5/16" x 4" Stainless Steel Lag Bolt

Stainless steel lag bolts are used to fasten L-feet to the roof structure. The length and diameter of the bolt depends on the pull-out strength needed, and the thickness of the non-structural material (shingles & sheeting) being passed through.

Because lag bolt requirements vary with design wind load and lumber used for the roof trusses, lag bolts are no longer provided with SolarMount L feet.

The table below (reproduced from Unirac's Technical Bulletin 103: Code Compliant SolarMount Installation) lists pull-out values for various roof truss lumber and lag screws. To ensure code compliance, the lag pull-out value must exceed the installation's design live load per footing multiplied by an appropriate safety factor.

Stainless steel lag bolts

Lag Pull-Out Values (lbs) in Typical Roof Truss Lumber
		Lag Screw Specifications
	Specific	5/16" Shaft	5/16" Shaft	3/8" Shaft
	Gravity	2 1/2" Thread Depth	per 1" Thread Depth	per 1" Thread Depth
Douglas Fir — Larch	0.50	665	266	304
Douglas Fir — South	0.46	588	235	269
Engelmann Spruce, Lodgepole Pine	0.46	588	235	269
(MSR 1650 f & higher)	0.46	588	235	269
Hem — Fir	0.43	530	212	243
Hem — Fir (North)	0.46	588	235	269
Southern Pine	0.55	768	307	352
Spruce, Pine, Fir	0.42	513	205	235
Spruce, Pine, Fir	0.50	665	266	304
(E of 2 million psi and higher
grades of MSR and MEL)
Sources: Uniform Building Code; American Wood Council.

The table below (reproduced from Unirac's SolarMount Canadian Code Compliant Installation Manual) lists lag bolt withdrawl resistance for some commonly available wood species in Ontario.

Lag Bolt Withdrawal Resistance
Wood Species	5/16” Ø Lag Screw Specifications
Wood Species	Factored Withdrawal Resistance (kN/mm x 103)
D.Fir-L	58.2
Hem-Fir	32.1
S-P-F	27.6
Northern	25.5

Popular Products