How to Measure a Warehouse or Commercial Roof for PBR Panels

You have a long steel building and a roof that needs panels. How do you turn a set of building dimensions into an order? If you have already read our guide to measuring for Tuff Rib Ag, the good news is that PBR works almost the same way. What changes is the scale, and one important detail at the eave.

PBR is the panel we usually see on warehouses, shops, and other industrial and commercial buildings, so expect longer panel runs and much longer buildings. A mistake in your numbers gets multiplied across a lot of panels, so the method matters.

Comparing profiles first? See PBR vs. Tuff Rib Ag. Roofing with Tuff Rib Ag instead? Start with how to measure your roof for Tuff Rib Ag panels.

Commercial PBR has a larger, stronger rib and is 26 gauge, Grade 80 steel. That is thicker than our glossy 28 gauge Tuff Rib Ag. The practical result is that PBR can safely hang out further past the eave, and that changes the length math.

PBR is typically installed on a steel building (steel trusses and purlins), though it can go on wood framing. For a PBR roof, purlins can be spaced up to 48 inches on center, and up to 72 inches (6 feet) on center on sidewalls.

For each roof plane, you need:

1. Panel length: from the ridge down to the eave.
2. Building width (the length of the roof): the length of the ridge, or the length of the eave. On a simple gable roof they are the same.

Label each plane and sketch the building with the numbers on it.

PBR covers 36 inches (3 feet) per panel. Divide the length of the building by 36 inches and round up.

For example, a warehouse that is 120 feet long:

• 120 feet = 1,440 inches
• 1,440 ÷ 36 = 40 panels per roof plane

A 125-foot building works out to 41.67, so you would order 42 panels. Always round up.

At the bottom of the roof, the panel hangs past the eave, and PBR gives you more room here than Tuff Rib Ag. The overhang can run from a minimum of 1 inch up to a maximum of 6 inches. Our recommended range is 4 to 6 inches, and if you want to play it safe, keep it to about 4 inches.

• Gutters: If gutters will go on, an overhang of about 1 inch (or a bit less) is usually right.
• No gutters: If you want the drip line further out and away from the wall, 6 inches works well. A little less is fine too.

Why not longer? Sliding snow and ice can catch the overhanging metal and, over time, bend that unsupported piece of panel downward. Six inches is the outer limit.

At the ridge, the rule is the same as for Tuff Rib Ag. Keep the panels back 1 to 2 inches at most on both sides, so panels from opposite sides never touch. The gap allows for venting and for thermal movement. If panels are installed touching on a cold day, summer heat can push them into each other and cause buckling or damage.

Measure the top chord of the truss (or the rafter) from the very top down to the end of the top chord. With trusses, start where the top chords meet. With rafters, start from the middle of the ridge pole.

Then:

1. Add the fascia thickness, or whatever your eave detail adds. Steel buildings may have an eave trim instead, so check with your installer. If there is none, add nothing.
2. Subtract the ridge setback (up to 2 inches).
3. Add the overhang you have chosen (4 to 6 inches, or about 1 inch with gutters).

Say your steel truss top chord measures 30 feet (360 inches). The fascia board is 1.5 inches thick. You plan a 2 inch ridge setback and a 5 inch overhang.

• Top chord: 360 inches
• Plus fascia thickness: 1.5 inches, for 361.5 inches
• Minus ridge setback: 2 inches, for 359.5 inches
• Plus eave overhang: 5 inches, for 364.5 inches

Your panel length is 364.5 inches, or 30 feet 4.5 inches. Unlike Tuff Rib Ag, the two end adjustments do not cancel out here. The bigger overhang makes the panel about 3 inches longer than the top chord plus fascia (5 inches of overhang less 2 inches of setback). Use your own numbers, since your fascia, setback, and overhang may differ.

The ridge cap covers the gap at the top. What goes under it depends on the building:

• Ridge cap with foam closure strips: Seals the ridge tight. It does not breathe. Use it when you do not want venting, for example when the building has gable vents, or when spray foam insulation is against the underside of the roof deck.
• Ridge cap with mesh (vent) closure: Lets the ridge vent while keeping rain and snow out. Use it for most attic applications, barns, and cathedral-type ceilings with fiberglass insulation and proper baffles or vents.

We make trim to order, in standard or custom profiles, in standard lengths of 10 and 12 feet. Ten feet is the most common, and 12-footers are used only where 10s would create too much waste. Add up each trim run, divide by 10 feet, and round up. On our 120-foot warehouse, a drip edge along both eaves is 240 feet, which is 24 pieces of 10-foot trim. A deeper trim guide is coming soon.

Screws go in the flat beside the rib, not in the rib itself. That is the same flat-beside-the-rib principle covered in our Tuff Rib Ag screw post, where to put your panel screws.

• Round up on panel counts for every plane
• Add a spare panel or an extra piece of trim for mistakes or damage
• Order extra screws. A large roof uses more than you think

With a 24 to 48 hour turnaround on stock-color coil*, a small top-up order is easy.

*24–48 hour turnaround applies to stock coil colors only. Custom colors may take longer.

A good request includes:

1. Commercial PBR, building type, and color
2. Panel length and count for each plane, or the building dimensions and a sketch
3. Eave plan: gutters or no gutters, and your preferred overhang
4. Trim list: the total length per trim type (or the piece count), and whether you need standard or custom profiles
5. Photos of the building
6. Delivery address or pickup plan, and your timeline

On a large building, one wrong number gets repeated across every panel. We recommend having your contractor or installer confirm the measurements before you order. Whoever is doing the install, whether that is a subcontractor, a contractor, or the owner, should verify the panel lengths, because they know exactly how they will install it.

We deliver across New England, New York, and New Jersey, or you can pick up at our shop in Westfield, MA. That is our only location.