Refurbishment of flats in Wandsworthprojects.bre.co.uk/partL_study/pdf/Wandsworth.pdf · Wandsworth case study Introduction Wandsworth Council began a major refurbishment programme

Part L1 (2002) in existing dwellingsRefurbishment of flats in Wandsworth

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IntroductionWandsworth Council began a major refurbishment programme to regenerate its housing stock in 1995 when it won a Single Regeneration Budget award from Central Government. Wandsworth is a large borough with 187 tower blocks and numerous low-rise blocks of maisonettes and flats. Many were built in the 1960s and were very run down with major management and crime issues.

Although there was no Regulatory guidance at the beginning of the programme to bring the properties up to current new-build standards, Wandsworth Council Housing Department took the decision to try to achieve this standard as far as possible. They were also encouraged to produce refurbishments that would be sustainable over a 30 year time span.

An options appraisal was carried out in the early stages and the only option that was truly cost-effective was to knock down some of the blocks and start again. However, another option was developed that offered a good standard of refurbishment, relatively low unit costs and addressed additional problems such as management problems and amenity. This option was to improve the comfort level of the flats by adding a ‘tea cosy’ of external insulated cladding, whilst addressing the management and security issues with new entrances and ground floor developments.

Arndale Housing EstateThere are four tower blocks close to, and two medium-raise blocks on top of, the former Arndale Shopping Centre (now Southside). Both the flats and the shops were run down and the flats were used for the most disadvantaged tenants. Many of the major stores were

trying to quit their leases, so it was necessary to up-grade both the flats and the shopping area in order to encourage shoppers back to Wandsworth, to improve social perception and to help with the ‘dignification’ of the area.

Three of the tower blocks have the advantage of facing onto an attractive park and the medium-rise blocks (Wentworth and Eliot Houses) have one side facing these blocks and one side facing the

shopping complex and Sudbury House. It was decided to give the flats closer to the park a white rendered appearance. Wentworth and Eliot Houses are being clad in the same material on the park side, but with terracotta tiles and steel finishes on the shop side to blend in with newly refurbished Southside shopping centre finishes. Tinted windows have been used so that the tenants’ choice of curtain colour does not show through. The advantage of the external cladding system chosen is that the choice of final appearance is very flexible.

▲ This image provides an aerial view of the Arndale Housing Estate from Sudbury House, comprising three high-rise blocks (Knowles, Albon and Edwyn Houses) and Eliot and Wentworth Houses which form the interconnected medium-rise blocks in the foreground. The image above right is a view from the base of Sudbury House, illustrating the new metal cladding system.

Arndale Estate Sudbury House

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The new insulated cladding system, consisting of terracotta tiles over insulated panels and double glazed windows, increases the SAP rating from around 60 points to over 90 points. The new wall make up achieves a U-value of 0.30 W/m2K, a significant improvement on current Building Regulations guidance (0.35 W/m2K) but not as low as the proposed elemental levels in the Part L1A (2005) proposals (0.27 W/m2K). The terracotta tiles are ‘A’ rated for sustainability in the BRE ‘Green Guide to Housing Specification’ although the extruded polystyrene foam used as an insulator is only rated ‘C’.

The detailed section below shows the cladding make up. The panels comprise terracotta tiles on aluminium fixings and box sections, 6mm Pyroc board with 90mm extruded polystyrene insulation. The panel is fixed to the existing concrete frame via steel brackets and anchor bolts.

The insulation system (Eliot & Wentworth)The insulated panels are fixed into a frame which is bolted directly onto the concrete walls of the flats. Wandsworth has the advantage that the concrete used to build many of its flats in the 1960’s was good quality in the first instance and that they were coated with an anti-carbonation coating 15 years ago. All the flats above and around Southside were of a construction that allowed the framing to be attached to the outside of the building. The micaceous textured coatings are factory fixed to the insulated rain screen panels; the terracotta tiles are fixed to an additional frame over the top of the insulated panels.

The images above illustrate the conditions at balcony terrace level of the south façade of Eliot and Wentworth. The original structure of Wentworth and Eliot Houses was a reinforced concrete frame filled with single-glazed storey height frames with large pivot openers, and light-aggregate breeze block and concrete bottom panels, covered with obscured glass or particle board panels. It was the concrete piers that forced the decision not to remove the lower walls but to build outside and have large window reveals. The original design was subject to massive thermal bridging and was subject to a lot of exposure being quite close to the river Thames.

▲ Before ▲ After

▲ The image above left shows the façade stripped back to the existing block work with the application of the new aluminium framework. The image above right illustrates the installation of the terracotta tiles and windows.

The insulated panelling forms a ‘tea cosy’ around the outside of the original structure and therefore can be put in place without decanting the residents. The residents are only affected in the final stages of the development when their original windows are removed and the spaces between the old walls and the new windows are covered with deep window sills.

