Structural calculations
Structural calculations for home alterations
Structural calculations size the beams, floors and roof members a loft or an extension needs. They are prepared for the particular house, with the drawings that show that structure. They are a separate stage from the planning drawings.
What is usually calculated
A loft usually needs additional steel. The ceiling of the room below is rarely suitable as a new floor, and a dormer or a hip-to-gable changes the roof members. Headroom and the stair are set out with the loft conversion drawings. More on that structure is in loft structural calculations.
An extension usually needs calculations where the back or side of the house is opened up, and for the lintels and roof of the new part. A single-storey opening and a two-storey extension are both assessed from the house. The types of extension are on the home extensions page, and the drawing stages are in extension drawings.
- Steel beams over new openings, in a loft or where an extension joins the existing rooms.
- A new loft floor, and the roof members for a dormer or a hip-to-gable.
- Lintels and the roof of an extension, including a wraparound roof where the design needs one.
Some walls are only partitions. Whether an opening needs a beam depends on that wall and the house.
What building control usually expects
The calculations normally form part of the building regulations information. A building control body checks the structure as part of that approval. Guidance on when building regulations approval is needed is on GOV.UK.
Planning, building regulations and calculations
The calculations sit alongside the other two stages. Each stage answers a different question.
- Planning applications and the permitted development and certificate route deal with the planning position.
- Building regulations drawings show how the agreed loft or extension is built. The calculations support that set for either project.
- This page is the structural stage: the beams, floor or roof for the loft or the extension.
Common questions
Do I need calculations to remove a load-bearing wall?
Normally, yes, if the wall is supporting floor or roof load. Some walls are partitions and do not. The answer depends on that wall and the house.
Are structural calculations part of the planning drawings?
They are a separate stage. Planning drawings show the proposal. The calculations size the beams, floor or roof that the agreed design needs.
Do the calculations replace building regulations approval?
They support that approval. A building control body checks the structure as part of the building regulations application. The calculations are the information for that part of the check.