Embodied Carbon Estimation for Central Hill Estate: Report by Model Environments

‘A conservative estimate for the embodied carbon of Central Hill Estate would be around 7,000 tonnes of CO2e, similar emissions to those from heating 600 detached homes for a year using electric heating, or the emissions savings made by the London Mayor’s RE:NEW retrofitting scheme in a year and a quarter. Annual domestic emissions per capita in Lambeth are 1.8 tonnes. The emissions associated with the demolition of Central Hill Estate, therefore, equate to the annual emissions of over 4,000 Lambeth residents.’

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Report by Model Environments on behalf of Architects for Social Housing

Central Hill: The Alternative to Demolition

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These images were presented to the Central Hill Estate Residents Engagement Panel on the 17 May, 2016. The proposals take on board comments from Lambeth’s planning   department, as well as comments from residents, neighbours and other architects following our previous exhibition on 20 February, 2016, as published:

(https://architectsforsocialhousing.wordpress.com/2016/02/23/central-hill-estate-design-proposals/)

The award winning Central Hill estate is a unique and highly successful piece of architecture and landscaping that is home to an established community, many of whom have lived here since it was built in the early 1970s by LCC architect Rosemary Stjernstedt under Ted Hollamby.

ASH’s proposals illustrate the potential to add around 222 new homes on Central Hill Estate, without demolishing a single home.

The proposals here reinforce the ideology and intentions of the original architecture of the estate, whilst allowing for the full refurbishment of the existing homes and public realm – bringing them up to a ‘decent standard’, and thus addressing any current concerns about their homes voiced by residents.

Lambeth’s arguments for the demolition of the estate do not stand up to scrutiny in any way other than increasing the density and land value of the estate. We believe this alone cannot justify the demolition of the 456 existing homes, and the uprooting of a long-standing community.

This is an initial feasibility study, and there are many possible design solutions to the fundamental proposition that architectural alternatives to demolition exist. What is presented here is an outline proposal to demonstrate the numbers of additional homes that could be gained on the estate.

The scheme has been costed by an independent quantity surveyor, and planning advice has been sought to ensure that all proposals correspond to local and national planning policies. Structural advice has also been sought to establish the feasibility of roof extensions.

If you would like to sign the petition supporting these proposals, see the ASH Petition

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Site Strategy

The new buildings fall into two categories: infill and roof extensions.

Infill

The infill homes are situated on currently underused spaces around the estate, which were identified by residents on walkabouts during the summer of 2015.

Many of the new infill buildings are located around the periphery of the estate. This addresses a common criticism of estates (and Central Hill in particular): that they don’t have clearly defined edges, or straightforward relationships to the traditional street patterns surrounding them. The infill architecture therefore creates material and formal links between Central Hill and the surrounding area; both knitting it into the traditional street fabric and distinguishing clear entry points, whilst also reinforcing the existing architecture and distinct sense of place.

The saw-tooth form of the fringe housing roofscape is intended to make reference to the Gipsy Hill part of the estate, while maximising the light into the remaining estate, and providing a durable low-maintenance roof.

ASH_CH_05_2016_plans+axo3Roof Extensions

The roof extensions are limited to one-storey extensions on the tops of some of the 1 bed ‘Prospect’ blocks and on the outer ring of low-rise housing, in order to minimise the effects of the reduction of light and obstruction of views on the rest of the estate.

The roof extensions are placed intermittently, with an undulating roof line, to ensure a rhythm of light penetrates the houses below.

Where light and privacy is a concern, distances between old and new buildings are a minimum of 12m. The 45 degree ‘rule of thumb’ has been applied to all new buildings to ensure that the right to light of the existing buildings is not affected.

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Public Realm and Street Surfaces: Accessibility

One of the criticisms of Central Hill is the steepness of the site and the difficulties navigating the pedestrian routes. We would propose a new street surface throughout. New ramps and lifts designed to serve the new housing along Central Hill (road) would also form part of the proposed communal circulation strategy, providing new access routes into the estate.

