[Greenbuilding] [BULK] Insulating slab legally in Texas
Lawrence Lile
LLile at projsolco.com
Fri Oct 19 15:50:27 EDT 2007
PS,
There are metal termite shields under all of the outside bottom plates.
These are galvanized steel (copper is better but $$$$) sheets formed in
a local sheet metal shop, they stick out beyond the slab under the
siding about 2", and down at a 45 degree angle. Inside, they come in
1/2" past the bottom plate, and turn up 1". This lips over the interior
sheetrock and shows on the inside. The lip is covered with the interior
trim, which in my case is tile, not too friendly to termites. So to get
inside, they either have to negotiate the outside edge in midair (they
hate sunlight) or tunnel underneath between the steel/concrete crack and
emerge under a piece of tile, negotiate the tile mastic and chomp
through sheetrock to get at wood. Not too likely.
The termite shields are stuck down with roofing tar, lapped 12" at ends
and lapped with roofing tar there too. On the outside edge, I took
tubes of roofing tar and caulked the entire edge of the shield where it
touches the concrete, so there are no inviting cracks. (actually my
teenage assistant did most of this, and we laughed at him because he was
totally immersed in tar when he got done, had it in his hair, face, etc.
I did part of the job that he didn't get to in a white shirt, which
remained so.)
Termite shields are a very effective method of dealing with termites,
and that statement is based on building science. If I was in heavy
termite country I'd use copper shields, and solder them together. I
have no idea if the tar is really effective, but I couldn't think of
anything better and my contractor said that's what he used often, he
didn't know if it really worked either, so I can't claim the tar has any
basis in building science but it makes sense.
Lawrence Lile, PE, LEED AP
Project Solutions Engineering
-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Lawrence
Lile
Sent: Friday, October 19, 2007 2:36 PM
To: Horacio Gasquet; greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] [BULK] Insulating slab legally in Texas
Here is how I did my house. I am also worried about termites, although
there is no state law.
1. I put wide eaves on the house. This was a natural on the solar
side, because I needed the solar overhang, but I put wide eaves wherever
possible. Termites like wet, they don't like dry. The lot is sloped to
a minimum 5% grade away from the house. These two measures are based on
sound building science - moisture is the friend of the termite and the
enemy of buildings.
2. I put a sand barrier around the house. There is a 3 foot wide by 1
foot deep layer of river sand at the edge of the house, with a roll of
weed barrier fabric underneath it. Termites can dig through sand,
however there are special sizes of sand that they CANNOT dig through.
Since sand is soft and easy to move, I can replace this sand with the
special sizes if I get an infestation. Termite sand is approved as a
termite control measure in Hawaii, (where the termites take steroids I
hear!), however it is too expensive to use unless the little buggars are
actually there. I believe, however, that a DRY area of sand will not be
preferred by termites, they will be prone to look elsewhere. My use of
river sand is NOT based on building science, just practicality and a
suspicion that any sand will make termites less than welcome.
3. I left a 6" termite inspection area of exposed slab edge. Under the
slab, there is a footing to 36" deep that is insulated with 2" EPS
Styrofoam, however the slab edge above that point is exposed. The
footing is actually recessed so that the Styrofoam is flush with the
edge of the slab. This is crucial to making the next step work neatly.
If you used insulation under your slab horizontally, then you need to
pay special attention to the edge detail so as not to make a termite
superhighway into your house via the horizontal slab insulation.
4. This was all peachy with the inspector. When he left, I waited till
the end of summer and I took 2" Styrofoam, and painted it to match the
house siding in strips 9" wide. I dug out the sand by hand (this was
really easy and brought back memories of many sandpiles as a kid), and
placed these strips of foam against the exposed slab edge and up tight
against the underside edge of the siding. I pinned them in place with
sand, which seems to work very well. This took 90 minutes to run this
stuff all the way around my house, an easy job, the only tools requires
were a paintbrush and a razor knife.
Sure, there is a great path for termites there. IF they can negotiate
through dry sand and past the treated wood bottom plate. It is a 60
second job to pull out these foam boards and inspect for the little
devils. I may leave the planks in place all winter, and pull them
after it warms up in the spring, or I may (more likely) just leave them
in place and pull them once a year to inspect.
You've got to paint the planks. Foam deteriorates in sunlight rapidly.
I have seen foam a year old, with all the printing standing up on little
pedestals, the rest of the foam eaten up by sunlight! Any barrier, even
the thinnest layer, protects the foam from damaging sunlight.
Termites work slowly. Termites love wet wood. They don't really like dry
wood much. There is no reason to panic if you actually see them. Horror
stories abound, but are mostly overblown. I've worked on houses that
were 100 years old, built in the soggy wet river bottoms and had wet
wood in contact with soil the whole time, and yeah, they had some
termite problems, but nothing insurmountable.
In Texas, depending on how cold it gets, I'd be tempted to leave off on
the insulation planks, and just go with sand, overhangs, and a 6"
termite inspection band on the edge of your concrete slab.
I really could feel the cold seeping in through the edge of that slab
before I put in the insulation planks - and ASHRAE calcs show that
exposed slab edges are just as bad as an open window. If you live in a
cold climate, your slab edge is a MAJOR heat leak. My town gets to zero
F regularly, if your area rarely freezes I'd just leave the slab edge
bare.
I am determined not to ever have to spray for termites, and I think this
scheme gives me flexible options to inspect and control them without
resorting to the Nuclear Option.
Lawrence Lile, PE, LEED AP
Project Solutions Engineering
-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Horacio
Gasquet
Sent: Thursday, October 18, 2007 9:18 PM
To: greenbuilding at listserv.repp.org
Subject: [BULK] [Greenbuilding] Insulating slab legally in Texas
Importance: Low
I have a different kind of slab insulation question for this group.
Texas state law requires some exposed concrete slab on the exterior
perimeter of a home to allow for termite inspection. In some cases,
the amount of such exposed slab amounts to huge surface area for
thermal transfer right under the walls. I don't care how well
insulated the walls are if you have a thermal leak right under them.
I have such a problem on an older home.
My ultimate goal is to insulate the slab well enough that the slab
and underlying ground serve as a thermal mass to help stabilize the
interior temperature. The question is how to do this without
introducing a sneak path for termites to the base plates for the
walls. I have looked for insulating brick or tile, and am only
really finding refractory bricks for industrial ovens (typically
Calcium Silicate).
I am currently picturing a termite mesh below grade, that will wrap
around whatever insulation to keep them from getting in between the
slab and the bricks/tile. But I still haven't found a good product
for serving as the insulator, that is also a termite barrier and
attractive as an unpainted exterior surface. Anyone have any ideas?
BTW. The paints that NASA uses ARE radiant barriers. They don't
have to worry about conduction in a vacuum. You can buy the hollow
ceramic spheres (looks like fine sand) and mix it with paint to get
some emissivity reduction for direct Sun on walls, or a metal roof.
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