A structural engineer for homes in London, Surrey and Sussex

How does a site visit work?

Most jobs start from what you send. When one needs a visit:

1. The fee. We say whether a visit is needed. Fixed fee, confirmed in writing before we start.
2. On the day. We look at what the design depends on: which way the joists run, what stands on the wall, what it all comes down onto, any cracks, and trees and drains near a new foundation.
3. Out of sight. Where the answer is hidden, we say what would settle it: a lifted floorboard, a hole in a ceiling, a trial hole beside a footing.
4. After. Calculations and drawings your builder can build from. We answer Building Control’s questions on our calculations as part of the job.

What do the local houses mean for the structure?

London: Victorian and Edwardian terraces

• Party walls. Often one on each side. Cutting into one for a beam’s bearing needs notice at least two months before. We keep every bearing in your half. We do party wall surveys.
• The back. The narrow rear wing many terraces have is where side-return extensions go: a new opening, with a beam carrying the wall above.
• Chimneys. Often in the party wall, so taking a breast out needs notice too.
• Basements. Underpinning a party wall is one of the Act’s rights; digging within 3 m of next door and below its foundations needs a month’s notice. We design the temporary support and the order of the dig.

Source: Party Wall etc. Act 1996, sections 2, 3 and 6.

Surrey: inter-war and post-war semis and detached houses

• Rear extensions. New foundations often go in beside mature trees, and in the north of the county and the Weald, often on clay. How deep they go depends on both.
• Lofts. A 1930s roof is usually cut timber, often converted with a hip-to-gable and a rear dormer. Later roofs are often trussed rafters, which can never simply be cut. How a loft changes the roof.

Brighton and Sussex: terraces, flint and sea air

• Terraces. Brighton’s Regency and Victorian terraces share party walls too, with the same notices.
• Flint and bungaroosh. Many older walls in Brighton and Hove are flint, or bungaroosh (in the council’s words, flint rubble), often behind render or mathematical tiles. Flint “makes poor corners and window and door openings”, so those were built in brick or stone, and a new opening needs the same.
• Lime. On listed buildings and in conservation areas, the council wants repairs to match, mortar included, and calls chemical damp treatments and tanking rarely appropriate in flint or bungaroosh.
• The sea. Pebble walls on the coast were often tarred “to protect against the salt-laden winds and driving rain”. Near the sea, we choose the protection of new steel for it.

Sources: Brighton & Hove City Council, Architectural Features Supplementary Planning Document (2009), and “Damp treatment”.

What is the ground like?

Four grounds are common here.

• London Clay. A silty clay under most of London, and the main clay of the London Basin, which runs out through north Surrey. The British Geological Survey calls it “very susceptible to volume change”: it shrinks as it dries and swells as it wets.
• Chalk. The North and South Downs are chalk, a fine-grained limestone that often holds flint. It is not a clay, so the seasons do not shrink and swell it. Its hazard is dissolving into hollows, especially under clay, which a leaking drain or a soakaway can set off.
• Clay-with-flints. In places on top of the chalk, along both Downs: a sandy clay full of flints. It is a clay, and it can run deep where it fills hollows in the chalk.
• Weald Clay. The mudstones of the Weald, between the Downs. Whether a clay is shrinkable is measured; where it is not known, NHBC says assume the worst.

Sources: British Geological Survey (Lexicon of Named Rock Units; Earthwise; “Swelling and shrinking soils”; “What causes sinkholes”). NHBC Standards 2024, chapter 4.2.

Sources: NHBC Standards 2024, chapter 4.2; British Geological Survey. Diagram drawn for this site. Not to scale, and not a design.

Key to the drawings

• Brickwork, new Single diagonal hatch. The outer leaf, and new brickwork in elevation.
• Blockwork, new Cross-hatch, so it can never be read as brick beside it.
• Concrete Aggregate triangles and fine dots, scattered at random: foundations, slabs, padstones, lean-mix cavity fill, encasement.
• Undisturbed ground Basket weave, as a band that follows the ground line and fades out.
• Insulation board The looped line, touching both faces, inside the board outline.
• DPC Heavy dashed line, as Approved Document C draws it.
• Load path Where the load goes, from the roof to the ground; dashed where it runs beyond the cut.
• Load marks Arrows at the symbol weight: loads down onto a member, bearing up under a foundation.
• Hidden, beyond or removed Out of the cut, beyond it, or taken out.
• Break line The drawing stops; the building does not.

Near trees on shrinkable clay, Approved Document A takes strip foundations down to where ground movement will not impair the building’s stability, “taking due consideration of the influence of vegetation and trees”. NHBC sets that depth from the clay, the tree’s water demand, its height and its distance, and treats the south-east, “the driest and hottest”, as the area of greatest risk, so its full depths apply here. Felling a tree causes trouble too: clay, trees and cracks.

Sources: Approved Document A, paragraph 2E4; NHBC Standards 2024, chapter 4.2.

What we need from you

• Where the house is: a town or the first half of the postcode.
• Photographs, and any drawings. A sketch is fine.
• Roughly when it was built, and whether it is terraced, semi-detached or detached.
• Where the big trees are, yours and next door’s, and any drains or soakaways near the work.
• For a flint or rendered wall, a photograph of its face.

Every design we do meets the Building Regulations.