R-panel or PBR: what's the difference on a shop roof?
R-panel and PBR panels look almost identical from the ground: wide flat pans with tall trapezoid ribs about a foot apart. The difference is at the side lap. PBR adds a small purlin bearing leg that sits on the purlin and supports the overlap, which keeps the seam from flexing under screws and foot traffic. R-panel lacks that leg and costs a little less.
On most enclosed shops and garages, PBR is worth the small upcharge because the stiffer lap seals better over time. On open hay barns, loafing sheds and equipment covers where a few drips don't matter, R-panel does the job. Both run in 26 gauge for most rural buildings, with 24 gauge available where purlin spacing is wide or hail is a big concern. If you're roofing a house rather than an outbuilding, the shallower ribs of 5V crimp panels suit a farmhouse better. Ribbed R-panel and PBR are built for buildings framed with open purlins, not for homes with plywood decking and finished ceilings below.
Purlins, spans and the framing under the panels
Outbuilding panels fasten directly to horizontal purlins, which are usually wood two by fours or two by sixes on older barns and steel Z or C purlins on newer pole buildings. Purlin spacing is what decides panel gauge. Most 26 gauge PBR spans two to three feet comfortably, while wider spacing calls for heavier steel or added purlins.
On older barns in Wilson and Atascosa counties, we often find purlins that have split around old nail holes, bowed between trusses or rotted where a leak sat for years. We replace those before new panels go on, because a screw can't hold in punky wood. Steel purlins get checked for rust at the eave and bolts that have loosened from years of wind flex.
Reroofing over existing tin is sometimes possible with a layer of spacer purlins on top. It saves tear-off cost and keeps the old roof as a backup layer, but it only works when the original framing is straight and solid. We'll show you from inside the building what we see before you choose.
How do you stop a shop roof from dripping condensation?
On a cool spring morning after a warm, humid night, the underside of bare steel drops below the dew point and collects water. It then drips onto tools, trucks and hay as if the roof were leaking. That's the single most common complaint we hear about uninsulated metal shops in South Central Texas.
There are three common fixes. A fabric-backed panel or a drip-stop membrane adhered to the underside of the steel holds condensation until it evaporates. Faced fiberglass blanket laid over the purlins before the panels adds insulation and stops drips. Closed-cell spray foam applied after the roof is on seals and insulates in one step, at a higher cost.
For a hay barn, drip-stop is usually enough. For a heated or cooled shop, a man cave or a garage with a workbench, insulation pays back quickly in summer comfort. Summer attic and shop temperatures here commonly pass 140 degrees under bare metal, so a layer of insulation changes how usable the building is in July.
Clear skylight panels without the leaks
Translucent polycarbonate or fiberglass panels in the same rib profile let daylight into a barn or shop without wiring lights. They're popular on hay barns and workshops. The trade-off is that they're the softest part of the roof, and hail cracks fiberglass panels long before it dents steel.
We set clear panels with matching rib closures and extra fasteners at the laps, and we avoid placing them where water concentrates near a valley or lean-to tie-in. On buildings in hail-prone corridors north of San Antonio, we lean toward thicker polycarbonate, which flexes instead of shattering. Replacing yellowed or cracked old skylight panels is one of the quickest wins on an aging barn roof.
Ridge caps, closures and fasteners that keep weather out
Exposed-fastener roofs live or die by their screws. We use long-life fasteners with EPDM washers, driven snug but not crushed, set in the flat pan on purlins and in the rib at side laps. Overdriven screws split the washer, and underdriven screws let water wick in. Getting that right across thousands of screws is most of the job.
Foam closures fill the gaps under the ribs at the ridge and eave so wasps, birds and wind-driven rain can't get in. Butyl tape seals end laps where panels overlap on long runs. Gable trim and eave trim tie it all together. When older roofs start leaking at the screws, our fastener and seam repair work can buy years before a full reroof makes sense. If the outbuilding is really a carport or an attached porch cover, our patio and carport roofing page covers the different framing and tie-in work those need.
Working on acreage in Comal, Bandera and Wilson counties
Rural jobs bring their own logistics. We check gate widths, caliche drive conditions after rain, septic field locations and where a delivery truck can drop 30 foot panels without rutting the pasture. Livestock need to be moved out of barns during tear-off, since old screws and metal scraps end up on the ground.
We run a magnet sweep across the work area when we finish, because a stray screw in a horse's hoof or a tractor tire is a real problem. Hail on the Hill Country side of Comal County and across Bandera County ranch land can be as damaging as in town, so we photograph old damage before tear-off in case you want to file a claim.
