What Grantham weather does to a conservatory
The grid reads like a calendar turned on its side: months down, hours across, colour for the average room temperature. Grantham's warmest month outdoors was August at 17.6°C on average, with a top of 30.2°C, yet a polycarbonate conservatory peaked at 46°C because the roof traps the midday sun.
A year inside a Grantham conservatory
Average room temperature, every month and hour of 2024 and 2025
- 1,311
- hours over 25°C
- 46°C
- hottest hour
- 32°C
- July, 3pm
- 1,458
- hours over 25°C
- 49°C
- hottest hour
- 34°C
- July, 3pm
- 314
- hours over 25°C
- 33°C
- hottest hour
- 25°C
- July, 3pm
Blue: heater weatherPale: comfortableAmber to plum: too warm
The hours you get back
Count only the hours people are awake, 8am to 10pm, and sort them by how the room feels. Cold hours can be fixed with a heater. Too-warm hours mostly cannot, short of opening everything and hoping. That is why the panel roof adds about 997 usable hours a year in Grantham: 3,803 becomes 4,800.
Hours above 30°C drop from 539 under polycarbonate (and 695 under glass) to 24 with panels.
- Polycarbonate roof1,311 h too warm
- Glass roof1,458 h too warm
- Panel roof314 h too warm
Too cold (under 12°C)Chilly (12 to 17°C)Comfortable (17 to 25°C)Warm (25 to 28°C)Too hot (over 28°C)
When the heat peaks in Grantham
Under polycarbonate the overheating peaks in June, when 45% of waking hours pass 28°C. With the panel roof the same month sits at 8%. Look at April and September as well: low sun through glass walls still warms the room, but not through the roof any more.
Polycarbonate roofInsulated panel roof
Winter in Grantham
January is Grantham's coldest month, averaging 3.6°C, with a lowest hour of -5.5°C over the two years. Holding the room at 19°C through waking hours takes about 1,701 kWh a year under polycarbonate (£448 on electric heaters at the 26.32p price cap) and 1,441 kWh (£379) under panels.
That saving is real but modest, because the glass walls still lose heat. The bigger winter change is the heater: on a freezing evening a 1.1 kW heater keeps up under panels where polycarbonate needs 1.7 kW.
Prices for Grantham conservatory roofs
There is no Grantham premium: size and shape decide the price. The survey is free and the written price is fixed. See the price page for every shape, or get a guide price for your roof in about a minute.
| Shape | Small (up to 12 m²) | Medium (12 to 25 m²) | Large (over 25 m²) |
|---|---|---|---|
| Lean-to | from £3,000 | from £4,000 | from £5,000 |
| Edwardian | from £3,150 | from £4,200 | from £5,250 |
| Victorian | from £3,300 | from £4,400 | from £5,500 |
Fitting day
Most roofs here take one day, larger or more complicated ones two. The old sheets come off in the morning, the frame is checked, and the panels, ridge or hub and trims go on before the light goes. The fitting day walks through it hour by hour.
Towns near Grantham
Compare your neighbours, or see all of the East Midlands and the full overheating league table.