Case studies - Propped Rafter
Cottage Grove, Lambeth, London
Client: London Borough of Lambeth Council
Project Management: Hunter & Partners
Main Contractor: Breyer Group plc
Installed by: Breyer Group plc
The quadrangle buildings of Cottage Grove, in Lambeth, were in serious state of disrepair and deteriorating rapidly. Leaks were apparent inside the properties which could not be identified on roofs due to water tracking thought the roof construction, often many metres from the point of ingress, rendering repairs virtually impossible.
This is a well known scenario across the borough and it was decided by the property management team that a familiar repair route should be adopted. Therefore a new Eternit 2000T slate roof at a 37 ยบ pitch with PVC Fascias and soffits were proposed over an FTP Systems structural framework to blend in with neighboring buildings at Fenwick Place, which also benefits from an FTP Systems structure.
The roofing contractor invited FTP Systems to carry out a detailed survey of the existing roofs and prepare structural calculations and drawings to assist in clearing planning consent and building regulations approvals.
The new structure was planned with a continuous ridge line and with 500mm roof overhands to the periphery. All services were extended through the new roof void and exhausted through the Eternit slates. Additional insulation was installed to enhance the buildings heating efficiency and internal walkways were created to allow access for maintenance. Five compartmentation (with five fire doors for the walkways) were provided by means of Envigorat fire curtains.
The FTP Propped Rafter Structure is lightweight, yet strong enough to carry the Eternit slate coverings. Having a minimum number of components it is quickly erected by trained operatives. Site pull-out testing allowed an accurate assessment of the holding down fasteners which were fixed through the existing failed waterproof membrane into the sub-structure. This method of construction allows the tenants under the roofs to be maintained in their homes during the renovation works.
The project, which again was on-time and on-budget, shows considerable aesthetic enhancement and has increased the asset value of the property. It also offers a significantly longer maintenance free life than could have been achieved by simply relaying a flat roof.
