[Greenbuilding] Crawl Spaces Again

[Sam Ewbank]

John and Eli,

Here is a link to a Building Science Corp. Insight article:
http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces?topic=resources/more-topics/homeowner_resources
which should be helpful in designing and understanding some of the variables
to consider in your respective projects.


Opinions worth the price charged.

Sam


On Wed, Apr 27, 2011 at 3:31 PM, John Beeson - Sunny Side Up <
emailme0617 at yahoo.com> wrote:

> 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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