Structural calculations in Lambeth

Listed buildings and who may certify the structure

For heavier structural schemes Lambeth is exacting about who signs. Its guidance says methodology statements must be prepared and certified by a chartered engineer, with the entry reading MICE or MIStructE certifies; CARE for listed. The qualification expectation tells you how seriously the council takes structure around historic buildings.

Lambeth has 64 conservation areas, and Historic England records 39 Heritage at Risk entries within the borough. A house in one of these streets may need conservation-sensitive structural design as well as arithmetic, with new steel kept away from decorative plaster and original joists retained where they can be.

Our calculations name the competent person who has designed each member, as the Building Regulations require.

Ground movement near an excavation

Underpinning and deeper excavation move the ground around them. Lambeth's guidance describes the effect in simple terms: zone of influence about 4 x excavation depth; Burland Scale.

For a terrace the lesson applies to neighbours as much as to you. Where the work is deep, a party wall award and a condition survey of next door protect both sides. We sketch the excavation on the survey and mark where it falls against the neighbour's footing, so the notice, the engineer and the builder work from one drawing.

Flats, shared houses and trees

Only 24.8 per cent of Lambeth households live in a house, and 33 per cent own their home. Many jobs are in converted houses, where a wall carries floors for more than one household and a beam has to be designed for the full stack above.

The borough also records 339 tree preservation orders and 226 protected zones, so check for protected trees near a rear extension. Roots near a new foundation affect how it is detailed.

Lambeth's decision figures

In its latest published year Lambeth decided 595 householder applications, granted 83.4 per cent and decided 93.4 per cent within eight weeks or an agreed extension. Our planning drawings in Lambeth cover that stage.

What a Lambeth loft asks of the floor below

Lambeth's loft charge is banded by floor area, and a loft is the job where our calculation does most of the work. The existing ceiling joists were sized to carry a ceiling and a few boxes, not a bedroom, so the new floor is usually a set of deeper joists or steel carried on the party walls and the front and rear walls.

The wall below then has to take the new line loads. In a terrace the party wall is shared, so bearing notches and any steel pockets are matters for a party wall notice as well as for the engineer. A stair opening takes out a section of floor, which brings trimming beams into the design.

We draw the new floor, the trimmers and the stair together, so every opening in the floor has a reason and a size, and the calculations follow the same numbering.

Fee and what Lambeth owners receive

A Lambeth calculation set starts at £295 with VAT included, fixed after we know the building and the work. It contains the calculations, a schedule of steel and padstones and a layout sheet, checked by a second chartered technologist before issue.

If the council asks for a change we revise without a further charge, and the figures flow through into our building regulations drawings in Lambeth.

Around Lambeth

Read architectural drawings in Lambeth for the borough overview, or compare how Merton handles the same calculations. The structural calculations guide holds the national rules.