Thursday, October 21, 2010

Is Your Home Being Eaten from the Inside Out?

In New Zealand our older housing stock is weakening each year as more wood boring beetle damage is accumulated. The larvae of the common wood boring beetles (Anobium punctatum and Leanobium flavomaculatum) are slow eaters; they chew through the interior of untreated timbers for 2-4 years before emerging from the wood between October and March. As they emerge they open the small (2-3mm) holes in the surface of the wood that we identify as borer or woodworm infestation. When we see these holes in our weatherboards, architraves, skirting, floorboards and furniture we only see the ‘tip of the iceberg.’ The vast majority of the damage is within the timber where a labyrinth of tunnels has weakened the wood.
Floor board showing majority of damage in lower half

Thankfully borer do not damage timbers as quickly as termites. If the slow increase in holes is noticed at all, the progress of the damage is often ignored for years. Each year the floor boards might creak a little more and the weatherboards might take a little more filling before painting; but until a floor board fails and you fall through, or the weatherboards start to rot because of water penetrating the borer holes, you may not be aware that your home is in danger.

It might take more than 50 years for damage to accumulate to the point of failure but the number of homes reaching such a venerable and vulnerable age is increasing. It is estimated that over six hundred thousand New Zealand homes are now over 50 years old.

Borer tend to attack softer timbers, so the older houses with structural timbers made of good quality heartwood are likely to be structurally safe, but even these houses often have decorative or non-structural timbers of softer sapwood. We often see weatherboards or floorboards riddled with borer holes next to undamaged boards. Even the same board may be heavily damaged in one area and undamaged elsewhere.

In the 1950s preservative timber treatment was introduced to new buildings and this has protected many timber homes of less than 60 years of age, but not all later houses used treated timbers and treatment loses effectiveness over time; it should not be expected the treatment will give protection for more than 50 years. There are many homes older than 50 years with susceptible timbers and the slow chewing of borer beetle larvae is now making more and more timbers fail. It might be too late for some parts of older houses but the borer damage can be stopped or at least slowed greatly by the use of protective borer products.

The cool damp conditions found in the south of New Zealand suit borer well and the homes of Southland, Otago and Canterbury suffer more than most from the ravages of borer. Borer control can be carried out effectively by the use of borer fluids that penetrate deep into the affected timbers and provide protection for many years. Even the timbers that are hard to reach such as roof timbers and floor timbers can be given protection by the use of borer fumigators during the flight season. These kill the adult beetles that have emerged from the flight holes and stop them mating and laying their eggs back on the timbers. There are also aerosol injectors that can be used to treat individual flight holes in damaged painted or varnished wood. This will kill larvae deep within the wood and prevent eggs being laid in the holes.

This is a good time to examine your home for sign of borer infestation. I suggest looking for fresh flight holes. These will have a clean appearance inside the hole. It may take examining the holes with a magnifying lens. Sand like dust known as frass may also fall out of the flight holes when the wood is given a tap. So check your home and protect it from damage now before you fall through the floor.

Surveyor: "This house is a structurally unsound. I wonder what is keeping it from falling down.
Owner: "I think the woodworm (borer larvae) are holding hands."

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