Can You Add a Roof Lantern to an Existing Flat Roof?
A roof lantern can often be retrofitted to an existing flat-roof extension. Learn what must be checked before cutting the opening.
Adding a roof lantern can transform a dark existing extension, but the project needs more than a hole in the roof. Structure, drainage, insulation, waterproofing and approvals must be assessed before work starts.
IS THE EXISTING ROOF SUITABLE?
A survey should identify the roof construction, joist direction, supporting walls, existing falls and the condition of the covering. The new opening may require trimmed joists or steelwork designed by a structural engineer.
CREATE THE RIGHT KERB
The lantern normally sits on an insulated upstand or kerb above the finished roof. Its dimensions, height and level must match the product requirements. The kerb also needs correct vapour-control and waterproofing details.
PROTECT ROOF DRAINAGE
The new structure must not block falls or outlets. Water should continue to drain freely around the lantern. In some cases, the roof covering may be near the end of its service life and replacing it alongside the retrofit is more sensible.
INSULATION AND BUILDING REGULATIONS
Cutting an opening changes the roof’s thermal performance. Building control may require calculations covering the extension as a whole. A thermally broken frame, suitable glazing and an insulated kerb help reduce heat loss and condensation risk.
PLANNING CHECKS
Many roof-lantern projects may be permitted development, but restrictions, listed status and previous permissions can change the position. Read our planning guide:
https://smartaview.com/blog/do-roof-lanterns-need-planning-permission
PLAN FOR ACCESS
Installers need safe access for the frame and heavy glass units. Protect the room below and plan temporary weather protection before the opening is made.
Explore sizes and options in the Smartaview aluminium roof-lantern range:
https://smartaview.com/product-types/roof-lanterns
CAN THE WORK BE DONE WITHOUT REPLACING THE WHOLE ROOF?
Often, yes, if the existing structure and covering are in good condition. A professional survey is essential because every existing roof is different.
Author at Smartaview, writing about aluminium glazing, home improvements and the buying process.
