Snow Guard / Retention Row Layout
The other side of sliding snow: keeping it on the roof instead of catching it below.
Example
You enter
- Design roof snow load (psf) 40
- Roof pitch (rise per 12) 4
- Rafter / slope length, eave to ridge (ft) 30
- Eave length to protect (ft) 40
- Guard tested holding capacity (lb each) 500
- Safety factor 2
- Rows of guards 1
You get
- Slope (deg) 18.4349
- Vector (psf) 12.6491
- Force (plf) 379.473
- Guards per ft 1.51789
- Spacing (in) 7.90569
- Guards per row 61
- Guards total 61
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method.
Details, formula, and sources
ScopeVector force = snow load x sin(roof angle), times the rafter length above the row; guards per foot = force x safety factor / the guard's TESTED capacity. 40 psf on a 4:12 with a 30-ft rafter pushes 379 lb per foot of eave - 61 guards at 7.9 in on center over a 40-ft eave with 500-lb clamps at a 2.0 factor. No capacity is shipped: it must come from the manufacturer's test data for your exact panel and seam.
Formula or tablevector force (psf) = roof snow load x sin(roof angle); force per ft of eave = vector force x rafter (slope) length; guards per ft = force x safety factor / tested guard capacity; spacing = 12 / guards per ft.
Source and editionManufacturer snow-retention design method (roof snow x sine of the roof angle, times rafter length and tributary width), by name - not a code section.
Free accessThe method is published across independent snow-retention design references and manufacturer design guides.
What governsEstimate. AHJ and licensed professional govern.
API field namesroof_snow_psf, pitch_rise_per_12, rafter_length_ft, eave_length_ft, guard_capacity_lb, safety_factor, rows, slope_deg, vector_psf, force_plf, guards_per_ft, spacing_in, guards_per_row, guards_total
- Vector force snow load x sin(roof angle); the cosine component is carried by the roof, not the guardsmanufacturer snow-retention method
- Capacity is an input no holding capacity shipped; use tested data for the exact panel, seam, and attachmentmanufacturer test data
- Slope length, stated rafter length used per the manufacturer method, conservative vs the horizontal projection by 1/cos(theta)stated conservatism