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Timber - oak, or elm...

There is something so satisfying about living with 500 year old oak beams.  Historic timber just goes to show how resilient our old buildings are, if they are treated right.  Still there, after all those years.  There is a lot of hype out there about timber - the need to treat - to soak these venerated beams in a chemical soup.  Strange that - they have been ok for hundreds of years, and then all of a sudden, in the last 50 years, they are being attacked by every beastie known to man, and every fungus on the planet.  Do you get the feeling you are being scammed here?  Perhaps a bit of high pressure 21st Century salesmanship?

You got it.  The Damp Industry.  Most surveys from valuation surveyors working for the banks and building societies are STILL carrying on with the ridiculous practise of asking for a "Timber and Damp survey from a timber and damp contractor".

As a result of such surveys, it is inevitable that there is going to be a sales quote for spraying every available bit of timber with toxic chemistry, and probably injecting chemicals, removing plaster and so on.  You get the picture - its all a bit boring and predictable.

The fact is that most timber has been soaked in several generations of toxic chemistry anyway by now, and if it was going to preserve it, I think we would have seen the end of rot and beetle attack, once and for all.

The simple fact is this:  

  • Timber does not need, and never has needed, to be treated. 
  • Dry timber will not rot.
  • Dry timber will not be affected by beetle (or woodworm, as some know it).

BS 7913: 2013 - Guide to the Conservation of Historic Buildings - is very clear on this - it states quite clearly in Section 6.10 that chemical treatment is not needed, and the best approach is to keep timber dry.

Dr Brian Ridout, in his Historic England Guide, examines every decay mechanism known to timber.  It is a mammoth publication, by the acknowledged expert in his field.  In his summary to each section, the conclusion is always the same - dry timber will not be affected.

If anyone tries to make you have historic timber treated, you now have the tools with which to respond - No, it isn't needed, as stated in BS7913, and by Dr. Brian Ridout - in his Historic England publication. If you are confronted with a diagnosis that claims active infestation of anything, demand evidence.  Active infestation is rare, and usually only in areas which are predictably damp - under stairs, in cellars, or in very damp and humid loft spaces.  Spraying in such situations does nothing - chemicals only sit on the surface anyway, and usually the solution is to ventilate the under stairs cupboard, ventilate the cellar, and ventilate the loft space.  

So - what do we, as surveyors, look for - what do we see?

Elm is always one of my targets.  Not many people can tell the difference between oak and elm at first glance.  Elm has a finer grain, which has a fleck to it.  The main distinguishing feature is that elm nearly always has some form of beetle attack.  It will be right through the timber - beetle don't avoid the heart wood of elm, like they do oak.  So if you have a large beam, holding up your lounge ceiling, and it is riddled with beetle flight holes, it may well be elm.  Oak beams on the other hand will have plenty of holes, but usually only in the soft sapwood - the lighter coloured timber close to surface.  The dark brown heartwood of oak rarely sees any beetle.

Elm is also a very brittle timber - and we see many cases of elm beams snapping under load.  Often you can see fractures - sometimes only hairline, but they will be right through the timber.  Oak rarely if ever breaks in this way.  

This little video shows a rare discovery I made in a Somerset house - elm floorboards, adzed to make them fit tightly.  As historic building surveyors, we get to see a lot of things - but this is quite rare:

Cracked elm beam in timber framed cottage

Oak versus elm:

Two photos which clearly show the differences between these timbers.  The first, below, is oak.  You can clearly see darker heartwood, which has not been affected by beetle.  The lighter sapwood is peppered with small flight holes, from animals which were probably living under the bark when the tree was felled.  As it dried out, they would emerge.  The holes are probably 400 years old.  This particular property was surveyed by a valuation surveyor who noted these holes and insisted on chemical treatment of the timber.  Naturally this was not done.  This is, though, a good case study of the stupidity and lack of training that the majority of surveyors have when it comes to old buildings.

The lower photo is of an elm beam, and shows very typical 'all through' beetle attack that is commonplace.  These creatures left the timber many years ago, but the owner of this property was told to have chemical treatment of the timber. Again, it did not happen - but I think you will begin to see our frustration as historic building surveyors with the average uneducated surveyor, who has only been trained on modern houses. These people should not be allowed anywhere near old houses such as these - they simply do not understand the fabric.

Oak, showing dark heartwood, and ligher sapwood with associated beetle flight holes. Beetle probably left the timber 400 years ago.

Elm beam, showing the lighter wood, and beetle holes throughout the timber.  

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