Solar Panels on Post-1965 Homes

What characterises post-1965 housing

From the mid-1960s onwards, British house roofs changed fundamentally. The cut roof — rafters, purlins and struts assembled on site by a carpenter — was replaced almost entirely by the trussed rafter: prefabricated triangulated frames, delivered to site, craned into place at regular centres and braced together.

At the same time the covering standardised on concrete interlocking tile, and the electrical installation moved to PVC cable, a modern earthing arrangement and a consumer unit that is either current or straightforwardly replaceable.

For solar work this is the easiest housing stock in the country. Most of the difficulty on older properties simply is not present.

The trussed roof is a system

This is the key structural point and it changes how the array is fixed. A trussed rafter roof is not a collection of independent rafters; it is an engineered assembly where each truss shares load with its neighbours through the bracing and the tile battens, and every member is sized for a specific set of forces.

Two consequences follow. First, anchors go into the truss rafter members — the top chords — and the array load is spread across as many trusses as possible rather than concentrated on a few. Second, nothing gets cut, notched or drilled. A gang-nail plate that has been disturbed or a web that has been trimmed for a cable run is a structural alteration, and there is no spare capacity built in.

The compensation is that truss centres are regular, usually at 600mm. Set-out is predictable, rail spans are consistent, and the array can be laid out to line up with the structure rather than fighting it.

Covering and membrane

Concrete interlocking tiles are the most forgiving covering we work on. They lift cleanly, the hook detail is well established, the tile relieves and sits back flat, and spares are available. Older concrete tiles do become brittle with age, and a roof of 1970s vintage will yield some breakages, but nothing like a slate or plain clay roof.

Beneath the tiles, the membrane type tells us how to proceed. Bitumen felt from the 1960s and 70s is stiff and perishes, tearing where it is disturbed at a fixing point. Modern breathable membranes are more tolerant but are part of the roof ventilation design and should not be punctured beyond the fixing itself. Either way, penetrations get dressed.

Layout, electrics and services

Roof shapes are simpler here — often a plain gable with a single large slope — which usually means a bigger, tidier array than an equivalent interwar house.

Loft space is the trade-off. Truss webs cut the loft into compartments and there is rarely a clear run or a sensible standing area, so inverter position needs planning around access for future service. On semis and terraces, cable routing has to respect the party wall and the fire separation at the head of it.

Electrically, boards are usually modern or easily replaced, earthing is conventional and supplies are typically adequate for an array with room for storage later. Generation above 16A per phase — roughly 3.68kW single phase — needs G99 approval before installation rather than a G98 notification afterwards.

Limitations

Some 1970s and 80s estates used low-pitch roofs that reduce winter yield. Some developments carry covenants restricting road-facing alterations. And a roof that has had trusses cut for a loft conversion needs a proper structural look before anything is added to it.