Siding · Glossary

Siding glossary

The siding terms that matter most in a quote are square (100 square feet of wall), water-resistive barrier (the sheet behind the siding that actually manages water), flashing (metal that directs water out of joints), kickout flashing (the small piece at a roof-wall intersection that prevents a very common rot failure), and exposure (the visible height of each course).

Get my free quote

Quotes are written in trade shorthand, and the shorthand hides where the money and the risk are. If a quote mentions siding, trim, and a color but never mentions the barrier or flashing, the quote is describing the visible half of the job only.

Learn five terms and you can read almost any siding quote: square, water-resistive barrier, flashing (especially kickout flashing), rain screen, and exposure. The rest is product naming.

How to choose

Square: 100 square feet of wall area. Material is ordered and priced by the square, so it's the unit that makes quotes comparable.
Water-resistive barrier (WRB): The housewrap or building paper behind the siding. This, not the siding, is the layer that keeps water out of your sheathing.
Flashing and kickout flashing: Metal pieces that route water out of joints. Kickout flashing sits where a roof edge meets a wall and diverts runoff away — its absence is a classic cause of hidden rot.
Rain screen: A drainage gap between siding and the barrier so water and vapor can escape. Standard practice in wet climates and worth asking about.
Exposure and course: A course is one row of siding; exposure is how much of it shows. Exposure changes material quantity and appearance.
J-channel and starter strip: Trim pieces that receive panel edges and set the first course. Sloppy J-channel at windows is a common water entry point.

0 of 6 live

All siding glossary

Cladding

Housewrap

J-Channel

Lap Siding

Rainscreen

Weep Holes

FAQ

Siding glossary — common questions

Still have a question? Talk to our team →

What's the difference between siding and a rain screen?

Siding is the visible cladding. A rain screen is the drainage gap behind it. A siding job can be built with or without a rain screen gap; ask which you're getting.

Is housewrap the same as a vapor barrier?

No. A water-resistive barrier sheds liquid water while allowing vapor to pass. A vapor barrier restricts vapor movement and belongs in a different place in the wall depending on climate.

What does 'exposure' change?

How much of each board shows, which changes both the look and how many boards are needed. It should be stated in the quote.

Why does kickout flashing keep coming up?

Because it's small, cheap, easy to omit, and its absence dumps a roof's worth of runoff into a wall. Ask specifically whether it's included where roofs meet walls.

Sources

Where these figures come from

This Old House — Siding Replacement Cost (2026) · retrieved 2026-07-25
ENERGY STAR — Recommended Home Insulation R-Values · retrieved 2026-07-25