barrier on the ground). The foundation is a rectangle and the code requires a vent within 3′ of each corner, so I’m figuring 18 sq.in. of vent near each corner would work.
I have not been able to find vents that specify how much vent area they acheive. How big a vent will I need to get 18 sq.in. of free space? I’d like to keep them as small as possible.
Any installation recommendations (water-proofing, insulation, etc.)?
-Rich
Replies
Hutchison lumber has what you want...
they're up by you...
Auto / climate controlled.. Cold - closed... Warm - open...
Put 'em like dryer vents... IIRC they are 9x14 and 10x16... They had 8x12's...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
I've seen these things at Home Depot that open and close on their own with no need to wire them up. They operate on a mechanical thermally activated spring coil. Check them out. They are for crawl space ventilation and don't cost very much at all.
I installed the automatic vents in my house. It's a crawl space house. I have noticed that they don't seem to close all the way until the temperature drops to around 10 - 20 degrees, and "all the way" is probably about 90% closed. I wouldn't use them again. Matt
Do they require you to vent if it's conditioned space? Insulate per code, throw some heat in, and call it a short basement?
Actually, in your dry climate, it probably doesn't matter much either way. The only harm venting is likely to do is to cause your heat bills to rise.
Andy
Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
Hi,
If you seal off the crawlspace with Tu-Tuf vapor barrier, sealed with mastic to the stemwalls and tape at joints, the county will let you reduce the vents significantly. At least, they ought to, it is provided for in the Code. Fewer vents is a better job, due to the aforementioned heat loss issues.
I used to live in Gold Hill, and I hear that Colorado is not so dry this year! Best of luck to you.
Bill
Normally , you require a Minimum of 1 sq ft of free vent air for every 500 sq ft of crawl space floor area.
A vent size of 18" free area may have to be approx twice as large (36) depending on the design louvres, etc. "Free area can be lowered by as much as 50 %
Best to have too much ventilation in a crawl space, rather than too little. As long as the floor above is well insulated what difference will it make?
I'm with Andy
Having been in a couple of thousand crawl spaces (In NW Ohio) I can assure you that the code specifications for venting crawl spaces bear no relationship to how they actually perform and what actually happens inside of them.
Check to see if your local code allows for conditioned crawls.
Also, how close to grade is the top of your foundation? How come they let you get away with less than 18"?
Be sure to keep grade well away from your siding and framing.
And, since grade is so high on your foundation, do not lap the vapor barrier up the foundation walls to the sill plate.
The key to forgiving others is to quit focusing on what they did to you, and start focusing on what God did for you. Max Lucado
Sojourners: Christians for Justice and Peace
The formula I've always heard and had enforced is 1 square foot per 150 square feet of area. The vents I've often used are stamped louvers and if you look closely they specify the area they allow, in square inches. Don't have one handy but the two sizes available locally are about 4x14 and 6x14, and the 6x14s allow about 50 square inches, so use 3 per square foot needed.
The only way I would go without venting is if the crawl were sealed and conditioned. Just sealed... no way... moisture will find its way in there and not come out.
Edit to say that the best time to install them is when siding. You can flash them nicely then. If you need to cut them in later, make small frames for them and caulk the hel out of them when installing. In shingled mine into my pony walls and had small flashing hoods made for them.
Edited 10/23/2004 5:21 pm ET by davidmeiland
Hey,
As already mentioned, typically metal and some foundation vents are actually stamped. They basically give you about 50% of the gross area of the vent itself. In Oregon (as w/ other states) we run the 1:1500 ratio, w/ a vent w/in 3' of corners. You "should'nt" have any grief w/ the 'spector if you do this...just remember..don't block the vents w/ floor insulation (baffle the insulation if needed).
Tony