Commercial Metal Roofing
R-Panel & Standing Seam Metal Roofs Installed by Our Own Crews
Commercial Metal Roofing, Installed In-House
Metal is one of the most durable roofing choices for commercial, industrial and agricultural buildings. McGuire Roofing installs two main commercial metal systems: R-panel (an exposed-fastener panel) and standing seam (a concealed-fastener panel). Our own crews do the work. We do not hand your metal roof off to a subcontractor, so the team that plans the job is the team that builds it.
This page covers how the two systems differ, which buildings suit each one, when metal makes more sense than a single-ply membrane, and what a metal reroof or retrofit with McGuire looks like. We are BBB A+ Accredited, we answer the phone 24/7 at 865-338-7663, and we serve clients in Tennessee, Kentucky, West Virginia, Virginia, North Carolina, South Carolina and Georgia.
R-Panel vs. Standing Seam: The Key Differences
R-Panel (Exposed Fastener)
Trapezoidal ribbed panels fastened through the panel face into purlins or deck with gasketed screws. Side laps overlap and are sealed. Cost-effective and quick to install. The usual choice for warehouses, shops, ag buildings and metal-over-metal retrofits.
Standing Seam (Concealed Fastener)
Panels joined at raised vertical seams that are snapped or mechanically seamed. Clips under the seam hold the panels down, so no fasteners go through the weather surface. Floating clips let panels expand and contract. Used where long service life, low maintenance or a clean look matter most.
- Fastening: On R-panel, screws go through the roof, and each one depends on its rubber washer. On standing seam, the fasteners are hidden under the seam.
- Seams: R-panel uses overlapping ribs with sealant. Standing seam uses raised seams that sit above the water line, and mechanically seamed versions resist water best.
- Expansion: R-panel is pinned at every fastener, so movement works the screw holes over time. Standing seam clips let panels slide.
- Slope: Exposed-fastener panels generally need more slope. Many manufacturers list about 1:12 or steeper for R-panel, depending on the profile. Some mechanically seamed standing seam systems are rated for lower slopes, down to about 1/4:12. The manufacturer’s published minimum always controls.
- Lifespan: Industry sources such as the Metal Construction Association generally describe well-maintained standing seam roofs lasting several decades. Exposed-fastener roofs can last a long time too, but they need fastener and sealant upkeep along the way. Actual life depends on the metal, the coating, the environment and the maintenance.
- Maintenance: R-panel needs periodic checks to re-tighten or replace fasteners and touch up sealant. Standing seam mostly needs inspection of flashings, penetrations and clips.
Building Types We Roof with Metal
- Warehouses, distribution and light-industrial buildings
- Pre-engineered metal buildings, shops and garages
- Agricultural, equipment and storage buildings
- Retail, offices, churches and schools where a standing seam look is wanted
- Multi-family buildings and mixed-use projects with steep-slope sections
- Canopies, covered walkways and mansard or accent roofs
Are you managing several buildings? See our multi-site roofing page. It is a new draft page.
Metal vs. TPO, PVC and EPDM: Which Fits Your Building?
Metal is not the right answer for every roof. On low-slope commercial roofs, a single-ply membrane is often the better tool. In general:
- Choose metal when the roof has enough slope, when you want a long-service-life roof with high impact and fire resistance, when you have a pre-engineered metal building, or when you need to retrofit an aging metal roof.
- Choose TPO or PVC on flat and near-flat roofs, roofs with many penetrations or rooftop units, or (for PVC) roofs exposed to grease and chemicals.
- Choose EPDM when you need a flexible, proven rubber membrane on a low-slope deck.
- Consider a roof coating when an existing metal roof is still structurally sound and mainly needs rust, seam and fastener issues addressed.
For membrane systems, Johns Manville is our main commercial manufacturer, we are Duro-Last certified (mainly PVC), and we are GAF commercial certified. We assess each building and recommend the system that fits it, not the one that is easiest to sell.
Retrofit Over Existing Roofs
Many aging metal and some low-slope roofs can be retrofitted instead of torn off. On a metal-over-metal retrofit, new sub-purlins or a framing system go over the old panels, and then new R-panel or standing seam is installed on top. A retrofit framing system can also add slope to a low-slope roof so it can take metal. Retrofits can reduce tear-off, landfill waste and disruption to the business inside.
Before we recommend a retrofit, we check the existing structure, fastener pull-out, moisture and the added load, and we review local code. Some buildings need an engineer’s review.
Insulation, Condensation and Ventilation
Metal moves heat quickly, and warm, humid air that reaches a cold panel will condense. That moisture can drip, rot wood framing, corrode fasteners and soak insulation. A good metal roof design controls condensation with:
- Continuous insulation, such as rigid board, or faced blanket insulation between purlins
- A properly placed vapor retarder with sealed laps
- Underlayment or a thermal break where the system calls for one
- Ventilation where it is appropriate for the building’s use
We size insulation to the energy code and to how the building is used. Cool-roof finishes and added insulation can reduce cooling loads.
