Design Documents

The tables are intended as a practical tool to assist contractors in the selection of footing widths and the determination of the quantity of wood studs required for supporting the end reactions of beams, girders, and/or headers. 

We have been specifying laminated veneer lumber (LVL) beams for some time now. The plans usually state, “Beam to be engineered and supplied by truss manufacturer.” What kind of liability issues do I need to watch out for?

I am thinking of using wood trusses for the roofing/ceiling structural systems on some houses I shall build. I remember, though, an engineer/volunteer fireman commenting back in 1989 that the connector plates are prone to expand and pop off, early on in a fire, causing catastrophic structural failure. Was this the case, and if so, has this problem been corrected?

Can I safely install 3/4 in. T&G, OSB on 2x4 trusses that are 24 in. O.C.? My roof was installed over 5/8 in. plywood without clips that have caused a lot of sagging and the shingles need replacing. I want to “fix” it one time and install architecture type shingles, but the garage is 24 ft. wide and 28 ft. long without any load bearing walls. My concern is the weight on the trusses. 5/8 in. plywood weighs 52 lbs. and the OSB weighs 78 lbs. for each 4 ft. x 8 ft. sheet. The roof will require about 84 4 ft. x 8 ft. sheets to cover, which equals about 2,184 lbs.

Is a Class A fire rating (provided by our liquid spray-on fire retardant) acceptable in certain situations?

I am looking for information on point loading trusses. We manufacture mounting structures for solar panels. Typically, 10 to 15 sq. ft. of solar panel is supported by one standoff. Under extreme conditions – 50 lbs. per sq. ft. of wind load - we can transfer 500 to 750 lbs. of force onto one point of one truss. Are there any standards on this issue?

What are the requirements on the permanent bracing of bottom chords? Can gypsum board diaphragms be used?

As an engineer, I have noticed truss designers in some high wind states routinely using “Main Wind-Force Resisting Systems” wind pressure coefficients as opposed to “Components and Cladding” coefficients to design for wind uplift. A roof truss is not a main wind-force resisting system and would have to have a tributary area of more than 1000 sq. ft. before qualifying for the lower Primary Frame coefficients. In my experience this practice is routine.

We are planning to add 1/2 in. cement board and 3/8 in. quarry tile to a kitchen floor. We need to know if the floor trusses will handle the additional weight. The floor trusses are 19.2 in. O.C. and the loading numbers are 40-10-0-5. What do these numbers mean?

What type of construction uses a fire cut truss? Could you describe a fire cut truss?