Question 1

How do I calculate roof load?

Accepted Answer

Roof load is calculated by adding the dead load (permanent weight of the roof itself, including framing, sheathing, roofing material, insulation) to the larger of the live load (people, equipment) or the snow load for your region. The result is expressed in pounds per square foot (psf) or kilopascals (kPa). For most US residential roofs, total design load ranges from 30 to 80 psf depending on snow zone.

Question 2

What is dead load vs live load on a roof?

Accepted Answer

Dead load is the permanent, unchanging weight of the roof structure itself: rafters, sheathing, shingles, insulation, drywall, and any fixed equipment like solar panels. Live load is temporary and variable, including workers performing maintenance, equipment, snow, and wind. Building codes require the structure to support both, with snow load substituting for live load when greater.

Question 3

How much does an asphalt shingle roof weigh?

Accepted Answer

A standard 3-tab asphalt shingle roof weighs about 2.5 psf (pounds per square foot), or roughly 250 lbs per square (100 sq ft). Architectural / dimensional shingles weigh 3 to 4 psf. For a 2,000 sq ft roof, that totals 5,000 to 8,000 lbs of shingles alone, before adding underlayment, deck, and framing.

Question 4

What is the snow load for my area?

Accepted Answer

Ground snow load varies by region. Southern US is typically 0 to 10 psf, mid-Atlantic 15 to 25 psf, New England and the Upper Midwest 30 to 60 psf, and mountain regions can exceed 100 psf. Always check your local building department or the ASCE 7 Hazard Tool for the exact ground snow load for your address. Roof snow load is typically 0.7 times the ground snow load for unobstructed slopes.

Question 5

Can my existing roof support solar panels?

Accepted Answer

Solar panels add about 3 to 5 psf to the dead load (panels plus mounting racking). Most modern residential roofs built to current code can handle this without reinforcement, but always have a structural engineer review the framing before installation. Older roofs (pre-1990s), roofs already at high snow load, or roofs with damaged framing may need reinforcement.

Question 6

What if my roof load exceeds the recommended capacity?

Accepted Answer

If calculated total load exceeds your roof's capacity, options include: switching to lighter roofing material (asphalt or metal instead of tile or slate), removing snow promptly in heavy snow zones, reinforcing rafters with sister boards, or adding intermediate support beams. For loads above 50 psf or any structural concerns, hire a licensed structural engineer rather than guessing. Roof collapse is a life-safety issue.

Component	Weight (psf)	Weight (kg/m2)
Asphalt shingles	2 - 3	10 - 15
Metal panel roofing	1 - 2	5 - 10
Concrete tile	9 - 11	44 - 54
Slate	9 - 12	44 - 59
1/2" plywood deck	1.5	7
Solar PV array + racking	3 - 5	15 - 25

Roof Load Calculator

Roof Area

Roofing Material

Roof Deck Material

Snow Load Zone

Additional Loads

Load Breakdown

How to Calculate Roof Load

Total Load Formula

Common Dead Load Weights

When You Need a Structural Engineer

Frequently Asked Questions