What to do with woodworm affected joists

[Van Bergan]

Working my way through my victorian renovation I have discover a couple of isolated 1st floor joists have been extensively attack by woodworm.
These particular joists appear to be a hewn face and a sawn face and interestingly the woodworm flight holes are always on the hewn face.

Photo below show the original face with flight holes. 1mm to 2mm of this surface can be easily scrape away.
Beneath that top surface the timber is reasonably solid, although peppered with horizontal burrows.
I chiselled a section in the centre of the joist which shows that the burrows seemingly only penetrate the timber to ~8mm deep from the original surface.



As the flight holes are on the surface and the horizontal burrows beneath, the joist must have been infested after it was sawn, but before it was installed as the house has not suffered damp.

The damage appears to be surficial and the joist is sufficiently strong to provide support as required.
I am wondering what action, if any I should take?
Perhaps I can just leave the joists as they are. Should I even bother to scrape of the frivolous surface timber, treat the joist with 5 star preserver,etc.

 

[Cubist]

What are the width and depth dimensions (length not required) and wood species are these joists? Also, are these joists located above or below a kitchen or bathroom?

 

[Van Bergan]

What are the width and depth dimensions (length not required) and wood species are these joists? Also, are these joists located above or below a kitchen or bathroom?

They are ~220mm x 45mm. For addition context the span is ~4.70m and they are installed at ~350mm c/c so just about conform to modern permissible spans.

I imagine they are pine or some type of soft/red wood.
Sitting room below and bedroom above so not particular high moisture level areas.

There are three affected joist in this particular room.
I could sister joists relatively easily but I feel it's borderline if necessary.

 

[Matt Green]

The outer, sapwood section, of the tree has been hewn, then the core sawn into smaller section timbers:



Furniture beetle and Powderpost beetle eat sapwood, which is high in nitrogen and can't eat the heartwood unless it gets wet and the chemicals that confer its durability wash out.

There is no treatment required here:



-Matt

Images sourced from here

 

[Van Bergan]

@Matt Green yes agreed, I imagine the beetles are long gone.
These timbers once fashioned as boards could have been sitting in a wet yard for years before they were installed in the house.

I suppose I just have to make a judgement whether I fell sistering them is necessary or if I can leave them as they are.

It seems likely that they were infested prior to installation.
I'm a carpenter myself and find it interesting to wonder if the woodworm was visible to the carpenters who installed them and they just installed them regardless.

 

[Matt Green]

With timberyard pests like Powderpost beetles, the exit holes would have appeared in the year after the timber was put into service. With furniture beetles it could have been up to 5 years after- it would depend on how long it was stored before use.

I'm trying to give the carpenters of the day the benefit of the doubt that there may not have been any visible flight holes.


Matt

 

[Van Bergan]

With timberyard pests like Powderpost beetles, the exit holes would have appeared in the year after the timber was put into service. With furniture beetles it could have been up to 5 years after- it would depend on how long it was stored before use.

I'm trying to give the carpenters of the day the benefit of the doubt that there may not have been any visible flight holes.


Matt

Thanks for the info.
Would I be right in thinking that with a hewn face having more crevasses and cracks (vs a sawn face) the beetle prefers to lay it eggs on that face and hence the sawn face escapes the attack relatively better?

 

[Matt Green]

The sawn faces are predominantly heartwood; the hewn faces are more likely to have sapwood on them. Otherwise, yes, you are right, female wood-boring beetles generally tend to prefer to lay eggs under the surface for protection and a rougher surface gives them more opportunity for that.

 

[Cubist]

The thought going through my mind was how much of the load bearing capacity may have been lost to the wood munchers. Circa 30% may be a wild exaggeration but if those joists are going to hidden behind a ceiling for donkeys years and a potential future PITA to get at I think I'd give them a coat of permethrin.... and maybe sister them, if I was also considering investing in a water-bed.