How to Install ProLock Snap-Lock Metal Roofing Panels
Solid deck, a square first panel, screws through the flange, a locked seam and the trims that finish a concealed-fastener roof.
- Professional
- 2 to 5 days for an average house
- Updated
The short answer
ProLock, 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.
In BC, ProLock usually means a concealed-fastener snap-lock panel, sold by the manufacturer Domtek Building Products as Pro-Lock and often called ProLock 12 for the 12 inch panel. The manufacturer lists 12 inch and 16 inch widths, 26 and 24 gauge steel, a 3/12 minimum slope, installation over minimum 1/2 inch plywood with an approved synthetic underlayment, and no clips. Rib options are striations, an XD profile or minor ribs. The rib height was not listed where checked, so use the installation manual for it.
The system is simpler than clipped standing seam. Each panel has a flat flange with slots on one edge and a female lock on the other. The flange is screwed to the deck, and the next panel snaps over the first flange, hiding the screws. The price of that simplicity is movement. Because the flange is fixed, long panels cannot float on clips, so panel length, colour and fastening details need attention.
This guide describes how nail-strip snap-lock panels of this type are installed in general. Always confirm fastener type, spacing, lap, trims and slope in the manufacturer's current installation manual, which governs. For related families, see metal roof panel types and standing seam installation.
Tools
- Impact driver and screw bits
- Aviation snips, offset snips and a hand seamer
- Panel shear or nibbler for long cuts
- Chalk line, laser level and tape measure
- Soft mallet or rubber hammer
- Sheet metal brake for trims
- Fall protection equipment
Materials
- ProLock panels cut to length, in the colour and gauge ordered
- Fasteners for the flange as listed in the manufacturer's manual
- High-temperature synthetic underlayment
- Ice and water shield at eaves and valleys
- Eave, rake, ridge and wall trims and closures from the same profile
- Butyl sealant tape and colour-matched touch-up paint
Safety first
- Snap-lock panels are slippery and sharp. Tie off, use cut-resistant gloves and never walk directly on the seam.
- Panels of any length act as sails in wind. Carry them on edge and stop work if wind rises.
- WorkSafeBC requires fall protection at 3 metres (about 10 feet) or wherever a fall could cause serious injury.
- Keep screws and offcuts off the roof surface, where they scratch finish and create trip hazards.
Step by Step
Step 1: Confirm slope, deck and underlayment
Measure every plane's pitch. Anything below the stated minimum needs a different panel or a low-slope roof. Check the deck: minimum 1/2 inch plywood is listed for Pro-Lock, and many installers prefer 5/8 inch for a flatter, stiffer surface. Replace soft or damaged sheathing and set all nail heads flush.
Install self-adhered membrane at eaves and valleys and an approved synthetic underlayment across the rest. See underlayment for metal roofs. Use an underlayment rated for metal roof temperatures.
Step 2: Install the eave trim and rake trim
The eave trim gives the drip edge and sets the overhang, and the rake trim sets the edge the first panel runs to. Install them straight and continuous, lapped in the direction of water flow, and fasten as the manual directs. See eave trim and closures and rake trim.
The eave line is the reference for the whole roof, so check it with a string. A curved fascia shows as curved panel ends.
Step 3: Square and set the first panel
Measure square from the eave and check with diagonals across the roof plane. On a gable roof start at a rake, placing the panel's edge into the rake trim as the detail shows. Snap a chalk line up the slope for the panel edge and set the lower end so the overhang clears the eave closure and drips into the gutter.
A first panel that is out of square by a fraction at the eave will drift by inches at the ridge. Re-measure the distance to the rake at both ends of the panel, and correct before fastening anything.
Watch out: Do not rely on the fascia or the rake board being straight. Square the panel to the roof, not to the edge.
Step 4: Fasten the flange at the manufacturer's spacing
Use the fastener type, length and spacing in the installation manual. Screws through a flange are commonly spaced about 12 to 24 inches apart, closer at the eave, ridge and rakes, and they must bite the deck, not just the underlayment. Where rafters run under the deck, hitting them can improve holding power, but follow the manual.
Drive each screw centred in its slot so the panel can still move a little as it heats and cools. A screw driven tight against the slot edge, or overdriven until it dimples the flange, fixes the panel in place and causes waves and noise. See metal roof screws.
Tip: Set the driver's clutch so screws stop snug. Check the first dozen screws by sliding a fingernail along the flange: the flange should lie flat, not dished.
Step 5: Engage the lock of the next panel
Hold the next panel so its lower end matches the last one at the eave, set the lock over the flange and press it down with a hand or a soft mallet. Work from the eave upward, feeling for each section to click. Do not hammer hard on the metal, which dents it.
