Orientation: which direction your roof faces
South-facing roofs produce the most electricity in the UK — roughly 15–20% more over a year than east or west-facing roofs. A due-south orientation at the right pitch is the ideal.
East and west-facing roofs are viable. They generate less total energy but produce more evenly across the morning and afternoon, which can actually improve self-consumption for households at home all day. Many installers now recommend east-west split arrays as a deliberate strategy.
North-facing roofs are generally not suitable for solar in the UK. The combination of low irradiance and steep angle of incidence means output is too low to justify the investment.
Pitch: the angle of your roof
The optimal pitch for solar panels in the UK is 30–35°. Most standard UK pitched roofs fall in the 30–45° range, which is close to ideal. Flatter roofs (under 20°) accumulate more soiling because rainwater drains less effectively, requiring more frequent cleaning but otherwise performing well with the right mounting system.
Very steep roofs (over 50°) are viable but make installation more difficult and expensive, and may require specialist mounting systems. Flat roofs can accommodate solar using tilt-frame systems, though planning rules and building weight limits need to be checked.
Shading: the most common cause of underperformance
Shading is the biggest variable that assessors look for. Trees, chimneys, neighbouring buildings, and dormer windows can all cast shadows on panels at certain times of day or year. Even partial shading — a chimney shadow crossing one panel for two hours a day — can have a disproportionate impact if panels are wired in series.
A good installer will carry out a shading analysis (often using software tools that model sun position across the year) and may recommend micro-inverters or power optimisers to mitigate shading losses where complete avoidance is impossible.
Self-shading between rows of panels on a flat or shallow-pitched roof is also a factor: panels need to be spaced far enough apart that front rows do not shade rear rows at low winter sun angles.
Structural strength
A standard UK rafter-and-tile roof built to modern building regulations is strong enough for a solar installation — panels add roughly 15–20 kg per m², which is well within the load capacity of a properly constructed roof.
Older properties, particularly pre-war terraced housing, may have lighter roof structures, and a structural survey may be recommended before installation. Signs of existing roof problems — sagging ridge line, cracked rafters, soft spots — should be addressed before panels go on.
Any good installer will check the roof structure during the site survey and will not proceed if they have concerns.
Roof material and condition
Concrete and clay tiles, slate, and metal standing-seam roofs are all suitable for solar. The mounting brackets vary by material, but all are well-established in the industry.
Flat roofs typically use ballasted frame systems (no roof penetrations) or mechanically fixed systems depending on the membrane type. Felt and GRP flat roofs both have established mounting solutions.
Roof condition matters. If your roof tiles are near the end of their serviceable life, it is worth replacing them before installation — working around an existing solar array is more expensive and disruptive than doing it beforehand.
Listed buildings and properties in conservation areas require specialist approval for solar panel installation. English Heritage guidance on solar and historic buildings is worth reading if your property is affected.