Metal Roofing: How Panels, Trims and Flashings Go On
18 step by step guides
A metal roof is a system of long panels, hidden clips or exposed screws, and a lot of small trim pieces. The panels get the attention, but the trims, closures, flashings and fastening pattern decide whether the roof lasts 40 years or leaks in five. These guides cover the whole sequence, from choosing a panel type and measuring and ordering to the last ridge cap.
Two panel families dominate residential work in British Columbia. Concealed-fastener panels, including standing seam and snap-lock profiles such as ProLock, hide every screw under the panel edge. Exposed-fastener panels, the ribbed panels common on shops and barns, are screwed through the face, which makes the screw pattern and washer compression the whole game.
Metal is unforgiving in ways shingles are not. Steel expands and contracts with temperature, cut edges can rust if abrasive blades are used, a wrong first panel shows at the ridge 40 feet later, and snow can release from a slick roof all at once. Each guide here covers the real order of operations and the failures that matter, with values to confirm against the panel manufacturer's installation manual, which always governs.
Metal Roofing Guides
- Guide 1Metal Roof Panel Types ExplainedResidential metal roofing comes in four families. Exposed-fastener ribbed panels are screwed through the face and suit shops and simple roofs. Concealed-fastener snap-lock panels, such as ProLock, click together over a nail strip and need about 3/12 slope. Mechanically seamed standing seam is crimped closed and handles low slopes. Steel shingles imitate shakes or slate. Gauge, finish and slope requirements vary by product.Beginner1 hour of research and site checks
- Guide 2How to Measure and Order Metal Roof PanelsTo order metal roofing, measure each roof plane's eave-to-ridge length and width, divide the width by the panel's coverage width (not its overall width) and round up to get the panel count, then add the eave overhang and ridge allowance to the length. List trims separately by linear foot: eave, rake, ridge, hip, valley and wall flashings. Panels are cut to length, so order waste mainly in trim.Intermediate2 to 4 hours
- Guide 3Underlayment for Metal RoofsMetal roofs need underlayment rated for high temperature because dark panels in summer sun run far hotter than the air, commonly 70 degrees Celsius or more, and heat the layer directly beneath them. Install self-adhered ice and water shield at eaves, valleys and penetrations, then cover the rest with a high-temperature synthetic or self-adhered membrane, lapped shingle-style, before panels go on. A vented air gap or slip sheet reduces condensation and abrasion.Advanced4 to 8 hours for an average house
- Guide 4How to Strap (Purlin) a Roof for MetalStrapping, also called purlins or battens, is horizontal lumber, commonly 1 by 4 or 2 by 4, fastened across the rafters or over old shingles to give exposed-fastener metal panels a fixing line. Typical spacing is 24 inches on centre, set by the panel manufacturer and loads, and screws must reach the rafters. Concealed-fastener panels such as snap-lock and standing seam usually need a solid deck instead.Advanced1 to 2 days
- Guide 5How to Install Standing Seam Metal RoofingStanding seam roofing is installed by squaring the first panel to the eave and rake, fastening concealed clips to the deck at the manufacturer's spacing, and engaging each panel's female seam over the previous male seam. Seams are then crimped with a hand or electric seamer. One row of clips near the ridge holds the panel, and the rest float so the panel can move with temperature.Professional3 to 6 days for an average house
- Guide 6How to Install ProLock Snap-Lock PanelsProLock, sold as Pro-Lock by Domtek Building Products, is a concealed-fastener snap-lock panel in 12 or 16 inch widths, 24 or 26 gauge, for slopes of 3/12 or steeper over solid plywood and synthetic underlayment. Install the first panel square, screw through its flange, snap the next panel's lock over it, and repeat, without clips. Confirm details in the ProLock installation manual.Professional2 to 5 days for an average house
- Guide 7How to Install Exposed-Fastener Metal PanelsExposed-fastener panels are laid from the end of the roof away from the prevailing wind, with each panel's overlapping rib lapped over the previous one and a bead of sealant tape between. Panels are screwed through the flat into purlins or deck with rubber-washered screws at the eave, ridge, laps and at intervals across the field, and foam closures seal the eave and ridge. Start square, because errors repeat.Advanced1 to 3 days for a shop or simple house roof
- Guide 8Metal Roof Screws: Pattern, Torque and WashersMetal roof screws are coated self-drilling or self-tapping fasteners with an EPDM or neoprene washer, usually number 10 or 12, long enough to reach 1 inch into wood. They go in the flat or rib as the panel manual shows, with extra screws at eaves, ridge and laps. Drive until the washer is slightly compressed and bulges evenly, not crushed, and replace any stripped screw with an oversize one.IntermediatePart of the install, or 2 to 4 hours for a screw replacement pass
- Guide 9How to Install Metal Eave Trim and ClosuresInstall the eave trim (drip edge) on the fascia before the panels, with underlayment lapped over its upper leg and self-adhered membrane at the edge. Fasten the trim every 12 to 24 inches, set panels to overhang it by about 1 to 2 inches, and fit foam or vented closures under the panels to block wind-driven rain, snow and pests. A hemmed panel end adds a drip edge.Advanced2 to 6 hours for an average house
