ᐅ Wood pest inspection for old buildings: House longhorn beetle and woodworm

We are about to purchase a house built around the turn of the 20th century (1885-1915), and an inspector has identified pest infestation in the attic and on the cellar ceiling. Attic: softwood; cellar ceiling: oak beams.

Attic: moderate infestation of some rafters and purlins by the house longhorn beetle.
Cellar ceiling: sapwood area affected by the common furniture beetle. The beam ends are especially affected.
The report cannot completely rule out an active infestation, even though no traces of predatory insects hunting the larvae were found, nor any wood dust (frass). The report recommends using a splitting axe, hatchet, and chisel to remove the damaged wood. A severe deterioration of the beam ends is described, and all beams should be inspected. Reinforcement of the beams is advised.

On the other hand, a local pest control company’s offer states:
“Fresh feeding galleries and exit holes were found in the attic and ceiling beams. To prevent the infestation from spreading to the healthy wood, urgent treatment according to DIN 68800 Part 4 is recommended.”
Method: wood pressure injections with Adolit Anti Insect 0.02% permethrin.
Duration: 4 days. Estimated cost: about 5,000 euros.

Has anyone had experience with this type of infestation? Can anyone give advice on whether this treatment is worthwhile? We need to decide within the next few days if we want to buy the house and would greatly appreciate any help. If needed, I can provide more quotes from the inspection report and the offer. Thank you!

Here, I would rely more on the expert report and have the beams thoroughly inspected. Consult a carpenter who can examine each beam individually.

Advice from a distance is, in my opinion, unreliable; however, treating damaged beams does not improve their condition. A pest control specialist can certainly apply the appropriate treatments, but I doubt their ability to assess which woods are "healthy." Personally, I would not want to invest 5,000 euros with an uncertain outcome.

Of course, old houses have their charm, but also their challenges.

The decisive factor is the assessment of a neutral expert in wood and building protection, who can draft the measures as a plan but does not carry out these construction services themselves. The so-called "free" inspections/recommendations offered by companies that also happen to supply the appropriate treatment are, of course, not independent. In the case of the described infestation, it may be structurally necessary and more economical to replace the affected component rather than spending extensive effort to remove the infestation, reinforce the cross-section, or restore it. I do not support the recommended wood preservative chemical treatments because the infestation cannot be precisely located and thus cannot be accurately treated. Removing the infested areas is safer in this case. Nevertheless, the house longhorn beetle can still emerge again after 7-10 years with acute, unnoticed infestation, leading to a second round of damage.

The basement ceiling may need to be completely renewed if necessary. It is a "wear part" and is usually—also in oak—more or less eaten through by wood-boring beetles or heavily degraded in the area of the masonry supports/beam ends. If the house is a timber-framed building, the timber framing should also be inspected for infestation and decay.

With the described damage pattern, the overall condition of the property should of course be thoroughly examined before purchase, and the actual renovation costs should be estimated. If extensive repairs are unavoidable, the purchase is probably not worthwhile.

Hello and thank you very much for the detailed and helpful answers. In one of the basement rooms beneath the living room area, a steel beam has already been installed, which the real estate agents and owner referred to as an "anxiety beam." The report states that the structural integrity is not at risk. Now, of course, we wonder why components would need to be replaced if existing structures could be reinforced with steel beams, etc. The house is partially basemented, so the floor in the other area is not supported by a basement.

You say that removing the described areas is more sensible. In another forum, the hot air method was also mentioned as a very effective option. Do you have an opinion on this?

Hello,

Cut1977 schrieb:

You say that removing the described areas makes more sense.

We are a bit less formal here; our "language" is the informal "you."

Best regards, Bauexperte

The hot air method is very costly and is typically used for valuable historic and listed buildings. For private budgets, it is usually not a viable option. If the ceiling structure is already supported above the basement, it is no longer load-bearing and, as described earlier, usually needs to be completely replaced using different materials (steel beams, load-bearing ceilings, or steel trapezoidal profiles with concrete topping/screed, etc.). Installing new wooden beam ceilings in this situation is generally not recommended. The floors in areas without a basement will likely be rotted. For energy-efficient renovations, a completely new insulated floor construction against the ground must be planned and installed here.

All of this should be carefully considered before purchasing. Having inspected many such buildings, I am familiar with the typical damage patterns and the associated renovation effort. I advise caution and a very realistic assessment of the property.