Termite Prevention and Construction

Excellent termite summaries are available from UC Davis Statewide Integrated Pest Management (links at end of this article).

Fighting off Subterranean (under ground) Termites:

You should probably have a termite inspection periodically. Someone should crawl the whole crawl space looking at the foundations for evidence of subterranean (under ground) termites. They make mud tubes from the soil over concrete to the wood. And look for damp or wet areas of ground under the house. This is more important if you live where the ground is usually damp, or you water a lot, or your neighbors have subterranean termites. The rest of the techniques in this post will help where applicable.

Replacing damaged wood plus removing and/or preventing the moisture they need are effective.  These may be labor intensive.  Handling moisture means 1) fixing any leaks or re-directing rain or other water 2) drying out the ground under and near the building. This may or may not be practical. 

If you have subterranean termites the standard treatments involve injecting chemicals into the soil, and rechecking later. I am not an expert, but it looks like treatments containing imidacloprid or fipronil are the most effective with the lowest toxicity to humans. (Although these have been suspected in bee colony collapse disorder, their use underground is probably not going to affect bees. This is not the same use as spraying of crops.)

Fighting off Drywood Termites:

Most important principle: prevent water from getting and/or sitting between boards.

If remodeling or building, follow building codes about heights of wood above the soil.  UC Davis recommends 12 inches minimum.

Many of these recommendations also help discourage subterranean termites.

Per building codes, the bottom boards of wall or floor framing that lie on concrete must be “Treated” lumber – treated with chemical preservatives to help protect the wood from attack by termites, other insects, and fungal decay. Also any cut ends should get wood preservative, twice. Supplies are wood preservative, rubber gloves (it is poison), a can and a brush.

Prevent water from infiltrating into the walls. There are a lot of codes aimed at this. Understand what you are doing and why, when building or repairing. And don’t let a roof keep leaking.

Fix plumbing leaks promptly, especially drain pipe leaks, which tend to be hidden.

All exterior wood should be painted or sealed occasionally. Even one coat of paint will discourage a surprising variety of insects. This includes, for example, carpenter bees. Paint is not highly effective against termites but it helps.

Making a Wood Deck Last Long:

The deck joists are a lot harder to replace than the deck boards you walk on.  The joists are the boards placed “on edge” holding up the deck surface.

The nail or screw holding down a deck board makes a path into the body of the joist. Over time this will allow water into the joist. If you put self-adhesive rubber roofing membrane on the joists, and then screw (or nail) your boards down, this will seal around the nail or screw. Cut rubber strips with a straight edge and utility knife a little wider than the joists, say 1-3/4” wide. The strips can be stapled down with a construction stapler.  This helps keep water out of the path the nail or screw makes into the body of the joist. It also separates the joist from the deck board. This reduces water being trapped on the top of the joist, as well as inside it. The bottoms of the deck boards can be treated with clear wood preservative. It will help if the joists are treated and they can be painted as well, all before the deck boards are installed.  It is almost impossible to keep water out of the joist to deck board contact areas after installation.  You cannot caulk the joists between the deck boards for example. All this work prevents water from repeatedly soaking into the joists.

Another option may be to use “treated” boards for deck joists – IF they will meet the strength requirements called for in building codes. Inspectors want to see “grade stamps” on the boards. The rubber strips will still be useful as the wood treatment does not penetrate to the center.

Excellent termite summaries from UC Davis Statewide Integrated Pest Management:

Overall Summary: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7415.html
Downloadable document available there: pntermites.pdf

More on Drywood Termites: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7440.html
Downloadable document available there: pndrywoodtermites.pdf

Copyright 2013 by Brandon D’Rion

 

Why did the termites stop eating six to eight inches back under the outside edge of the house on most joist boards?

Here is the sequence:
1. Continued wetness of wood allows the growth of fungus. This occurs when it rains a lot. This is worse when water is trapped between two touching boards. Fungus rots the wood, making it soft. Rain does not fall under a house, so those parts of the joists remained dry and hard at all times.

2. Termites prefer soft wood. They even like soft redwood. This is the most important lesson in this series.  When they find soft wood, they come and feast.

What other evidence is there that termites like soft wood?

A. Pine is a really soft wood. Termites are often found inside indoor pine moldings such as door and window casings, and baseboards, even when these have never been exposed to water.

B. They rarely attack house framing, especially fir, that has not been softened by water and fungus. House framing is usually fir, which is harder than pine or redwood. When they do attack a house framing board they usually leave most of the nearby framing boards alone. Based on the above, I believe they choose the softest ones. Of course a leak can result in many boards being softened. Besides a roof leak, a leak can just be – the wall or the trim around a window or door was not maintained, or poor quality caulk was used, which cracked, and water gets into the wall every time it rains.

C. I have rarely seen a termite in a sound oak board. Oak is much harder than fir.

So do termites like redwood and cedar? If in good condition, termites usually leave it alone. So it seems to last longer IF it is not set up to soak but can dry out when it gets wet. That is true for other types of wood too. Air on all sides works wonders.

The above observations apply for sure to drywood termites, and at least some of it applies to subterranean termites.

After I wrote this, I discovered a website, by an exterminator who discusses the resistance of various woods to termites.  He says, in the comments, “The only thing I can tell you for sure is that the harder the wood, the more resistant it is to termites.”
http://www.asktheexterminator.com/termites/Termite_Resistant_Wood.shtml

What I have added to that recognition is that water and fungus makes the wood soft, and termites then get a lot more interested in almost any wood.

 

Visit my next post (next week) where we will look at Defending Against Termites – When Building.

 

 

Copyright 2013 by Brandon D’Rion