How much weight can my roof support?

Most residential roofs are designed to support 20 PSF (pounds per square foot) of live load plus dead load. Standard stick-frame roofs support 15-25 PSF live load, engineered trusses 20-30 PSF, and heavy-duty structures 30-40 PSF. Total capacity includes dead load (roofing materials, decking, structure) plus live load (snow, maintenance workers, equipment). Always consult a structural engineer before adding significant weight.

How do I calculate snow load on my roof?

Snow load is calculated using: Ground Snow Load × Roof Factor × Safety Factor. Fresh snow weighs about 5 PSF per foot of depth, packed snow 15-20 PSF, and ice 57 PSF per inch. For flat roofs, multiply ground snow load by 0.7. For pitched roofs, multiply by a slope factor (lower for steeper pitches). Your snow load zone determines base ground snow load: Zone 1 (Southern US) = 5 PSF, Zone 4 (Great Lakes) = 50 PSF, Zone 7 (Extreme) = 100 PSF.

Can my roof support solar panels?

Most roofs can support solar panels if they are in good structural condition. Standard solar panels weigh 2.5-4 PSF (about 40 lbs per 17.5 sq ft panel). A typical 6kW system adds about 3 PSF distributed load. Your roof needs adequate remaining capacity after accounting for dead load (materials) and expected live loads (snow, maintenance). Roofs over 15-20 years old or with existing damage should be inspected by a structural engineer.

What is dead load vs live load on a roof?

Dead load is the permanent weight of the roof structure itself: decking (1-4 PSF), roofing material (2-15 PSF), insulation, and framing. Live load is temporary or variable weight: snow, rain, maintenance workers, and equipment. Building codes require roofs to support both simultaneously. Typical residential codes require 20 PSF live load capacity minimum, plus all dead loads.

What is the snow load in my area?

Snow load varies dramatically by region. Myrtle Beach, SC (Zone 1) has minimal 5 PSF ground snow load. The Mid-Atlantic averages 20 PSF, Northeast 40 PSF, Great Lakes 50 PSF, and mountain regions 60-100+ PSF. Local building codes specify exact requirements. For coastal SC, wind load is typically more critical than snow load, but both must be considered for structural calculations.

How much does roofing material weigh?

Roofing material weights vary significantly: 3-tab asphalt shingles (2.0 PSF), architectural shingles (2.5 PSF), metal roofing (1.5 PSF), wood shakes (3.5 PSF), clay tiles (9.5 PSF), concrete tiles (12 PSF), and slate (15 PSF). When re-roofing, ensure your structure can handle the new material weight. Upgrading from asphalt to slate adds 12+ PSF - often requiring structural reinforcement.

Can I put an HVAC unit on my roof?

Rooftop HVAC installation requires careful load analysis. A medium 4-5 ton unit weighs 300-400 lbs concentrated on about 25 sq ft (12-16 PSF point load). Large commercial units can exceed 800 lbs. The roof must support this concentrated load plus vibration and service access (workers + equipment). Most residential roofs need reinforcement for rooftop HVAC. Always get a structural engineer evaluation.

What is a safe roof load safety factor?

A safety factor of 1.5-2.0 is standard for roof load calculations. This means if your total calculated load is 30 PSF, your roof should be rated for 45-60 PSF. Safety factors account for unexpected loads (heavy snow events, multiple workers), material degradation over time, and calculation uncertainties. Using 70% or less of rated capacity is considered safe; 70-85% requires monitoring; above 85% needs immediate evaluation.

Roof Load Calculator

Calculate snow load, dead load, equipment load, and total roof capacity. Free tool for homeowners and contractors.

Snow Load by ZoneSolar Panel WeightHVAC EquipmentSafety Analysis

Calculate Load Type

1Roof Information

Roof Area (sq ft)

Roof Pitch

Roofing Material

Roof Decking

Roof Structure Type

2Snow Load ❄️

Enter custom ground snow load (PSF)

Snow Zone (Approximate)

Myrtle Beach, SC is Zone 1 (minimal snow load)

3Equipment Load ☀️

Equipment Type

Quantity

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Enter Your Roof Details

Fill in your roof information and click "Calculate Roof Load" to see your analysis.

Need a Professional Assessment?

Our experts can evaluate your roof's load capacity and recommend solutions for solar panels, HVAC, or other equipment.

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