[Greenbuilding] Crawl Spaces Again
John Beeson - Sunny Side Up
emailme0617 at yahoo.com
Wed Apr 27 14:31:11 CDT 2011
Eli,
Can you pass along the location of the article you mentioned in Journal of Light
Construction? (vol, edition, or just link?)
I have a similar circumstance with a client and my recommendation was just that
(to insulate the underside of the floor and move the thermal envelope up away
from the crawl space). This house is on a very very low crawl space (maybe 6")
and then a separate full basement in the rear where the mechanicals are.
the framing would be "protected" from humidity as the foam becomes the vapor
retarder (ensure you know the actual PERM of the foam you are installing).
Masonry, on the other hand, is a little tricky and is dependent on the type of
mortar used. For my project, the house is soooo old that the mortar was
certainly not "designed" in any way for any condition except to hold some stones
together. If the moisture builds up enough (the hygrothermic cycle of the
masonry becomes fully saturated or just beyond a "safe" saturation level) and
the entire thing freezes, then things will either start to spall (from dissolved
salts, freeze thaw cycles, or in extreme cases, exfoliation).
My thoughts... always looking for others.
-John
--------------------------------
I am looking for advice on crawlspace humidity issues when the floor defines the
thermal barrier.
I have a client that lives in a low spot in an urban neighborhood. Recent heavy
rains and flawed city storm drainage resulted in his crawlspace being flooded.
Fortunately it did not reach the floor. However, the original installation
aspired to be a sealed crawlspace. It had plastic on the ground and coming up
the walls stapled to anchor plate below floor. Walls were covered by fiberglass
that was trashed in flood.
The crawl space has ducts and a 15 year old forced air gas furnace. It appears
to have survived the flood. I understand how to install a better sealed
crawlspace using foam instead of fiberglass. I also am encouraging him to
insulate the ground if he goes that route. However, we are also considering
removing the old furnace and ducts to replace with a high efficiency mini split
heat pump. This avoids the need HVAC equipment in crawlspace. Therefore, the
thermal barrier can be defined at the floor. I have seen Journal of Light
Construction report that floor installed thermal barrier is more energy
efficient than sealed crawl space. The installation they described did not
include insulation on the ground, however. With floor defined thermal barrier,
the efficiency would be even greater if no HVAC is located in crawl space.
Also, this puts the installation out of harms way if another similar event
occurs again. The authors of the study article were advocates for sealed crawl
space that were dutifully reporting the results of their study. The main
advantage for sealed crawlspace is that the humidity is better managed with
house HVAC system than ventilation with outside humid air during hot time of
year.
I am considering recommending the floor bottom be sealed with closed cell foam.
This would provide a vapor barrier to protect the floor framing. Currently the
house is not cooled. However, the mini split heat pump would provide this
option. Therefore the conductive U value would need to be low enough to avoid
condensation on the warm humid crawlspace side (bottom of floor) during the
cooling season. If all framing is covered with layer of 1or more inches of
foam, are they protected from humidity? My assumption is that the masonry
foundation is not vulnerable to damage from humidity or similar flooding?
As always, your thoughts are appreciated.
Eli
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