Perceived Safety and Natural Surveillance

Lighting on the estate is currently extremely poor, and good uplighting would address many of the concerns people have walking around at night. The new roof extensions on top of the existing low-rise blocks would also increase ‘eyes on the street’ and improve the natural surveillance of the pedestrian ‘ways’ which traverse the site. Another proposal discussed with some residents last year was the possibility of reducing the heights of the garden gates which would enable greater visibility from the kitchen and front garden into the street. Another possibility is to lower the heights of garden storage units to allow for better surveillance of the streets here. Trellises could be installed for growing plants but would still allow for a more open relationship to the pedestrian streets.

Bio-Diversity

Central Hill’s existing ‘natural’ landscape is unique, diverse and rich, catering for a wide range of birds and wildlife. ASH’s proposal intends to respect and retain as many of the existing trees and habitats as possible. Green roofs have been proposed to be added to the remaining flat roofs of the existing low rise houses which would enhance the existing eco-system.

We also propose to reinstall the original ‘green fingers’ which were intrinsic to the original design, and which have been destroyed in the recent years – with green roofs on the bin stores, trees outside doorways, and ivy and other climbing plants on the retaining walls.

Design: Context, Form and Materials

Cities are not homogeneous places, but the places of cumulative memory. Our proposal celebrates the existing architecture and community while also offering the potential for a significant number of new homes. The distinctive character of Upper Norwood/Crystal Palace is rooted in the diverse and eclectic range of styles that have appeared as the area has evolved. From Victorian mansions, to 1960s towers and the award-winning Central Hill Estate, the ongoing palimpsest at Central Hill is entirely in keeping with the history of the area.

We would look to use materials and forms which would create close relationships between the old and new; in particular making use of similar white flint lime bricks in the new infill housing, and echoing the existing Gipsy Hill housing with saw-tooth zinc roofs on the new builds. Pitched roofs also relate to the surrounding vernacular.

Community

Our proposal supports and retains the community and environment which has matured and bonded over the last 40 years. The role of the existing community in the formulation and execution of the regeneration of Central Hill is a fundamental aspect of this proposal. The engagement of this longstanding community in the process to date has enhanced community cohesion, and a sense of ownership of these proposals has evolved. This will contribute to the continued success of the estate, and have an impact on the effective use, maintenance and safety of the communal spaces.

Environmental Sustainability

The retention of the existing buildings is a huge environmental benefit. The amount of embodied carbon which would be unnecessarily released through the demolition of the existing masonry buildings and the concrete foundations is a pending environmental disaster. The life-cycle carbon impact of the demolition scheme must taken into account as this goes entirely against Lambeth’s own sustainability policy.

There is the possibility for the implementation of renewable energy sources, such as solar/PV panels on top of all new roofs, and wind turbines on the boiler towers.

New Building Sites

Site 1. The Old Boiler House

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Site 1a

28 homes of which all are wheelchair accessible (46% currently specified)

Site 1 retains the chimneys of the old boiler house, establishing a new entrance to the estate. The existing boiler house structure is retained (as far as practical) and the lower double-height space occupied by two floors. The lower floor could be renovated for commercial or workshop use (subject to resident and local neighbourhood consultation) – or simply parking – and cycle and bin storage for the new housing above. Two lifts facilitate an additional 7 floors of wheelchair accessible housing provided above, with the 7th floor set back to reduce its impact on the surroundings.

A 45 degree Right to Light exercise has been undertaken which illustrates that the new buildings will not have a significant impact on the closest adjacent buildings. Planning have made comments indicating that a more slender plan might be preferable, and we would reiterate that plenty of other design solutions are entirely possible. We have illustrated the example of occupying the maximum footprint of the boiler house, generating an equal mix of 1B2P and 2B4P units, and ‘standard’ and wheelchair accessible units.

Workspaces

The proposal for workshops in this location was the result of community consultation. The Designation of Crystal Palace as an ‘Enterprise Centre’ would support this application.ASH_CH_05_2016_report3

Site 1b

4 no 1B2P flats over parking (Or 2 no 3B6P maisonettes over parking – subject to a detailed survey of existing parking provision) form a street frontage to Lunham Road.

