Slab Edge Insulation and Termites: A Solution

Slab Edge Insulation and Termites: A Solution

Posted on 13. Jun, 2009 by in Insulation, Interviews

Interview with Bill Michelson, CEPE, San Joaquin County Building Inspector from November 2008

In GCP No.12, we had published an explanation of the slab edge insulation requirements which are required by Title 24 when specifying radiant heated floor slabs. We illustrated that prior discussion with examples of slab edge insulation as shown in the 2005 Residential Compliance Manual.

However, being practicing architects and architectural engineers ourselves, we also push projects through permitting, construction and final inspections, which allow us firsthand knowledge of how Title 24 requirements interface with building inspection requirements. So, after discussing those slab insulation details last week with one of our colleagues, Bill Michelson, CEPE who is a San Joaquin County Building Inspector, he mentioned one glitch in those Title 24’s details which Building Inspectors find troublesome in zones where termites are a problem, but he also recommended a solution, and here is that interview.

HUGENOT: Bill, as we have discussed previously slab flooring with built in radiant heat is becoming quite popular in residential design, because it has several advantages under title 24:

  • Design simplicity.
  • It can be poured in the slab which provides additional thermal mass.
  • It requires no ducting and no duct maintenance.

But, from your onsite experience you have found that not all of the “approved” slab edge insulation details which are suggested on Page 3-45 of Title-24’s 2005 Residential Compliance Manual actually satisfy the termite ingress prevention requirements?

MICHELSEN: That’s right, while three of those shown do satisfy the requirements the fourth one, which shows the insulation on the “inside”, actually allows a path for termite ingress. It may look like it is sealed to someone without first hand on-site construction experience, but it is not sealed.

HUGENOT: So, then if I understand this correctly, the other three exterior insulation details satisfy because they are outside the slab. But, the detail entitled “inside insulation” actually allows a path for termite ingress?

MICHELSEN: Yes, and unless it is properly sealed against termites the insulation actually creates a path for termite ingress, unless it has a termite shield and is sealed with a gasket or caulked.

HUGENOT: So then, in order to prevent termite ingress, this detail needs to be modified, by the addition of a sill gasket (sealer) over a termite shield at the top of the foundation, similar to that shown in the details on page 11 of the attached PDF, to prevent termite ingress?

Note: The attached PDF is a two-page reprint from a longer document. Bill is referring to the printed page number.

MICHELSEN: Yes, most of those details do have termite shields, but may require additional caulking. Also some of them have the galvanized metal shield showing on the outside of the house, and this is most effective against termites. But, many owners find this distasteful because the exposed metal it may rust. The detail on the right on page 12 does not have this exposed metal, but may require additional caulking under the exterior fascia. Actually, most of these details will solve the problem if properly installed. But, I would prefer to see them use a system similar to the detail on the right of page 11 in the attachment which is the most effective.

Reprinted from Green Compliance Plus Vol. 1, No. 15, originally published November 17, 2008

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2 Responses to “Slab Edge Insulation and Termites: A Solution”

  1. Casey

    26. Jan, 2010

    Another option to be considered is the EnergyEdge slab forming, insulating, & protecting system. These stay in place concrete forms provide insulation that is pour intergrally into the slab edge. The insulation contains borax- a natural termite deturrant. These products are self-consuming, saving time, labor, energy, and money. They meet the intent of Title 24 requirements.

  2. Vinz @ Termite Control

    05. Aug, 2014

    Great article! I agree that in order to prevent termite ingress, that statement needs to be modified, by the addition of a sill gasket over a termite shield at the top of the foundation.

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