Proper Siding Installation

Proper siding installation is the difference between an exterior that stays straight, drains correctly, and holds up through seasonal change — and one that develops waviness, loose panels, trapped moisture, or recurring repair points. Good results come from following a consistent system: wall preparation, a weather-resistive barrier, correct detailing at openings and transitions, and fastening that allows normal material movement.

Because each siding type and profile can have its own requirements (fasteners, expansion gaps, substrates, and accessories), proper installation also means following the published installation instructions for the specific product being installed — not guessing or “installing everything the same way.” 

Before any siding goes on, the wall needs to be stable and reasonably flat. On re-siding projects, that means removing or moving exterior fixtures (where required), securing loose areas, and replacing decayed material so the new system has a solid base. Gentek specifically notes to nail down loose boards/shingles and replace decayed material, and to check walls for level/straightness. 

Where walls are uneven (including masonry), strapping may be required and shimmed to keep the finished siding straight and uniform. This is especially relevant when tying in partial upgrades, dormers, and bay build-outs so the finished elevations don’t look patched.

Siding is designed to shed water, but a proper wall assembly also needs a dedicated weather-resistive barrier behind it. Our standard practice is to use housewrap on siding installs, and then build the siding system and trim details in a way that encourages drainage and drying.

When insulation boards are part of the system, the weather barrier and detailing need to work with that assembly so moisture isn’t trapped at seams, transitions, and openings. The goal is always the same: a system that manages water and air reliably over time.

Vinyl expands and contracts with temperature change. Gentek provides a clear reference: approximately 8 mm (1/3") over a 3 m (10') length for a 55°C (131°F) change. 

That movement is why Gentek’s basic rules emphasize leaving clearance where panels fit into accessories:

• 6 mm (1/4") clearance for normal conditions

• 12 mm (1/2") minimum clearance when installing in freezing temperatures 

Other siding types and profiles can have different requirements, but the principle remains: proper installs allow the material to move as designed instead of binding inside channels or being locked in place.

One of the most important manufacturer rules for vinyl siding is that it should not be nailed tightly. Gentek states vinyl siding is not “nailed” to the wall — it is “hung” on the nails so each panel can move freely. 

Key Gentek fastening requirements include:

• Place fasteners in the center of the nailing slot (unless the manual specifies otherwise) 

• Never nail through the siding itself 

• Use corrosion-resistant roofing nails with minimum 8 mm (5/16") head diameter 

• Fasteners must be long enough to anchor minimum 20 mm (3/4") into solid wood framing or cladding 

Different products (including insulated vinyl, vertical profiles, or specialty panels) may change fastening schedules and details — so this page sets the standard principles and your specific product pages should still be followed for the exact requirements.

Proper installation also includes correct engagement between courses and correct overlap practices. Gentek’s basic rules include:

• When nailing horizontal siding, gently lift the top panel so the locks just touch (not forced tight) 

• Accessories should be overlapped except where noted, and siding/accessories should be installed in the proper sequence 

These details help prevent stress points, keep lines clean, and reduce long-term distortion from seasonal expansion and contraction.

Windows, doors, corners, roof-to-wall transitions, and trim terminations are where water and movement issues show up first. Proper installation is as much about correct trim planning as it is about the siding panels themselves.

Gentek notes caulking is required where water penetration is possible (for example, penetrations through walls or J-channel areas at openings), and specifies using quality caulking with sustained flexibility and to avoid oil-based caulking. 

Dormers, bay build-outs, gables, and accent areas often require vertical applications, beltline transitions, or different trim strategies. Gentek’s guide covers using appropriate trims and proper setup for vertical siding applications, including using a vertical J-channel as a starter/receiver and maintaining straight reference lines. 

The important takeaway: accents and architectural areas should be planned so the transitions look intentional and the wall assembly remains consistent — not “patched.”

Ontario’s freeze-thaw cycles and wide seasonal temperature swings make correct movement allowances and proper fastening even more important. Vinyl movement that isn’t accommodated can show as buckling, oil-canning, or stress at terminations, especially after the first full winter.

A proper install is built to stay stable through those cycles while maintaining clean alignment and consistent finishes over time.

Some of the questions we receive are:

•  Why do vinyl siding panels buckle or look wavy? 

•  What expansion gap should be left at channels and trim? 

•  What fasteners should be used for vinyl siding? 

•  Is caulking a substitute for correct trim and overlap? 

•  Can the same install rules be applied to every siding type? 

Please visit our FAQs page for detailed answers.

Material selection matters, but performance depends on installation standards: wall preparation, a complete weather barrier, correct trim planning, and fastening that allows normal movement.

If you’re planning a siding project and want guidance on scope, materials, or what proper installation should include, reach out to Century Aluminum for a free estimate.