Inspector wants a fan in crawlspace…. Make any sense???
I previously posted about the foundation for an addition we are planning. We’ve decided to go with an insulated crawlspace (or more accurately a short basement). The crawlspace will not be open to the existing basement… it will be standalone. There will be an AC air handler in there, nothing else.
Apparently, our local building department (in CT) still thinks crawlspaces need venting. I have been feeding my contractor articles from the Building Sciences site and posts from Breaktime on the logic behind unvented crawlspaces.
He has gotten the inspector to agree to no venting, but only on the condition that we include a fan in the crawlspace to “move the air around.” Does this make ANY sense?
I haven’t heard the logic from the horse’s mouth, but I am trying to make sense of this myself before I talk to the contractor again.
Thanks.
-RG
Replies
In short, no
You can put the fan in and not use it. Often, appeasement is the simplest course.
Appeasement at my expense!
Andy- Yes I thought of that. It just annoys me that if there is no good reason to do this, I need to pay an electrician to run a line, buy and install a fan, etc. As with any project, I am bumping into budget limits, so this is an annoyance. I'd rather "educate" the BI and help myself and those that follow after me....
You're right, but...
...see my tag line. It's probably not worth your time.
IRC governs in your local?
Same mentality as some state legislatures in the past passing a law that pi = 22/7 !
IRC says stairs have to not pass a 4" ball. OK, inspector shows up with a 4" ball, one spot allows it to pass, you stick a piece of scrap wood onto that spot with double back tape, viola!! YOU PASS!!
tear it off later,
like andy says, appeasement -- you can hold up your permit in the air, wave it around, and cry 'peace in out time', eh?
If there's any possibility that your local code requires a crawl to be vented, then this inspector is throwing you a huge bone. You'd be wise to take it. Analogous to junkhounds story of the ballustrade... you may get away with a simple breeze box fan plugged into the outlet near that ac unit. Once inspection is done, either return the unused fan to home depot or use it to cool your jets during the summer.
If code is on your side, and you like a good fight, you can tell the inspector to go pound sand.
Sounds to me like you didn't get the full story, or maybe the inspector doesn't understand how a fan would be used to meet the requiremens of IRC section 408.3 that addresses unvented crawlspaces. The fan is not intended to just "move air around."
That section allows you to not install the usual vents in the crawlspace walls if you meet certain other requirements. One option is that you install a continuously-operating fan that exhausts to the outdoors at a rate of 1 CFM/50 sq. ft. of crawlspace area.
The other option is to have a small opening for conditioned air to flow into the crawl at the same rate, along with return air transfer pathway to the common area above,
In both cases, the walls must be insulated and the exposed earth of the crawl must be covered with a Class I vapor retarder, like 6-mil poly with any joints sealed and overlapped by 6", and extends up the stem wall 6" and is attached and sealed to the stem wall.
You are correct...
I did not get the full story. I don't think my contractor did either. Sounds like a series of phone messages being exchanged with no real discussion yet.
I would point out that the "crawlspace" will in fact be a basement.... with insulation, vapor retarder and concrete floor. The height will be 4-5 ft., so it is being called a crawlspace. I'm not familiar with code, but aside from openings to the floor above (ie door at top of stairs), I don't see any venting in most basements. Maybe code defines a basement differently...
Will post back here when I learn more.
Since it's an addition, could you just connect it to the main basement and have it be a conditioned space?
I did this with a small addition to my own home, but it was easy because there were already basement windows in that wall and I just left the panes out. One reason I did this was because there are water lines in the "crawlspace" and I didn't want them to freeze. I also insulated the exterior walls of the crawlspace with foam boards.
Would be nice but won't work...
Thanks, but the addition is adjacent to the garage and a part of the house this is on slab, so no basement to tap into.
Crawl space - old fashioned, not needed.
A crawl space is perhaps useful for running cables - anything else?
Constructing a crawl space involves time and money - what do you get back for it?
About two hundred times a year warm wet air arrives and we get frost or dew on the ground. This air is pulled into our homes by the passing wind and the stack effect. We then spend a lot of money heating this air. If our joists and other wood items are below the dew point we get condensation - this can lead to mold and wood rot.
Tell me, why do people have crawl spaces?
A nice solid concrete pad, is draft proof and if insulated correctly, is warmer.
The air in a crawl space is best left alone, air is not good at transferring heat, left alone it does nothing, move it and it will transfer heat from the floor to the walls and ground - why would anyone want to do this?
That post seems pretty much irrelevant.
I'd install the fan and be done with it. Spending time to educate and change the mind of someone who appears on the surface to not be all the sharp sounds like a lot of wasted effort. Fans are cheap. Tapping into a crawlspace wire for power is cheap. Time spent butting heads with an inspector is time taken away from other more worthwhile activities.
RG,
It sounds like a misunderstanding in regards to the fan just moving air around vs. actually exhausting that air. There are certainly benefits to a continuously operating, low CFM, low-draw fan exhausting the air in your crawlspace to the outside. In fact, I'd see it as good insurance, even in a well sealed and insulated basement/crawlspace because it ensures that the space will always be under negative pressure, eliminating the chance that your house will unintentionally suck on your crawlspace, bringing potentially nasty stuff into your indoor spaces.
It was a few years back, and my google-fu on both sites is poor, but I remember an article in FHB or JLC about intalling a very small always on fan to remove radon gas.
It consisted of a 3 or 4" plastic pipe leading outside, with a very small computer case fan at the bottom that pulled air up and out.
Running fan to produce reduced air pressure in crawl space.
If you run an exhaust fan in a sealed air tight basement or crawl space wall, to reduce the pressure inside the basement or crawl space you will merely run the fan for the sake of it. There will be no air pulled in and nothing will come out - rather a waste of money.
If the basement or crawl space is not air tight (as is most likely) you will pull air from the home or the outside. Both of these instances run the risk of pulling warm wet air into the basement or crawl space with the likelyhood of condensation on the below dew point joists and floor boards, this will lead to mold and wood rot.
Ventilated crawl spaces are old technology, there was a belief that the stack effect would pull air through the crawl space and the moving air would keep the timbers dry. People didn't realise that the stack effect pulled in warm wet air, that lead to water vapor absorbsion into the timbers and in so doing caused mold and wood rot.
The OP stated that the crawlspace will be insulated, thereby becoming part of the conditioned space of the house. This means that it's very unlilkey that the framing in the crawl would ever reach the dewpoint and produce condensation.
Also, the capacity of the code-required exhaust fan (20 CFM/1000 sq. ft.) is low enough that, even in a tightly air-sealed house, there will be plenty of leakage into the crawl to be exhausted. Additionally, the code requires a transfer grille or duct that communiates between the main living space above and the crawl. This could be quite small (like a 3" duct) to balance what the 20-50 CFM fan exhausts.