Fasteners, Sealants, Flashing and Penetrations
Most metal roof leaks come from the details, not the panels. We pay close attention to:
- Fasteners: Correct length, coating and gasketed washers, driven to the right torque. Over-driving crushes the washer, and under-driving leaves a gap. Stitch screws go at R-panel side laps.
- Sealants: Butyl tape sealant at laps and end laps, plus closures matched to the panel profile at eaves and ridges.
- Flashing: Ridge, eave, rake, valley, headwall and sidewall trim, fabricated or supplied to suit the profile.
- Penetrations: Pipe boots rated for metal, and curbs for HVAC units and skylights, installed so water is diverted around them and not dammed behind them.
Thermal Movement and Snow Retention
A long metal panel can grow and shrink noticeably between a summer afternoon and a winter night. Standing seam systems handle this with floating clips and with ridge and eave details that allow movement. On R-panel, correct fastener placement and panel lengths reduce wear at the screw holes.
Metal sheds snow and ice quickly, which can be a hazard over entrances, walkways, parking and lower roofs. We can lay out snow retention: clamp-on guards for standing seam, so the seam is never penetrated, or fastened systems for R-panel.
Wind Uplift Testing and Approvals
Commercial metal roof assemblies are often tested for wind uplift. Common standards include UL 580 / UL 1897 testing, which can lead to an assembly rating such as UL Class 90, and FM Approvals listings for specific assemblies. A rating applies to the whole tested assembly: the panel, the gauge, the clip or fastener, the spacing and the substrate. It is not a property of the panel by itself.
When your insurer, code official or project spec calls for a rated assembly, we build to that listed assembly. Edge and corner zones get the closer fastener or clip spacing the design requires.
Coatings and Finishes
Panels come with factory finishes such as polyester, silicone-modified polyester (SMP) and PVDF (often sold under trade names like Kynar 500), along with Galvalume bare finishes. In general, PVDF holds its color and chalk resistance longest, and SMP is a common value option.
Older metal roofs that are still sound can often be restored with a field-applied coating system. This includes rust treatment, fastener and seam reinforcement, and a reflective topcoat.
Our Commercial Metal Reroof Process
- Inspection and assessment: Roof walk, structure and deck check, moisture check, measurements and photos.
- Recommendation: R-panel, standing seam, retrofit, coating or membrane, with the reasons for each.
- Written proposal and scheduling: Scope, materials and a schedule built around your operations. Financing is available.
- Safety and site setup: Fall protection, material staging and protection of the building’s occupants. See roofing safety (new draft page).
- Installation by McGuire crews: Tear-off or retrofit framing, insulation, panels, trim and penetrations.
- Final walkthrough: Punch list, cleanup, photo documentation and warranty paperwork.
- Ongoing care: Optional commercial roof maintenance to check fasteners, sealants and flashings.
Leak right now? Call us 24/7 at 865-338-7663, or see emergency roof tarping. We also install commercial gutters sized for metal runoff.
Commercial Metal Roofing FAQ
What is the difference between R-panel and standing seam?
R-panel is an exposed-fastener panel screwed through its face into the structure. Standing seam uses concealed clips under raised seams, so no fasteners go through the weather surface and the panels can expand and contract freely.
Which is better for my commercial building?
R-panel is usually the most economical choice for warehouses, shops and ag buildings with enough slope. Standing seam suits buildings where long service life, low maintenance, lower slopes or appearance matter. We recommend a system after inspecting the building.
Can a metal roof go over my existing roof?
Often, yes. Metal-over-metal retrofits use new framing over the old panels, and some low-slope roofs can be framed up to take metal. We check the structure, moisture and code requirements first.
Do exposed-fastener metal roofs need maintenance?
Yes. The fastener washers and lap sealants age, so periodic inspection and fastener re-tightening or replacement are part of owning an R-panel roof.
How do you prevent condensation under a metal roof?
We use correctly sized insulation, a sealed vapor retarder and the right underlayment or ventilation for how the building is used.
Is metal or TPO better for a flat roof?
On flat and near-flat roofs, a single-ply membrane such as TPO, PVC or EPDM is usually the better fit. Metal needs enough slope for the panel profile, unless the roof is framed up to add slope.
Do you install metal roofs with your own crews?
Yes. McGuire Roofing installs commercial metal roofs with our own in-house crews.
Do you offer financing and emergency service?
Yes. Financing is available, and we answer the phone 24/7 at 865-338-7663.
Get a Commercial Metal Roofing Assessment
BBB A+ Accredited. Serving Nationally. In-house R-panel and standing seam crews. Call 865-338-7663 24/7. Financing is available.
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