Guide
Structural calculations for a loft conversion
Turning a roof space into a room changes how the house carries load. The new floor has to support people and furniture. New beams often pick up load where a wall or a rafter is altered. A dormer or a hip-to-gable changes the roof. For that reason a liveable loft normally needs structural calculations as part of the building regulations information.
The Planning Portal’s page on building regulations approval for a loft conversion lists structure among the items a building control body checks. Whether every member needs a new calculation depends on the existing roof and on the agreed design. Tekneca confirms that when quoting.
What is normally included
- The new floor, where the ceiling joists of the room below are not suitable to become a floor.
- Beams that support the new opening, the dormer or the remaining roof.
- The roof members affected by a dormer, a hip-to-gable or a set of rooflights, where those members change.
A rooflight-only loft can need less new structure than a dormer. It can still need a floor check and a check of the rafters that are cut. That is confirmed from the house, not from the name of the loft type alone.
How Tekneca quotes it
Structural calculations are quoted for the agreed structure. They are not part of the loft planning drawing pack, which starts from £1,350, unless a written quote includes them. The calculation sheets are issued for that project. They are not published on this website.
Common questions
Are calculations needed if the loft is permitted development?
The planning route does not answer the structural question. A loft that is permitted development can still need building regulations approval, and that approval normally includes the structure. The two decisions are separate.
Does removing a wall in the loft always need a beam?
It depends on whether that wall is carrying load from the roof or the floor. Some partitions do not. Tekneca looks at the wall as part of the agreed project before saying what is required.
Can I add the calculations after the planning drawings?
Yes. Many projects are quoted in stages. Send the planning drawings, or ask for them together, and the structural work is priced for the loft that is going to be built.
Service pages: loft conversion drawings and structural calculations.
Request a structural calculation quote