Structural calculations in Merton

Clay, roots and the evidence Merton asks for

Merton's tree strategy uses British Geological Survey maps to find shrinkable clay and past subsidence claims. For low-value trees its evidence level reads: Borehole log to at least 3 m depth (low-value tree). That is a useful measure of what the council counts as proper investigation of the ground.

That standard is for tree work, not for a beam, yet it shows the way the borough thinks about soil. If your foundation sits in clay near a tree, the calculation should say what depth and spread of root we assumed, and a borehole or trial pit is how that assumption is tested.

We record trees and levels on our survey, and flag in the calculation where the engineer should confirm foundation depth on site.

Chartered engineers on bigger structural work

For larger schemes beyond a house beam, Merton's basement guidance expects a chartered engineer to design and monitor construction. The entry reads Chartered Engineer retained through construction. Where a listed building is involved, the council asks for written confirmation that the applicant will pay for independent review: Listed buildings; applicant pays for review.

A domestic beam does not reach that level, but the principle holds. Someone competent designs the member, checks the temporary works and confirms it was built as designed. Our calculation set identifies who designed what, and includes the temporary support the builder should use.

Merton homes, prior approvals and householder timing

Merton is a borough of houses: 60.4 per cent of households live in one, and 55.6 per cent own their home. The council granted 22 larger home extension prior approvals in its latest return, and an extension with a wide rear opening needs a beam.

Householder planning applications are decided quickly in most cases but not all: of 759 decisions, 92.9 per cent were granted and 85.2 per cent were decided in time. The latter is the lower figure to plan around, as steel orders wait on the design being settled.

The borough has 28 conservation areas, and Historic England lists 23 Heritage at Risk entries here. Our planning drawings in Merton cover the permission stage.

Deciding which of Merton's fee lines your job sits on

Because Merton separates a single wall from a larger structural scheme, it pays to describe your job accurately before you apply. A through room formed by one wall is a single line. Two walls, a chimney breast and a floor strengthened for a bathroom above is a scheme, and the council scales its charge by the cost of the works.

We help by writing up the structural scope on one page: each wall, each beam, each support. You can send it to the council, or to a registered building control approver, and ask for a fee against it. The scope also keeps your builder's price honest, because each item on it has a reason and a size.

If the scope grows during the work, tell us. A beam added late still needs a calculation, and it is cheaper to add it to the set than to retrofit.

Our fee and the package

Merton calculations start at £295, VAT included, fixed once we know the work. You receive the calculations, a schedule of beams and padstones and a layout, checked by a second chartered technologist before issue.

Revisions after a council query are included, and the same figures feed our building regulations drawings in Merton.

Neighbours and further reading

Next door in Kingston upon Thames the council prices an opening in a load-bearing wall on a different scale, and Lambeth has its own rules for deeper work. For Merton as a whole see architectural drawings in Merton, or the structural calculations guide.