Tag Archives: strength of timber

Timbers Checking In

One of our clients, Matt from Chapel Hill, NC, sent us a few photos showing a concern of “timber checking” to Justine, the Hansen Pole Buildings Productions Wizard (she loves it when I come up with interesting titles for what she does).

 Here is what Matt had to say:

“Been a while since we spoke.  First off, want to say we are very happy with our new barn.  Turned out great.  Going to be photographing it soon.  Attached a few pics in this email.

 I do have a concern I wanted to get your feedback on.  Many of the wood columns have pretty large cracks in them.  Not sure what is normal and what may be an issue.  We did do an interior buildout in the part of the barn.  Not sure if that created an excessive load or not.  But are also similar cracks in the barn area that doesn’t have buildout.

 Let me know what your engineer thinks.”

I live life for clients who are happy with their new buildings. There are lots of them, which makes life very rewarding.

What the client is seeing is called “checks”.  These are a separation of the wood normally occurring across or through the rings of annual growth and usually as a result of seasoning.

Checks occur because drying stresses exceed the tensile strength of the wood perpendicular to the grain, and they are caused by tension stresses which develop in the outer part, or shell, of timbers as they dry around the still wet and swollen core. Surface checks usually develop early in drying because the lumber surfaces dry too quickly as a result of low relative humidity.

In timbers, surface seasoning checks are not limited. Columns are subjected to primarily tension and compression loads, so surface seasoning checks have a negligible effect on all strength properties.

Matt’s post frame building happens to be a rather unique monitor barn, with a roof only side shed along one side and a partial loft. I’m looking forward to seeing the photos of the completed project, I hope you are as well.

Does Aged Lumber Get Stronger?

I’ll never be mistaken for either Jamie Hyneman or Adam Savage of the Discovery Channel’s popular and long running series MythBusters, however I can occasionally do some debunking of urban (and rural) legends.

I do have to admit, watching MythBusters can become addicting – especially when it can be tuned in on Netflix and watched commercial free episode after episode!

Getting onto some sort of relevant topic…..

APole Barn Framings a popular legend has it – sawn lumber grows stronger with age, supposedly even more so as it approaches its one hundredth anniversary of being milled from a log.

How could this aged lumber legend have begun?

Well, it may be more than just a legend. Old wood can, in fact, be significantly stronger than on the day it was first milled.

Huh? How could this happen?

It is not like the tree is going to grow any more – it is now a board, joist, plank or timber!

Because wood does gain strength as it loses moisture content. At around 12 percent moisture content, it might be as much as 50% stronger than as rough-cut green lumber!

Read more about green lumber vs. dry lumber here: https://www.hansenpolebuildings.com/2011/09/499green-lumber-vs-dry-lumber/

Aged lumber, unlike fine wine or whiskey, generally does not get better with age. As a rule, the mechanical (strength) properties of wood show little change over time.

Typically, age works against lumber the same way it works against our bodies – I know I am realistically not near as spry at 57 as I was in my 20’s!

Other than a reduction in moisture content, everything else works to weaken wood. Over decades there is more than a passing chance the lumber has been exposed to evil stuff which can significantly weaken structural wood.

This would include nasty insects, fungi (not “fun guy” like me), being excessively loaded (too much weight on it) or elevated temperatures (think of roof framing on the south side of buildings).

Want to go further? Test the strength of a sample of rough-cut green lumber for strength properties today, come back in a hundred years or so and retest. I’ll watch for your results!