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Siding Guide: Materials, Estimating & What Goes Behind It

Siding is a rain screen, not a seal. Every cladding material leaks somewhere — at a nail head, behind a butt joint, around a window — and a wall that lasts is one built to let that water drain back out rather than one built to keep every drop from getting in. Nearly every siding failure traces back to that principle being ignored.

This guide covers the common materials, how to estimate them, and the assembly behind the visible layer.

What goes behind the siding

Working outward from the sheathing:

  1. Water-resistive barrier. House wrap or felt, lapped shingle-fashion so upper courses overlay lower ones. IRC R703.2 requires it behind most claddings. Taped seams help, but lapping direction matters more — a perfectly taped barrier lapped the wrong way still channels water inward.
  2. Flashing. At every horizontal interruption: window and door heads, deck ledgers, roof-to-wall junctions, and the base of the wall. Head flashing over a window with a drip edge does more for the life of a wall than any upgrade in siding material.
  3. Drainage gap. Furring strips creating a rain-screen cavity let water that gets behind the cladding run down and out. This is standard practice in wet climates and increasingly common everywhere. It is also what makes board and batten over existing siding practical.

Skipping the gap is survivable in a dry climate. Skipping the flashing is not, anywhere.

Board and batten

Wide boards set vertically with narrow battens covering the seams. Traditionally an agricultural cladding, now common on farmhouse-style and modern homes.

Estimating starts from effective coverage rather than board width. Each board is covered on both edges by the battens, so a nominal 1×12 — which actually measures 11.25 inches — with half an inch of overlap per side covers 10.25 inches. Divide the wall width by that figure, not by 12.

The nailing pattern is what makes it last. Wide boards move seasonally across the grain, so they are fastened near the centre only, letting them expand and contract. Battens are nailed through the gap between boards, not through the boards themselves. Nail a board at both edges and it will split the first dry winter.

Deduct openings for material volume, but not from the board count — a board interrupted by a window still runs the full wall height in two pieces, which is why 10% waste is a floor on walls with many openings.

Use the board and batten calculator for board and batten counts and linear footage.

Lap siding

Horizontal boards, each overlapping the one below. Available in wood, engineered wood, fibre cement, and vinyl.

Exposure is the visible height of each course — the board width minus the overlap. A 8.25-inch fibre cement plank at 1.25 inches of overlap gives 7 inches of exposure. Courses needed is wall height in inches divided by exposure, rounded up.

Minimum overlap is typically 1.25 inches for fibre cement and 1 inch for wood. Less than that and wind-driven rain tracks up between the courses by capillary action.

Material comparison

| | Cost/ft² (material) | Lifespan | Maintenance | |---|---|---|---| | Vinyl | $1–4 | 20–40 yr | Wash occasionally | | Engineered wood | $3–6 | 20–30 yr | Repaint 7–10 yr | | Fibre cement | $3–6 | 30–50 yr | Repaint 10–15 yr | | Pine (painted) | $2–4 | 15–30 yr | Repaint 5–7 yr | | Cedar | $5–9 | 30–50 yr | Stain 3–5 yr |

Installation usually at least doubles the material figure, and fibre cement costs more to install than the others — it is heavy, dulls blades fast, and cutting it produces silica dust that requires respiratory protection and a dust-collecting saw.

Cedar and redwood resist rot naturally, which is why they survive in wet climates where painted pine does not. In dry climates the difference matters far less and the price gap is hard to justify.

Estimating any siding

  1. Measure gross wall area with the square footage calculator — width times height for each wall face. For a gable end, use half the base times the height of the triangle.
  2. Deduct openings larger than about 10 square feet. Small windows are usually left in as waste allowance.
  3. Add waste: 10% for straightforward walls, 15% where there are many openings, corners, or angled cuts on gables.
  4. Count the trim separately. Corner boards, window and door casing, frieze, and water table are all linear-foot items and are easy to forget until the siding is up and the corners are open.
  5. Fasteners matter. Use stainless or hot-dip galvanised. Electro-galvanised nails corrode against cedar's natural tannins and bleed black streaks down a new wall within a year.

Paint and stain

Prime all six sides of wood siding before installation, including the cut ends. Field-cut ends left bare are the most common entry point for water into a board. Back-priming — coating the hidden face — is what stops moisture entering from behind and pushing the finish off the front.

Estimate coverage with the paint calculator, and note that rough-sawn surfaces absorb far more than smooth ones; a rough cedar wall can take nearly twice the paint of a smooth one for the same area.

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