Conservatory roof cost and heat loss calculator
Enter your conservatory's style and size to see a guide price for insulated roof panels, the heat your current roof lets out and what that costs you each year.
How the calculator works
The price comes from roof area and style. We work out the roof area from the floor area you enter, add 12 percent for the pitch and the overhang, and apply our fitted rate for that style. A lean-to is the simplest roof to fit. Edwardian, Victorian, gable end and P-shaped roofs have more hips, cuts and trims, so they cost more per square metre.
The heat loss uses the standard sum every energy assessor uses: U-value times area times heating degree days times 24 hours. Heating degree days measure how cold a place is over a year. Pick your nearest town and we use its own figure, averaged over 2021 to 2025. The England average we use when no town is chosen is 2,150.
The U-values behind the numbers
| Roof | U-value (W/m²K) | Heat lost through 12 m² on a 0°C night |
|---|---|---|
| 16 mm polycarbonate | 2.3 | 552 W |
| 25 mm polycarbonate | 1.6 | 384 W |
| 35 mm polycarbonate | 1.4 | 336 W |
| Glass, fitted before 2002 | 2.8 | 672 W |
| Glass, fitted since 2002 | 1.2 | 288 W |
| 75 mm insulated roof panels | 0.43 | 103 W |
A U-value is the watts that pass through one square metre of roof for each degree of difference between inside and outside. Lower is better. Our panel figure is worked out from a 75 mm solid foam core between two aluminium skins. U-values explained in full.
Using the result
If the guide price looks right, the next step is a free survey. The surveyor measures the roof, checks the frame and the glazing bars, and gives you a fixed written price. Nothing is ordered until you say yes. Book a survey or read the full price guide first.
Questions about the calculator
How accurate is the price?
The guide price uses the same size and style rates our surveyors start from, so most final quotes land inside the range. Frame repairs, awkward access or several roof lights can take it higher. The survey gives you a fixed written figure.
Why does the calculator ask for width and depth?
Roof area drives both the price and the heat loss. We multiply the floor area by 1.12 to allow for the pitch of the roof and the overhang at the gutter, which is close for most conservatories.
What are heating degree days?
A measure of how cold a place is over a year. Each day adds the number of degrees the average temperature falls below 15.5°C. Our town figures are averages of 2021 to 2025 from Open-Meteo historical weather data.
My conservatory is not heated. Is the saving real?
The kWh figure is the heat the roof would lose if you kept the room at a comfortable temperature. If you never heat it, you will not see a bill saving, but the room will sit several degrees closer to the rest of the house and be usable for far more of the year.
Want the fixed price?
A surveyor measures up, checks the frame and hands you a written quote. Free, no obligation.