In most cases it is recommend to seal your crawlspace totally. It is new to some people but ask any building science engineer, and they will probably say in most cases sealing the crawlspace totally is the standard.

The trick is to keep humid air out of the crawlspace. If they require mechanical vent, that could be costly. I would seriously consider fighting this issue with the building commission. I've attached a link to some helpful info about the subject.

Here is a link that might be useful: Info about Sealing Crawlspaces

Washington uses the 2003 International Residential Code which permits unvented crawlspaces by way of exception. Under the 2006 IRC, however, unvented crawlspace construction will become the norm and recommended practice.

The requirements for having an unvented crawlspace under the 2003 Code are:

R408.2
EXCEPTIONS:

1. "Where warranted by climatic conditions, ventilation openings to the outdoors is not required if ventilation openings to the interior are provided.

4. Ventilation openings are not required when continuously operated mechanical ventilation is provided at a rate of 1cfm for each 50 square feet of underfloor space floor area and the ground is covered with an approved vapor retarder material.

5. Ventilation openings are not required when the ground surface is covered with an approved vapor retarder material, the space is supplied with conditioned air and the perimeter walls are insulated in accordance with Section N1102.1.7"

In most situation, the criteria listed in #5 above are what is usually followed in order to eliminate vents.

You can also eliminate vents if the crawlspace is open to a conditioned basement.

manhattan42, I'm confused about how compliance with #5 would be achieved.

I assume conditioned air means heated or the same air supplied to the living quarters via the HVAC. If thats true, it seems a return would need to be provided from the crawl space somehow.

Would that same return not then circulate the air from the crawl through-out the home?

You don't want to return the air from the crawlspace. You can comply with #5 by adding 6 mil plastic on the ground and 6 inches up the wall, sealing the whole perimeter wall and add a register off the supply plenum or a duct line. I have done it and it should satisfy the requirement.

As with anything else you touch in your own home, check with the a building official.

So if you add a register to the crawl space and not have an "outlet" for the added pressure to vent to, will it not simply force the crawl space air into the home?

While the crawl and such are in very good shape, my concern would be instituting odor and dust into the living area.

TIA

No you never want to return air from a crawlspace. It would be under the same category as a garage or mechanical closet. As for forcing dust and odors into the house, I don't think that would happen, but to prevent that just install the register for the crawlspace away from the entrance.

If your crawlspace is sealed perfectly, a residential forced air unit wouldn't make dust fly into the house, maybe make a suction sound if you open the door, but we're not talking airplane pressure. The goal is to simply keep air dry, and humid air out.

Thanks for the help, hopefully I can pursuade Mr. Inspector.

By IRC code definition, a conditioned space is a

"space within a building that is provided with heating and/or cooling equipment systems capable of maintaining, through design or heat loss/gain, 50F during the heating season and 85F during the cooling season, OR communicates directly with a conditioned space. For mechanical purposes, an area, room or space being heated or cooled by any equipment or appliance."

What this means is that you can add any type of heat to the under space and condtioning it. Doesn't have to forced air at all. It can be steam pipes that radiate enough heat to maintain and heating season temp of 50F or above...A strip of electric heat, radiant baseboard or any other means.

Likewise, the space can be conditioned in summer by running AC to it.

Likewise, the space is considered condtioned if it opens to another portion of the basement that is already heated and cooled by design or default.

Likewise, the space is considered conditioned if it simply naturally falls between the 50 to 85 range at all times...even without mechanical means.

The key to #5 above is that you cover the floor with a vapor retarder....insulate the walls from the top of the rim joist to a point at least 2 feet below the frost depth...and then to condition the space by design or default.

My foundation wall including the footing thickness is 24"'s. So I'm not sure about being able to insulate 2 feet below the frost depth, atleast not very easy!

I did not put any venting in the foundation when poured as I was going to install vents into the rim joist if pushed.

Thsnks for the info manhattan42!

The code requires that if you cannot insulate 2 feet below the frost depth along the walls, you need to insulate 2 feet in from the walls on top of the crawlspace floor to achieve the same effect.

You cannot install vents in the rim joist because the rim joists need to be insulated.

Your only option in this case is to either create an unvented crawlspace (preferred method) or to insulate the ceiling of the crawlspace and install vents through the foundation walls.