Who do I talk to first?
You should ideally consult both an architect and a structural engineer on your design, although some engineers will be able to offer the complete design service.
When you have a design you should consult your local authority planning department, although full planning approval is often not needed — loft conversions are often within ‘permitted development’ rights for a property.
However, you should obtain a certificate of lawful development to formally confirm this (otherwise selling can be complicated).
What sort of work is involved in converting a loft?
This will depend on the existing structure, but usually there will be structural members passing through the space — meaning structural alterations are required to allow conversion (whether installing new elements or strengthening the building below).
In almost all cases the existing ceiling is not adequate to carry floor loads, and a new structure is required.
Typically loft conversions fall into two categories; “roof window” and “dormer”. A roof window conversion sees windows added to the existing roof plane, while a dormer conversion sees a new (usually flat) roof section projected from the existing roof.
Roof window conversions are typically cheaper as they involve less work and are less disruptive to the building’s weatherproofing.
Why is a structural engineer necessary?
A structural design will need to be proved for Building Regulations approval purposes.
A suitably experienced engineer can also help design stairs, which can be a critical part of the feasibility of the scheme.
Crucially, changing the structure incorrectly could damage the roof, which in turn causes weathering issues.
You could also damage the structure below the loft, because loads have been redirected to inappropriate elements of the building.
Ultimately you could end up devaluing your home.
What can I expect the structural engineer to provide and/or guarantee?
A suitably experienced engineer may be able to provide a complete design package to meet Building Regulations and provide construction information, over and above structure, but as a minimum the engineer should provide drawings detailing the structure and calculations for Building Regulations approval.
Just calculations will leave your builder unclear on details and will likely mean he charges more than necessary for the build as a result.