Site 2, 3, 4. Communal Facilities and Existing Green and Play Spaces.

ASH_CH_05_2016_report4The existing community facilities currently occupy a large amount of area within the centre of the estate. ASH proposes that the existing communal facilities are demolished, and re-provided (day care centre, nursery, and community hall) along the edge of the estate along Lunham Road. This would allow an increase in the size of the green space, and improved play facilities.

Alongside this, the existing housing office is to be demolished and moved on to the main road – also freeing up green space.

Above these new community spaces new housing is to be provided.

2 lifts and deck access enable this to be wheelchair accessible, allowing for 38 new flats of varying sizes in total.

The deliberately fragmented nature of development is a key feature of the existing estate which our proposals seek to emulate. Blocks here are discontinuous in plan to reflect the houses opposite, and the heights of these blocks are varied in order to create a punctured skyline when viewed from the estate, ensuring that everyone from the estate retains views of London across and between the new undulating roofscape. This also minimises the reduction of light to the existing houses on the Northwest side of Lunham Road.

Site 5. Access from Central Hill Road

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12-14 new flats with 2 lifts of which 100% currently specified as wheelchair accessible

Central Hill is steep – and, towards the top, considerably higher than the access road of Oakwood Drive. In order to address the difficulty of disabled access into the estate at this point, this block could incorporate a double lift core – to not only enable wheelchair accessibility to the whole block, but also to the rest of the estate below

This block, like all the buildings along Central Hill (road), is nestled well within the trees. It would have little impact on the houses on the other side of the road, and negligible impact on the neighbouring blocks on Central Hill itself – being predominantly adjacent to flank walls.

Site 6, 7, 8, 9. Fringe Housing

The new housing along Central Hill continues the theme of accessible housing and increasing permeability into the estate. We propose terraces of houses elevated above the access road (Oakwood Drive). If refuse and / or fire access is needed along here, this can be accommodated. However, with our suggestion to review the current refuse strategy, the soffit might be able to be reduced from 4.5 m. We are also under the impression that necessary fire access is achieved without the use of this access road, but this would need to be checked.

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The housing proposed consists of maisonettes on the lower 2 floors, and one bed flats above. Access to the maisonettes is achieved via walkways directly off the main road (with associated individual bins and cycle storage), and deck access and amenity space to the top flats can be provided either to the North or South. The roofs are either proposed as shown with sawtooth profile, or pitched down towards the North to reduce their impact on the one bed Prospect extensions. The distance between the existing and proposed windows are a minimum of 12-13 metres apart.

At various points along the main road, we propose ramps to enable disabled access into the site. Stairs would also be introduced at regular intervals, improving the estate’s porosity and permeability.

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Site 10 and 11. A Gateway to the Estate

On the site of the existing hostel (which we believe to be only partially occupied in a temporary manner) we are proposing the construction of a new 5-7 storey block of flats (site 10), and a smaller block closer to the low-rise housing to the north (site 11). The site is adjacent to wide roads, so the buildings would not have any detrimental impact on any of the existing neighbouring houses. We would propose that the form and material of the new buildings emulate those of the existing buildings, to establish a sensitive relationship with their surroundings.

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Site 10 is designed to ensure minimal loss of trees, and the creation of a communal garden for the flats, as well as individual back gardens for the ground floor maisonettes.

Two lifts would allow this whole block to be wheelchair accessible, with maisonettes on the ground floor accessed directly from the street, enabling an architectural transition from the urban grain of the street to that of the estate. Roofs could be pitched to correspond with the roof extensions to the adjacent existing flat blocks, or green roofs (or a combination of the two).

The existing hostel facilities (8 hostel dwellings) could be provided within this block, or elsewhere within the estate.

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Site 12. New Edge Block

A small 3-4 storey block of flats is proposed above the existing parking (assuming the parking is required to remain). This height of this has been reduced to minimise its impact on the neighbouring buildings. Although it would not noticeably affect the light conditions, a taller building might be less appropriate in this location.

