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CROSS Safety Report

Dangerous modification during construction of five storey block of flats

Report ID: 699 Published: 1 January 2018 Region: CROSS-UK

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Overview

A reporter was asked to investigate a five storey timber framed block of flats after the leaseholder of the top floor reported gaps appearing between oak floorboards.

The reporter found that gallow brackets and a boundary wall were used instead of a flank walls at ground floor level.

Key Learning Outcomes

For construction professionals:

  • Any alterations to structural arrangements should be approved by the design engineer prior to works being carried out on site

  • Quality management and competent supervision on site can help to ensure that the structure is built in accordance with the design

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A reporter was asked to investigate a five storey timber framed block of flats after the leaseholder of the top floor reported gaps appearing between oak floorboards. The reporter found that a flank wall was missing at ground floor level.

Instead, steel gallows brackets bolted back to the timber frame using six screws, were supporting a steel beam at first floor level that supported three storeys of brickwork (Figures 1 & 2). The other end of the steel beam was supported on a boundary garden wall with a shallow foundation.

According to the reporter, the entire assembly was inadequate, and the wall had dropped and moved laterally at first floor level, thus pulling the top floor, and creating gaps between the floorboards on top of the joists. The gaps between the floorboards had been filled and opened up again, showing that the movement was ongoing.

According to the reporter, the entire assembly was inadequate, and the wall had dropped and moved laterally at first floor level, thus pulling the top floor, and creating gaps between the floorboards on top of the joists

The flank wall at ground floor level was apparently omitted due to a setting out issue i.e. the building would not fit on the site, so the flank wall was replaced by an existing boundary garden wall at ground floor level. The reporter feels that this should have been picked up by site inspections but was not.

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Figure 1: steel gallow bracket arrangement
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Figure 2 : flange of steel column screwed back to timber frame

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