Solar + roofing integration

Roof truss load capacity calculator

Enter your truss type, spacing, and condition. See how your pre-engineered roof structure compares to typical solar load requirements.

Your truss details

Educational planning estimate, not professional, financial, or engineering advice. Confirm figures with a licensed contractor or installer before making decisions.

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Truss type and layout
Check the metal plate stamped where truss members meet, in your attic.
Measure from the center of one truss to the center of the next.
3 Condition and requirement
Check the metal connector plates for rust, cracking, or looseness.
Leave blank to use a typical residential requirement of 35 psf.

How it works

Three steps to a truss check

Step 1

Find your truss's metal connector plates

Look in your attic where truss members meet at angles. The metal plate connecting them often has a manufacturer stamp and rating printed or embossed on it.

Step 2

Note your truss type and spacing

Most residential trusses sit at 24 inches on center, but check yours directly since some homes use tighter spacing. Scissor and attic trusses look visually different from standard triangular trusses.

Step 3

Check the result against your requirement

If your margin is tight or negative, the structural engineer assessment cost tool shows what a professional confirmation typically costs before you commit to a mounting plan.

Why trusses play by different rules than rafters

What a standard truss can carry

A standard residential truss at 24 inches on center in good condition has an estimated capacity of about 40 psf, which clears a typical 35 psf requirement with a modest margin, a threshold consistent with minimum wind and snow load standards. Since trusses are factory-engineered, their rated capacity is often more reliable than an estimate for site-built rafters of similar size.

Why the metal connector plates matter so much

Trusses rely on metal gusset plates at every joint to transfer load between wood members, which means the plates themselves, not just the lumber, determine real-world capacity, a system PNNL's roof anchor systems guide covers alongside conventional framing. Rust, corrosion, or a loosened plate at even one joint can weaken the entire truss system, which is why condition matters more here than it does for solid-sawn rafters.

Why scissor and attic trusses need extra caution

Scissor trusses, built for vaulted ceilings, and attic trusses, designed for room-in-attic layouts, both trade some structural capacity for their unique shapes. This doesn't automatically disqualify them from solar, but the design margin is often tighter than a standard triangular truss, which is why these two types are more likely to benefit from a closer engineering look, and once your system size firms up, the roof space vs output estimator and the inverter oversizing calculator round out the planning picture.

Why you should never modify a truss on your own

Trusses are engineered as a complete system where every member and connection works together, so cutting, drilling holes larger than specified, or removing any part can compromise the whole structure in ways that aren't visually obvious. Any structural changes needed for a solar mount should go through a structural engineer familiar with truss design, not a general contractor working from a rafter mindset. The rafter spacing and load calculator covers the related conventional-framing scenario, and the structural engineer assessment cost estimator shows what a professional evaluation typically costs. The inverter oversizing calculator covers the inverters & equipment angle of the same decision.

Questions

Frequently asked

Trusses are pre-engineered in a factory with a specific rated design load stamped on a metal plate at the truss, while rafters are cut and assembled on site without a factory rating. Trusses are usually spaced wider, at 24 inches on center, but their engineered design often gives comparable or better capacity than site-built rafters.

Look for a metal connector plate stamped with a manufacturer name and design specifications where truss members meet, usually visible from your attic. If you can't find a legible rating, the truss manufacturer or a structural engineer can often confirm the rating from your home's original building plans.

Trusses are engineered as a complete system, so modifying one, including drilling or cutting members, can compromise the entire structure without proper engineering review. Any changes to a truss roof for solar mounting should go through a structural engineer familiar with truss design.

Scissor trusses, used for vaulted ceilings, typically carry lower load ratings than standard trusses because of their shape and reduced web bracing. This doesn't rule out solar, but it does mean a closer look from an engineer is more likely to be worthwhile before installing.

Related tools

Three checks before touching a truss

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