ENGINEERING COLLABORATION PROVIDES EFFICIENT TOWER BLOCK RECLAD SOLUTION
Much of the social housing stock of the UK constructed in the post war building boom between 1950 and 1970 consists of tower blocks. Many of these blocks are now showing general signs of age and with the importance of providing more energy efficient and attractive living spaces recognised for their social benefits, Registered Social Landlords and councils are increasingly looking for innovative, efficient and affordable means to rejuvenate these properties.
Renovation work on these buildings will usually include the replacement of kitchens, bathrooms, windows, heating systems and insulation within apartments. Gas, water, electric and waste services will be brought up to date and security improvements and enhancements made. These can include the installation of secure entry systems and the renovation of lobby, lift, stairway and landing areas.
One of the most important factors in improving the energy efficiency and aesthetic appearance of these buildings is the innovative use of exterior rainscreen overcladding. Economic, attractive and easily installed, rainscreen cladding can often be assembled to the existing exterior of a tower block without any requirement for additional reinforcement to the building structure. With the incorporation of window pods and prefabricated balcony fittings, rainscreen cladding provides a new and efficient outer skin for buildings that can be installed without the necessity for tenants to vacate their homes.
This practical and efficient method of building regeneration was recently chosen by Enfield Borough Council to refurbish Dorset and Keys, two of their apartment blocks, each of 13 storeys height. As such projects require a high degree of engineering, logistical management and skilled installers, they called on a range of specialists to help take this challenging project from the drawing board to completion, including Cladding Solutions Ltd. (CSL) and its sister company, Eurofox Engineering Ltd. (EEL).
Although work on these tower blocks has only recently been completed, the planning process commenced as far back as 2003. To meet the stringent standards expected of public works, Enfield Council Design Services set out to select construction materials that would meet a strict set of criteria, ranging from safety, 'buildability', and aesthetics, through to sustainability, system life expectancy and recyclability, all supported by independent testing and certification.
Following a thorough evaluation of a wide variety of exterior façade materials, Enfield Council selected Trespa Meteon High-Pressure Laminate (HPL) panels. These would be fixed to a combination of Trespa's System 700 floor spanning system, produced by CSL for the UK market, and MTA-v-100 MacFox brackets 'T' and 'L' profile system, supplied by Eurofox Engineering, the UK's leading rainscreen systems supplier. Each of these elements is supported by independent British Board of Agrément (BBA) certification.
Working in collaboration with Trespa, CSL and Eurofox have extensive experience in providing cladding support systems and façade materials for a wide range of complex structures. To carry out the installation, specialist contractor Cladding UK Ltd was handpicked for its expertise and proven ability to undertake this type of project.
Selection of the System 700 floor spanning support system for the main elevations of the building meant that brackets only needed to be fixed at floor slab positions. Double storey height cladding rails were then assembled to these brackets. Sliding spigots provided the connection between each vertical cladding rail to accommodate thermal expansion and contraction of the framing system. To support framing around the windows, shorter profile sections with welded assembly end plates were fixed horizontally between vertical profiles, providing a full grid to which both the cladding panels and window pods could be assembled.
Made of aluminium, and therefore fully recyclable, the System 700 intelligently engineered framing solution can accommodate the fixing of window pods and balcony fittings without the need to vacate buildings. The Meteon panels are simply secured to the subframe with colour- matched low profile blind rivets making, the cladding system practical and straightforward to install. This was a key stipulation of Enfield Borough Council, which wanted to keep disruption to the tenants of the Dorset and Keys apartment blocks to a minimum.
Where floor-spanning profiles were not a requirement, notably for the cladding of the apartment balconies, communal entrances and storage areas, the lighter weight Eurofox MTA-v-100 aluminium system was specified and installed. Rivet fixing of the Trespa HPL panels to CSL System 700 and EEL MTA-v-100 was the common assembly feature of both systems.
The Trespa Meteon panels were of central importance to the project due to their fire resistance. Made from 70% wood based fibres, these durable panels also met the green standards expected in public works. Chosen in an attractive light beige for the main body of the building with contrasting lavender blue panels framing the corners and parapet of the tower blocks, they are highly resistant to impact, UV light and extreme weather conditions. In addition to this, the panels are strong, relatively lightweight and very easy to clean and maintain. External corners of Trespa cladding are finished with a durable curved extruded aluminium trim that is colour matched to panels.
