[Greenbuilding] Crawlspace

[Stuart Fix]

Regarding:

I wrote:
Humidity within the crawlspace should be controlled via poly on the ground
and proper ventilation (either passive screens or active fan/humidistat).
The crawlspace walls are there to stop animals and excessive wind washing.
The site must be properly graded if you have any hope of a dry crawlspace.

Eli's comment:
The issue I am trying to understand is how to maintain in a ventilated
crawlspace to be warmer than dew point.  The vapor barrier on the ground
only stops ground sources of humidity.  A high standard thermal barrier in
the floor keeps the ac cooling from cooling the bottom surface.  However,
the shading will keep the crawlspace cooler than outside.  Could this
cause condensation?

Response:
The goal is to minimize the transportation of moisture into the crawlspace
from the ground (via poly ground cover), from the home above (through
proper floor design), and from the exterior (through a rain screen & site
grading). The point of ventilating the crawlspace is to dry out any
naturally occurring moisture that may end up in the crawlspace, despite
the efforts described above.

The only way to STOP condensation from occurring, in the situation you've
described, would be to heat the crawlspace, or to ventilate the space at a
high enough rate that it maintains the same conditions as outdoors. Both
are likely a waste of energy.

Keep in mind that I operate in cold climate north America. If you're
living in a cooling dominant climate, then you should consult with a local
professional who has more experience with your specific concerns.

Cheers,

Stuart Fix, P.Eng., LEED® AP
PHI Certified Passive House Designer
MASc. Building Science
Mechanical Engineer
ReNü Building Science Inc.

52 Airport Road | Edmonton, Alberta | T5G 0W7| C. 780.554.8192
| sfix at renubuildings.com