PVC Trim in Ontario: The Only Board You Install to a Thermometer
Key points
- Cellular PVC moves 0.36 in. in an 18 ft board across Ontario's temperature range, less than the vinyl siding beside it
- Five Ontario months sit below the 10 C gap threshold, and no month ever reaches the install tight row
- A 14 window house needs 446 linear feet of trim, and 58 percent of it comes from the openings
A contractor in Newmarket called us in July about a garage door surround his crew had wrapped the previous November. The mitres were tight enough to hide a pencil line the day they left the site. Eight months later there was a visible step at every corner, and he wanted to know which batch of board was defective. None of it was. The PVC trim had done exactly what the manufacturer's own installation guide says it will do, and the crew had worked to a gap rule written for a different temperature than the one they were standing in.
Cellular PVC is the only exterior board on an Ontario house specified partly by the weather on the morning you cut it. Wood is specified by species and grade, fibre cement by thickness, vinyl by profile. This guide covers what the material is, the two different gap schedules the brands we stock publish, which Ontario months land on which side of the line, and how many feet of it a real house swallows. For the wider picture the trim sits inside, our Ontario siding cost pillar prices the whole wall.
What Is PVC Trim, and Why Does It Move?
PVC trim is cellular polyvinyl chloride milled into boards, sheets, corners and mouldings. It contains no wood fibre, absorbs no water, and cannot rot, split or feed insects. The trade is dimensional: it expands and contracts with temperature far more than the wood it replaces, so every joint has to be gapped to the day you install it.
At Pro Materials we carry the trim line in two families. CertainTeed Restoration Millwork covers the cellular PVC side with trim boards 3/4 in. thick in widths to 16 in. and 1 in. thick in widths to 12 in., one piece corner boards in 4 in. and 6 in., brickmould for window and door surrounds, sheets to 4 by 12 ft, beadboard, column wraps for 4x4 and 6x6 posts and 24 specialty exterior profiles. Ply Gem PVC Trim and Mouldings, distributed here by Mitten, adds skirt boards that can sit against concrete, post wraps, and a mouldings line that runs from a 5-1/4 in. crown down to quarter round. Both carry a Class A flame spread rating under ASTM E84 and both meet ICC and CCMC code requirements.
The material's one real weakness is movement, and the size of that movement is a published constant. Cellular PVC has a coefficient of linear thermal expansion of 3.2 x 10⁻⁵ in./in./°F. Run that across the 28.6 C° spread between Toronto's coldest and warmest monthly daily maximum normals and an 18 ft board changes length by a little over a third of an inch.
| Material | Coefficient of expansion (in./in./°F) | Movement in an 18 ft board across 28.6 C° |
|---|---|---|
| Aluminum trim coil and fascia | 11.7 to 13.7 x 10⁻⁵ | 1.30 to 1.52 in. |
| Rigid PVC, as in vinyl siding | 4.5 x 10⁻⁵ | 0.50 in. |
| Cellular PVC trim board | 3.2 x 10⁻⁵ | 0.36 in. |
| Steel | 0.8 x 10⁻⁵ | 0.09 in. |
| Concrete | 0.4 to 0.7 x 10⁻⁵ | 0.04 to 0.08 in. |
| Glass | 0.4 x 10⁻⁵ | 0.04 in. |
Read that table twice, because it says the opposite of what the trade usually says about this material. PVC trim is not the biggest mover on the wall. The aluminum trim coil and fascia running beside it travel roughly four times as far, which is part of why our metal siding guide treats fastening and expansion as the whole job, and the vinyl siding it frames travels about 40 percent further. What separates them is restraint, not chemistry. Siding hangs from a nail slot and locks into a hem that is designed to let each course slide, which our vinyl siding pillar covers as the nail-it-loose rule. Aluminum fascia is bent, hemmed and lapped. A trim board is screwed flat to the sheathing at 16 in. on centre, so its movement has exactly one place to go, and that is the joint you left at the end of the run.
Cellular PVC Trim Stocked at Pro Materials
The Board You Install to a Thermometer
Because the movement is real and the restraint is total, both manufacturers publish the gap as a lookup table keyed on air temperature rather than as a single number. Here is where it gets awkward for a crew that runs both brands, which is common across York Region and the GTA, and it is a difference our Mitten and Kaycan comparison does not have to deal with because the panels themselves share an install method. The two tables do not agree.
| Brand | Install tight | Standard gap | Cold band gap |
|---|---|---|---|
| CertainTeed Restoration Millwork | 38 C (100 F) and above | 10 to 38 C: 1/8 in. at joint, 1/16 in. at edges | Below 10 C: 1/8 to 1/4 in. at joint |
| Ply Gem PVC Trim, by Mitten | 32 C (90 F) and above | 10 to 32 C: 1/8 in. | Below 10 C: 3/16 in. |
Both brands put the lower break at the same place, 50 F, which converts to exactly 10.0 C. After that they diverge. CertainTeed holds the standard gap another six Celsius degrees before it lets you close the joint, gives a range rather than a figure in the cold band, and adds a 1/16 in. edge gap that Ply Gem does not call for at all. Ply Gem answers the cold band with one number, 3/16 in., which sits in the middle of CertainTeed's range.
