Do you need house wrap under siding?

Yes. Siding sheds the bulk of the rain, but the weather-resistive barrier behind it is the actual water control layer — the thing that keeps the wall assembly dry when water inevitably gets past the cladding. Hang it bottom to top with each course lapping over the one below, shingle-style, so gravity carries water down and out. Installing siding directly over bare sheathing is a wall that will eventually rot, and it is invisible until it is expensive.

How do you flash a window before siding?

In strict bottom-up order so every layer sheds onto the one below: sill pan first, then the jamb flashings lapping over the sill, then head flashing lapping over the jambs, and finally the weather barrier lapping over the head flashing. Reversing any single lap turns that joint into a funnel aimed into the wall. Window openings are where the large majority of siding-related water damage starts, so this sequence matters more than any other detail in the job.

Why can't you nail vinyl siding tight?

Vinyl expands and contracts substantially with temperature — a long run can change length noticeably between a winter morning and a summer afternoon. It is designed to hang from its nails and slide, not to be pinned. Nail in the center of the slot and leave roughly a sixteenth of an inch of play under the head. Driven tight, the panel cannot move and buckles into visible waves on the first hot day, which is the single most common vinyl siding failure and is entirely an installation error.

Should you caulk the laps on lap siding?

No. Caulk the junctions where siding meets trim, corners, and penetrations, but leave the horizontal laps and the weep slots at the bottom of vinyl panels open. Those gaps are drainage paths — they let incidental water that gets behind the cladding escape. Sealing them traps water inside the wall, which is worse than the small amount it was keeping out. This is a common and well-intentioned mistake.

Do you have to paint cut edges of fiber cement siding?

Yes, and it is the step most often skipped. Factory-finished fiber cement is sealed on its faces, but every cut you make on site exposes raw material that wicks water. Unsealed cut edges are where fiber cement fails first — swelling, then delaminating. Prime every field cut before installation. Cutting fiber cement also produces crystalline silica dust, so use a respirator and a dust-reducing blade or shear, not a standard circular saw blade in a cloud.

How to Install Lap Siding — Step-by-Step Guide

An eight-step guide covering tear-off and sheathing inspection, the weather barrier, opening flashing order, trim, a dead-level starter strip, consistent exposure, material-specific fastening, and what to caulk (and what never to).

Siding is really two jobs stacked together. The one everyone sees is the cladding — straight courses, tight joints, even exposure. The one that actually determines whether the wall survives is the water management layer underneath: the weather-resistive barrier and, above all, the flashing at every opening. Siding sheds most of the rain; the barrier behind it handles what gets through. Get the laps backwards at a window head and you have built a funnel into the wall that nobody will find for a decade. Size the order first with the Siding Calculator.

Tools & Materials

Tools: a circular saw with the right blade for your material (a fiber-cement blade or shears for Hardie-style board), a snap-lock punch and unlocking tool for vinyl, a chalk line and 4-foot level, a story pole for consistent exposure, a nailer or hammer, snips and a utility knife, and scaffolding or ladders with standoffs. If you are cutting fiber cement, a respirator is not optional — the dust contains crystalline silica.

Materials (size the order with the calculator below):

Siding in squares — count them with the Siding Calculator
Weather-resistive barrier (house wrap or felt) and seam tape
Flashing tape, sill pans, head and Z-flashing
Starter strip, corner posts, J-channel and trim
Corrosion-resistant nails sized for your material
Exterior caulk, plus primer and paint for cut edges

Step 1: Tear Off and Inspect the Sheathing

Strip the old cladding and inspect before ordering anything else. Probe sheathing and framing for rot, concentrating below windows, at corners, and anywhere the old siding was stained or bulging. Any structural repair has to happen now — everything you install afterward makes it inaccessible. This is also the moment to add exterior insulation if that is in scope, since it changes trim depths.

Step 2: Hang the Weather-Resistive Barrier

Install house wrap or felt over the sheathing, bottom to top, each course lapping over the one below like shingles, so gravity carries water out rather than in. Tape the seams per the manufacturer's instructions. Remember what this layer is: the barrier, not the siding, is the water control layer. Siding sheds the bulk of the rain; the barrier handles everything that gets past it.