Site 14. Police Station

A block to the rear of the existing police station was a preliminary proposal which has since been discounted partly due to the fact that it is not within the boundaries of the existing estate.

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Site 13. Maisonettes

A pair of maisonettes are proposed to the north of Hawke Road, in the garden of Pear Tree house. The impact of this on the adjacent existing homes is to be minimised.

Site 18. High Limes

Buildings refurbished and extended. 6 new flats in the new block, 3 new flats on top of the existing ones.

We propose a new flat block to the west of the 1 bed studio block. New housing is proposed on top of the existing block, similar to Site 15 above. The addition of a lift here would enable the existing flats to have step-free access.

There is the potential to provide additional community space on upper ground floor above the parking entrance, and the lower ground access to parking and refuse is to be retained.

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Sites 15. 1-Bedroom Roof Extensions on the Prospects

One additional floor is proposed on top of the existing 1 bed flat blocks, adding 43 additional homes. Access is achieved by extending the existing staircases. The present water tanks are to be incorporated into the proposals, but the way in which this happens requires more detailed survey information not available to us at this time.

Material and construction. These are to be made of prefabricated timber (or similar construction) and craned on to site. The zinc pitched roof allows light to pass through to the flats to the north, and simultaneously requires lower maintenance than a flat roof.

Structurally, the 3-4 storey blocks are deemed by Arups (the engineers of the original estate) to be capable of accommodating an additional storey.

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Site 161-2 Bed Roof Extensions to Low-Rise Maisonettes

Adding 22 additional homes. 16a is built on top of 3 person 4 bed homes, 16b on top of 3 bed 5 person homes, and 16c, on top of the 4 bed 6 person homes.

Access to these new prefabricated flats (construction as above) varies for each block, but typically is via a new stair either central to the blocks or to one side. The individual flats are accessed via a deck to the north side, and overlooking into gardens below can be moderated by the use of deep planters if necessary. Roof gardens are accommodated for each property – the orientation of which could be to the north or south, or in some cases both. Views from these can be moderated by the use of deep planters as before.

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Again, the water tanks on the roofs of the existing buildings are to be incorporated into the proposals.

The zinc sawtooth / pitched roof form both relates to the Gypsy Hill side of the estate, while letting a rhythm of light through to the flats behind and below, and, again, simultaneously requires lower maintenance than a flat roof.

Two storey options have been explored, but structural analysis is yet to establish the capacity of the existing buildings for the additional storey.

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Structure to roof extension. Additional floors to the existing low-rise maisonettes need further calculations to confirm application.

Arups have considered a number of building types ie 2 storey (ground, 1st + roof), 3 storey (ground, 1st, 2nd & roof) and 4 storey (ground, 1st, 2nd, 3rd & roof).  In each case they have assumed a section as per the IStructE article whereby the building is stepped from the back to the front.  When reviewing loads they have considered only the front or rear portions, so there is some conservatism in the central portion, albeit not much.  They have assumed that there is not much by way of superimposed dead load on top of the concrete slabs at each level (ie no screed).  If there is any screed, this will make the numbers below slightly better (ie it will reduce the percentage increase in load for the additional storey).

In each case they have considered adding a single level timber pod at roof level.  They have assumed that the pod will weight a maximum of 1.5kN/m2 on plan, including the walls, and that it will effectively span from wall to wall.  They have not checked whether the existing roof slabs (which would almost certainly have been designed for a lower imposed load than the floor slabs) have enough rebar to carry the required residential loading.  They have the rebar drawings so this is a check that someone could (and indeed should) do if they were to take the review to the next level, and they had permission from the building owner to obtain the drawings.

