Solar Panel Sizes UK: How Much Roof Space Do You Actually Need? (2026)

A standard residential solar panel measures around 1,700mm × 1,000mm and weighs 20–25kg. Most UK homes fit a 4kW system in 20–22m² of usable roof space, using 10 panels rated at 400W each.

Standard panel dimensions

The solar panels fitted on UK homes in 2026 are almost always monocrystalline, typically rated 400–450W. Physical size has settled into a fairly consistent range:

Panel type	Width	Height	Area	Weight
60-cell (older)	990mm	1,650mm	1.63m²	18–20kg
72-cell / half-cut	990mm	2,000mm	1.98m²	22–25kg
Modern 400–450W	1,000mm	1,700mm	1.70m²	20–24kg

Commercial panels run slightly larger. Most UK residential installers use panels in the 400–450W range, which balance output, physical size, and roof loading.

How much roof space does a system need?

The quick calculation: allow roughly 2m² per panel, including mounting gaps and edge clearances.

System size	Panels (400W)	Roof space needed
3kW	8 panels	16–18m²
4kW	10 panels	20–22m²
5kW	13 panels	26–28m²
6kW	15 panels	30–32m²

These figures assume a south-facing roof with a 30–45° pitch and no shading. Your usable area will be less than your total roof area once you subtract the 30cm border required around the edges, chimneys, skylights, and any shaded zones.

What eats into your usable space?

A full roof and a usable roof are different things. Common factors that reduce your available area:

Chimneys create a shading zone extending roughly 3× the chimney height downslope. Panels placed in this zone underperform year-round.

Skylights and roof windows need 30cm clearance on all sides, both for fire safety regulations and to allow inspection access.

Edge clearances of 30cm are required around all roof perimeters. On a standard semi-detached with a roof pitch of 35°, this alone can remove 3–4 panels from the calculation.

Roof vents, aerials, and pipes each need individual clearance. A surveyor will map these during a site visit.

Panel efficiency and roof space

Higher-efficiency panels generate more electricity from the same area. If your roof is tight, moving from a standard 20% efficiency panel to a premium 22%+ panel can recover one or two panels' worth of output without needing more space.

Efficiency	Output per m²	Panels for 4kW (approx.)
18–19%	~190W/m²	11 panels
20–21%	~210W/m²	10 panels
22–23%	~230W/m²	9 panels

Premium panels cost more per panel but can make a meaningful difference on constrained roofs.

Roof orientation and how it affects sizing

A south-facing roof at 35° captures the most energy. Move away from that and your output drops, which means you may need more panels to reach the same generation target.

Orientation	Output vs south-facing
South	100%
SE / SW	93–95%
East / West	80–85%
North	Not recommended

East- and west-facing roofs work well, particularly as east-west split systems that generate power across a longer daily window. An installer will model your specific roof before recommending a system size.

Flat roofs

Flat roofs always need mounting frames to set panels at an angle — typically 10–15° for commercial installations, 30–35° for residential. The frames take up more horizontal space than pitched installations, so factor in around 25% extra area compared to a pitched roof calculation. Ballasted frames (no roof penetration required) are the standard approach.

Weight

Most UK roofs handle solar panels without structural modification. The total load across a typical 10-panel system is around 200–250kg spread across the mounting rails. A structural check is standard practice before installation. Older roofs or those with previous modifications may need assessment by an engineer.

Getting an accurate figure

Satellite imagery gives a rough idea of your roof's area, but it misses shading, vents, and structural details that affect the final layout. A site survey, which CRG Direct carries out free of charge, produces a panel-by-panel layout and accurate output estimate for your specific roof.

Book a free survey →