Office to resi: reaching to the converted
Plans to promote office-to-residential conversions by side-stepping planning approval could deliver wins all round. But what are the technical implications for contractors that will carry out the adaptations? Stephen Cousins reports.
Oxford House on London’s Oxford Street is undergoing an office-to-residential conversion by Land Securities
In January, the government announced plans to relax permitted development rights to allow the conversion of Class B1 (offices) into C3 (residential) without the need for planning permission. The planning shortcut feels intrinsically right for our times: faded, redundant office stock that no longer meets the requirements of today’s occupiers is brought back into use, while conversion projects encourage regeneration and deliver new homes, particularly in urban areas where the shortfall is greatest.
However, the announcement was followed by a significant backlash. Opponents fear that an uncoordinated building boom could flood the market with sub-standard properties and alter the long-term character of towns and cities, turning vital employment-generating centres into less active residential neighbourhoods. Opposition is so strong that around 700 local authorities have written to the government requesting exemptions from the rule, and planning experts now warn that ministers may be forced to delay the policy’s implementation or face legal challenges.
But the property sector is largely backing the proposal, particularly in London and the south east where the relatively buoyant housing market – combined with a plentiful supply of old, tired 1960s office space – makes the sums stack up. According to the Financial Times, average residential values in the capital are £3,000 per sq ft compared with £2,375 for office space.
London could soon have several office-to-residential flagships, including the proposed conversion of the 47-year-old Centre Point into 82 flats and duplexes. As offices, it has never been commercially viable, but homes will create additional value and bring new owners to pay service charges in perpetuity.
Croydon will also be flying the flag: Legal & General has just won planning permission to convert the former Nestlé headquarters to apartments. The company left St George’s House in January 2012, citing narrow floor plates as a key reason for the move. Under a scheme by EPR Architects, it will now be converted into 288 flats and its slab-style aesthetic given a makeover by adding storeys to give it a stepped skyline.
In future, the hassle-free switch from office to residential could also make economic sense in regional towns and cities. According to figures from the Department for Communities and Local Government, a potential 22,000 (net additional) new homes could be created as a result of the relaxation of rules.
Ironically, much of the vacant space is in the hands of councils themselves. “Many councils have consolidated their services and have significant empty and unlettable office space that’s creating blight,” says Ben de Waal, head of residential at Davis Langdon. “Where buildings are close to local amenities and transport links, I can’t see an argument for not converting.”
There will still be considerable technical challenges in office-to-residential conversions – which are likely to add up to a significant per sq m cost. Typical post-war office blocks, with deep floor plates and solid concrete frames, are likely to require extensive modification to allow sufficient daylight and ventilation, as well as to incorporate more extensive drainage and service runs.
Offices with large windows and curtain walling may fall well below thermal requirements under Part L1B, as well as compromising tenants’ need for privacy, perhaps making a complete reclad the only option. Construction and design teams will also face issues related to sound transmission, fire protection and provision of outside space, depending on an existing building’s specific structure and location.
BDP converted Witham Wharf in Lincoln (above left), adding balconies to make the most of city views (top right) and open-plan interiors (above right).
“The perceived savings by converting rather than building new can be a bit of a myth,” says de Waal. “A lot depends on the suitability of the structure, foundations and the cladding system. Not having to erect a primary frame and floor structures is a plus, but you may have to implement an entire services, core and escape core strategy that requires a fundamental change to the building’s structure, and this remodelling work may prove very expensive and offset any other savings,” he points out.
Buildings that lend themselves to conversion will be those where project teams can retain large amounts of their existing structural frame and foundations, avoiding the need for alterations or demolition. “In many cases, the cost and timescale of modifications to the structural frame and cladding go to the heart of whether a building will be viable for conversion, or whether the developers instead opt for a wholesale demolition,” says Mark Farmer, head of private residential at consultant EC Harris.
Farmer also points out that the ability to retain the existing facade is a big advantage, as installing a new facade system can account for 20-25% of the entire building cost, and can also affect water tightness and delay the start of internal fit-out.
Period properties are an obvious candidate for residential conversion as many were originally designed as housing before being converted to offices, and could revert to their original character. However, on listed buildings there would be a ban on alterations to facades, or the carving out of voids to accommodate new service and drainage runs.
London’s Centre Point is subject to proposals for 82 flats.
Stephen Marshall at architect BDP says there are plenty of post-war concrete-framed, concrete-clad office blocks built during the 1960s and 1970s that are ripe for a revamp. He designed the recent conversion of Witham Wharf, a seven-storey concrete 1970s office block in Lincoln. “There’s a surfeit of this type of building, much of it empty and under local authority ownership,” he says. “The 3m floor-to-floor heights, great views and relatively open concrete structural frame make it much better suited for residential than improvement to grade A office space standards,” he adds.
Perhaps more challenging are post-1970 commercial offices, many of which were designed with air conditioning in mind and so have very deep floor plates, making it necessary to insert atria and courtyards to bring daylight and ventilation into a residential plan. This type of layout, designed around an internalised aspect, is quite common in the Middle and Far East but nothing like what UK house builders and residential developers are used to. However, if the concrete floors are pre-stressed, the project team will be restricted on where they can cut openings to create atria,
soil stacks and other services.
Creating multiple dwellings out of a large-scale office building means ensuring adequate means of escape, in which case extra stair and lift cores may be required.
