Termites usually invade homes by way of the foundation, either by crawling up the exterior surface where their activity is usually obvious, or by traveling inside hollow block masonry. One way to try to deter their activity is to block their access points on or through the foundation.

METAL TERMITE SHIELDS
Metal termite shields have been used for decades to deter termite movement along foundation walls and piers on up to the wooden structure. Mermite shields that are installed improperly (i.e., not soldered/sealed properly) or become damaged or deteriorated over time may allow termites to reach parts of the wooden floor system. Shields should be made of non-corroding metal and have no cracks or gaps along the seams where sections are attached. If your house is being built with metal termite shielding, make sure that it extend at least two inches out and two inches down at a 45^o angle from the foundation wall.

(Image: T. Myles, University of Toronto)

MASONRY CAPS
In place of using termite shields on a hollow-block foundation, you can fill the block with concrete or put a few courses of solid or concrete-filled brick (which is often done anyway to level foundations). The same approach can be used with support piers in the crawlspace. Solid caps (i.e., a continuously poured concrete cap) are best at stopping termites, but are not commonly used. Concrete-filled brick caps (as seen below) should deter termite movement or force them through small gaps that may allow you to spot them during an inspection.