A Glossary of Siding Terms for Homeowners

Siding contractors compress an entire wall system into a page of shorthand. Here is what the words mean, and which ones are worth a question before you sign.

Licensing, permit, lien and tax rules vary by state and city and change over time. This guide is general information, not legal or tax advice; check with your local building department, state licensing board or a professional for your situation.

Siding bids are short documents written in shorthand. One line might read “Dutch lap over house wrap, J-channel at openings, aluminum fascia wrap.” If you do not know the words, you cannot tell whether the bid describes a careful installation or a fast one. This glossary covers the terms that come up most often, what each part does, and which ones deserve a question before you sign.

Why Siding Estimates Sound Like Another Language

A siding job is more than the panels you see. Every wall is an assembly: sheathing, a water-resistive barrier, flashing and trim, layered in a specific order with the visible siding attached to the outside. A good estimate names these parts. A vague one prices “siding” and leaves you to assume the rest.

Two things help you here. Local building codes set requirements for sheathing, barriers and flashing, and those requirements vary by location, so ask what applies to your house. Manufacturers also publish installation instructions, and a crew that follows them builds a different wall than a crew that improvises. The vocabulary below is how you tell the difference on paper.

Wall Assembly Terms: What Goes Under the Panels

Sheathing. The flat material applied over the studs and under the siding to provide a smooth, even surface. Vinyl siding should never be applied directly to studs without sheathing, so a bid that says nothing about wall preparation is worth a question.

House wrap (water-resistive barrier). A continuous layer installed over the sheathing to stop incidental water that gets behind the cladding. Codes address where a barrier is required, and the specifics depend on where you live.

Flashing. Thin, flat material placed under and behind trim, windows, doors and corner posts to route draining water back out of the wall. Code-compliant flashing should be integrated with the house wrap, and it also belongs at wall and roof intersections. Water leaking through exterior cladding is a common cause of construction defects, and missing or poorly executed flashing is a usual suspect.

Drip cap. A piece of trim installed over the top of windows, doors or vertical siding to keep runoff from getting behind the panels.

Some jobs also use furring strips, thin boards applied to even out a wall surface before siding goes on. And at the base of certain wall types, details such as weep holes in brick or a weep screed under stucco let water exit at the bottom, which is why flashing at the bottom of an exterior wall should direct water down and out.

Siding Material and Style Terms

Lap siding (clapboard). Horizontal siding installed from the bottom up so each plank overlaps the one below. That overlap is what hides the fasteners from view.

Dutch lap. A variation of clapboard with a slightly concave face and a notch at the top of each plank, creating a distinct shadow line. The notches were once hand carved into wood, but modern vinyl produces the same look.

Board and batten. Vertical boards with narrow strips, called battens, covering the joints between them. It is the classic barn siding look, and the same style is behind the modern farmhouse aesthetic.

Gables, the triangular wall sections where two roof pitches meet, often get an accent material such as shakes or shingles even when the rest of the house is lap siding. Ask which material the bid prices for gables, because accent areas are usually priced separately.

Profile, Exposure and Coursing on Your Quote

These words describe how panels are shaped and laid out, and they drive material quantities.

Course. One row of panels, one panel wide, running the length of the house, or top to bottom for vertical siding. The term shows up mostly during layout and estimating.

Exposure. The height of siding that stays visible after the overlap is deducted. A narrower exposure means more overlap, which takes more material to cover the same wall.

Buttlock. The bottom edge of a panel, opposite the nailing slots, that locks onto the piece below it.

Starter strip. A strip installed around the base of the house that locks the first course in place. Estimating it is straightforward: measure the linear feet around the entire base.

Trim Terms: Soffit, Fascia and Channels

Soffit. The material that encloses the underside of the eave, running from the wall to the fascia. Soffit comes in solid and vented panels, and vented soffit allows air to move in and out of the attic while keeping out water and insects.

