Siding buyer's guide: vinyl, aluminum and wood compared

Why siding fails

Siding is a rainscreen, not a waterproof seal. Its job is to shed the bulk of the water, breathe, and protect the wall assembly underneath. When it fails, the cause is usually one of four things:

• Water gets behind it and cannot drain. Bad flashing at windows, doors or roof-to-wall junctions traps water inside the wall.
• The wall cannot dry. Vinyl installed tight to a damp wall, or over a failed house wrap, holds moisture against the sheathing.
• Rot starts at the bottom. The lowest course of siding, and the trim around it, takes splash-back from the ground and from roof runoff.
• Sun and thermal movement. Vinyl expands and contracts; panels nailed tight buckle and crack instead of moving.

Vinyl, aluminum and wood compared

Vinyl siding

The dominant choice in this region. It never needs repainting, handles freeze-thaw cycles and is the least expensive to install. Heavier profiles with a foam backing resist impact and wind far better than thin builder-grade panels. The trade-off is that vinyl cannot be repaired invisibly — a cracked panel is replaced, not patched — and colour choice is limited to what the manufacturer runs.

Aluminum siding

Common on mid-century homes in Montgomery and Bucks counties. Aluminum takes paint well, does not rot and can be repaired. It dents, however, and if the original installation trapped moisture, you may find corrosion on the back of the panels. Where aluminum is sound, repainting and repairing trim can be a sensible alternative to a full re-side.

Wood siding

Cedar and engineered wood look best on traditional houses and can be repaired piece by piece. They require painting or staining every few years, and end grain and joints need to be primed properly or rot starts within a season. Wood is the most expensive option to own over twenty years, but it is also the most repairable.

What belongs behind the siding

This is the part of a re-side that nobody sees and that decides whether the job lasts.

• House wrap. A weather-resistive barrier installed with correctly lapped seams, so water that gets past the siding drains down and out.
• Flashing. Window and door openings need head flashing and sill pans. Roof-to-wall junctions need step flashing. Caulk is not flashing.
• Insulation. Foam board in 1/2″, 3/4″ or 1″ thickness reduces air infiltration and raises the wall's surface temperature. Homasote and Celotex brand sheathing are also used where a solid backing is needed.
• A drainage gap. A small gap between the wrap and the siding back lets water and vapour escape instead of sitting against the wall.

Trim details that decide how it looks

• Window and door trim. Width and profile carry most of the visual weight of an elevation. Wider trim usually reads as more traditional.
• Corner treatment. Corner posts, mitred corners or corner boards — each looks different and each behaves differently as the house moves.
• Soffit and fascia. Visually part of the roofline, functionally part of the ventilation and gutter system.
• Designer accessories. Door surrounds, dentil moulding, frieze boards and octagon or circle vents finish an exterior so it looks designed rather than assembled.

What we find when the siding comes off

On older homes in this area, the answer is usually “something”. The most common findings are soft sheathing at the bottom of a wall, rotted window sills, failed or missing flashing at a door head, and crushed or missing sheathing behind a downspout. None of these are visible from the outside, and all of them are far cheaper to fix while the wall is open than to reopen later.

Questions to ask a siding contractor

• Which specific siding profile and thickness is being quoted?
• Is the existing siding removed, and if not, why is an overlay appropriate here?
• What kind of house wrap and flashing is included?
• How is rot found behind the wall handled, and at what price per sheet or per board?
• Are soffit, fascia and gutter work included or excluded?
• What does the workmanship warranty cover, and for how long?

Next step

Call 215-675-6180 or request a free estimate and we will walk the elevations with you, show you samples, and tell you honestly whether you need a full re-side or a targeted repair.