Yes, a new metal roof can go straight over an existing R-panel roof, and on most metal buildings it is the cleanest way to replace a worn-out roof. Notched sub-purlins sit over the old ribs and fasten through the old panels into the purlins below, the new roof attaches to those sub-purlins, and the gap between the two roofs takes new insulation. The old roof stays on as a lid during the work, so the building keeps operating. It succeeds when the purlins and frame can carry the extra load and every edge, gutter and penetration is designed into the job from the start.
How notched sub-purlins fit an R-panel roof
R-panel, and its close relative the PBR panel, has trapezoidal ribs at regular spacing with flat pans between them, and it is screwed through the face into the purlins. A retrofit sub-purlin is a steel zee section with notches cut into its bottom flange to match that rib profile. Set on the roof, the notches straddle the ribs and the flange sits down onto the pans, so the member bears on the roof without crushing it. Roof Hugger is a well-known maker of these factory-notched members, and other suppliers make similar parts.
Each sub-purlin runs directly over an existing purlin line and is fastened through the old panel into that purlin. That gives the new roof a clean load path: new panel to sub-purlin, sub-purlin to purlin, purlin to frame. The old sheeting is simply sandwiched in the connection and is not asked to carry anything.
The fit depends on an accurate profile. We measure rib height, rib spacing and pan width on the actual roof, because older buildings and later additions often carry a different panel from the one shown on the drawings. Where a profile has no standard notched part, sub-purlins can be custom notched, or a stand-off framing arrangement can be designed instead.
Check the purlins and frame before anything is ordered
Pre-engineered metal buildings are designed lean. The purlins, their connections and the main frames were sized for the original roof and the design loads of the day, with little to spare. A retrofit adds dead load from the sub-purlins, new panels and insulation, and the new roof has to resist wind uplift under the building code that applies now, with the highest forces at corners and edges.
So the structure is checked first. The retrofit design includes structural review by an engineer, using the original building drawings where they exist and site measurements where they do not. From inside, we look at the purlins for rust running down from old leaks, rolled or twisted sections, missing bracing and damaged connections at the frames. Localized damage can be reinforced as part of the job. A frame that cannot take the added load is a reason to stop and reconsider the approach, not something to discover halfway through installation.
Put new insulation in the cavity
The existing blanket insulation stays where it is, under the old panels. The depth of the sub-purlins creates a new space above it that can be filled at full thickness, because the new insulation is no longer squashed flat over every purlin the way the original blanket was. That is often the biggest performance gain in the whole project, especially for buildings changing use, such as an Austin flex building converted for manufacturing or a San Antonio warehouse taking on cooled storage.
Three details separate a good cavity from a problem one. The insulation has to fill the space without gaps beside the sub-purlins. A thermal spacer or break between the new panels and the sub-purlins stops the steel from carrying heat straight through. And vapor control has to be worked out for the actual building, because indoor humidity, the state of the old roof and the new insulation together decide whether moist air could condense inside the cavity where nobody would see it.
Choose the new roof panel
Standing seam
A standing seam roof attaches with concealed clips, so no fasteners pass through the weather surface. Floating clips let long panels expand and contract, which matters on warehouse runs that bake all afternoon and cool off overnight. Standing seam also performs at lower slopes than a through-fastened panel. For a building you intend to keep for the long term, it is our usual recommendation.
Through-fastened panel
A new R-panel roof over the old one costs less in materials and goes on faster. It is a sound choice for smaller buildings, outbuildings and roofs with enough slope, provided it is installed with new long-life fasteners and properly sealed laps. Bear in mind that every fastener is a point you will inspect again in future. We are certified installers for MBCI and Morin metal roof systems, and we also install our own specification R-panel systems. Manufacturer data sheets for profiled metal panels are in our Technical Library.
Where the existing roof is very low slope, the sub-framing can be built up to increase the pitch of the new roof. That has to be settled at design stage, because it changes the height at the eave or the ridge.
Eaves, rakes, ridges and gutters
The new roof sits higher than the old one, and every edge has to account for that. At the eave, closures and trim seal the cavity against wind, rain, birds and insects, and the gutter is normally replaced to line up with the new roof edge and sized for the cloudbursts that hit San Antonio and Austin. Downspouts are rerouted to suit. At the rake, new trim covers the build-up and has to tie neatly into the wall panels below. At the ridge, a new cap with profiled closures finishes the roof.
On multi-span buildings with internal valley gutters, the retrofit is a chance to rethink drainage. Sometimes the new framing can carry water to the outside walls instead, which gets rid of a gutter that has been overflowing into the warehouse for years. That choice belongs at the start of the design, not after the panels are ordered.
Penetrations and rooftop equipment
Every pipe, vent, exhaust fan and HVAC curb has to come up to the new roof level. Pipes are extended and get new boots that suit the new panel, curbs are raised or replaced, and units may need lifting while their curbs are rebuilt. We list each penetration in the scope so nothing is left to be improvised on the roof. Equipment that is no longer used is a good candidate for removal, with its opening closed off in the old roof before the new one covers it.
Skylights
Translucent skylight panels in an old R-panel roof are usually brittle, yellowed and cracked by hail. A retrofit gives you three options: carry daylight through with new skylight panels lined up in both the old and new roofs, close the old openings and fit new curb-mounted skylights, or remove the skylights altogether and rely on electric lighting. Each has trade-offs in light, heat gain and upkeep. Old skylights are also a fall hazard, so they are guarded or covered before the crew works across the roof.
Keeping the building open during the work
Because the old roof stays on, rain stays out and the work below can carry on. The disruption is real but manageable. Drilling sub-purlin fasteners through the old roof drops fine metal shavings, so sensitive equipment, food areas and finished goods under the fastening lines get covered. There is noise from drilling and from moving material. Crane lifts are timed around loading docks and shift changes, and we agree work zones and timings with your site team so trucks keep moving at a distribution building near Schertz or production keeps running at a plant along SH 130.
Our metal roof retrofit service sets out the complete scope from survey to finished roof. The city pages for metal roof retrofit in San Antonio and metal roof retrofit in Austin add the local picture.
If you are weighing a retrofit over an R-panel roof, send us the address, any original building drawings and a few photos of the roof and its underside. We will check the profile, the purlins and the details and give you a clear scope. Reach us through the contact page, or phone (210) 775-0995 to talk it through.
To upload drawings, specs and plans please go to the form on our contact page.
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