Solar Panels on Victorian Terraces

What a terrace gives you to work with

A Victorian terrace is a narrow building with a long, shallow plan and a roof divided by party walls. The main roof spans front to back with a ridge parallel to the street, and behind it sits the back-addition — the two-storey outrigger over the kitchen — with its own lower roof and a valley gutter where the two meet.

That produces two or three small roof planes rather than one large one, all of them bounded, and most of them with a chimney stack somewhere in the way. The design job on a terrace is fitting a sensible array into a constrained area, not choosing between options.

Covering and structure

Natural slate, in most cases, laid on sawn rafters at irregular centres over lath or early boarding. Slate of this age is often nail sick: the slate itself is fine but the fixings have corroded, so slates slip and the roof is closer to re-covering than it looks. We check that in the loft and from the scaffold, because loading an array onto a roof that needs stripping within a few years is a poor sequence.

Slate is holed rather than nibbed and cannot be relieved over a hook the way a tile can, so fixing method differs and fewer slates should be disturbed. Some of what is lifted will break. That is allowed for rather than discovered.

Rafter centres on these roofs move around, and rail-based mounting is what accommodates that — once the centres have actually been measured from inside.

Shading and layout

Party wall stacks are the defining shading problem. They sit at the top of the slope on one or both sides, and their shadow tracks across the array through the morning or afternoon. On a slope that is only four or five panels wide, a stack can affect a meaningful proportion of the array.

Per-panel electronics — optimisers or microinverters — earn their place here more than on almost any other property type, because the shaded panels are a large fraction of a small system. They limit the loss; they do not remove it. Where a stack takes out most of a slope for half the day, the honest answer is a smaller array positioned clear of it.

The back-addition roof usually runs as its own string or its own MPPT input, since its pitch and orientation differ from the main slope.

Electrical implications

Consumer units on terraces of this age are frequently older boards, sometimes with no spare ways and occasionally with earthing and bonding that predates current requirements. Meter positions are often in a hall cupboard or under the stairs, and cable runs from the loft down through the house need planning to avoid destructive routing through finished rooms.

Access and scaffolding

This is usually the hardest part of a terrace job. There is no side access on a mid-terrace; the scaffold either goes up from the street at the front, requiring a highway licence and lead time from the council, or comes through a shared alley or a neighbour garden at the rear. Rear gardens are often long and narrow with restricted material access.

Limitations

A terrace array is a modest array. Frontages are often constrained by conservation designation, stacks eat into the usable area, and the roof planes are small. Storage is frequently the better lever on a terrace — a smaller array with a battery holding what it makes usually beats trying to force more panels onto a roof that will not take them tidily.