One of the first things people ask us is whether their roof is big enough. It is a fair question, and the answer is usually more encouraging than people expect. Here is how to work out what you need, what quietly eats into your usable space, and what to do if the numbers do not quite add up.
The rough rule of thumb
A modern domestic solar panel is roughly 1.7 metres by 1.1 metres, so about 1.9 square metres each. Allowing for small gaps between panels and clearance from the roof edge, plan on around 2 square metres of clear roof per panel. A typical home system of 8 to 12 panels therefore needs somewhere in the region of 16 to 24 square metres of usable roof.
That is smaller than most people picture. Many ordinary semi-detached and detached roofs have a single slope comfortably above that. If you are not sure how many panels your home actually needs, our free size estimator is a good starting point, and our guide on how many panels you need goes into the detail.
Usable space is not the same as total space
The area of your roof and the area we can actually cover are different things. A surveyor will look at several things that reduce usable space:
- Edge clearances. Panels need to sit back from the ridge, eaves and verges, partly for fire safety and partly so wind does not get underneath them.
- Obstructions. Chimneys, roof windows, vent pipes, satellite dishes and dormers all take up space, and some need a gap around them.
- Shading. A section of roof that is shaded for much of the day may be better left empty. Our guide to shaded and north-facing roofs explains when it still works and when it does not.
- Roof condition and structure. If the covering is tired, it is worth sorting first. See does my roof need replacing before solar panels.
Which way the roof faces matters as much as size
South-facing is the textbook ideal, but east and west roofs are very good for most households, because they spread generation across the morning and late afternoon, which is often when people are actually using electricity. An east-west split can mean slightly lower peak output but a better match to a typical day. North-facing slopes are generally the weakest choice, and we will say so plainly rather than fit panels that will not earn their keep.
What if your roof is small or awkward?
A smaller roof does not rule you out, it just changes the design. Bungalows are the most common example of this, and we have written a separate guide to solar panels for bungalows. There are a few sensible routes:
- Higher-output panels. Modern panels produce more per square metre than older ones, so a compact roof can still carry a worthwhile system.
- Panels on more than one roof face. Splitting an array across two slopes, or onto a garage or extension, can recover space a single slope cannot offer.
- Optimisers or microinverters. These help where part of the array sees shade at certain times of day.
- A flat roof, outbuilding or ground mount. If the main roof is limited, these can help. We cover flat roofs in a separate guide, and ground-mounted systems suit larger gardens and farms.
- A battery. If you cannot fit as many panels as you would like, storing what you do generate becomes more valuable. Our battery storage page explains how that works.
When it honestly is not worth it
If only two or three panels would fit, the fixed costs of scaffolding, the inverter and the paperwork are spread over very little generation, and the economics are usually poor. We would rather tell you that than sell you a system that disappoints. Likewise, if your roof is heavily shaded all day with no workaround, a different approach may serve you better.
How we check your roof properly
Online tools and satellite images are useful for a first look, but they cannot see roof condition, loft access, rafter spacing or the exact position of that vent pipe. Our own employed surveyors and installers visit, measure and design around what is really there, and every system is installed to MCS standards, which also keeps you eligible for the Smart Export Guarantee. Because we are based in Wimborne, a survey is a short drive rather than a national call centre appointment. If you would like a quick sense check first, try our free suitability checker.
Talk to a local installer
Not sure whether your roof is big enough? We will give you an honest answer, including if the answer is no. Request a free, no-obligation quote and one of our local MCS-certified team will assess your roof. We cover Dorset, Hampshire, Wiltshire and the surrounding counties.