A Garage Inspection

 I was asked to examine a townhouse. During the examination, I ran into a neighbor who informed me that the roof of another garage, 2 buildings down, had actually collapsed the previous winter under a snow load.

So, I chose to keep my eyes large open as I went through the garage.

Above: trusses and truss connections

Some flaws you have to look for, and some are very apparent. These first two defects were apparent from the doorway:

inappropriate alterations; and
incorrect bearing points.

Trusses can not be altered in any way without the approval of a structural engineer. When you see plywood gussets added at truss connections like these triangular gussets, then an alteration of some sort has actually obviously been made and you need to recommend examination by a structural engineer. So, that condition entered into the report

Trusses are designed to bear loads at extremely specific points. Normal roof trusses must not touch any interior walls and must bear only on the exterior walls. The two trusses at the left of the above photo are bearing upon an offset portion of the garage wall.
A portion of the structural roofing load was being moved down chords of the trusses at a point at which they were not designed to support a load.

Above: the connection

I walked over and looked more carefully at the connections where the trusses attached to the wall and found these issues:

inadequate metal adapter (hanger);.
insufficient fasteners (deck screws); and.
inappropriate fastener setup (through drywall).

These trusses would have best been supported by bearing directly on wall framing. The next best option would be an engineer-designed ledger or engineer-specified hardware. Which may have been how they were initially developed, however by the time I inspected them, 24-foot roofing system trusses were supported by joist hangers developed to support 2x4 joists. The hangers were attached with four gold deck screws each.

Gold deck screws are developed to withstand withdrawal. Fasteners for metal connecters such as joist hangers are designed to withstand shear.

Withdrawal force resembles the force which would be produced if you got hold of the head of a fastener with pliers and tried to pull it straight out.

Shear force is what's utilized if you take a pair of heavy-duty wire cutters and cut the fastener. Fasteners created to resist withdrawal, such as deck screws, are weak in shear resistance.

So, there were considerably undersized metal adapters secured by badly under-strength fasteners.

To make matters worse, the screws were attached through drywall, which does not support the shaft of the screw and breaks down the connection even additionally.

And, as soon as I looked really carefully, I found more truss modifications. The gangnail had actually been pried loose and the spikes which form the real mechanical connection were damaged. In their location were a few bent-over nails. This condition represented a great loss of strength and this roofing system, too, was a candidate for devastating structural failure.

In summary, look carefully at connections for issues which might lead to structural issues, as some are more immediate than others. Be sure to call these out in your report. Also, all electrical receptacles in garages have to be GFCI-protected, without exception.


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