The property
An Edwardian terraced house in East Dulwich, built around 1900 to 1914 and divided into a ground-floor and a first-floor flat, with a two-storey rear addition. It has solid brick walls, timber floors and a traditional timber roof, and stands on London Clay.
The client's concern
The owner of the first-floor flat had a vertical crack in the party wall shared with the house next door, which also showed in the flat below. The house had a known history of movement. An earlier report by another engineer had recommended repairs, but there was no record of what had been done.
What we saw
In the roof space over the rear addition there was a 20 mm stepped crack in the party wall, where the addition meets the main house, with air passing through it (BRE Digest 251 Category 4, severe). A vertical crack ran through the full thickness of the party wall in both flats, 5 mm wide at first floor and 4.5 mm at ground floor, and had reopened through an earlier repair (Category 3, moderate). There was also a 45-degree crack where a concealed beam bears into the wall.
In the roof space we found bricks missing right through the party wall, split diagonal struts under the purlins, and part of the wall above the beam replaced with boarded stud framing sealed with expanding foam, with no visible fixings.
How we investigated
A targeted inspection of the party wall in both flats, the roof space over the rear addition and the front elevation, together with a review of the earlier report. Nothing was opened up, and the other side of the party wall, in the neighbouring house, could not be inspected.
What we found
The cracks did not share one cause. The loft crack sits at the junction of two parts of the building that behave differently, with defects in the roof structure and unconfirmed support that may be adding to the movement. The crack through both flats was almost the same width over two storeys, showing movement through the full height of the wall; ground movement was one possible cause, but it needed investigating before a permanent repair. The 45-degree crack pointed to the way the beam bears on the wall, which could not be assessed until the beam was exposed.
The missing bricks were the most urgent item, because they left a hole in the fire separation between two homes. There was no sign of imminent collapse, but the cracks were active and needed dealing with in months rather than years.
What we recommended
Rebuild the missing brickwork and fire-stop the party wall within two weeks. Serve notice under the Party Wall etc. Act 1996 and inspect the neighbour's side before designing any repair. Commission a CCTV drainage survey, a trial pit at the junction and a tree survey. Expose and assess the beam, and design its padstone or spreader plate from the actual loads rather than adopting a size suggested before the beam had been identified. Stitch the through-crack on both faces only once its cause is understood, renovate the roof structure as a whole rather than patching it, and monitor the cracks for at least 12 months.
Because the work had to be designed stage by stage, across two flats, a party wall and a freeholder, we also recommended appointing a project manager or chartered building surveyor to run it.
Related services
This was a Specific Structural Inspection (SSI). Read more about our structural inspections, cracks in walls and our work in Dulwich, or see more case studies.
