Sealed and Encapsulated Crawl Space in Dry Denver
I am building a new 280 sq foot addition with crawl space. Climate zone 5B. The Denver code specifies that with a sealed crawl space, the concrete walls are insulated but not the ceiling. I don’t want cold floors, so I am going to insulate the ceiling/floor of the room and ventilate the crawl space, which only needs 30 square inches of free air flow. I will have a radon blower under the membrane covering the floor and part of the wall. The Denver code does not allow concrete wall insulation unless the crawl space ceiling is left uninsulated. (Seems weird)
My intent after passing inspection is insulating the concrete walls and then closing up the two vents. As well, I don’t understand the code requirement to ventilate the crawl space with air from the living area. Can someone explain why this is required? It seems a waste to take conditioned air from the room above and blowing it into the crawl space, which will have around 1,400 cubic feet. Is my thinking erroneous?
Denver is quite dry, two other crawl spaces with a single small vent are completely dry with absolutely no smell of mold or mildew after 30 years.
My intent has been to install 12″ of fiberglass batts between the i-beams and then 1.5″ of XPS to air seal the space filled with the batts.
The building inspector suggested not insulating the crawl space ceiling and just insulate the walls. Then install an electric heater to keep the crawl space at a desired temperature, such as 50* or so.
I’m really at a loss of what will give the most comfort and energy efficiency.
Advise would be appreciated.
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User ..478,
Sorry I somehow deleted my response.
Once you go with an un-vented crawlspace you need to condition it - that is heat and if necessary de-humidify the space. That's why Denver precludes insulating the floor, and wants you to connect it to the rooms above with vents, or include it in the house's ventilation system.
There are two other ways of conditioning crawlspaces:
- You can install an exhaust fan on the wall, and and a grill in the floor above. The advantage of that is you don't end up sharing air from the crawlspace, which is often not very clean.
- You can add dedicated heat (and if necessary de-humidification) to the space.
Depending on how close to the indoor temperature you intend to leave the space, insulating the floor may not buy you much.