Most London loft conversions need a structural engineer. Turning a loft into a room means the floor, the roof and often the walls below will carry loads they were never designed for, and Building Control will expect structural calculations showing that the new structure works. This guide answers the questions London homeowners ask us most often before a loft project starts.
Do I need a structural engineer for a loft conversion?
In almost every case, yes. A loft conversion needs Building Regulations approval even when it does not need planning permission, and Part A of the Building Regulations covers structure. Your building control body will normally ask for structural calculations and details before or during the work. A structural engineer produces these and makes sure the design suits your particular house, not just a typical one.
Why can't the existing loft floor be used?
The ceiling joists in most London terraces and semis were sized to hold up a plaster ceiling, not people, furniture and partition walls. A converted loft usually needs new, deeper floor joists, often running between steel beams or bearing on the existing walls at new positions. The engineer sizes these joists and checks what they rest on.
What do loft conversion structural calculations cover?
Every house is different, but a typical London loft package covers:
- New floor joists and how they are supported
- Steel beams, for example to replace roof purlins and struts removed to open up the space, or to support a dormer
- Padstones and bearing checks where beams sit on existing brick walls, including party walls
- Roof alterations such as new rafters, ridge beams and dormer framing
- Connections, fixings and restraint details the builder needs on site
- A check of the load path down through the house, and a note of anything that needs investigating, such as a wall below that may not be able to take more load
What about chimney breasts in the loft?
If a chimney breast has already been removed on a lower floor, the brickwork above it in the loft may be poorly supported. This is common in London houses and is often only found when the loft is opened up. A loft conversion is the right time to have it checked. Our guide to chimney breast removal calculations explains how this is normally dealt with.
Does a loft conversion affect the party wall?
Often, yes. Cutting into a party wall to seat a steel beam, or raising it for a mansard, is usually notifiable work under the Party Wall etc. Act 1996. For work to a party wall, notice is normally served at least two months before work starts. Your calculations will show where beams bear on the party wall, which the party wall surveyor will want to see.
Do I need planning permission as well?
Many rear dormer conversions can be built under permitted development, within volume limits (40 cubic metres for terraced houses and 50 cubic metres for detached and semi-detached houses) and other conditions. Mansards, front dormers, flats, and homes in conservation areas usually need planning permission. Planning is a separate question from structure: even a permitted development loft still needs Building Regulations approval and structural calculations.
What will the engineer need from me?
- The architect's or designer's drawings, if you have them
- Access to the loft and the rooms below, so the engineer can see the existing timbers, walls and any old alterations
- Anything you know about the house's history, such as previous chimney breast or wall removals, extensions or signs of movement
An engineer's visit before the design is finalised avoids surprises on site, such as a wall that turns out to be timber stud rather than brick.
When in the project should I bring in an engineer?
As early as possible, ideally once you have a layout you like and before builders price the job. Builders can only give an accurate quote when they know how many steels are needed, how big they are and where they go. Late structural design is one of the most common causes of delays and extra costs on loft projects.
How long does it take?
It depends on the size of the conversion and how much is known about the existing structure. Call us on 020 3983 5057 with your drawings and we will tell you the timescale and fee for your project.
Loft conversion structural engineers in London
Laytoe Structures is a firm of chartered structural engineers based on Turnham Green Terrace in Chiswick, working across London. Since 2016 we have carried out more than 2,700 projects, including structural surveys, and we provide structural calculations and steel beam design for loft conversions and extensions, load-bearing wall removal and chimney breast removal, ready for Building Control.
Book online or call 020 3983 5057 for a quotation.