As the work was part of a public project, the design and products had to meet high environmental standards. To achieve this, Kingspan K15 insulation was specified for use between the cladding and structure, with a minimum 40mm clear air gap between the insulation layer and the inside face of the Meteon panels. This proven combination has the effect of significantly improving the energy efficiency of aging structures by bringing them up to the performance expected of modern buildings.
The free movement of air between the panels and the insulation layer produces the rainscreen cladding principle of preventing any rainwater that penetrates the exterior panels from reaching the insulation layer or the original building facade, keeping the building structure ventilated, dry and in good health.
Product selection, specification and initial design was completed in 2005, when a project budget was set. The scheme threw up a number of technical challenges for the team as work progressed, including the fact that when work commenced the actual dimensions of the tower blocks were found to differ to those in the original building plans. This necessitated a great deal of surveying and design to ensure that the cladding would precisely match the building outline. Despite this additional work CSL and EuroFox Engineering still managed to deliver the project materials within the original 2005 budget price.
The replacement of the original windows was a key part of the refurbishment work. Modern thermally efficient window units were specified, with the interface between these and the cladding being provided by window pods. These were formed from 3mm thickness folded and welded aluminium sheet, the largest of which was over 1.4Mtrs in height x 3.4Mtrs wide. 423 of these panels were supplied by CSL and Eurofox Engineering to the project.
A key requirement of Enfield Council was that the cills of these pods should have a steep 70º slope to prevent pigeons perching. This presented technical challenges in terms of producing a clean appearance to the large surface areas of these welded assemblies, whilst the steep angle required the removal of masonry below window openings to accommodate the fall of the cills. This could not be done until the pods were being installed, which in turn was timed to coincide with the replacement of the windows.
To ensure there was no need for tenants to leave their flats whilst work progressed, Enfield Council stipulated that the removal of an apartment's old windows, fixing of window pods, installation of new windows and making good both internally and externally had to be completed during the course of a single working day. The accurate framing of the cladding system allowed this to be achieved, with the window pods providing a datum for the windows to be aligned to. The pods were supplied already finished with Polyester Powder Coat (PPC) RAL 1013 to match the window frames and main body of cladding panels.
To provide additional fire safety, firebreaks between adjacent apartments and floors were included in the overcladding design. In the horizontal plane this took the form of solid stainless-steel plates supplied by CSL, which were tailor cut to fit closely against the cladding support rails. These plates were fitted in storey height bands around the building. In the vertical plane fire resistant insulation was fitted behind the vertical cladding support rails up the entire height of the building. This was done to compartmentalise a fire outbreak and slow the spread of fire to other apartments.
As much of the cladding system was prefabricated, Eurofox Engineering and CSL went to great lengths preparing the necessary materials. This entailed the offsite fabrication of much of the framing system, which was supplied ready for immediate installation. The scheduling of the 2,850 Trespa Meteon panels and their delivery to site proved logistically complex, though with careful project management the task was completed on time and on budget.
Such meticulous planning work ensured that the project proceeded without any major difficulties. The vertical brackets for the support rails were fixed to the concrete beams between each floor, the floor slabs being known to be structurally sound elements of the original buildings. This element of the build was easily and quickly completed.
Following this, cladding rails were fixed to the brackets with 316 grade stainless steel nut, bolt and washer assemblies, observing fixed and floating point bracket locations to allow for thermal expansion and contraction of the rails. The K15 insulation was then fixed to the existing structure of the buildings and fire resistant mineral wool was fitted behind the vertical rails. Cladding panels, firebreak plates, window pods and windows were then installed in sequence.
Scaffolding was erected around the building for the installation of cladding and windows. This was to ensure total safety for both the workforce and residents, as the project necessitated the removal of all window frames throughout the building. The new building envelope was installed from the top floor downwards. This was done to tailor the work to the residents' wishes and aid the economy of the build, as it was then possible to dismantle the scaffolding, with cladding panels being fixed at former scaffolding attachment points, as work was completed on each upper floor.
Tailored to the structure, through careful design and installation, the facades fit the exteriors of the Dorset and Keys apartment blocks like a well-made suit. Enfield Borough Council now has two properties brought up to modern standards of aesthetics, fire safety, thermal efficiency and sustainability thanks to ingeniously engineered facades courtesy of Eurofox Engineering, CSL and Trespa UK.