Check that the lock is fully engaged along the whole length. A partly engaged lock sits proud and will lift in wind. Step back and sight along the seam for a consistent line. Then fasten the new panel's own flange as in the previous step and repeat.
Step 6: Keep the panels straight and correct drift
Small errors accumulate. After every three or four panels, measure from the rake to the newest seam at the eave and at the ridge. If the two measurements differ, move the next panel slightly to bring it back, but never more than the lock will accept without strain.
Do not force a panel that will not engage. Check for a bent lock, debris in the seam, a high screw head or a panel that has gone out of square.
Step 7: Cut, hem and trim the ends
Use shears or a nibbler to cut panels, not an abrasive wheel, which leaves hot particles that rust. See cutting metal roof panels and hemming and bending panel ends. At the eave, a hem or drip bend keeps water off the fascia. At the ridge, the panel end turns up as an end dam, or fits a profile-matched closure.
Keep every screw out of the water path at valleys and penetrations. See valleys and pipe flashing on metal roofs.
Step 8: Finish with ridge, hip caps, wall flashings and cleanup
Set the closures, fasten the cap through the closure line and lap sections the distance in the manual. See ridge and hip caps and wall flashings.
Sweep off every offcut and shaving. Touch up cut edges and scratches with matched paint and check for loose locks and missed screws.
What Has and Has Not Been Confirmed About ProLock
Domtek Building Products of Carroll, Manitoba lists Pro-Lock as a hidden fastener panel in 12 inch and 16 inch widths, in 26 and 24 gauge, with a 3/12 minimum slope, installed without clips over minimum 1/2 inch plywood with an approved synthetic underlayment. Finishes include premium, textured and woodgrain paint colours. Rib height, fastener spacing and lap dimensions were not stated on the public page, so use the installation manual or ask the supplier for them before ordering.
Thermal Movement on a Fixed-Flange Panel
Because the flange is fastened, the panel cannot slide on clips. Slotted holes and centred screws allow a little movement, but long panels and dark colours push the limits. Steel expands about 0.78 inch over 100 feet with a 100 degree Fahrenheit swing, so keep panel lengths to what the manual allows and read thermal movement in metal roofs.
Common Mistakes
- Installing below the minimum slope, which leaves the lock unable to shed water reliably.
- Overdriving or off-centre screws that pin the panel and cause waviness or noise.
- An unsquare first panel, with the error growing toward the ridge.
- Hammering the lock hard, which dents the panel or bends the lock so it will not seat.
- Mixing trims and closures from another profile, so nothing seals at the eave and ridge.
- Cutting with an abrasive wheel, leaving swarf that rusts on the paint.
- Letting panels get too long for the fixed flange and ignoring thermal movement.
When to Call a Professional
Concealed-fastener roofs show every mistake for decades and the warranty often depends on correct installation. The first panel, the trims and the valleys and wall flashings are where errors are hard to fix later.
If the roof has valleys, hips, multiple planes, skylights or any slope near the minimum, hire a roofer who installs snap-lock panels regularly, and keep the manufacturer's installation manual on the roof.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Metal Roofing service or the towns we cover.
How to Install ProLock Snap-Lock Panels: Questions
What is ProLock metal roofing?
ProLock, sold as Pro-Lock by Domtek Building Products, is a concealed-fastener snap-lock panel for roofs and walls. The manufacturer lists 12 inch and 16 inch widths, 26 and 24 gauge steel, a 3/12 minimum slope and installation over solid plywood with synthetic underlayment, without clips. Panels are screwed through a flange and locked over by the next panel.
What slope does ProLock need?
The manufacturer lists a 3/12 minimum slope, meaning 3 inches of rise for every 12 inches of run. Anything shallower should use a different product, such as mechanically seamed standing seam or a low-slope membrane. Confirm the current minimum in the installation manual, since warranties depend on following it.
Do ProLock panels need clips?
No. The manufacturer describes the panel as installing without clips. The flange has slots and is fastened with screws straight through into the deck, and the next panel's lock snaps over it to hide the screws. That is simpler than clipped standing seam but means the panel is fixed, so length and thermal movement need care.
Is snap-lock metal roofing as good as standing seam?
Both hide the fasteners and give a clean look. Mechanically seamed standing seam usually handles lower slopes, heavier gauges and longer panels, and its clips let panels float. Snap-lock is faster and cheaper to install and works well at 3/12 and steeper on solid decking. The right choice depends on slope, panel length and budget.
Can ProLock go over shingles?
Not directly. The manufacturer specifies a solid plywood substrate with underlayment, so a roof with old shingles should be torn off, or a new solid deck built over it, rather than screwing the flange into soft shingles. Ask the supplier and your building department before choosing any overlay approach.
Related Guides
All Metal Roofing guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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