“Conversion will in many cases require breaking out the existing floor slabs,” says BDP’s Marshall. “The problem is that you’re not always going to know exactly what’s inside the structure until you start work on site. Our initial survey at Witham Wharf failed to reveal that some of the floor plates were different sizes, which held things up and added to our risk profile. The biggest alterations were needed at ground floor level where we transferred drainage connections outside the building perimeter – it meant a lot of work breaking out the slab,” he explains.
A change of use from office to residential will have an immediate impact on Building Regulations compliance, specifically the sections on structure (Part A), fire safety (Part B) and conservation of fuel and power (Part L). Buildings that fall under Section 20, typically those within inner London that are above 30m, might also require extra fire safety measures.
Energy performance requirements dictated by Part L1B will often mean over-cladding or completely recladding the facade, which has the added advantage of increasing the building’s lifespan and improving its appearance for potential tenants. Again, office buildings can be split into an earlier generation with concrete cladding – typified by London’s Centre Point – and later arrivals with some form of curtain walling.
If the wall structure is being upgraded rather than replaced, insulation manufacturers offer high-performance insulated render systems and internal wall linings, explains Tom Cox, product manager at Isover. “On an office high-rise, internal wall insulation may prove cheaper because it doesn’t require scaffolding and at around 100mm thick or less it won’t eat into your floor areas. When a facade is being renovated and scaffolding is already in place, external wall insulation may be more suitable: our product is typically fixed to the wall then covered by either a vented facade or a render finish,” he says.
Internal wall insulation might better suit period properties with protected facades, although Cox warns that when applied behind porous brick walls this can cause moisture build up, perhaps causing bricks to blow out. In such cases, a breathable insulation such as mineral wool used in conjunction with an invisible, external, breathable treatment could prove a more effective option.
Sound transmission is a concern when upgrading offices to meet residential needs, particularly in 1960s blocks where numerous service cavities and ducts transmit airborne and impact sound. Solid concrete superstructures also tend to allow impact sounds to bridge from one dwelling to another.
St George’s House, Croydon
Designing the necessary level of acoustic separation in these structures can be costly and as a result many projects could struggle to meet the necessary standards, warns Cox. “Part E sets a requirement for a minimum 43dB airborne sound insulation between dwellings. However, many conversion projects will aim for ‘deemed to satisfy’ levels of performance, ie, the best they can achieve with the given structure. It’s a big concern that could lead to substandard properties and complaints of noise nuisance,” he says.
Any deviation from prescribed construction details in Building Regulations guidance could create problems, says Kevin Dawson, planning officer at Peterborough City Council and former chair of the CIOB’s Faculty of Building Control and Standards. “Improvements to design knowledge post-1940 meant that buildings grew lighter, making compliance with today’s acoustic requirements more costly and harder to achieve, although with modern materials and techniques there really should be no excuse,” he says.
Final details of the change to permitted development rights will be decided by late April, and local authorities had until 22 February to submit their proposals for preferred exclusion zones.
There remain several questions regarding how the changes will be implemented in practice. Although the policy is intended to simplify the planning process and bring schemes to site faster, it is unclear whether deregulation will allow design teams to circumvent other aspects of development control, such as planning permission for material changes to facades, listed buildings consent, or requirements for renewable energy.
Another bone of contention is whether developers can convert buildings without liability for the provision of affordable housing or section 106 payments, which will impact on the economics of the land market as well as local authority coffers.
But architect and developer Roger Zogolovitch, who runs Solidspace, is optimistic that the move could attract investment and deliver innovation. “It’s going to be so subject to that particular area that it won’t result in a wholesale transformation of our towns and cities where every empty office building immediately becomes a block of flats. I think it will stimulate local economies, but it’s a freedom in an area of such heavy regulation I think the imagination and intelligence of the architect will find a fascinating route through this and I think we will all be surprised by the amazing buildings that come out of it.”
A Roman conversion
Roman House was one of the first buildings to be constructed as part of London’s landmark Barbican mixed-use development in 1956. It is currently being converted from office use and extended by developer Berkeley Homes to create 90 studio, one-, two- and three-bedroom apartments including three individually designed exclusive penthouse apartments with private terraces.
Located on the corner of Fore Street and Wood Street, north of the historic London Wall, the existing L-shaped office block is an example of the fast-disappearing 1950s style of Utilitarian Modernism. Its straightforward design is the result of a tight budget and a desire to quickly provide flexible office accommodation, bathed in natural light.
Roman House (top) has been converted into 90 homes and residents will have access to St Alphage gardens (above)
The building’s two wings of eight and six storeys are supported on a grid of pillars spaced at 12ft intervals, which define its external facade of glazing panels separated by Portland stone cladding. For some time in the 1950s the building stood pristine and white amidst bombed out ruins and can be seen in numerous pictures of the time.
Berkeley Homes and architect A&Q Partnership have set out to respect Roman House’s Modernist heritage and retain its Portland stone facade. New infill panels are being installed to create Juliet balconies and bring the glazing up to modern standards, while an extra storey has been added to each wing to increase accommodation.
The interiors, designed by space planner and interior designer The Manser Practice, will reflect the area’s classical heritage and incorporate natural materials. Each apartment will offer the latest in home technology, allowing residents to control the heating, lighting and audio electronically.
Residents will have access to the existing St Alphage public gardens, next to Roman House, and a new gymnasium in the basement. The first apartments are expected to complete in 2014 and prices start from £565,000 for a studio.