Below is a table which shows the percentage increase in working load (dead load plus live load) at the top of the piles and the base of the cross walls due to the extra floor. The old Building Control rule of thumb says that if loads are increased on foundations by less than about 10 per cent then all will be OK. This assumes of course that the structure is in good condition to begin with and not showing any signs of distress. So, without looking in more detail at pile loads and capacities, they might conclude that adding an extra floor to a 2 storey building could be challenging, but adding to a 3 storey or more building should be possible. It obviously gets easier as the existing building gets taller.  Again, we have pile drawings with design loads on so someone could do a more detailed check and they might manage to justify that the extension on the top of the smaller buildings is OK too.  They are much less concerned about the increase in load at the base of the walls as the stresses are relatively low. A structural engineer should be appointed to undertake a proper review of the drawings before any commitment is made to increasing the height of the existing blocks.

Height of existing building Percentage increase in load at top of piles for 1 extra floor* Percentage increase in load at base

of walls for 1 extra floor*

2 storey 14% 19%
3 storey 10% 12.5%
4 storey 8.5% 10.5%
* Assumes lightweight timber pod

Refurbishment Strategy

Beyond the environmental advantages, which are enormous, the refurbishment of the existing homes is considerably cheaper than demolition and reconstruction. The homes are structurally sound, and could easily last another 60 years. The current problems which need to be addressed are typically mould and leaky roofs. All the roofs on the outer ring will be replaced as part of the new roof extensions, and it is suggested that green roofs be installed across the remaining low rise flat roofs. All that remains is to deal locally with cold bridging problems which, on closer inspection, is most likely to be dealt with by applying external render to the slab edges.

The existing buildings have cavity walls, so blown-in insulation is an option if necessary.

The tops of walls need to be adequately protected from water ingress, and the glazing to the balconies needs to be replaced. Roofs to balconies will need to be re-made throughout. The key to quality construction is to ensure good workmanship and warranties to the work throughout.

Following conversations with various residents of the estate over the last year, we know there are problems with the existing homes, such as mould and condensation. These are common problems, caused often by badly designed and fitted windows, and are very easily remedied by well-designed and careful refurbishment. The solutions are improved ventilation strategies, better double glazing and local insulation to cold bridges. We are currently working on a similar scheme in West London, where we are proposing precisely this solution to the same problems. In no respect are these problems justification for demolishing an entire estate.

We also propose to renovate the existing walkways to improve the surfaces, with a new lighting strategy, and to replace the wonderful planting throughout the estate that was part of the original scheme (as mentioned earlier)

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Landscape Strategy

Central Hill currently has the key role of a green corridor between Ravenscourt Park and Crystal Palace. Demolishing the estate would separate the two green areas and have a detrimental impact on the well-being of local wildlife as well as that of the residents.

In spite of the negative representation of the estate by PRP architects, who were appointed by Lambeth Council to come up with the redevelopment plans, Central Hill is a beautiful place to walk through and both residents and neighbouring communities recognise the value of their estate’s green spaces. Residents’ participation in the Open Garden Estates event in June 2015 demonstrates this, as does the daily use of the playgrounds and alleys by children.

Over the summer of 2015 ASH worked closely with Central Hill residents to come up with proposals for improvements to the landscape of the estate. The proposed interventions, which were developed in open consultation with residents, are light additions that tap into Central Hill’s great potential. These include new designs for balconies and patios, the introduction of a marketplace in the main square, vegetable gardens and playground improvements, and proposals for the reuse of the recycling castles, some of which the residents are already putting in motion.

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Priced Schedules

Robert Martell and Partners very kindly agreed to undertake a pricing of ASH’s design proposals. This currently only contains the new build proposals because Lambeth Council’s own surveyor has already made a proposal for the costs of refurbishment based on their own survey. Due to lack of funds we have been unable to undertake our own survey of the same degree of detail, so have simply accepted Lambeth’s costs for refurbishment at this time. According to Lambeth’s surveyor the refurbishment will cost around £18.5m, of which £6.2m are internals that should be covered by the decent homes funds.

Below is the summary of the costed schedules:

Central Hill cost summaryGD.xls

Conclusion

ASH’s proposal is the most cost effective, social and environmentally sustainable future for Central Hill Estate, and one that respects the unique architecture and landscape of the existing estate. Above all, it allows the existing community to remain in their homes. Please show your support for this proposal and Save Central Hill Community.

