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Specifier's choice:Cargo Fleet, north London

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Sutherland Lyall talks to Stephen Chance of Chance de Silva about the second house that he and partner Wendy de Silva are building for themselves in north London

Stephen Chance and Wendy de Silva are at it again: building their own house in Highbury, north London, just down the road from their award-winning copper-clad end of terrace which they call Venus. This one they are calling Cargo Fleet.

Their new home is a curiosity in an area of standard late 19th-century terrace houses. It is on Whistler Street, a road of working men's terraced cottages arranged in an elongated loop. The western section has houses only on the inner side - facing over a long brick wall guarding a railway cutting. In the middle is a defunct commercial laundry where most of the original inhabitants worked, almost certainly servicing the families in the smart terraces and semi-detached mansions on Highbury Fields, a street or so to the south.

This is backland, side-of-the-tracks territory, and the steep little street has such an air of a cobbled footpath-less northern village that it was used as the setting for the fi lm Distant Voices, Still Lives. Soon there will be a kind of landmark at the head of the western section, in the form of a vertical boarded box at second-fl oor level that will be visible almost all the way to the nearby Arsenal tube station to the north. Close up you will see that it sits on a ground- and fi rstfloor fl ank wall of purple-brown Cor-Ten panels in front of which, the architects hope, plants will be persuaded to climb. However, one school of thought suggests that plants don't much like the proximity of Cor-Ten.

If you think of this as the end of terrace of a street running east-west, with its rear garden backing on to the fl ank wall of the end of a terrace running north-south, you have the arrangement of the plot. The profi le of the side elevation is more or less that of its neighbour - but with the timber clad box inserted at ridge height. In the back garden is a timber-clad pavilion.

Behind the Cor-Ten garden wall is a courtyard with a conservatory/link between the main building and this pavilion. At ground level, the latter has a street entrance from the side, a bedroom, bathroom and access to the conservatory, and a semi-spiral stair leading up to a multipurpose living/ kitchen space with a sit-out balcony facing the old railway embankment.

The main block has two bedrooms either side of a common bathroom on the ground floor, the main street entrance access to the linking conservatory and stairs up to the big living/kitchen space. More stairs lead up from there to the simple rectangular space of the loft. A lot has been packed in to a standard, smallish London terrace plot.

Stephen Chance explains the back? ground: 'I suppose we started out with the opportunity rather than deciding the house was for something specifi c. We found the site ourselves. It had been doing nothing.

Islington owned it and it was some time before the council released it. We were hoping it wasn't going to be in a big package of other properties. It wasn't, and we bought it at auction. Our own house was on the site of a little workshop for a sewing business and when the owner retired we said to him, 'Why not sell it to us?'. Since then we have been trying to find other sites. It's a way to get our work across.' Assembling the finance Chance explains the crucial issue of paying for the project. 'When we did our first house we made a proposal to the bank that we would buy an option until we had gained planning. And then we put the money with some of ours and made a proposal to the bank [about fi nancing building work] and they said they would lend it if we promised to sell when it was finished. But when it was completed they said: 'You don't have to sell, ' and they converted the loan to a mortgage.

'This time we are doing two properties [front and back buildings] and we went back to the bank, and the finance is basically structured around the value inherent in the site. It had planning for one building and we got permission for a larger house, or alternatively two smaller ones, and we built up the development value on the basis of local property values. The bank split the fi nancing between acquisition and development. So this is the constraint on the financing of the site.

'Planning took a long time. Originally we put in for two live/work houses in which at some stage you might have grandparents in the smaller part or a grown-up child - or a business. It would change over a long time.

And we wanted to do more with the corner of the site. The conventional solution would have been a blank wall. Not only would that present a completely blank wall to the street;

it also overshadowed its own back garden and cut off the neighbour's sunshine. So we took the same fl oor space and distributed it in a different way. We elevated all the living rooms because there is no pavement.

Not that there is a library of details of larch siding plus Cor-Ten panelling to draw on.' The architect asked four or five small builders to pitch and they tendered. The successful tenderer, TBA, was on the list because it had successfully taken over a contract that had gone wrong. The tenderers' main fear was accessibility. There is no front garden and the street is narrow, there are no footpaths and an embankment forms one side of the street, so accessibility is a real problem. Chance continues: 'We got the tenders and worked out how to get the price down. We went through it with the builder we had selected and we had a dialogue that ended up with us agreeing to make some savings at the time and some later. We said we would come back with revisions.' Rusty skills One of the big design decisions about Whistler Street was the choice of Cor-Ten steel. It had the same found quality as the larch boarding and the concrete. Chance says: 'We spent a lot of time researching CorTen. It's not diffi cult to fi nd suppliers in the UK, but none wanted to do the fixing. We wanted someone to get the steel from the supplier and form the panels and fix it all.

