Choosing a rooflight and skylight for Rainford's dormer bungalows and old barns

Rainford sits where the old coalfield country meets the flat farmland of west Lancashire, and coal and clay shaped its past. Brick is the material you see most in the older rows near the village centre, and the pitched roofs over them are mostly slate or tile. These cottages and short terraces are small in plan, with attics under steep roofs, and the rooms below are often dim because the windows were made modest long before anyone asked for bright interiors.

The inter-war and post-war houses begin on the roads leading out of the centre. Hipped, tiled semis are common alongside bungalows, and plenty of those bungalows have gone upwards with a dormer or a loft room. A bungalow loft is a common job in a village like this, since the footprint is wide, the roof space is generous and the ground floor below is often the darkest part of the house.

The newer estates, built from the later twentieth century, are the third group. Their roofs are almost all concrete-tiled and framed with trusses, a point that matters a good deal later. The fourth group is on the edges, where farm buildings have been converted into houses. Those keep their old purlins and thick timbers, their walls are deep and their windows few, and a roof opening is often the obvious way to let light in.

The way a roof is framed decides what is possible before the question of look or cost even arises. An older cut-timber roof has separate rafters and a purlin, and an opening can be framed in with trimmers. A trussed roof is a factory-made lattice, in which every member carries load, and cutting through one is an engineering job rather than a carpentry job. That difference is why we look in the loft before we talk about the glass.

Dormer bungalows deserve a closer look. The cheeks of a dormer and the roof around them are often framed differently from the main slope, so a roof window usually goes on the main slope beside the dormer, or in place of a small window the dormer never needed. Either way the rafters on both sides are checked before the opening is marked out. Weather also plays a part in the choice of slope: the prevailing wind comes in from the south-west across the farmland, so a rear slope facing the other way is often the calmer place for a new opening, though it will gain less sun.

Rainford is in the St Helens borough, so St Helens Borough Council decides planning applications here and runs the local building control service. Where an ordinary house still has its permitted development rights, a pitched-roof rooflight usually goes in without an application, within the conditions in the permitted development rules for skylights. A flat, or a house that has been converted to flats, does not carry those rights.

The unusual case in Rainford is the converted farm building. A barn that won planning permission to become a house often did so with a condition in its decision notice that removed the permitted development rights any house would normally have. Where that is so, a new rooflight needs an application, even though the same unit on a semi down the road would not. The decision notice is a short document, and it is the first thing worth finding. Older buildings in the village centre may also be listed, in which case listed building consent comes first. The list entry on historicengland.org.uk shows what is protected.

Every case involves Building Control: fitting a rooflight is notifiable, so the paperwork reaches St Helens Borough Council through us (rooflights and the Building Regulations explains the rules), and the council publishes its planning and building control pages at sthelens.gov.uk.

Loft conversions in the bungalows bring Building Control into closer focus, because the job is not a rooflight alone: the stair, the floor, the escape window and the insulation all fall under it. A roof window supplied for such a room is chosen with the regulations in mind from the start.