CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: Pneumatic Pressure Testing   Next in Forum: What to do with a Radon Level of 8.3 pCi/l
Close
Close
Close
8 comments
Power-User
United States - Member - New Member

Join Date: May 2008
Location: Arizona
Posts: 356
Good Answers: 4

Crawlspace Vents

10/09/2015 9:13 AM

HOW DO YOU CALCULATE CRAWLSPACE VENT REQUIREMENTS?

Register to Reply
Pathfinder Tags: CRAWLSPACE
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru
Technical Fields - Project Managers & Project Engineers - New Member

Join Date: Jun 2014
Posts: 631
Good Answers: 33
#1

Re: Crawlspace Vents

10/09/2015 12:08 PM

Check the local building code or ask the inspector or a licensed carpenter in your area.

__________________
Hey Isaac, catch! ...oops, that's gonna leave a mark...
Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18312
Good Answers: 1062
#2

Re: Crawlspace Vents

10/09/2015 12:23 PM
__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that, still doing it. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 12004
Good Answers: 758
#3

Re: Crawlspace Vents

10/09/2015 2:18 PM

At some point girth will also matter.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply Score 1 for Good Answer
Guru

Join Date: Sep 2008
Posts: 683
Good Answers: 27
#4

Re: Crawlspace Vents

10/09/2015 10:46 PM

If it's for Flood Vents in a crawlspace foundation, it's 1 square inch for every square foot.

__________________
Spinco
Register to Reply
Guru
Safety - Hazmat - New Member Engineering Fields - Retired Engineers / Mentors - New Member Engineering Fields - Piping Design Engineering - New Member Hobbies - DIY Welding - New Member Fans of Old Computers - PDP 11 - New Member

Join Date: Feb 2007
Location: Stronger Than The Storm
Posts: 2366
Good Answers: 201
#5

Re: Crawlspace Vents

10/09/2015 11:44 PM

Contact the local municipal Building Dept. They are the ones who give the final approval on drawings and building plans, etc. They are the ones who check everything to make sure it meets code and works with you for a solution if necessary. They are also the dept that the Building Inspector works for. In most areas, if the contractors/builders need to be licensed, they are not tested on something as infrequently as this for their qualifications.

Good Luck, Old Salt

__________________
Any day on the green side of the grass is a GREAT DAY!, --- me +++++++++. I believe creativity is an inherent part of everyone. --- Kermit T. Frog
Register to Reply Score 1 for Good Answer
Guru

Join Date: Jul 2006
Location: Eastern Kansas USA
Posts: 1100
Good Answers: 99
#6

Re: Crawlspace Vents

10/11/2015 8:07 PM

Friend,

Look in the International Residential Code (IRC), Section R408. My 2003 edition states a requirement of 1 sq.ft. for each 150 sq.ft. of under-floor space. There are a number of exceptions to this, generally related to the presence of a vapor retarder film or coating on the dirt, and other logical reasons. I don't have a more recent code, but doubt that this section has had serious changes since then.

--JMM

Register to Reply
Power-User
United States - Member - New Member

Join Date: May 2008
Location: Arizona
Posts: 356
Good Answers: 4
#7
In reply to #6

Re: Crawlspace Vents

10/12/2015 9:54 AM

THX FOR ALL GREAT POSTS. FOR THIS ROOM ADDITION, I FOUND A FLOOR DROP-IN FAN & REGISTER THAT COULD BE USED TO EXAUST A SEALED UNDERFLOOR SPACE, BUT SINCE THE DESIGN AND CONDITION OF THE 4TH STEMWALL IS UNKNOWN, I HAVE FILED THIS DESIGN AWAY FOR POSSIBLE FUTURE USE ON ANOTHER PROJECT. ALSO, BECAUSE I AM UNSURE OF HOW THE OWNER WOULD RESPOND ABOUT A FAN RUNNING 24/7.

I WOULD LIKE TO SPEC OUT A 8"x16" "FOUNDATION VENT" TO BE INSTALLED IN THE 11.875" TALL x 1.25" RIM BOARD, BETWEEN THE 2x6-16" OC STUDS, AS OPPOSED TO INSTALLING IT IN THE 8" THICK CAST CONCRETE STEMWALL, MAINLY BECAUSE THERE IS ONLY A VERTICAL HEIGHT OF 10.5" BETWEEN THE TOP OF THE STEMWALL AND THE DIRT.

IF FOR SOME REASON I CAN'T INSTALL IT IN THE RIM BOARD, HOW BEST TO INSTALL IT IN THE STEMWALL?

Register to Reply
Guru

Join Date: Jul 2006
Location: Eastern Kansas USA
Posts: 1100
Good Answers: 99
#8

Re: Crawlspace Vents

10/18/2015 2:45 AM

Flyinghigh,

There's a good chance that the concrete wall will have some horizontal steel in its top 8". However it is probably close to the center. Therefore, take a circular saw and use a diamond blade to cut the sides and bottom of you vent hole (make sure that you are about 1/4" oversize for the portion of the vent that actually fits into the hole). You will need to then take a good hammer drill and make closely spaced holes thru the wall just inside the saw cut (definitely not outside it!) Finally take a good sledge hammer and break out the hole. Plan on this much taking a bunch of time, probably 3-hours.

Hopefully you have not cut the vent hole right where a foundation anchor bolt is! Be sure to wear good PPE--goggles or safety glasses with side shields, hearing protection, and good gloves.

--JMM

Register to Reply
Register to Reply 8 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

flyinghigh (1); jmueller (2); Massey (1); old salt (1); redfred (1); SolarEagle (1); Spinco (1)

Previous in Forum: Pneumatic Pressure Testing   Next in Forum: What to do with a Radon Level of 8.3 pCi/l

Advertisement