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Geraldine Dening
Architects for Social Housing

In Defence of Central Hill

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In June 2015, Architects for Social Housing (ASH) were contacted by residents of Central Hill, a council estate in Crystal Palace. They has started the Save Central Community campaign that February, and were fighting to save their homes from demolition at the hands of Lambeth Council, who had formally added the estate to their regeneration programme in December 2014.

Contrary to Lambeth’s slur campaign, the estate is extremely well designed. The streets, houses and green open spaces work in conjunction with the rolling landscape, the light and the different degrees of privacy, from south-facing front courtyards to balconies with views across London. It is no surprise that this is a coveted spot. Land values are correspondingly high, and are the main reason for the proposed demolition of a unique and innovative piece of urban design that should be a model of social housing and community living.

Over the last nine months ASH has been working with the residents, getting to know the estate and the community that lives there. Many residents have called the estate home since construction was completed in the early 1970s, with families of several generations living within a few yards of one another.

We began by getting to know the residents, and with their help and support organised a series of design workshops. From these we were able to identify sites where ASH might be able to add additional homes without demolishing any of the existing ones. We also studied the architecture of the buildings in order to establish whether we might be able to add additional homes on top.

Lambeth has admitted that the existing foundations are extremely strong, and are in fact proposing to leave them intact in their own redevelopment proposal. In consultation with a surveyor, we have concluded that the existing buildings are capable of accommodating an additional 1-2 floors. Combined with the significant number of areas that could accommodate infill housing, without building on the extensive green spaces across the estate, ASH’s proposal will provide the much-needed homes for those on Lambeth Council’s waiting list, while some of the remaining flats could be sold to finance the scheme. We believe this is the best future for Central Hill estate, one which respects its present community, the social vision of its past, and its future as council housing for Londoners.

As keen admirers of the estate architecture and its ideological origins, ASH is keen to retain the ethos of the estate, and our proposals will be sympathetic to the existing architecture. There are no structural or other problems with the existing buildings. On the contrary, they are extremely robust and well designed. Any problems of maintenance or design that have been raised by residents can be dealt with by minor refurbishment. Lambeth’s own surveyor’s report has estimated refurbishment costs at around £18 million, less than £40,000 per home.

Environmentally, it is absurd to demolish perfectly good housing, unnecessarily releasing tonnes of carbon back into the atmosphere. Such an act goes completely against the council’s own charter and commitment to sustainable construction practices. In paragraph 6.4 of Lambeth’s Supplementary Planning Guidance for the Vauxhall development they state:

‘An important aspect of delivering sustainable development is the re-use of existing buildings and the conservation of heritage assets. Re-use and minimum intervention approaches when accommodating changes in historic buildings minimises demolition and construction waste, reduces the need for new materials and is more energy efficient than new-build construction. Historic assets should not be compromised by new development and should be fully incorporated into redevelopment schemes to ensure they remain in a viable use.’

Finally, Karakusevic Carson Architects, who are working on another of Lambeth’s regeneration projects, the Fenwick estate in Clapham, has estimated the cost of replacing existing homes at around £225-240,000 per unit. On this estimate, replacing Central Hill’s 456 homes would mean building costs of between roughly £100 and 120 million. That’s before a single new home has been added. In the light of Lambeth Council’s cuts to services throughout the borough, and with the £18 million refurbishment costing less than a sixth of that, this is an unacceptable misuse of money and resources and must be challenged.

There is absolutely no reason to demolish the homes of Central Hill estate, but there are a large number of reasons not to. The first, last and most important of these is that it is home to around 1,500 residents — residents whose wishes have been completely ignored by Lambeth Council, but whose futures they threaten. In the middle of a housing crisis, it stands to reason that the demolition of London’s council estates is not the solution to the shortage of genuinely affordable housing for Londoners. Indeed, it will only make that shortage worse.

Geraldine Dening