- Guide 10How to Install Metal Rake (Gable) TrimRake trim caps the gable edge of a metal roof. Fit it with the underlayment under the trim (the opposite of the eave), lap sections 2 to 4 inches in the direction water flows with sealant between, and fasten on the roof leg at the manual's spacing, commonly 12 to 24 inches. Close the ends with a cap at the eave and ridge and seal the panel edge with closures or tape.Advanced2 to 5 hours
- Guide 11How to Install a Metal Ridge and Hip CapFinish the top of a metal roof by fitting profile closures or Z-closures above the last fasteners, then the ridge cap over them, lapped about 3 to 6 inches in the direction away from the prevailing wind, fastened through the panel rib or closure with sealant tape. Hips get a hip cap starting at the eave. On vented roofs leave a continuous slot with vented closures and mesh.Advanced3 to 6 hours for an average house
- Guide 12How to Install a Metal Roof ValleyLine the valley with a 36 inch strip of self-adhered membrane, then lay a formed valley pan or W-valley over it, fastened only along its outer edges with cleats or screws outside the water path. Cut panels to the valley at an angle, hem or fold the cut edges, leave a gap of about 1 to 2 inches each side of centre and seal the panel edge with butyl tape.Professional3 to 6 hours per valley
- Guide 13How to Flash a Pipe on a Metal RoofFlash a small pipe on a metal roof with a rubber or silicone boot on a flexible flange that seals to the panel flat, fastened around its edge with washered screws and butyl tape beneath. Place it on the flat of the panel, never across a rib or seam. For larger penetrations, build a curb with a back pan and diverter so water flows around them and fasteners stay out of the water path.Advanced30 minutes to 1 hour per pipe
- Guide 14How to Flash Sidewalls and Endwalls on Metal RoofsOn a metal roof, a sidewall (along the slope) gets a formed sidewall trim that runs up the wall behind the cladding, sits on the panel edge over a closure, and is fastened high on the wall leg. An endwall (across the top of the slope) gets a headwall flashing with a Z-closure, tucked under the wall's weather barrier. Stucco or masonry uses a counter flashing over the base flashing.Advanced3 to 6 hours for an average wall
- Guide 15How to Cut Metal Roof Panels Without Damaging the FinishCut pre-painted metal roof panels with electric shears, a nibbler, or aviation snips, which cut cold and leave a clean edge. Avoid abrasive chop saws and angle grinders, because hot steel particles embed in the paint and rust within weeks. Mark the cut on the back, support the panel on both sides, sweep every shaving away and touch up the edge with paint.IntermediateMinutes per cut
- Guide 16How to Hem, Fold and Bend Metal Panel EndsHem a metal panel end by marking a fold line about 1/2 to 1 inch from the edge, clamping the panel in a hand seamer or brake, and bending steadily to a flat hem. At the eave the hem forms a drip. At the ridge, notch the ribs and turn the top up about 1 inch into an end dam. Bend slowly, from the centre out, to avoid cracking paint.Advanced5 to 10 minutes per panel end
- Guide 17How to Install Snow Guards on a Metal RoofSnow guards hold snow on a metal roof so it melts off gradually instead of releasing in a sheet. Place rows above doors, walkways, gutters and lower roofs, starting near the eave about 12 to 24 inches up, and stagger guards in rows spaced roughly 4 to 8 feet apart up the slope. Use clamp-on guards on standing seam and fasten guards through ribs on exposed-fastener panels.Advanced2 to 6 hours
- Guide 18How to Allow for Thermal Movement in Metal RoofsSteel expands about 0.0000065 inch per inch per degree Fahrenheit, roughly 3/4 inch over a 100 foot panel with a 100 degree swing, and aluminum moves about twice as much. Allow for it with sliding clips or slotted fasteners, anchor each panel at one fixed point (usually near the ridge), leave gaps at trims and keep panel lengths within the manufacturer's limits to prevent buckling, noise and oil canning.ProfessionalPlanning step, part of the install
Also on this site
Metal Roofing: Common Questions
What is ProLock metal roofing?
ProLock, sold as Pro-Lock by Domtek Building Products, is a concealed-fastener snap-lock panel. It comes in 12 inch and 16 inch widths in 24 and 26 gauge steel, needs a minimum 3/12 slope over solid plywood decking, and is fastened through a flange so no screws show on the face. Confirm current specifications in the manufacturer's installation manual before ordering.
What is the difference between standing seam and exposed fastener metal roofing?
Standing seam panels have raised seams that hide the fasteners, which are clips or a nail strip under the seam. Exposed-fastener panels are screwed through the flat of the panel with rubber washers. Standing seam costs more and handles thermal movement better. Exposed fastener is cheaper and fast to install but depends on screws and washers that need periodic checking.
Can metal roofing go over existing shingles?
Often it can, using strapping or a vented sub-purlin system over a single layer of shingles, but the old roof is then trapped and hidden defects stay in place. Many installers prefer tearing off to inspect the deck and install proper underlayment. Check the local building code, the panel manufacturer's requirements and the condition of the deck first.
Is metal roofing noisy in the rain?
On a solid deck with underlayment, a metal roof is not much louder than shingles indoors. The noisy metal roofs are exposed-fastener panels over open purlins with no sheathing, like a barn. Solid plywood decking, underlayment and attic insulation absorb most rain sound, so the deck and assembly matter more than the panel.
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