With the continual pressure to provide additional homes, particularly in congested city and town centres where developable land is difficult to find, organisations in the housing market are looking for new ways to meet the demand.
We have seen some life-expired 1960’s estates completely demolished and replaced with new homes to current standards. Relaxation of planning rules has enabled some cost effective conversions of office buildings to take place. Old garage courts have been demolished and infilled with limited numbers of houses. But when the available land has been used, resort has to be made to other means to increase the number of homes that can be provided.
One approach is to add additional storeys to existing buildings. calfordseaden has been involved in undertaking this work for a number of years. Our projects have varied from adding several storeys to existing buildings to converting substantial loft spaces in mansion blocks to accommodate new apartments.
Work of this nature demands a multidisciplinary approach. Issues that need to be considered when testing the suitability and viability for adding storeys include:
- Compliance with Building Regulations including ensuring appropriate fire control measures are incorporated and adequate means of access and escape are maintained
- Potential upgrade of existing utility services supplies
- Potential to incorporate lifts where none exist at present
- Potential for the existing superstructure and foundations to take additional load from the new storeys
- Potential to carry out the extension without decanting the occupants whilst the work is being undertaken
- Selection of the most appropriate structural solution for the additional storeys, given the nature and strength of the existing building, and the constraints imposed on access for construction
- Planning considerations and resident consultation events
- Rights of Light and sunlight and daylight issues, which might constrain overall development height
- Compliance with the Party Wall Act 1996 and other neighbourly matters
- Selection of procurement route
- Opportunities for modular construction i.e. off-site manufactured “pods” to minimise construction time on-site and resident disruption
- Financial planning including consideration of Leaseholder implications e.g Section 20 of the Landlord and Tenant Act 1985
We are working with private, registered providers and local authority clients and are in discussions with a number of contractors in relation to potential opportunities. Current schemes include adding five storeys to an existing 25 storey, 1960s, reinforced concrete framed building in South East London and the conversion of the loft space in a Mayfair mansion block to accommodate two luxury penthouse suites.
When assessing the potential of an existing building to be vertically extended from an engineering viewpoint, we initially review the general condition of the structure to ensure it is in generally good order – there is little point in proposing extension if the existing building is in poor condition. We then identify the form of construction used and identify the paths that transfer the load from the superstructure to the foundations. Based on this data, and working closely with the architect, we then review the proposed floor layouts for the vertical extension and seek to manage the design so that the new extension adopts the same load paths as the original building. This ensures that the loads are transferred to the existing foundations by the most straightforward route. We invariably require that a site investigation is carried out to establish the ground conditions and also to determine the form and size of the existing foundations. We then assess whether the foundations are capable of supporting the additional load, and what the likely impact is in terms of induced additional settlement etc.
Having established that the foundations may carry the additional load, we then check the existing superstructure. Depending on the form of construction, this may include non-destructive testing, but for framed buildings and certain types of load bearing masonry construction we may arrange for opening up of parts of the structure for visual examination and to enable samples to be removed for laboratory testing.
In making these assessments, we exercise considerable skill and judgement, based on our years of experience as structural engineers. However, for a number of projects it is not possible simply to reuse the existing superstructure or foundations without some form of strengthening. This might include, for example, underpinning the existing foundations or strengthening columns in framed structures to enable them to carry more load, or adding a level of transfer structure at the old roof level so that the new loading arrangement can be safely transferred to the existing frame. Whilst these solutions can appear challenging, if well researched in advance and the design fully developed to minimise the risk to contractors carrying out the work, they still prove a cost effective means of providing additional accommodation.
There is little doubt that where existing buildings have the potential to be extended vertically, adding additional storeys presents an economic means for increasing the number of homes, particularly in town centre sites, and especially when compared with the alternative of decanting, demolition and construction of new buildings.