Select Committee on Environment, Transport and Regional Affairs Appendices to the Minutes of Evidence

Memorandum by Sheffield City Council (ROF 24)

  Please see the following internal memo from Sheffield City Council's Architects Division. I apologise for simply passing on the information you require in this way but your enquiry did not reach me until very late and it seemed like a reasonable expedient in order to meet your deadline.

S. Jenkinson,

Technical Services Manager


  There are only two major multi-storey housing developments within your stock that have received overcladding in recent years, Hyde Park Block C and the various Hillside and Netherthorpe Tower Blocks. An explanation of the situation regarding fire spread for both developments is as follows:

Hyde Park Flats Block C

  Any fire involving an overclad building appears to invoke widespread concern regarding other buildings with claddings of this type. This was also the case during the design of Hyde Park Block C (Harold Lambert Court), as two significant fires occurred which informed the design process.

  Sheffield Design & Property engaged foremost fire consultants Arup Research and Development to resolve the fire issues relating to the overcladding with the consultant specialist over cladding Architects Peter Bell and Partners. The Sheffield Building Control Office in 1990 had little experience of dealing with construction of this type and the approval of the overcladding with respect to section B2—Internal fire spread (linings), B3 (2)—Internal fire spread (structure) and B4 (1)—External fire spread was referred to the Secretary of State for the Environment for determination. In his letter of 28 February 1991 and after due consideration the Secretary of State approved the details put forward for meeting the requirements saying. . . "In all the circumstances the Secretary of State determines that the proposals comply with the requirements of Regulations B2/3/4 of Schedule 1 to the Building Regulations 1985".

  The building is constructed with a brick plinth to separate the cladding system from fires that may be started at the base of the building. The cladding itself has a system of fire barriers within it which serve to prevent fire spread between the dwellings. The cavity behind the cladding contains some timber members and the insulation, this has been carefully detailed to the satisfaction of the Secretary of State to meet the requirements of the regulations in respect of fire spread. The overroof contains no fire barriers as this was not required.

  Since the installation of the overcladding there has been a serious fire on Block A (the cream and red block) at deck access level. This fire whilst breaking out onto the facade through the glazing was successfully restricted to a small area of the facade and failed to move beyond the installed fire barriers.

Hillside and Netherthorpe Tower Blocks

  Fire risk due to external spread via cladding systems was an emotive issue at the time of the development of the Hillside (Phase 1) design. There had recently been a fatal incident due to a gas explosion at Solihull, and a serious fire via external overcladding (ventilated airspace) had occurred at Knowsley Heights, Liverpool. This meant that South Yorkshire Fire Officers took a keen interest in what was being proposed, including a visit to their colleagues at Knowsley, and Building Control took a similar interest.

  It is correct that until that time there had been blocks refurbished elsewhere where a board overcladding system had been used which was full-height ventilated. This is in fact a principle of rainscreen overcladding as explained in the CIRIA guide. Some blocks had fire separation at intermediate points in the elevation. The solution agreed in Sheffield took on board the lessons learnt in these incidents.

  In response to the Knowsley incident board cladding manufacturers devised a fire barrier solution which consisted of a perforated steel member coated with intumescent paint which would expand in a fire incident. This was rejected in Sheffield as we felt that the active life of the paint would be less than that of the refurbished building, and this would be an impossible item to maintain.

  The main principles of fire safety in the Hillside and Netherthorpe blocks are as follows:

    1.  The new window is set within the opening of the original window, such that the curtilage of the dwelling for Building Control purposes remains the brick external wall. The integrity of the dwelling is maintained by the dwelling door and habitable room doors being self-closing fire standard, apart from additional precautions within the circulation areas of the block.

    2.  The periphery of each dwelling horizontally and vertically is protected by mineral wool insulation bridging the cavity between the original external wall and the new cladding. This is repeated around every window perimeter.

    For this reason we had to use aluminium cassette panels to allow movement of air within the cavity across the face of each dwelling. Ongoing research with Hallam University has confirmed that this achieves acceptable air movement conditions to prevent detrimental action within the cavity (eg steel reinforcement corrosion and concrete spalling). These panels are colour-coated and not paint finished.

    3.  All supporting members to the overcladding are steel or aluminium with separation to prevent electrolytic action.

    4.  The ground floor in every block is brickwork which is fire-stopped at first floor level to prevent fire at the ground (eg rubbish, car vandalism) ingressing behind cladding.

    5.  All new metal overcladding is incorporated in the lightning protection of the block.

    6.  New windows are aluminium, not UPVC.

  It may be of interest that there was a deliberate arson incident to a first floor flat in Martin Block before the conclusion of Hillside (Phase 1) contract. Due to its nature this fire burnt unattended for longer than the design precautions had anticipated. There was smoke-logging of the circulation area outside but the fire did not spread beyond the flat involved.

  I hope the foregoing assures you that the Sheffield stock which has been refurbished using rainscreen overcladding has been carried out with full involvement of Fire Officers and Building Control Officers, and that no known risk has been accepted. In both cases the panels are colour coated and redecoration should not be required.

JD Breakey

Practice Manager

Architects Practice

July 1999

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