Siding installation cost

Ask a siding calculator for a figure and it will want length and height. That works for a flat-topped wall and fails on the two ends of any house with a pitched roof, where the wall carries on upward into a triangle.

The awkward part is that you cannot measure the triangle. Its apex is at the ridge, thirty feet up, and nobody is putting a tape on it. But you do not have to: the height follows from the roof pitch, which is a number you can get with a level in the attic.

Half the wall width is the horizontal run from the eave to the ridge. Multiply by the pitch — rise over twelve — and you have the height. The triangle is then half of base times height, the same as any triangle.

One practical note: a gable is also the hardest part of the wall to work on. It is the highest, the most awkward to stage, and where the cuts are all angled. Labour per square is genuinely higher up there, which is one reason a house with steep gables costs more to side than its area suggests.

Like roofing, siding is quoted in squares of a hundred square feet. Unlike roofing, how that converts into things you can buy depends on which material you picked.

Vinyl and aluminium come in boxes, and almost every box is two squares. That makes the count straightforward: squares with waste, divided by two, rounded up.

Lap planks — fiber cement and engineered wood — are sold individually, and here is the conversion people get wrong. A plank does not cover its own width. Each course overlaps the one below, so what it covers is its exposure: an 8¼ inch plank installed at 7 inches of exposure covers seven inches of wall. That is a 15 per cent difference between the plank you are holding and the wall it covers.

Phone a supplier with a square footage and you will be quoted siding. What arrives on the truck is siding. What you then discover, standing at the first window, is that siding needs somewhere for its cut edges to go.

J-channel receives those edges — around every window, every door, and along the top of every wall where it meets the soffit. It is measured in linear feet and on an average house there are several hundred of them.

Corner posts run full height at every external corner, and both walls die into them. A plain rectangular house needs four; an L-shaped one needs six outside and two inside.

Starter strip goes along the bottom of every wall, and the first course locks into it. It is the cheapest item on the list and the most consequential: set it out of level and every course above repeats the error, getting more visible as it climbs.

This is the single most important thing to know about vinyl siding, and it is counter-intuitive enough that plenty of otherwise competent installers get it wrong.

Vinyl expands and contracts substantially with temperature — a twelve-foot panel moves more than half an inch between a winter night and a summer afternoon. The system is designed for that: panels hook onto the course below and are nailed through slots, so they can slide sideways as they move.

Which means the nails must not be driven tight. They go in the centre of the slot, straight, and are driven until the panel still slides by hand — about a thirty-second of an inch of play behind the head. Panels are also cut about a quarter inch short into the channels so they have room to grow.

Nailed tight, the wall has nowhere to go. It buckles into waves on the first hot day, and the repair is to remove and rehang it. It is the commonest failure in the material, it is entirely avoidable, and it costs nothing to do right.

As with roofing, the allowance here is not about carelessness. It is about how many pieces get cut at both ends and how many of those offcuts can start the next course.

Gables deserve a mention of their own here. Every course in a gable is cut at an angle at both ends, and the offcut from one course is the wrong angle for the next. A house with two steep gables genuinely wastes more than its area suggests, which is part of why the complexity setting exists rather than a flat percentage.

And keep a box back. Siding colour is batched like everything else, and the panel you need in year six after a ladder goes through one will not match unless it came off this delivery.

Siding is not waterproof and was never meant to be. It is a rain screen: it sheds the bulk of the water and accepts that some gets behind. What handles the rest is the weather barrier on the sheathing, and it only works if it is lapped correctly.

Siding sheds most of the water and the wrap handles what gets past it. Skipping it, or lapping it the wrong way, puts water inside the wall where nobody sees it for ten years.

The rule is the same as roofing: upper pieces lap over lower ones, so water running down the face always meets the outside of the next sheet rather than its edge. Around windows, the sequence matters even more — the head flashing goes over the wrap, the sill under it, and getting that order wrong funnels water into the wall at the one place it will do the most damage.

The two materials that account for most re-siding, and the comparison people arrive looking for. These are the four options run over the identical house this page opens with, same elevations, same gables, same tear-off.

Per year owned they are closer than the sticker suggests — and unlike metal roofing, where the long life genuinely pulls the annual cost level, fibre cement does not come out cheaper per year unless it goes the full distance. At 50 years it is about $638 against vinyl’s $443 to $886: a range that overlaps rather than a win.

And the repainting has to go in the sum. Fibre cement is painted, and a repaint every twelve to fifteen years on a house this size is several thousand dollars each time. Factory-finished products push that out but do not remove it.

What actually decides it is not the arithmetic. It is that vinyl is the colour it arrives, forever, and fibre cement is whatever colour you want, repeatedly — and how close people get to your walls.

About $722 a square installed — roughly $7 a square foot — with the old siding stripped off. On the house this page opens with that is $17,715, and $604 of it is accessories: J-channel, corner posts, starter strip, utility trim.

Accessories look small against the siding and they are the line a supplier leaves off when you phone for a price. They are also not optional and not interchangeable — vinyl hangs loose and moves, and every one of those pieces exists to let it move without showing. A quote missing them is not cheaper, it is incomplete.

The other number people underestimate is the gables. A triangle of wall two storeys up is slow work and it is easy to leave out of a measurement taken from the ground, which is why this page works it out from the roof pitch instead of asking you to guess.

Gable areas come from the roof pitch you set, using the same geometry as the roofing calculator. Plank coverage uses exposure rather than width, from the manufacturer’s installation instructions. Fastening and expansion requirements follow the vinyl industry installation manual. Accessories are counted as linear items and priced per piece, and removal is priced by what is coming off — because that line varies more than any other in a re-siding quote. All of it is on the sources page, dated.

One simplification worth stating: corner post length uses the height of the first wall you entered. On a house where elevations differ in height — a split level, or a walk-out basement — count the corners against the taller wall, or add a wall entry for each distinct height.

Nothing you type is sent anywhere — the whole calculation runs in your browser.

Exposure and J-channel are the two that decide whether the order is right.