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BuyRoof Snow Load Calculator
ASCE 7-16 balanced roof snow load from mapped ground snow — pf = 0.7 Ce Ct Is pg, then slope factor Cs. Planning estimate, not a stamp.
This is structural load, not a shingle takeoff. Look up pg for the site, then convert it. Rafters and beams that have to carry this: joist span calculator and deck beam span calculator. Pitch from framing: rafter length calculator. How to find pg: guide. Sag vs creep: troubleshooting. Why ground ≠ roof: comparison. Roofing index: roofing calculators hub.
Calculator Inputs
Ground snow load from your jurisdiction, then exposure, thermal condition, occupancy, pitch, and surface. ASCE 7-16: pf = 0.7 Ce Ct Is pg, then ps = Cs pf. Not a whole-roof square count and not a span table.
Read this before you treat the result as the answer. Output is a balanced-load planning estimate. Look up pg for the site. Hire a licensed engineer for drifting, unusual roofs, or anything that will be built.
There is no universal default. Get pg from the local building department (IRC Table R301.2 climatic criteria), the permit, or the free ASCE 7 Hazard Tool for the adopted edition. Case-study mountain zones need a site-specific value. Do not paste a city-average rumor. This field is empty on purpose.
Same X/12 as the rafter calculator. Slope angle α = arctan(X/12). Steeper roofs shed: Cs stays 1.0 until a thermal/surface breakpoint, then falls to 0 at 70° (ASCE 7-16 Figure 7.4-1).
Assumed suburban roughness B (typical house). Partially exposed is the usual residential default. Fully exposed = no shelter from terrain, taller structures, or trees. Sheltered = tight in among winter-obstructing conifers. Open/coastal (C/D) can be slightly lower when fully exposed; this tool does not undercut B.
Heated = ordinary occupied house. Cold ventilated = kept just above freezing, or a cold roof with R > 25 between the vented space and the heat. Unheated / open-air = barn, carport, unconditioned garage. Freezer buildings (1.3) and greenhouse reductions (0.85) are out of this dropdown on purpose.
Risk Category II (Is = 1.00) is a typical house. Do not drop to RC I to shave load. ASCE 7-22 removed Is from pf and uses separate strength-level maps per risk category — do not mix a 7-22 Hazard Tool pg with this 7-16 formula.
Default is not slippery: shingles, and any roof that cannot freely slide at the eave (gutters, snow guards, dormers). Unobstructed slippery is a warm or cold metal roof that can actually dump snow — do not pick it to lower the number on a shingle roof.
Results
Starting point from ASCE 7-16 balanced-load equations. Confirm local mapped pg, adopted edition, and — for anything that will be built — a licensed engineer. Do not treat this as a final structural answer.
Governing balanced roof snow load
—
Enter ground snow load and pitch
Ground snow pg—
Flat roof pf—
Sloped roof ps—
Governing balanced—
Exposure Ce—
Thermal Ct—
Importance Is—
Slope factor Cs—
Roof slope α—
CodeASCE 7-16 §7.3\u20137.4
ASCE 7-16 §7.3 / Eq. 7.3-1: pf = 0.7 Ce Ct Is pg. Eq. 7.4-1: ps = Cs pf, applied on the horizontal projection. Cs from Figure 7.4-1 (linearized between α0 and 70°). §7.3.4 minimum pm for slope \u2264 15°. Ce from Table 7.3-1 roughness B; Ct from Table 7.3-2; Is from Table 1.5-2. Not included: drifting, unbalanced, sliding, rain-on-snow, partial loading. ASCE 7-22 uses risk-category maps and drops Is from pf — do not mix editions. IRC Table R301.2 is where most houses get pg. How to look it up: guide. Sag and cracking: troubleshooting. Why pg \u2260 ps: comparison. Span tables that still assume 40 psf live: joist span, deck beam span.
