# Home Addition Cost Calculator — United Kingdom

> Build a scoped home addition budget from an explicit area rate and itemized allowances rather than a fabricated national price. GBP planning view; stated limitations apply.

Page: https://askcalculators.com/uk/home-addition/
Definition: https://askcalculators.com/uk/home-addition/definition.json
JSON Schema: https://askcalculators.com/uk/home-addition/schema.json
Version: 20.16.0
Maintained by: AskCalculators (software project; not a credentialed reviewer)
Qualified review: pending. Automated checks do not establish professional approval.
Page status: Live
Review status: Pending

## Use
Open the calculator page and enter values. Query-string parameters can restore and bookmark a calculation.
Example: https://askcalculators.com/uk/home-addition/?unitSystem=metric&area=30&fixtures=0&demolition=0&wastePercent=10&unitRate=0&laborCost=0&deliveryCost=0&otherCost=0&costMultiplier=1&spreadPercent=15&taxRate=0

## Inputs
- unitSystem: Measurement system; type=select; optional; default=metric; values=imperial|metric
- area: Addition floor area; type=number; required; default=30; min=0.01; max=1000000000000
- fixtures: Separately scoped fixtures/cabinets/appliances; type=money; required; default=0; min=0; max=1000000000000
- demolition: Separately scoped demolition and disposal; type=money; required; default=0; min=0; max=1000000000000
- wastePercent: Cutting/waste allowance; type=percent; required; default=10; min=0; max=100
- unitRate: Material price per area unit; type=money; required; default=0; min=0; max=1000000000000
- laborCost: Total labor allowance; type=money; required; default=0; min=0; max=1000000000000
- deliveryCost: Delivery allowance; type=money; required; default=0; min=0; max=1000000000000
- otherCost: Other fixed costs; type=money; required; default=0; min=0; max=1000000000000
- costMultiplier: Material/labor multiplier; type=number; required; default=1; min=0.1; max=10
- spreadPercent: Low/high sensitivity around the entered total; type=percent; required; default=15; min=0; max=100
- taxRate: Explicit tax allowance; type=percent; required; default=0; min=0; max=100

## Outputs
- pricedArea: Area including explicit allowance; format=number
- materialCost: Material cost; format=currency
- laborCost: Labor allowance; format=currency
- deliveryCost: Delivery allowance; format=currency
- otherCost: Other specified costs; format=currency
- tax: Entered tax allowance; format=currency
- low: Low cost scenario; format=currency
- mid: Middle cost scenario; format=currency; primary
- high: High cost scenario; format=currency

## Formula
area-based material allowance = measured scope area × (1 + allowance) × entered material rate; add separately priced work.

Inputs are converted to canonical units before evaluating this stated formula.

## Rules
- Empty optional inputs are undefined, not zero.
- Hidden conditional inputs are ignored.
- Do not invent missing required inputs.

Notice: Illustrative defaults are not local quotes or verified legal rules. Dated reference components and user-entered assumptions are explicitly distinguished. Professional review is pending.