Does Rooflight Replacement Need Building Control?

The rules look at what is being replaced, so the same misted rooflight can fall under different routes depending on the work.

A controlled fitting is a window, rooflight or roof window that has to meet energy rules when it is installed. Approved Document L defines it as the entire unit, frame included. It also says that replacing the glazing in an existing frame is not providing a controlled fitting, so that work does not have to meet the energy figures and falls outside the notification.

In practice, the first thing we check at the survey is the state of the frame. That settles which row of the table your job sits in.

When the whole unit is replaced, the new one has to reach the performance set in Part L of the regulations. A rooflight is held to 2.2 W/m²K. The limit for a roof window is tighter, at 1.4 W/m²K, with Window Energy Rating Band B as an alternative. The notification puts on record that the new unit meets the figure.

Each maker publishes the rating for every unit. We compare it with the target before ordering, so a unit that falls short never reaches the roof. To read a data sheet yourself, start with the U-value explainer.

The rules apply to the new unit. A like-for-like swap does not oblige you to upgrade the insulation in the roof around it.

In Bournemouth the local authority service is BCP Council Building Control, which covers Bournemouth, Christchurch and Poole. Owners may also use a private building control body, now named a registered building control approver. Either route ends with a completion certificate on file for the work.

Your quote states which route applies to your job and who submits the notification. Keep the certificate when it arrives. A buyer's solicitor may ask for it when you sell, and it shows the new unit was recorded.

Timing is mostly outside the roof work. For a straight replacement, the notice goes in before the work starts, and the certificate follows once the building control body has what it needs. Our replacement timing answer covers the visit itself.

A bigger rooflight needs a bigger hole. In a pitched roof that means cutting through a rafter and fitting trimmers, short beams that frame the new opening and carry the cut rafter's load to its neighbours. In a flat roof it can mean altering the joists around the kerb.

Approval comes first, before any timber is cut, and an inspector may ask to see the trimming before it is covered over. Our answer on replacing a rooflight with a bigger one covers the practical side of the job.

Where the new unit changes the look of the roof, planning can come into it as well. Rooflights frequently fall under permitted development, with conditions attached. The planning guide shows how to check your own address.

Before you accept a quote for a whole-unit replacement, check that it answers these in writing.

• Which Building Control route applies, the council or a private approver, and who submits the notice.
• The U-value or Window Energy Rating of the new unit, so you can compare it with the target.
• Whether the quote is for the frame as well as the glass, and what happens to the old flashing.
• When you can expect the completion certificate, and whether it is sent to you directly.

A quote that names each of these gives you a clear record. One that is silent on them leaves you to chase the answers after the roof is closed up.

If the unit lights a bedroom in the roof, its size and height can matter for escape. Approved Document B limits an escape window to a storey within 4.5 m of the ground. Where the rooms sit in the roof of a single-storey home, a correctly sized roof window can do the job. Over two full storeys, the upper room relies on a protected stair, and a window is not the escape route.

When a replacement window serves a room of that kind, we measure the opening size and the sill height at the survey and report what we find against the guidance. The detail sits with Building Control, and your quote notes anything that needs a conversation with them.

Approved Document B asks an escape window for a clear openable area no smaller than 0.33 m², with neither its height nor its width under 450 mm, and with the lowest edge of the opening no higher than 1100 mm above the floor. Where an existing window is big enough for escape, the replacement should give at least the same potential for escape. The maker's data gives the clear opening of each model, and the survey records where the window sits above the floor.

New openings, extensions and structural changes are covered across the wider rules in our guide to rooflights and Building Regulations. The practical choice between new glass and a whole unit is in our answer on glass or a whole new rooflight.