I am going to be building a house in Southern California (the hot part of Los Angeles, where summer temps are regularly over 95, and many days over 100). The plan is to do a vented raised foundation (Los Angeles Building and Safety hasn't quite warmed up to unvented raised foundations).  There will NOT be a basement, only a foundation that is approximately 24-30 inches above grade.  The foundation will be poured concrete.

What is the BEST way to insulate below the plywood floor sheathing?  I think fiberglass batts are the most common method.  I suppose cellulose is best method, but it would seem difficult to go into the crawl space to spray it, some sort of netting would have be installed to hold the cellulose up to the bottom of the sheathing, and it would kind of eliminate one of the benefits of the raised foundation, namely the ability to repair plumbing if needed - all the cellulose would fall if you needed to work on something.

Is some sort of barrier recommended over the dirt in the crawl space?  This would seem difficult to achieve since there will be piers set in concrete throughout the crawlspace holding up beams beneath the floor joists.


Thanks 

Any idea what percentage of homes in your area are done now with a crawlspace instead of a slab?

Maybe rigid foam - either on the bottom of the floor joists or sandwiched in the floor itself.

In the Southeast where I live, spray foam installers are spraying either open or closed cell foam between the floor joists.  This allows full access to utilities under the floor and since it is on the bottom of the floor there is no worry about termites hiding in the foam since they would have to build dirt tunnels up to the floor.  If you use open cell concrete blocks for the piers and foundation walls, then consider installing termite shields on top of them.

We use vinyl on the ground to hold down moisture.

ICFHybrid - I dont have any numbers of slab vs raised foundation.  I have decided on slab since this is a house I plan on living in for the next 20+ years and I think access to the plumbing will be a good thing in the future?  I couldnt find any good information comparing raised vs slab.  Slab is cheaper, so I am guessing the majority of homes these days are slab in so cal.

 

jonr - can you elaborate about the ridgid foam sandwiched?  How thick would the foam need to be?  Would this still be a vented crawl space?

 

Alton - if you do spray foam, then aren't we talking about an unvented crawl space?

 

Thanks for the guidance.

ICF Hybrid,

By spraying the bottom of the sub-floor between the floor joists, the crawl space is still vented.  The termites will have to climb up inside the blocks or build dirt tunnels where they can be seen from inside the crawl space in order to get to the wood floor joists or sub-floor.

If the foundation walls in the crawl space are sprayed with foam, then the crawl space is unvented (sealed but not fully insulated).  This method requires an inspection band be left open all around the foundatin wall for termite inspection.  That is, the termites will have to build dirt tunnels to get across the gap - they can not hide in the foam where the foam is missing.  With this method, there is a 6" band all around the inside of the foundation walls that is not insulated.  I like insulating between the floor joists instead of spraying the foundation walls although it requires much more spray foam.  I have been using open cell foam under the floor but now considering using closed cell in the future.

Many homes are built with concrete block foundation walls and with no termite shields on top of the open cell blocks.  I think the blocks should be filled with grout and capped with a termite shield or the foudation walls should be cast-in-place (CIP) solid walls.

For a home with a crawl space I really prefer concrete for the floor.  This can easily be done by using structural metal decking and a few temporary braces (shoring).  For long floor spans, metal beams under the concrete and rebar in the slab tied to the foundation wall can be used to eliminate intermediate piers in the crawl space.  Using post-tensioning can elimate all of the metal beams and some of the rebar in the slab.  We have a local post-tensioning company that does the engineering and installation for slabs on grade and over a crawl space.  Of course, these systems will cost more initially, but in the long run there will be less maintenance and worry about termites plus the insulated slab can act as thermal mass to even out the temperature swings in the house.

And while I am still on the subject that includes termites, I do not like for the brick exterior to extend below grade.  However, all builders in my area do allow the first few courses of brick to be below ground level.  I think this is a waste of good brick and although the space between the brick and concrete block foundation wall is supposed to be filled with grout, I still think this area can provide a hidden path for termites to travel up to wood.  Another thing to keep in mind is that any grout below ground should contain cement that is designed for below grade.  I think the brick should be set on a ledge about 4" above finished grade.  Landscaping or mulch can hide the ledge.  After seeing termite inspectors digging around homes to get down to the bottom of the brick convinces me that setting the brick on a ledge above grade would be as helpful as leaving a gap in the sprayed foam on a foundation wall.  At least with an above ground ledge for the brick, the termites would have to build tunnels on the outside to travel upwards.  No more digging around the house to look for termites.