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Conditioned Crawl Space Right for South West?

adamflyer's picture

Hi All,

I am considering doing a conditioned crawl space. It sounds appealing because I think it would be easier to keep the critters out and would be more energy efficient.

I am getting close to finishing up the plans on a 1.5 story I am going to build in Dewey, AZ (outside of Prescott). Its in Zone 4 and fairly dry, the relative humidity is usually in the teens or twenties with the exception of the monsoon season in July/August where it gets up over 40% for a while. The building site is on the side of a hill and while there is a fair amount of clay and rocks and drainage is not good for septic (will be needing an alternative septic), I don't think there will be much issues with moisture coming up from the ground, and no concerns of flooding.

The entire attic of the house will all be in conditioned air space and I plan on running most of the air ducting up there so energy savings from running ducts in a conditioned crawl space are a mute point.  I plan on sealing the house off fairly so I am planning on installing an HRV.

If I did the conditioned crawl space I would probably insulate the 4' high 8" CMU stem walls with R-10 ridged foam board vs R-30 fiberglass bats between the floor joists. I am planning on using a heat pump for heating and cooling with central hydronic air handler or several ductless units.

So my questions are:

1. Is a conditioned crawls space right for my area?

2. Is a conditioned crawl space for new construction going to cost more/less than a traditional vented one?

3. Are there any heating/cooling energy savings to be had?

4. What are the best options to consider for plumbing an ERV with a conditioned crawl space?

 

https://buildingscience.com/ (post #215300, reply #1 of 3)

https://buildingscience.com/

 

These guys have all the answers you need. Don't have time to find it right now but they have a book about energy efficient building in Hot Dry Climates that will answer your questions. Great books!

Florida Licensed Building Contractor, 50 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.

Though you probably don't (post #215300, reply #2 of 3)

Though you probably don't have to worry about moisture rising from the soil, you should consider the possibility of radon.  If the soils in your area are known to produce significant quantitties of radon you should seal the floor of the crawl with plastic and run pipes under it to suck out radon.  Also install the pipe to the roof you'd need to exhaust it.  But you can hold off on installing the radon fan itself until a test is positive for the gas, after a year or two of occupancy.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

florida, Thanks for the (post #215300, reply #3 of 3)

florida, Thanks for the link!

DanH, Thanks for the warning. I talked to my building inspector and he said he has yet to encounter radon being an issue in my area but that is still a good idea to plan for it just in case.

So I am thinking of the “2.1. Continuously operated mechanical exhaust ventilation....” for the unvented crawlspace option. My plan is to put a remote weather station down there and monitor the humidity and run the fan if needed, I'm doubting it will be needed. 
 
The link below is a draft that shows where I plan to run the HRV ducting. Heating/cooling will be from ductless (hydronic) units shown in each room. Any feedback is appreciated. 
 
ERV Ducting Plan--> http://www.goldenfab.com/temp_share/House/House_Ducting_20170822.3dm.pdf