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Windows, heating and ventilation (Eliot & Wentworth)The new glazing is all aluminium double-glazed dual colour windows with thermal breaks and Pilkington ‘K’ glass™ to reduce solar heat gain from the large areas of glazing. The windows are fully reversible to aid window cleaning (this can be done from inside), with child locks for security.

Overheating was a big problem in the original flats as they were of very low thermal mass except for the concrete floor slabs. Solar gain was a serious problem in the summer and a very poorly controlled communal heating system was a problem in the winter. When the heating system was on, there was no way to control the temperature in the heated rooms. The latter problem has been solved by putting thermostatic radiator valves on all radiators and installing a new system of control that operates on pressure differences to provide a balanced heating system. The heating has been extended to previously unheated rooms to give an overall more comfortable environment.

The flats were also very stuffy previously with no ventilation provision other than the large pivot windows which would, undoubtedly, be draughty. This situation has been remedied by the inclusion of trickle ventilators in the window frames of the habitable rooms, the upgrading of air transfer grilles to the internal doors and the addition of mechanical extract fans to the bathrooms and toilets (these rooms are internal and have outlets to communal extract ducts). The kitchens are also fitted with mechanical extract fans which are humidity controlled and pass the air through a heat recovery system before discharging it to the outside wall. Rapid ventilation of rooms can also be achieved by opening the windows.

Castlemaine TowerAnother tower block, Castlemaine Tower, and the three maisonette blocks adjoining it are being given a similar treatment. There are two main differences between the Castlemaine scheme and the Arndale scheme. Firstly, the reinforced concrete frame of Castlemaine Tower is not as robust as the Arndale buildings and so the cladding cannot be hung directly off it. Instead, a series of concrete pads have been placed on top of the party walls at roof level and horizontal steel beams have been placed on top of these pads. A vertical steel frame has then been fixed to the horizontal steel beams and hung down the outside of the building. These beams are held away from the original wall with brackets, but these brackets are not load bearing.

Secondly, the original structure of Castlemaine Tower was simply single-glazed windows over the top of an asbestos-containing board with 100mm of low density expanded polystyrene. Therefore these original walls are relatively easy to remove and the room sizes will be increased by nearly 600mm each when the outer skin is completed and the original walling is removed. A bespoke system is being developed by British Gypsum to extend the party walls, which will address the dual issues of providing fire breaks and acoustic barriers between flats. Although this process is likely to be more intrusive for the tenants than that at the Arndale Estate, the Council in dialogue with the tenants have decided to attempt this process without decanting the tenants.

An additional feature of Castlemaine Tower is that the original open balconies will be enclosed to provide ‘Winter Gardens’ or small conservatory areas.

▲ The north façade of the block is finished in textured rendered ’Stenni’ panels. The detail (top) shows the make up of this panelling system and the relationship of the panels to the double-glazed windows. The image above shows the same system on one of the three tower blocks.

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Advantages• Improved appearance of buildings• Improved tenant’s feelings of worth and

ownership – dignification• Minimal internal disruption in Arndale Estate – tenants

do not need to move during work• Increases internal space• New-build standard of insulation• Window glass should reduce summer overheating• Cost-effective on large-scale schemes• Sustainable solution with 30 year life expectancy• Refurbishment allowed identification of ‘hidden homes’

providing cost-effective new homes

Drawbacks• Need to design well to avoid acoustic bridging• Needed careful structural survey to find suitable load-bearing

positions• Complicated programme of works and highly dependent on

tenant’s co-operation Costs and ‘hidden homes’.Some of the costs of the improvements have been offset by other means. All the blocks had some wasted space associated with them that was not utilised mainly because of security concerns. There were communal storage areas and open spaces at ground level that were usually populated with burnt-out cars.

All these spaces are now being converted into new flats (called ‘hidden homes’ by Wandsworth Council) to increase the revenue from the blocks. In some cases the flats are single sided with internal corridors and in these cases solar light pipes are being used to provide daylight.

The cost of the works based on the Edwyn House refurbishment worked out at 72% of the total for refurbishment and 28% for providing new homes. The unit cost of the refurbishment element was in the region of £38,000. The other blocks have comparable unit costs although they have received slightly more treatment.

All the refurbishments have increased the popularity of the blocks and have raised their status allowing higher rents to be charged. The sense of pride in the improved surroundings has reduced the graffiti and other management problems. In particular, the increased security measures and CCTV installations have reduced the vandalism, personal attacks and other anti-social behaviours.

▲ The image above left illustrates an internal view of the cladding system at Castlemaine Tower. It shows the cladding attached beyond the line of the existing rainwater gutter. The image above right illustrates the enclosure of a balcony into a ‘Winter Garden’.