I saw a catastrophic failure waiting to happen during a drive through New Brunswick a few days ago (September 26, 2020). A barn roof that was sagging a good 10 feet in the middle. For sure, a barn that was no longer in use because of the risk.
Of course I added it to the list of failures I posted last July 23 that are everywhere in the built environment. (Ref. 1)
It was the magnitude of the sagging ridge that caught my eye. Even at a distance it was easy to imagine, maybe just see the bulging eaves. The eaves of a roof bulge out when the ridge sags.
You see lots of large and small buildings in the country with roofs that are sagging a little or a lot. Many are abandoned, but not all. And some are only a few years old, not gray with age and many decades old.
You can also see buildings in town – houses, for example – with sagging ridges. A tiny sag, a few inches at most, just enough to catch your eye from the street.
The large sags are probably due to inadequate design of the roof trusses or the rafters. Many of the tiny sags are design failures too.
But some tiny sags are due to green lumber shrinking as it drys after construction is complete. This is a planning failure because less suitable green lumber was accepted for building design and construction.
Reference
- You could be excused for thinking that everything is falling down. Posted July 23, 2020 (Scroll to July on the right of the blog page and see Item 9 in Section C. Large and Catastrophic Failures)
(Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia. ejorden@eastlink.ca)