Internal insulation of Linden Lea and Wenlock Edge, Dorking, Surrey
Two tower blocks in Surrey have provided a testing ground for a new way of increasing the energy efficiency of hard-to-treat existing homes.
Just over a year ago a new approach to internally insulating hard-to-treat homes was piloted on a Victorian property in Camden, north London. Now the process, called WHISCERSTM (which stands for Whole House In-Site Carbon and Energy Reduction Solution) has been applied to 104 1960s-built apartments on the Goodwyns Estate in Dorking, Surrey. The technique has provided a solution for a housing association client keen to avoid the high costs of scaffolding buildings or decanting tenants.
Linden Lea and Wenlock Edge are typical products of the 1960s. The two 13-storey tower blocks have uninsulated concrete walls, leaving the occupants of one and two bedroom apartments with high heating bills. When owner Mole Valley Housing Association, part of Circle Housing Group, came to consider upgrading the energy efficiency of the homes it was conscious of the costly double glazing works to the blocks some 15 years earlier which had been carried out using external scaffolding. Internal insulation was therefore favoured as more cost-effective, and the WHISCERSTM approach had the benefit of obviating the need for both scaffolding and decanting residents from their homes, which alone could save up to £4,000 per flat.
Contractor United House is carrying out the insulation work in a project that also involves fitting new kitchens and bathrooms with an improved ventilation system, soil stack replacement, electrical upgrades and redecoration of the areas where work has taken place.
Key features of the process
The WHISCERS™ process, developed by United House with the Sustainable Energy Academy uses lasers to measure the dimensions of a room so thermal insulation board can be cut precisely to size and shape with an accuracy of 3mm. The board is then delivered to site as a ‘kit’ of parts, which can be rapidly put into place.
On the Goodwyns Estate, United House did not survey all 104 homes, but instead measured homes at the top, middle and base of the blocks. John Wright, WHISCERSTM project surveyor with United House says, “Because of the uniformity of the blocks we didn’t need to survey every flat. In reality dimensions were similar although there were some small differences.”
Most of the apartments in the blocks are occupied and residents remained in situ while upgrading work was carried out. The overall work has been carried out in two stages, with bedrooms and lounges worked on first, followed by kitchens and bathrooms. For the insulation, residents have to clear a 1m space around the perimeter of the external walls of a room which is the site operatives’ confined work space.
The insulation element of the work begins with removal of any coving and skirting and the extension of existing sockets, to allow for the new wall lining. Insulation board (Kingspan Kooltherm K18 insulated plasterboard) is installed to the inside surface of the external walls by the team of two carpenters. The installation process has changed slightly since WHISCERS™ was first trialled. Wright explains: “In Camden the plasterboard was fixed by dot and dab, but that meant that we couldn’t work on the boards till it had gone off, the next day. Now we batten it so that we can continue working straight away. It means we can finish a room in a day. Where we find the plaster is bowed, we simply reduce the batten size.” The contractor uses 25mm battens to allow for cables and pipework.
There is one other change from the Camden trial: chamfering at window reveals to ensure the correct level of insulation on the returns. Loose fill insulation is added behind the plasterboard on the returns to prevent cold bridging.
The plasterboard panels are all numbered and come to site as labelled packs, designed to fit into place in a room like a jigsaw. When the process was first developed, there was talk of cutting the plasterboard entirely to size in on-site factories. Wright says, “The need for that never arose here because we have our own storage facilities. It could perhaps still be done on a bigger site.”
There was, however, some cutting of the plasterboard on site where differences in dimensions did occur. Wright explains, “We set up a carpenter with a work bench outside the blocks. If the team inside the flats needed anything cut, it was done there to avoid doing it inside the homes.”
The lining results in an external wall loss of 62mm for the plasterboard, with 3mm for the skim coat and 25mm for the battens, total reduction in room size is only 90mm. United House reckons the WHISCERS™ process cuts the time taken to install internal wall insulation in each flat from five days to between two and a half and three, and it is still working to refine and improve the process.
Jeffrey Adams, group chief executive of United House, says, “The results of the work have been well received, with customer satisfaction surveys showing that residents are very happy with the outcome.”
Expected outcomes are:
- U values are expected to be reduced 1.7 to 0.3, and heat loss in each flat to fall by 40 percent
- Energy bills are expected to drop by around 30 percent – saving £450 approx in cash terms.
- The building’s carbon efficiency is expected to improve by up to 77 per cent.
- The product, schedule of work and site management are all equally important to success, meaning that electricians reconnected switches and sockets immediately the boards were fitted, and that work was concentrated in one room at a time, minimising disruption to the residents.
- Air leakage and sealing of gaps are critical to prevent cold bridging and to ensure no penetration of the vapour barrier.
- United House used its best carpenters on this project to ensure the job was done well and quickly but all qualified carpenters and dry lining installers will be able to fit this product.
- United House had a back up team which went into each home to make sure it was protected before work began, and then to ensure it was left clean and safe at the end of work
- Aftercare is critical. Residents are made aware of how to fit cupboards, heavy electrical items such as flat screen TVs and shelving, etc, on the wall. United House provides an aftercare package.
Sources and links
Client: Mole Valley Housing Association
Contractor: United House