There are many things in life that will sag as the years pass. I for one am not concerned about such things. That said, it is not uncommon these days to hear of people paying big dollars to reverse this common side-affect of age.

Well put, Thane!

Jim

This made my day. Thanks Thane!


Too bad acupuncture and meditation do not work on old structures...

Sounds like in the end it's a balance between how much risk versus cost versus desire to preserve. Who owns it? Who would be liable if something were to happen? Because if it can be shown that the risks were considered, and a decision was made to retain the status quo, and something failed and hurt someone, who is starring down the barrel? What is the risk? Is there insurance? Has the building been insured? Can it be? Maybe not if the insurance company's engineer says it's deficient. You and I might decide to retain the status quo, but it would seem to depend on who is liable to make that decision, eh? It's seems more in the realm of perceived integrity by an insurer, with an engineer who may or may not be familiar with timber framing, and may or may not be overly conservative. I'd use my own judgment to an extent. If strength improvements can be made without being readily visible where they'd detract aesthetically, I'd then probably try to work with the proper engineer to make some improvements in order to get the proper insurance. Take what I say with a grain of salt as I am just being an armchair quarterback and am not an "expert". I'm just hoping to give some ideas to think about.

Jim, even without seeing it I believe it is fine. You have looked at it and I know your character, somewhat, and it leads me to trust your judgement.

I don't think it is broken, it has a clear track record, let it stand, as is.

Perhaps the process Jim is leading the building through is a form of acupuncture and meditation. Keep it out of the hospital and away from the doctors. Has the building been checked with picks to test for rot?

Tim

Thanks guys;

Does anyone have an opinion about how much sag (deflection) is acceptable in an old building?

Jim

Just my opinion but I don't think sag of any amount has any (zero) effect on the strength of a piece of wood.
Whether the sag/warp/bend took place over a hundred years of hot, cold, humid, again and again... or a few hours in a steamer then bent into a shape by a skilled hand. The worst thing you could do is to try and straighten them after it took 100 years to make them the way they are now.

Hi Jim & Thane,

As sag deformation increases then a rafter will be subject not only to axial forces but will also be subject to bending due to the sag offset. This type of creep can be progresive and might eventually result in buckling of the component concerned.

I think that quantitative measurement and calculation will help demonstrate the suitability or otherwise of the deformed rafters.

Regards

Ken Hume

Regards

Ken Hume

Ken,
Are you theorizing or have you seen this happen in the real world. I have seen a lot of really saggy rafters but none that have failed as a result of this.
Jim,
The roof is not going to collapse tomorrow or next year but to make some people feel better, maybe an annual inspection where the sage could be measured and recorded would be warranted.

Hi Thane,

I have seen plenty of progressive roof collapses which have been the result of all sorts of failure mechanisms though generally it takes a combination of effects to be at work in order to to give rise to catastrophic failure.

What is really important for the long term survival of a roof is that secondary load paths are available to allow for load shedding and sharing. This will help prevent a localised failure of an individual component from progressing to become a disproportionate failure.

Its also worth keeping in mind that most rafters will contain defects such as knots and these are more likely to be the cause or focal point for the start of a localised failure.

I have taken some shots of roof, rafter, crown post and purlin failures and I will try and look some of these out to post.

Regards

Ken Hume