How to Use This Roof Snow Load Calculator
Look up ground snow load pg for the site. Enter it. Leave exposure on partially exposed and thermal on heated unless the roof is actually sheltered or unheated. Keep Risk Category II for a house. Type pitch as X/12. The tool builds the flat-roof load, applies the slope factor, then (on low slopes) checks the code minimum.
pf = 0.7 × Ce × Ct × Is × pg (ASCE 7-16 Eq. 7.3-1)
ps = Cs × pf (Eq. 7.4-1, horizontal projection)
Cs = 1.0 for α \u2264 α0, then linear to 0 at 70° (Figure 7.4-1)
if α \u2264 15°: governing = max(ps, pm)
ps = Cs × pf (Eq. 7.4-1, horizontal projection)
Cs = 1.0 for α \u2264 α0, then linear to 0 at 70° (Figure 7.4-1)
if α \u2264 15°: governing = max(ps, pm)
This is a load in psf, not a span. Take it as context to the joist span calculator and deck beam span calculator — those IRC tables are 40 psf live, not this snow number. Where to find pg: guide. Sag vs creep: troubleshooting. Why you must not use pg as the roof load: comparison.
What This Number Is (and Is Not)
The headline is the balanced design snow load on the roof, in pounds per square foot on the horizontal projection. It is not the ground snow load, not a rafter size, and not permission to skip an engineer in snow country.
Assumptions baked into every result
ASCE 7-16 service-level pg with Is. Ce from Table 7.3-1 roughness B only. Ct is one of 1.0 / 1.1 / 1.2. Cs is the linearized Figure 7.4-1 curve (not a scanned graph). One pitch, one exposure, one thermal condition. No drifting, no unbalanced gable, no sliding from an upper roof, no rain-on-snow surcharge, no parapets, no sawtooth. ASCE 7-22 maps are a different pg and a different equation.
A 40 psf joist table is not this load.IRC deck/floor span tables in the joist and beam tools assume 40 psf live / 10 psf dead. Snow-country deck beam rows are R507.5(2)–(4). Convert snow here, then do not pretend the 40 psf cell still applies.
When this tool is the wrong tool
Shingle squares belong in the roofing square calculator. Ice-barrier width belongs in the ice & water shield coverage calculator. Attic NFA belongs in the attic ventilation calculator. Common rafter length belongs in the rafter calculator.
Need a span, not a psf?Joist and beam tables are a different job. This number is an input to that conversation, not the span itself.
Open Joist Span Calculator →Any trade
Checkout opens here — you stay on this page.
Snow-Load Gear
The calculator returns a balanced roof snow load in psf. A roof rake is how you take snow off an existing deck from the ground. CSV rows 400–412 were nailers, vents, gutters, and ice barrier — not snow-removal tools — so these two SKUs are new.
Goplus 21 ft Aluminum Snow Roof Rake
21 ft extendable aluminum rake with wheels and oxford slide. Size the balanced roof snow load first; this is how you take snow off the deck from the ground — not a substitute for an engineer.
View on Amazon →
Garelick 89421 21-Foot Aluminum Snow Roof Rake
24 in blade with shingle-saver rollers so the edge never rides the asphalt. Relieving weight is not the same as designing for it — run the snow-load number before you argue with a sagging ridge.
View on Amazon →
Run the Balanced Snow Load
Look up pg, then Ce, Ct, Is, and pitch. Flat-roof pf, slope factor Cs, governing psf. Planning estimate only.
Open Roof Snow Load Calculator →
Joists Under That Load
IRC joist tables assume 40 psf live. A roof or covered deck in snow country is a different load path — size the snow first.
Open Joist Span Calculator →
Beams in Snow Country
Table R507.5(1) is 40/10. Tables R507.5(2)–(4) are snow rows this tool does not replace. Convert pg to roof snow, then talk to the table or an engineer.
Open Deck Beam Span Calculator →As an Amazon Associate, TestTalkHQ earns from qualifying purchases.