Ideally, the best time to treat for termites is before the home is constructed or during the construction. If you use pre-treated wood that has been sprayed with a chemical like Timbor, you will have less chance of termites.
After the footings are poured and the foundational walls and/or piers have been constructed, apply the termiticide to a trench in the soil about 12 inches wide and 6 inches deep adjacent to the foundation.
Soil on both sides of the exposed foundational walls and soil surrounding should be soaked down to the foundation footing at the labeled rate. Apply at the diluted rate.
Poured in with a watering can or bucket is easier than using a sprayer. There is no need to dig the trench any deeper than the top of the footing. Soil at the bottom of the trench can be loosened with a spade or iron bar to allow further penetration.
For outside basement walls (where the footing is deep) most pest control operators apply the chemical by injecting it along the foundation through a hollow rod attached at the end of the hose in place of a soil nozzle. This is called "rodding". The result is a continuous chemical barrier from footing to surface.
This should be applied to both the inside and outside of the foundation and also around piers, chimney bases, pipes, conduits, and other structures in contact to the soil. Use at the rate of 4 gallons per 10 linear feet. The diluted termiticide should be mixed in with the soil, as it replaced.
For effective pretreatment termite proofing, much of the chemical barrier needs to put under the concrete slabs. Obviously it is easier to put out the barrier termite treatment BEFORE a slab has been poured.
After it has been poured, it will need to be drilled and a chemical injected under the slab to seal off termite entry points. This is not a "do it yourself project". Apply a diluted termiticide at the rate of 1 gallon per 10 sq. feet, covering the square footage.
Along both sides of the foundational walls and interior foundational walls and plumbing, apply this diluted rate at the rate of 4 gallons per 10 linear feet. A hose end sprayer hooked up to your sprayer, makes this job a lot easier.
It is also possible to do a termite treatment yourself on a house that is already built.
Post-Construction Treatment
A thorough inspection is the first and most important step. Basement construction may require treatment which injects termiticides into the soil through holes drilled in the basement floor at regular intervals.
Crawl space treatment also involves trenching or rodding soil along the foundation walls and around piers and pipes, then applying termiticides to the soil.
Dig narrow trenches along both the inside and outside of foundation walls and around piers and chimney bases, applied at the rate of 4 gallons per 10 linear feet. Also be sure to trench and treat around sewer pipes, conduits and all other structural members in contact with the soil. The trench should be as deep as the top of the footing.
Mix the termiticide with the soil as it is replaced. The State regulations differ state to state on treatment and drilling activity required.
You will want to be sure and do what you can to treat inside the walls. You can do this from the attic or basement or choose to drill a small hole in a hidden place and inject the chemicals in that way.