Do I need a structural engineer for a new flat roof?

Question

We're replacing the flat roof on our extension and the builder says we don't need a structural engineer but I want to check. Is it required and when does it become necessary?

Jake · Answer

No you do not need a structural engineer for the flat roof

Eleanor · Answer

No you don’t need a structural engineer for an existing roof even if stripping back a completely replacing, you might if changing to pitched.

Steven · Answer

No you dont need a structural engineer for a flat roof

Benjamin · Answer

In many cases, no, you do not need a structural engineer just to replace an existing flat roof on a like-for-like basis.

You are more likely to need a structural engineer if any of the following apply:

* The roof structure is being altered, not just re-covered.
* New steel beams, timber joists, or supports are being added.
* The roof span is increasing.
* A heavier roofing system is being installed than before.
* A roof terrace, balcony, or green roof is being added.
* Rooflights, lanterns, or large openings are being cut into the structure.
* There are signs of sagging, movement, cracking, or structural defects.
* Building Control requests structural calculations.

For a straightforward replacement where the existing joists and structure remain unchanged and are in good condition, builders commonly carry out the work without structural engineering input.

One point worth checking is whether the new roof will meet current insulation requirements under UK Building Regulations. Even if the structure stays the same, Building Control may become involved depending on the extent of the work.

A practical approach would be:

1. Ask the builder whether the work is a true like-for-like replacement.
2. Confirm whether any structural elements are being changed.
3. Check with your local Building Control department if approval is needed.
4. If there is any doubt about loadings, spans, or the condition of the existing roof, a structural engineer’s inspection is usually money well spent.

Sean · Answer

The builder is right you don’t need a structural engineer for a flat roof replacement. You would only need one if you were installing something heavy on top of the roof. Hope this helps
Peter
Cordell Renovations

Izmir · Answer

If it a big project or more than 50 m2 roof then you would need a structural engineer

Marcus · Answer

Good Morning Sarah,

if your simply replacing the existing roof covering and the roof Dec and supporting joists remain exactly the same and in good condition then no you don't.

Hope this helps

Paul · Answer

In my professional opinion you do not require the above.

Adam · Answer

Not if your just changing the covering however if more than 25% of the roof is getting change it’s advised to inform building control to make them aware of the changes been made

Do I need a structural engineer for a new flat roof?

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