A termite shield is a barrier installed in the foundations of a house which is designed to prevent termites from crossing into the foundations and flooring. Termite barriers can be put in place during construction or renovation, and the inspection and replacement of such barriers can be a routine part of the maintenance of a structure. Many home supply and hardware stores carry termite barriers, and they can order specific brands, sizes, and styles by request from customers or contractors who have accounts at the store.
Termite shields are made from metal such as galvanized iron or copper. Metals which are not as readily subject to corrosion are usually chosen so that they will hold up over the life of the structure, ideally without needing to be replaced. The termite shield is used to create a barrier between the wooden elements of the foundation and flooring and elements such as slabs, perimeters, and piers used to support them.
When termites encounter a termite shield, they are forced along the barrier as they seek out the edge. This forces them into the light. Since termites do not like light, they will usually seek out easier sources of food than the wood above the barrier. They also cannot tunnel through the barrier or create tunnels which will allow them to work around it. This keeps termites away from the wooden elements of the foundation, and, in turn, away from framing, joists, and other wooden parts of a structure.
Obviously, a foundation termite shield cannot keep all termites out. It's also important to take other steps to repel termites. These can include regular inspections to make sure that there is no wood to ground contact, as might happen, for example, if dirt accumulated next to a deck, potentially allowing termites to cross from the deck to wooden parts of the building. Likewise, it's important to keep trees and shrubs cleared as they can also be used for cover by insects which might damage or destroy wood.
When inspecting a piece of prospective real estate for purchase, it is advisable to confirm that a termite shield has been installed and that it is working properly. This can be done during a termite inspection in which the structure is examined for signs of infestation. If termites are present, it can be grounds to cancel a contract, to request a reduction in price, or to ask that the situation be remedied before the property changes hands.