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Unvented Crawlspace With Vapor Retarder, Perimeter Insulation, and Conditioned Air

Daniel Allen | Posted in GBA Pro Help on

I’m an architect designing an addition with an unvented crawlspace to have  vapor retarder, perimeter insulation & conditioned air per CBC R408.3.
https://up.codes/viewer/california/irc-2018/chapter/4/foundations#R408.3

Our Title 24 consultant is having trouble getting their software to show the configuration correctly. Has anyone done this successfully? I believe they are using EnergyPro by EnergySoft.

I found this reference in the CA energy standards, so I assume it should be viable:
https://www.energycodeace.com/site/custom/public/reference-ace-2019/index.html#!Documents/27crawlspaces.htm

2.7 Crawl Spaces

The crawl space type is either a (1) normal vented crawl space (has a conditioned space above with raised floor insulation), (2) insulated with reduced ventilation (as used in the California Building Code), or (3) sealed and mechanically ventilated crawl space (also called a controlled ventilation crawl space or CVC).

The software user will model the crawl space as a separate unconditioned zone, selecting the appropriate crawl space type, with the perimeter of the crawl space (in linear feet) and the height of the crawl space.

The standard design has a typical vented crawl space when a crawl space is shown. Otherwise, the raised floor is assumed to be over exterior or unconditioned space.

The crawl space zone type and characteristics shall be reported on the CF1R. A controlled ventilation crawl space shall be reported as a special feature on the CF1R.

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Replies

  1. Daniel Allen | | #1

    Addition ended up passing Title 24 model w/out underfloor insulation, and consultant confirmed EnergyPro 8 does not have an option to model unvented crawlspace assemblies.

  2. Walter Ahlgrim | | #2

    Seems to you may want to think about crawlspaces in 3 ways vented, conditioned or moldy.

    Vented has worked forever but without floor insulation seems silly today.

    Conditioned is the way to go but without premier insulation seems just as bad.

    Trying to split the difference between vented and conditioned is like threading a needle to keep the dew point of the air in the crawlspace and the walls temperatures above that number seems more like a hopeful dream than real a plan to my ear. Maybe in a desert it is a no brainer. I don’t live in CA but somewhere in that big a state they must be a spot that gets hot, cold and wet from time to time.

    Getting you plans thru the approval process is important but I think you should make sure the space is not living at the dew point and getting wet every day.

    Walta

  3. Daniel Allen | | #3

    We are encapsulating the addition crawlspace, insulating the perimeter with rigid insulation, and providing conditioned air per CBC R408.3. However the Title 24 software, Energy Pro, used by our consultant will not model/document this in the compliance report. Instead the consultant showed the addition passes performance method without modeling insulation in the crawlspace.

    Ideally the compliance report would show what we're actually building. If it was a critical issue I could investigate the other two approved compliance programs, CBECC-Res or Right-Energy Title 24.
    https://www.energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/2019-building-energy-efficiency-2

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