Where a New Roof Meets an Old One
homeowner with an existing flat roof extension asking about compatibility
Many houses have a single-storey flat roof extension, such as a kitchen extension, and a new veranda often needs to interface with that roof rather than the main house wall directly, which raises specific weatherproofing and structural questions worth understanding before a design is finalised.
Why an abutment needs careful detailing
An abutment, the junction where a new structure meets an existing roof, needs flashing and weatherproofing detail specific to both roof types involved, since a poorly detailed junction is one of the more common sources of leaks in extension projects generally.
Assessing the existing flat roof's condition and age
An older flat roof covering, particularly felt approaching the end of its service life, may need attention before a new structure interfaces with it, since building against a failing roof covering simply extends the same problem into the new project.
Fixing to the wall above a flat roof extension
Where a veranda fixes to the house wall above an existing flat roof extension, the fixing height and any scaffolding access, covered in more detail elsewhere on this site, both need planning around the extension roof rather than assuming ground-level access throughout.
Considering roof replacement as part of the same project
Where an existing flat roof is ageing, some homeowners choose to have it re-covered as part of the same project, simplifying the weatherproofing detail at the new abutment and avoiding two separate disruptions to the same area.
Common questions
Can a veranda simply sit on top of an existing flat roof extension?
This depends on the specific design and the flat roof's structural capacity, and is generally assessed carefully rather than assumed to be automatically compatible.
Does an old flat roof need replacing before a veranda project starts?
Not always, but its condition should be assessed, since building against a roof nearing the end of its life can simply transfer the same problem into the new structure's junction.
How is the junction between the two roofs weatherproofed?
Through appropriate flashing and detailing specific to both roof types, which a competent installer should be able to explain clearly for your particular combination of roofs.
Does fixing above a flat roof extension need scaffolding?
It can, depending on height and access, and this should be assessed at survey alongside the general scaffolding considerations covered elsewhere on this site.
In short
Where a veranda meets an existing flat roof extension, careful abutment detailing and an honest assessment of the existing roof's condition both matter before building against it.
What to do next
Tell us about your existing flat roof extension and we'll assess the abutment detail properly at survey.
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