Ask a tradesman


We would like to remove a window and open the aperture to the maximum to fit bi-folds. how do we work out how wide is structurally safe and what type/length lintel to use?

Existing window 188cms wide, set in existing wall 346cms wide, single storey, flat roof projecting 122cms from main house structure.

6 Answers from MyBuilder Extension Builders

u need structrial calculations done by serveyor we have 1 if u need thank u


Answered 6th Aug 2011

Good afternoon to carry out this work you will need to apply for building regs first. Lintels typically span 150mm longer each side than the original size of the opening. So you will need a new lintel if the bi fold is bigger than the width of the window. The lintel depends on the build of the house eg. cavity wall, nine inch solid etc.

Hope this helps


Answered 6th Aug 2011


My advice is play it safe and seek advice from a structural engineer and also speak to local building control about building regs.



Answered 7th Aug 2011

2300 max


Answered 11th Aug 2011

years ago builders used rule of thumb, but nowadays the correct way is to use the services of a structural engineer.

The width of the opening would be governed by the minimum lengths of brickwork left standing, or if an opening larger is required then alternative support would normally be required to strenghthen the walls, usually by thicker piers or extra structural or steel columns, (this presumes standard construction).

Secondly the span and loading from the roof above needs to be accounted for, and also any loading from the door system if it is hung from the beam above, this would dictate the type and strength of lintel or beam needed. (standard steel lintels come in many differing types & loading capabilities)

This work would need to comply with building regulations, the structural engineer would ensure this, and the builder would have the correct information.

Steve Nicholls BSc(Hons)Residential Development


Answered 28th Aug 2011

Any width is possible really.
You need to contact a structural engineer for a design though. £300/ £400 pounds usually.


Answered 23rd Jul 2019

Post your job to find high quality tradesmen and get free quotes

Can’t find an answer? Ask a new question

Question Categories