Fascia. The horizontal board at the roof’s edge that covers the ends of the rafters and supports the gutters. A bid mentioning “fascia wrap” or a fascia cap means the crew covers the existing board rather than replacing it.

Corner post. The accessory at inside and outside corners that has built-in channels to receive the siding panels.

J-channel. Trim named for its shape that receives siding and soffit panels wherever they end at an edge or opening, such as around windows and where the wall meets the soffit.

Installation Words That Signal Good Work

Nail hem. The section of a panel where the nailing slots are located. Fasteners belong in those slots and should be corrosion resistant, such as aluminum, galvanized steel or stainless steel.

Face-nailing. Driving nails through the visible face of a panel instead of the hem slots. This is generally not part of proper siding installation, so if you see it happening, ask before the crew moves on.

Expansion gap. Vinyl moves with temperature, so installers leave room for movement, for example cutting soffit panels a half inch short of the measured span and leaving a quarter inch where channels meet adjoining walls. A crew that butts everything tight is creating buckle problems for later.

The fastening detail also depends on the wall. Fasteners need to penetrate nailable material, usually about an inch and a quarter, and foam plastic sheathing does not count toward that depth, so fasteners must reach through it and into the wood framing. Estimators also typically leave windows and doors in their measurements as an allowance for waste and add extra siding on top of the total, rather than deducting every opening.

Performance Terms: R-Value, Wind Rating and Impact Resistance

R-value. A measure of a product’s resistance to heat flow. The higher the number, the better the thermal performance, which is the argument behind insulated vinyl siding.

Wind rating. Codes place stringent performance requirements on cladding in coastal and other high-wind areas, and manufacturers publish specific fastening techniques for those conditions. If your home is exposed, ask how the bid’s fastening plan accounts for it.

Impact resistance, or how a panel holds up to hail and stray baseballs, gets marketed heavily. Rather than accepting the phrase from a brochure, ask what test the product’s rating comes from.

Questions to Ask When the Bid Uses a Term You Don’t Know

You do not need to out-talk the contractor. You need the bid to name its parts. Ask:

• Can you show me where the house wrap, flashing and starter strip appear on the bid, and which trim pieces are included?
• How will flashing be integrated with the water-resistive barrier at windows, doors and corners?
• Which manufacturer installation instructions will the crew follow, and what does our local building code require for sheathing and barriers?
• What happens to the price if you open up a wall and find damage?

Be extra careful after storms, when crews sometimes show up uninvited; door-to-door repair scams follow storm damage, and pressure to sign fast is a red flag. It also pays to confirm who you are dealing with before signing anything, and our guide to checking a contractor’s license walks through it. Once the terms are clear, get them into writing: what a home improvement contract should say covers the clauses that turn a detailed bid into a contract you can hold someone to.

Keep reading

• Roofing Terms to Know Before You Sign an Estimate: a matching glossary for the other half of your exterior project.
• What a Home Improvement Contract Should Say: the specific clauses and details a signed contract should include.
• How to Check a Contractor’s License: verify the installer’s credentials before any of these terms matter.

Homeowners ask

What is the difference between lap siding and Dutch lap?

Lap siding, also called clapboard, is horizontal siding installed from the bottom up so each plank overlaps the one below. Dutch lap is a variation with a slightly concave face and a notch at the top of each plank that produces a deeper shadow line.

What does exposure mean on a siding quote?

Exposure is how much of each plank stays visible after the overlap is deducted. A narrower exposure means more overlap, which requires more siding material to cover the same wall.

Why does flashing matter so much on a siding job?

Flashing directs water that gets behind the cladding back out of the wall, and it should be integrated with the house wrap at windows, doors, corners and wall-to-roof intersections. Missing or poorly executed flashing is a common cause of leaks and callbacks.

Is face-nailing vinyl siding acceptable?

Generally no. Fasteners belong in the nail hem slots, which are designed to let panels move as vinyl expands and contracts. If a crew drives nails through the visible face of the panels, ask why before they continue.