Rear extension rooflights

Roof lanterns and rooflights for rear extensions

A rear extension pushes the back wall of the house further from the original rooms, so daylight from above becomes essential. Roof lanterns, flat rooflights, long slot rooflights and walk-on glass each solve the problem differently, and the right choice depends on the roof, the room below and which way the house faces.

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Large aluminium roof lantern above a kitchen island in a rear extension with blue sky above

Which rooflight should you choose?

A roof lantern gives height and a feature over an island or dining table. Flat rooflights are slimmer and suit minimal interiors. A long slot rooflight against the house wall washes light down the old back wall into the middle of the plan. Walk-on rooflights bring light into a basement or lower room under a terrace.

Lanterns are typically aluminium with double or triple glazing and solar-control coatings; the upstand they sit on is insulated so it does not become a cold bridge.

How much do rooflights cost?

Allow £2,200–£4,500 including VAT for a roof lantern of about 2 m × 1 m supplied and fitted with its upstand, £1,200 to £3,000 for a flat rooflight, and £2,500 to £6,000 for a walk-on unit, depending on size.

Glazing and Building Regulations

New fabric must meet Approved Document L (2021 edition incorporating 2023 amendments): walls 0.18, roof 0.15 and floor 0.18 W/m²K, windows 1.4 W/m²K or Band B. Under the simple route, new windows, doors and rooflights should not exceed 25% of the extension floor area plus any openings removed; more glass is possible with a whole-house calculation.

What is included?

Daylight planning for the room below
Roof lanterns
Flat and slot rooflights
Walk-on rooflights
Opening vents for summer cooling
Insulated upstands
Blinds and solar-control glass
Fitting into new or existing flat roofs

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FAQ

Rear extension rooflights questions

Lantern or flat rooflight?

A lantern gives height and a feature; a flat rooflight is cleaner and lower-profile.

Do rooflights count towards the 25% glazing limit?

Yes, in England's simple route; more is possible with a calculation.

Can a rooflight open?

Yes, manually or electrically, with rain sensors.

Will it leak?

Not when fitted on a proper upstand with the membrane dressed up it.

Can I add blinds?

Yes; integral or fitted blinds help in summer.

Can you add a lantern to an existing extension?

Often, if the roof structure can be trimmed around it.

Where