Neither is wrong. They are different extrusions with different published tolerances, and each schedule is validated against its own warranty. The practical consequence is that a gap habit learned on one brand is wrong roughly half the time on the other, which is the single most common cause of the opened mitre our Newmarket customer was looking at. CertainTeed also publishes a flat allowance that is worth carrying in your head as a sanity check: 1/4 in. per 18 ft of product, split as 1/8 in. at each end of a run. The full schedule is printed in the Ply Gem PVC installation guide, and the profiles it applies to are listed on the CertainTeed Restoration Millwork specialty profile page.
Which Ontario Months Fall in the Wide Gap Band?
Five of the twelve months in Toronto sit below the 10 C threshold even at the warmest hour of an average day, so November through March are wide gap months by default. No month reaches the 32 C line at all, which means the install tight row of both tables is unreachable on a normal Ontario day and the province only ever uses two of the three bands.
- Wide gap, 3/16 in. · 5 months
- Standard gap, 1/8 in. · 7 months
- Install tight · 0 months
- Jan-1.2 C
- Feb-0.3 C
- Mar5 C
- Apr12 C
- May19.2 C
- Jun24.5 C
- Jul27.4 C
- Aug26.3 C
- Sep22.3 C
- Oct14.6 C
- Nov7.9 C
- Dec1.9 C
Two details in that chart are worth pulling out. The first is that the chart uses daily maximum normals, not daily averages, which is deliberately the most flattering number available. Measured on the daily average instead, April joins the cold band and six months qualify. The second is a coincidence that makes the rule easy to remember. October's daily average normal for Toronto Pearson is 10.0 C, and the threshold both manufacturers publish is 50 F, which is 10.0 C exactly. October is the month the rule changes, almost to the day. You can check both figures yourself in the Environment and Climate Change Canada normals for Toronto Pearson.
Contractors in York Region and the GTA tell us the wide gap is the part clients push back on, because a 3/16 in. joint on a November install looks like sloppy carpentry in the driveway inspection. It is the opposite. That joint is the reason the mitre is still shut in July.
What Else Changes When the Temperature Drops?
The gap is the rule everyone knows. Two more change with it, and both are easier to miss because they are buried in the fastening and spanning sections rather than the expansion section.
- Pre-drilling becomes mandatory. CertainTeed states that pre-drilling is not needed except when you use large fasteners or install below 4.4 C (40 F). Below that, a fastener driven near a board end is where a split begins.
- Unsupported span halves. Restoration Millwork sheets used as soffit normally span framing at up to 24 in. on centre. At 4.4 C or below, the manual caps the span at 12 in.
- Fastener spacing tightens. Ply Gem calls for 16 in. on centre in the field, reduced to 12 in. on long runs, and reduced again with wider joints on southern exposures where the board sits in direct sun.
The last of those points at the other end of the thermometer. Air temperature is not what a dark board actually reaches. Cellular PVC begins to deform somewhere around 145 to 150 F, and a dark surface in full sun runs well above the air around it, which is why both manufacturers cap paint colour by reflectance rather than by hue. Use a 100 percent acrylic latex with a light reflectance value of 55 or higher. Anything at LRV 54 or lower needs a heat reflective formulation such as Sherwin-Williams VinylSafe, and post wraps in dark colours without one will warp. The same logic governs dark cladding generally, which we cover in the vinyl siding colour guide.
How Much PVC Trim Does a House Actually Need?
Trim quantity scales with the perimeter of the openings and corners, not with the area of the wall. On a two storey Newmarket house of 32 by 26 ft with fourteen windows, two doors and four corners, the take-off comes to 446 linear feet of trim, and 258 of those feet, 58 percent, is casing around openings the siding order never sees.
Our siding cost pillar works a re-clad on a 32 by 26 ft two storey at nine feet per floor: 116 ft of perimeter, two gables, fourteen windows and two doors, and 1,992 sq ft of net cladding once the 252 sq ft of openings come off. That article makes the point that accessories scale with edges rather than faces. Run the trim take-off on the same house and you can put a number on it.
| Trim run | Basis | Linear feet |
|---|---|---|
| Window casing, 14 openings at 3 by 5 ft | 16 ft of casing per opening | 224 |
| Door casing, 2 openings at 3 by 7 ft | head and two jambs, 17 ft each | 34 |
| Outside corner boards, 4 corners | full 18 ft wall height | 72 |
| Frieze board under the eave | house perimeter | 116 |
| Total | 446 |
The openings are the interesting line. Those fourteen windows and two doors were subtracted from the siding order as 252 sq ft of wall that does not need cladding, and they come straight back as 258 linear feet of trim that does. The square footage that leaves one order creates the other. In boards, the 374 ft of casing and frieze works out to 23 pieces of 5/4 x 4 x 18 ft with a ten percent cut and waste allowance, the corners take four 20 ft one piece corners so an 18 ft height runs with no seam, and 446 linear feet of face fastening takes two 250 LF packs of Cortex hidden fasteners.
