Conditioned crawl space

[Maineman]

We live in central Maine and are completely rebuilding our MH. We made the exterior 4" walls into 6" walls, jacked the house up and built a 2x6" knee wall underneath the house. The house sits on the knee wall and the knee wall sits on 8x16” hollow cement blocks. The house is on a 5” poured concrete pad. We then re-insulated the exterior walls and added 7/16” OSB that extends down to the cement blocks and covered the entire exterior wall with Tyvek. Next year we plan to finish the exterior with white cedar shingles.

Our main question now is what are the advantages of creating a conditioned crawl space. We have a book my wife bought on the subject and a document I downloaded from the internet. Haven’t read them yet but the overview seems to be a conditioned crawl space is a heated, airtight space designed to control humidity. To achieve that, heat from the house is first directed down into the crawl space. A fan, some distance from the heater, draws air up out of the crawl space and back into the house. This removes moist air from the crawl space and introduces it into your living space, making your house feel warmer for a given temperature. The floors of your house will also be warmer, preventing the cold floors from absorbing heat from inside the house. All in all, by pumping heat into an un-used crawl space your living space will be warmer for less energy $$$$ spent.

To make the crawl space airtight we plan to insulate the knee wall from the interior with 6” fiberglass insulation, cover the cement blocks from the inside with 2” Styrofoam insulation and cover the whole knee wall from the inside with Tyvek.

Have I got it right? Are our plans overkill? Do I not understand what a conditioned crawl space is and what it is supposed to do? Is creating a conditioned crawl space worth the effort and expense?

I attached a couple of photos so you can see what we have done.

Thanks,

Tom

[flcruising]

First I'd like to say congratulations on completing such a large project! Seems all my comparatively small projects never get completely finished.

Now.
There's little benefit, if any, to having a conditioned crawl space. There's no way to save $$$$ by adding 50±% more (uninhabitable) volume that must now be heated/cooled, and still expect the same furnace to deal with it. (Ok, well maybe the wall insulation upgrades you did before will limit that, but any benefit you get there will probably be negated by heating the crawl space too.) Your floors WILL be warmer on your feet since the air under the floor is close to the same temperature as the air above the floor, but don't expect anything drastic. You really want your floors to be hotter then the air above, not the same temperature, THAT'S when it will become noticeable.

The best approach in this situation is to heat the floor via radiant heat (hydronic) and insulate underneath that. The floor will then be warmer than the upper volume of the space, and all will be happy, especially your feet.

[troyster]

Maineman if your gonna go through with your plan I would strongly recommend above all to lay 6 mm plastic over the ground and run it a couple of feet up your skirting walls and all the concrete/wood supports. Then seal with caulking and construction tape ( Tuck Tape)
Then all your vents would have to be sealed off. The crawl space cannot contain any moisture at this point.

[Greg]

Tom, I would question heating the space, If you have the skirting insulated and air tight, there really should be no need to heat it if you leave the insulation in the original underbelly. Mark in South Dakota has said that the space under his home rarely goes below freezing with just insulated skirting.

I would still use vents in the summer just to keep the air moving. Greg

[iafirebuff]

We have vinyl skirting with vented pcs every so often. The vents are open. We live in Iowa. Last week we were down to -34 with a wind chill of -45 below. I have a wireless thermometer under our house - the coldest it got was 19 above zero! Usually it has been stayin around 32 or 33 with an occasional dio into the high 20's. I was shocked at how warm it stays! I just put new heat tape, foam pipe wrap then added about 4-6" of fiberglass around that and wrapped with vapor barrier. Not even sure I would need the heat tape So all in all I am very surprised how warm it is under our house!

[Steve S.]

We have vinyl skirting with vented pcs every so often. The vents are open. We live in Iowa. Last week we were down to -34 with a wind chill of -45 below. I have a wireless thermometer under our house - the coldest it got was 19 above zero! Usually it has been stayin around 32 or 33 with an occasional dio into the high 20's. I was shocked at how warm it stays! I just put new heat tape, foam pipe wrap then added about 4-6" of fiberglass around that and wrapped with vapor barrier. Not even sure I would need the heat tape So all in all I am very surprised how warm it is under our house!

Indeed, my main waterline from the riser to the bellywrap is similarly wrapped in fiberglass and sheet plastic. I made it through 2 or 3 winters w/o a heat tape. LOL, actually I had a heat tape on the pipes but it wasn't plugged in! It was plugged in the wall outlet(so I assumed it was working), but come to find out the wall outlet was an add-on and it was not plugged in under the home in the crawl-space. I wished the previous owner had told me about this