'When we did the house we live in, Venus, the copper [used extensively as cladding for the upper two fl oors of the end of terrace in Highbury] was done by Broderick Structures: they detailed it and supplied and fi xed it. I happened to be talking to Broderick and they said the company has formed an alliance with Ranilla, a Finnish steel company that does Cor-Ten and would perhaps be interested. Broderick could act as a middleman and would liaise in getting the material and prefab elements and would arrange the site fixing.

Unfortunately Broderick went bust. But our main Broderick contact went to work with Roles and eventually that company agreed to resume where Broderick had left off, and it established its own Ranilla relationship.'

In the middle of February, the CorTen panels had been delivered to site and the fi xing team was preparing to clean the surfaces with mild detergent to get rid of the traces of oil left from the pressing process.

Chance says: 'They are going to clean the panels and then fix them. There may be advantages with pre-patination, but it would have meant taking them off the truck and fi nding space to set them out on site.

You would use the fact that the Cor-Ten is going to react to the site. The steel is going to go orange, brown and fi nally purply brown after a couple of years - just as the external timber will go grey, the steel will weather.

We had a panel nailed to the back fence and it went orange in a couple of weeks.

'The way we did this was to sketch out what we wanted the details to look like and the panel sizes (1,500 x 500mm) and sent off to Ranilla for them to adapt their standard system. We wanted to take advantage of their production line.' The panels are fixed to vertical, reverse top-hat rails with fixings at each corner. So the laying pattern is like brickwork courses, with fl ash gaps as the metaphorical mortar. Cor-Ten panels need to have air circulating around them. Chance says: 'If you butt two bits together, water can be drawn in by capillary action - which you try and avoid by using fl ash gaps. But the corners are trickier. You are trying to bring three planes together into a tidy edge detail.

The natural tendency is to joint them all up, not keep them apart.' Timber pragmatism The building is of timber-frame construction on trench footings. The main problem was that the exposed flank walls of the neighbours had brick buttresses running the height of the blank wall. The frame had to be built and braced against the wall before the buttresses could be removed safely. Engineer Price and Myers designed the structure as a panel system, but how it would be carried out was left to the contractor. So TBA did it in a way with which it was comfortable - as an on-site bolted stud/sole plate/head plate construction - but followed the engineer's methodology for the sequence of construction. Chance says: 'A different contractor might have decided to prefabricate off site.' Intermediate fl ors are of timber construction, but the ground floor is concrete. It has a reddish rough-tamped fi nish, which is hardened and coloured right the way through. The external timber cladding is larch. Chance says: 'We put in cedar in the planning application, and in our original proposal we thought of doing the loft in concrete. Then we thought it should be done in, say, shuttering timbers. So we went through that again, and then we wanted rough-sawn timber. We went through how it should be lapped and so we came to a squareedged larch with square edges and 6mm joints with insect protection behind it. But you have to be careful with larch. The runoff from it attacks zinc.' Zinc had been the original proposal for the conservatory roof but, because of the run-off problems, this was changed to terne-coated steel.

The band of glass separating the new building visually from the adjacent terrace is a Danish Vitral roofl ight supplied and installed by Hi-glaze Concepts. The smaller block has an Esha green, sedum-based roof installed by Lakehouse Contracts. This, says Chance, 'is a felt roof with green growing stuff, a build-up of layers rather like growing cress'. The projecting roof light towards the back of this roof is in Lexan (now known as Stereon) from G E Plastics.

Insulation is generally 200mm Rockwool slabs with75mm Kingspan slabs under the fl oor screed. Chance says ruefully: 'We did the most complicated version of getting regulations approval. Because there is so much glazing we specified insulation for particular performances. We had a consultant do the calculations using the Carbon Index method. In some cases we have an additional 10mm of Celotex quilt under the Rockwool.

'This is the first time we have used metal window frames. But Metal Casements went bust over Christmas after trading for 70 years. It set the project back a few months and cost money. We are now hoping The Steel Window Company will do a good job.' Chance decided on Cairney Hardware architectural ironmongery because, he says, 'they are very helpful in doing specials such as our entry-phone panels. And they are very helpful in sourcing unusual products such as our big sliding door and sliders to bathrooms - and in coping with different finishes. For example we have a bead-blasted finish. We have had good experiences of them.'

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