The missing piece. Metal Plate Connected Wood Trusses. Cle Elum Home Inspections
It is very important when during a home inspection to try to traverse the attic space if possible, and it is require by Washington State Home Inspection Standards when we are able to do so. But often this is very difficult in truss design roof structures. With a 4:12 pitch or less and blown in insulation often it is not really possible to fully traverse the attic space or get much past the access hatch.
So on a recent home inspection I can across a situation. We had a HVAC air handler installed in the attic space. This is nice because I get a platform to view the attic from. To install air handler, whomever the installer was, had to cut a truss to install the unit. The number one rule with “Trusses” is that they are not be cut, notched, drilled, spliced or altered without proper approval to do so. Well I am pretty darn sure that did not happen.
Something is missing
What gets complicated is that most modern trusses are metal plate connected (MPC) wood trusses. Trusses are designed for specific design criteria on proprietary software packages by the plate manufacturer. So when you order your truss package you will provide the truss manufacturer information; Live and dead loads, snow loads, wind speed, roof design (slope and heel height), bearing points etc… This also includes any unusually items such as a concrete roof, attic space or equipment in the attic so the truss system has to be designed to handle all the loads and design features.
The Missing Piece
So the question is, was this truss system designed to have even have an Air Handler in the attic and can the truss system handle this additional loading? You would need to know what the original design analysis was that determines the axial, shear and bending forces of a given area of the truss design.
If you can find the truss manufacturer stamp (typically on the bottom cord) that will be the easiest path to pursue. If that information is not found then an engineer/registered design professional will be needed to design a repair.
From the 2012 Residential code on truss alterations-
R802.10.4 Alterations to trusses.
Truss members shall not be cut, notched, drilled, spliced or otherwise altered in any way without the approval of a registered design professional. Alterations resulting in the addition of load (e.g., HVAC equipment, water heater) that exceeds the design load for the truss shall not be permitted without verification that the truss is capable of supporting such additional loading.
So any time a truss is damaged or has been modified an engineer/registered design professional or truss manufacturer will be needed to design a repair
“If you think it's expensive to hire a professional to do the job, wait until you hire an amateur.”
Red Adair
NCW Home Inspections, LLC is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…
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Instructor- Fundamentals of Home Inspection- Bellingham Technical College
www.ncwhomeinspections.com 509-670-9572
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