Glazing

Rooflights are what turn an extension into a room people want to sit in. They are also among the longest lead-time items on the schedule, easy to undersize at the planning stage, and a specification where the gap between a stock pitched roof window and a bespoke aluminium unit is one of the biggest single choices in the glazing budget.

These guides cover the two families of roof glazing used on domestic extensions: stock pivot-type roof windows, typically available from merchants within a week or two, and made-to-order large-format fixed aluminium rooflights from specialist suppliers, typically on an 8 to 16 week lead time. Each page explains who fits the product, what flashing or upstand it needs, where building regulations come into play, and how to choose between them.

Where to start

Read both before you approve the structural drawings, because the rooflight size sets the trimmer rafters or the flat-roof opening around it. The pitched roof window guide explains size codes and flashing kit selection, and the collar detail that causes most leaks. The bespoke aluminium rooflight guide explains why the upstand or kerb is your builder's responsibility and has to be ready before the supplier's crew arrives.

The guides

Pitched roofs. Pitched roof windows, covering size codes, flashing kits, brand comparison, U-values and escape requirements.

Flat roofs. Bespoke aluminium rooflights, covering opening types, glass build-up, upstand construction and programme sequencing.

Where these fit in the build

The opening is framed during roof structure, and the units themselves are ordered and fitted under roof windows and rooflights, alongside the roof covering that has to seal around them. Order early: a bespoke unit ordered on stock-window timings can cost you weeks of programme.