Step 3: Flash Every Opening — In Order

This is the most consequential step in the entire job. Work strictly bottom-up so every layer sheds onto the one below:

Sill pan first, across the bottom
Jamb flashings lapping over the sill
Head flashing lapping over the jambs
Weather barrier lapping over the head flashing

Reverse any single lap and that joint becomes a funnel pointed into the wall. The large majority of siding-related water damage originates at window openings, and essentially all of it is a lap order error — invisible for years, then very expensive.

Step 4: Install Trim and Corner Posts

Set corner posts, J-channel around openings, and any band or frieze trim before the field siding, so courses cut into them cleanly. Get this work plumb and square — every course above references it, so trim that is slightly out telegraphs into siding that looks visibly wrong.

Step 5: Set a Dead-Level Starter Strip

Snap a level chalk line near the bottom of the wall and install the starter strip to it. This one line sets the angle of every course above it, so an error compounds all the way up — a starter off by a quarter inch produces a wall that is visibly crooked at the eave. Check with a level, and specifically do not measure down from the eave, which on most houses is not itself level.

Step 6: Run Courses at Consistent Exposure

Work upward keeping the exposure — the visible height of each course — identical, using a story pole or gauge rather than measuring each piece, which accumulates error. Stagger end joints between courses by at least a couple of feet so seams don't stack into a vertical line, and keep them away from the corners of windows and doors where stress concentrates.

Step 7: Fasten Correctly for Your Material

Vinyl must hang, not be pinned. Nail in the center of the slot, leave about a sixteenth of an inch of play under the head, and never drive tight. Vinyl moves substantially with temperature; a panel that cannot move buckles into waves on the first hot day. That is the most common vinyl siding failure and it is purely an installation error.

Fiber cement and wood are fastened tight, but blind-nailed or face-nailed exactly as the manufacturer specifies — the pattern is part of the warranty. Use corrosion-resistant fasteners throughout; ordinary nails will rust and streak the wall within a few seasons.

Step 8: Caulk, Prime, and Paint — Selectively

Caulk where siding meets trim, corners, and penetrations. Do not caulk the horizontal laps or the weep slots at the bottom of vinyl panels — those are drainage paths that let incidental water escape. Sealing them traps water in the wall, which is worse than what it was keeping out. It is a well-intentioned and very common mistake.

Prime every field cut on fiber cement. Factory faces are sealed but your cuts are not, and unsealed edges wick water — it is where fiber cement fails first. Unfinished wood siding should be primed on all faces, including the back, before it goes on the wall.

Common Mistakes

Reversed flashing laps. The costliest error in the job, and invisible for years. Bottom-up, always.
Nailing vinyl tight. It has to slide. Center of the slot, slight play under the head.
Caulking the laps and weeps. Those are drains. Sealing them traps water in the wall.
An unlevel starter strip. The error compounds course by course into a visibly crooked wall.
Unsealed fiber cement cut edges. Prime every cut. It is where the material fails first.
Stacked end joints. Stagger them, and keep them off the corners of openings.

Cost: DIY vs. Contractor

DIY vinyl is the realistic homeowner project here — it is light, cuts with snips, and needs no finishing. The work is slow and fussy rather than difficult. Budget serious time for staging and for the flashing details, which is where care actually pays.

Contractor-installed pricing in our dataset puts standard vinyl lap at roughly $7.50 per square foot installed, from 2026 cost guides quoting a $3–12/sq ft installed range (traditional lap $2–7), with labor running 30–50% of the total. Fiber cement costs more on both material and labor — it is heavy, needs specialized cutting, and generates silica dust — but lasts substantially longer. See what drives siding costs for the full picture.

Related Guides

Siding Types Compared — Vinyl, fiber cement, wood, and metal side by side
How Much Siding to Order — Squares, openings, gables, and waste factors
What Drives Siding Costs — Material, tear-off, wall complexity, and labor

Related Calculators

Siding Calculator — Squares of siding after opening deductions and waste
Insulation Calculator — If you are insulating while the walls are open
Gutter Calculator — Commonly replaced in the same exterior project

Written by Daniel McCarney — AceCalc