Now hold the house still and change only the window count. Wall area barely moves. Trim moves a long way, and in the opposite direction.
Same house throughout: 32 by 26 ft footprint, two storeys at 9 ft, two gables, two doors at 3 by 7 ft, windows at 3 by 5 ft. Absolute values are 2,082, 1,992 and 1,902 sq ft of cladding against 350, 446 and 542 linear feet of trim.
Going from eight windows to twenty drops the cladding area by 8.6 percent and lifts the trim by 54.9 percent. That single divergence is why two builders can order the same number of squares of horizontal vinyl siding for houses of the same size and one of them buys half again as much trim. It is also why we quote trim as a supply package against an opening and corner count rather than publishing a rate per linear foot. We do not have a sourced Ontario installed figure for trim the way we do for the cladding materials priced in the pillar, and a rate invented to fill the gap would be the least useful number in the conversation.
How Do You Install PVC Trim So the Joints Stay Shut?
The sequence below follows the published manuals for both brands. Steps two and five are the ones that change with the season.
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Let the board reach outdoor temperature. Allow the trim to acclimate to the outside air before you cut it, and install long runs at 16 to 21 C where the schedule allows. Store the boards flat on a level surface, off asphalt and out of direct heat, with the protective film left on.
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Read the thermometer, then pick the gap. Take the air temperature and look up the gap for the brand in your hands. Below 10 C, Ply Gem calls for 3/16 in. and CertainTeed for 1/8 to 1/4 in. Apply the gap once per 18 ft of run, at the ends of boards or at an inconspicuous joint, and never fill that joint completely with sealant.
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Fasten into solid substrate. Use stainless steel or hot dipped galvanized fasteners and drive them 1-1/2 in. into framing. One inch of penetration is acceptable through 1/2 in. structural OSB. Over foam sheathing the fastener still has to reach a full 1-1/2 in. into framing, so it has to be longer, and the house wrap or insulating sheathing behind the trim has to be sealed before the board goes on.
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Match the fastener count to the board width. Boards under 6 in. wide take two fasteners, 6 to 12 in. take three, and anything wider takes four. Space them 16 in. on centre in the field, and tighten to 12 in. on long runs and on south facing walls where the board sees direct sun.
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Pre-drill below 4.4 C. Pre-drilling is not needed in normal conditions, but CertainTeed calls for it below 4.4 C or when you are using large fasteners. Cold cellular PVC is less forgiving, and a driven fastener near a board end is where a split starts.
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Glue the field joints and gap the ends. Bond scarf and mitre joints with a two component PVC adhesive and place fasteners on both sides of each joint. Gluing the field joints pushes all of the movement out to the ends of the run, which is where you left the designed gap.
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Paint only above LRV 55. Scuff sand with 100 to 120 grit, then use a 100 percent acrylic latex with a light reflectance value of 55 or higher. Below LRV 54, use a heat reflective formulation such as Sherwin-Williams VinylSafe, because a dark board in direct sun approaches the heat distortion range of cellular PVC.
Two things stay off this list on purpose. Staples, brads, wire nails, ring shank nails and fine threaded wood screws are all excluded by both manufacturers, and adhesive alone never attaches trim to a substrate. Cellular PVC is also non structural in every application, so it wraps a post but never replaces one. Ontario's requirements for the wall behind it sit in O. Reg. 332/12 under the Building Code Act.
Where to Buy PVC Trim in Ontario
We stock the cellular PVC line alongside the cladding it finishes, which matters more than it sounds: the trim, the soffit and fascia, the eavestrough and the panel all have to arrive in matching colour and on the same day, or the crew works twice. The soffit panel ordering guide shows how the vent split on the eave line quietly adds a carton to that same purchase order. Contractors ordering Kaycan lap siding from the Kaycan range, LP SmartSide and CanExel, or the vertical profiles in our board and batten guide generally take their casing and corners off the same purchase order, and the full vinyl trim range sits in the same aisle. Board and batten is the profile where PVC trim earns its keep twice over, since every batten is an edge and every edge is a joint.
Send us the perimeter, the opening count and the corner count and we will price the trim package as supply, so you can set your own labour against a material number that is not a guess. We deliver across York Region, the GTA, Simcoe County and Southern Ontario from Newmarket, and the full list is on our service areas page. To start a package, use the quote request form.
NEWMARKET SHOWROOM Unit 5, 1235 Journey's End Cir, Newmarket, ON L3Y 8T7
Phone: +1 (905) 836-7272 Email: info@promaterials.ca
Sheets, Wraps and Fastening for a Complete PVC Trim Package
Priya Nair
Building Materials Buyer & Pricing Analyst
Priya manages purchasing and pricing at Pro Materials. She tracks material cost fluctuations across Canadian suppliers and helps contractors understand volume pricing, lead times, and the real cost breakdown of exterior systems.
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