Quick answer
On a semi the two main faces point in opposite directions, so one may be good and the other poor. If neither faces south, splitting panels across east and west faces can work well. A hipped end adds a smaller third face. Keep the whole array on your own side of the party wall.
How common semis are in Winsford
In the 2021 Census, semi-detached houses made up 52.7% of households in Gravel and 48.8% in Dene, in each case the largest single type of home. They were about a third of households in Wharton (33.4%), Swanlow (32.1%) and Over & Verdin (31.8%). Across the borough the figure was 36.3% (Census 2021). Taken together, roughly 5,494 households in the five wards live in a semi.
That makes the semi’s roof the most typical starting point for solar in much of the town. The other types, ward by ward, are on Winsford homes by ward.
Two faces pointing opposite ways
A semi with a simple pitched roof has its ridge running across the pair of houses, giving each house one slope to the front and one to the back. Those two slopes always face in opposite directions. If the front faces south, the back faces north; if one faces east, the other faces west. That simple fact settles a lot: whichever way the street runs, one of the two slopes will usually be the better one, and on some houses both will be middling.
| One face | kWh/kWp | Other face | kWh/kWp |
|---|---|---|---|
| south | 954 | north | 519 |
| south-east | 901 | north-west | 594 |
| south-west | 896 | north-east | 596 |
| east | 761 | west | 755 |
The table shows the pattern. A south face at 35° makes about 954 kWh per kWp in a year, and the north face behind it about 519. A south-west face makes about 896, with its north-east partner at 596. For the east and west pairing, the two sides are close to equal, at 761 and 755 (PVGIS). The figures for every pitch are on what panels make in Winsford.
Front or back makes no difference to the sun
Which slope looks onto the road has no effect on output; only direction, pitch and shade matter. Many owners assume panels belong on the front, or that the back is somehow second best. If the rear slope faces south or south-west and the front faces north, the rear is the obvious place. For planning, on an unlisted house outside a conservation area, both slopes are treated alike: the panels must keep within 0.2 m of the roof covering and below the top of the roof (Part 14 of the order). Planning rules covers the exceptions.
Splitting the array across east and west
When the faces point east and west, neither is ideal on its own but together they work well. Two kWp on each side would make about 3,030 kWh a year, against about 3,817 kWh for four kWp on a single south face, so the split roof gives up about 21% of the south figure. It also spreads generation across the day: the east side is strongest in the morning, the west in the afternoon and early evening, which can suit a household that is out at midday.
Pitch matters a little more for east and west faces than for south. In the Winsford runs, an east face makes about 793 kWh per kWp at 10° but 734 at 45°, because a steep east or west slope turns further away from the midday sun. On a south face the curve is much flatter. So a shallow east–west roof gives up less than a steep one.
Splitting does add some design work. Each face needs its own string of panels, the inverter has to be able to track the two separately, and the cable runs are longer. A quote for a split array should say how the two faces are wired, show the panel count on each, and give an MCS performance estimate for each face rather than one figure for the whole.
South and north: use one face
Where one face points south and the other north, the answer is usually simple: put the panels on the south face. A north slope at 35° makes a little over half what a south slope does, and filling it adds cost for a small gain. If the south face is small, a slightly larger system there is usually a better use of money than spreading onto the north side. South-east and south-west faces behave much like south; their opposite faces, north-west and north-east, are weak.
Hipped roofs, in general terms
Not every semi has a plain gable end. On a hipped roof the end of the house slopes too, so instead of two rectangles each house has a front face, a back face and a triangular end face. The main faces are then trapezoids rather than rectangles, narrower at the top, and they hold fewer panels than their area suggests, because panels are rectangular and need clearance from the edges and hips.
The upside is a third direction. If the front and back point east and west, the hip end may point south, and a few panels there can be worth having. If the hip end points north, it is best left alone. Survey drawings should show every face with its direction and the panels it can take.
The party wall: keep to your own side
The two halves of a semi meet at the party wall, whose line continues up through the roof. The array should stay entirely on your own roof, clear of that line, with no panels, rails or fixings crossing onto the neighbour’s side. That keeps ownership simple, avoids work to a shared structure, and leaves the neighbour to make their own choices about their half. Ask the firm how far from that line it keeps the array, and why.
Fixing panels to your own slope does not normally involve the party wall itself. If any part of the job would cut into or attach to the wall, or to a chimney stack that sits on it, speak to the neighbour first and ask whether formal party wall procedures apply. Scaffolding that needs to stand on the neighbour’s drive or garden also needs their permission. Telling them the dates in advance costs nothing and usually makes the week easier.
Shade from next door
Semis are close to their neighbours, so shade often comes from the other half: a shared chimney stack, a taller extension, a dormer or a tree in the next garden. A survey should record shade on each face through the day. Where part of an array is shaded for some hours, wiring and electronics that stop one shaded panel holding back the rest are worth asking about.
Shade also changes with the seasons. A tree that clears the roof in June can cast a long shadow across it in December, when the sun is low, and a neighbour’s extension that looks harmless at noon may cover the lower rows in the late afternoon. Ask the firm which months its shade figures cover.
Next steps for a semi
If you own the house, owner-occupiers sets out the route from first look to commissioning. If you rent, the landlord decides; see who decides about solar. Before comparing quotes for a split array, read choosing an installer; for how an east–west roof’s output fits a household’s day, see export and self-use. The who-decides tool gives a yearly figure for any direction and pitch, and the question form takes anything specific.