[Greenbuilding] Insulating shallow crawl spaces

[elitalking]

I have a deep energy retrofit project on an old framed house where there was no excavation for the crawls space.  The result is that the front, downhill side of the house has adequate room for installing insulation.  However, much of the house has less (18"-24").  The floor condition is good enough that we are not considering removing the floor.  The room height is insufficient to consider adding insulation to the top of the floor.  How do I insulate the floor.  

 

For the rest of the house, we are planning on installing new ceiling rafters parallel to the roof pitch to define 14" space to fill with open cell foam.  We are installing furring strips installed with 2" gap in front of old wood siding.  We are adding continuous 2.5" closed cell foam to fill the gap.  The old plaster is gutted.  We can fill with adhered cellulose or open cell foam in the 2x4 framed walls.  On another similar job, I came to the inside of the foundation to continue closed cell foam thermal barrier and came across the ground with closed cell foam.  All of that was covered with the high cost spray ignition barrier.  In hind site, with that job, I would have preferred to use rigid board insulation such as XPS.  I would create a ground plane with combination of digging high spots and filling low spots with crush and run (small gravel), lay one layer of extruded board to provide puncture protection, a layer of poly for continuous vapor barrier and another foam layer.  I put osb on top for cheap ignition barrier that protects the foam from traffic damage.  The whole house is provided with HRV for fresh air.  

 

However, this house does not have adequate space to work in.  

 

Do I need to hand excavate to a minimum clearance for the work? If we did that, I could install either of the approaches describe above.   I was wondering if I could fill the whole space with open cell foam.  I realize that 1/2 # open cell foam is not a vapor barrier, therefore likely not a good idea.  

 

I am encouraging my client to use a mini split heat pump to avoid the need for ductwork in the crawl space.  Therefore, I can define the thermal barrier at the floor plane instead of the ground.  Because we would still have moisture issues below, I am leaning towards ground insulation.  However, a closed cell foam application to the bottom of the framing could provide the vapor barrier to protect the wood.  Below that the stone and concrete surfaces are not vulnerable to humidity. 

 

Right now, I consider the hand excavation to be the most likely scenario. Because the mini split will cool the house, I am against the traditional ventilated crawl spaces with fiberglass batts in floor framing because the cool shadow will pull in hot humid air and cool it to dew point creating humidity problems.    

 

This is a common situation with old house.  I hope our list can offer some good ideas for cost affective ways of upgrading to a high standard.  

 

Eli 

www.conservationarchitect.net
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