We know that trusses are not supposed to be altered, but I’m wondering about reinforcement. It doesn’t seem like reinforcement would put improper loads on the trusses, but typically they’re being reinforced because someone intends to load them, probably use them for storage.
So… is the defect the reinforcement, or is it the reason for the reinforcement: the intent to load the trusses in a manner for which they were not designed.
So I see required flooring added to roof trusses for mechanical equipment such as HVAC. Is mechanical and live loads taken into consideration when the design professional draws the plans?
Does expanding the floored areas for storage have other ramifications such as fire protection? I think it does.
More questions than answers for me.
“Reinforcing” them, without a SE seal, IS altering them, IMHO.
And therein lies the problem… someone is “reinforcing” the trusses… but WHO is engineering the reinforcement? Just because someone THINKS they know what they are doing, doesn’t mean they actually do… thus the Truss Engineer’s Certification!!
How could reinforcing trusses compromise their structural integrity?
It is common sense that reinforcing trusses help them work as one for added strength.
You would need to ask a Truss Engineer that question, but make sure you have all the homes specs so he/she could make the necessary calculations to make such a determination.
Both, unless the load and reinforcement was designed by the truss company or a structural engineer. What came first the chicken or the egg? A person adding load to the truss without without a P.E. license is improper by itself, then adding reinforcing to the truss, which can change the load distribution in the truss is improper without the P.E. license.
Thanks Randy! I was hoping you’d chip in here!
From what I understand the bottom chords aren’t designed to hold more than the weight of the ceiling materials and insulation.
As for HVAC, again from what I’ve been taught is that they must not be installed with weight on the bottom chords but instead should be suspended from above.
But as with everything truss related, an SE would need to make the final call.
That makes sense, however I have never see it done in a residential application. When I have time, I will go down that rabbit hole and see what information is available.
In some states it is “standard operating procedure” like AZ for example. They don’t get much snow in Phoenix. In northern states, the trusses would have to be disigned differently for the additional load. Just food for thought. I haven’t seen any HVAC equipment in attics locally but then I’m someday I am sure I will…
Bottom chords are typically designed for 10 psf. Drywall and insulation takes up most of that. Any unusual loads on the truss should be given to the truss company, which can easily account for that in the design. The Truss Plate Institute (TPI) manual is the truss design manual. The TPI manual relies on the “Building Designer/Engineer" for that information. The TPI manual list the following responsibilities:
Building Designer/Engineer - a design professional, individual or organization, having responsibility for overall building design. Within the scope of wood trusses, the building designer / engineer, shall specify the following:
(a) Design loads in accordance with various sections of the National and / or Provincial Building
Codes.
(b) Truss profile and intended support locations.
(c) Vertical and horizontal deflection limits.
(d) Moisture environment for intended end use.
(e) Any special requirements to be considered in the truss design.
(f) Additional loads from mechanical, electrical units, which may induce extra load to various truss
members and their locations. As this standard does not cover the design for the complete structural system of a building, the building designer / engineer shall provide the following in the design and detailing of the building:
(a) Truss supports and anchorage accommodating horizontal, vertical or other reaction or
displacement.
(b) Permanent truss bracing to resist wind, seismic and any other lateral forces acting parallel or
perpendicular to the plane of trusses.
(c) Method of connection or anchorage of mechanical, electrical units to various truss members.
IMO here is the reason for most truss problems. The truss company relies in this mysterious Building Designer/Engineer to give them the information they need to design the truss and to ensure the tie down and bracing system is in place. But in reality the building contractor orders the trusses directly and doesn’t know or care where the HVAC is going. The contractor doesn’t typically know how to read truss plans, so he/she doesn’t know the standard hurricane clips may not be adequate for all trusses within the roof framing system. The contractor probably doesn’t know some girder trusses need additional support all the way down to the foundation. The contractor doesn’t know the truss designer may have relied on and interior wall for support on long truss spans. Some body needs to get the truss designer, contractor, homeowner, engineer and home inspector in one room and hash this out. Everyone thinks someone else is taking care of the details.
Truss calcs I get will usually indicate lightweight storage or similar, if trusses were altered to accommodate additional weight or loads without design by qualified persons, that’d be wrong.
Well said!