A newly completed office building at Stansted airport represents the latest stage in the development for client baa Lynton of a building type aimed at achieving the objectives of the Egan report. baa Lynton describes this building, Endeavour House, as the fourth generation of its 'office products' and, as one of the Movement for Innovation demonstration projects, it aims to be:
cost-effective to build
cost-effective to manage.
Like all the buildings in the sequence, Endeavour House's floor area is in the range 7000-8000 m2, a size that baa has determined as ideal to allow occupants access to daylight. By continuing to work closely with the teams from the previous building, baa has achieved both organisational and technical improvements, largely as a result of better communications between the teams.
The sequence of projects started with the two phases of the World Business Centre at Heathrow, designed by Bennetts Associates. Then, with its framework agreements in place, baa decided to switch to Geoffrey Reid Associates, initially for the First Point building at Gatwick and then for Endeavour House.
Refining the process
Alistair Taylor, associate director of baa Lynton, explained that one of its targets was to bring the period for design and construction down to less than 12 months. 'The shorter the time for which we tie up capital,' he explained, 'the faster we can get it generating income.' Another consideration is the occupiers; most are happy to wait 12 months to get into their space, but they start getting fractious if the wait extends beyond that.
The length of the construction period is also vital - baa estimates the cost of being on site at £50,000 per week. It has successively driven down the time taken for both phases, from a total of 89 weeks for the first phase of the World Business Centre, including 46 weeks on site, to only 47 weeks at Endeavour House, with 30 of those on site.
Some of this has been achieved through familiarity with the project - the same framework consultants, contractors and suppliers worked on both First Point and Endeavour House. baa estimates that 80 per cent of the total capital expenditure has been channelled through framework suppliers. There was also some continuity of personnel - about 50 per cent of those involved worked on both projects.
Importance of familiarity
Familiarity with the design and the construction process has also been vital. The design has been refined through the series of projects; lessons learned on one have been taken on board in the next. There is a careful balance to be struck between retaining things unchanged for efficiency of operation and changing them to allow for improvement. But First Point and Endeavour House are obviously closely related. Endeavour House looks like a cool well-considered office block. What is not immediately obvious is the amount of sheer business thinking that has gone into it, to make it as inexpensive and as efficient as possible.
Size is one element. The floor plan has been devised so that nobody is more than 9m from natural light, from either the exterior or the atrium. And the plan is the largest it can be without the need for a third eternal fire exit. The building is a rectangle, 45 by 36m, with an entrance atrium broken in two by the services core. Moving the services core forward was a development used for the first time at First Point. It makes it easier for people to find their way around, and to split floors for letting. One of baa's objectives is to maximise the amount of net lettable space, and the net to gross ratio has now reached the impressive figure of 85.16 per cent.
The buildings are all concrete framed. On the Heathrow buildings the concrete was poured in-situ, but this brought attendant problems of mess and a long time-scale. At Gatwick, therefore, the decision was made to switch to precast construction.
There were some problems with the connections between the columns and beams, which could have been sorted out, but more crucial was the need for downstand beams to support the precast planks. In addition there was a problem with watertightness, which was achieved quite late - rain could pour through the joints between the precast planks.
Frame contractor O'Rourke came up with the solution - to use precast columns with two-way prestressed concrete floors. This is the first time, believes baa, that this approach has been used on an office building. It makes the building 100 per cent watertight beneath the slabs as they are finished. More crucially, with the floor only 250mm thick, it allows a floor-to-floor height of only 3.5m - compared with 4.5m on the Heathrow buildings - while the internal floor-to-ceiling distance remains at 2.8m.
Without this height saving, the Stansted office would probably never have been built, since the planning restrictions only allowed a three- storey building, which would not have been economic. With the reduced height however, baa was allowed to squeeze in an extra floor.
The air conditioning has been put in the floor void which acts as a giant plenum, leaving only the lighting and fire detection systems to be accommodated in the shallow ceiling void. A logical next step could be to abolish the ceiling void altogether, but Taylor reckons there would be no true saving. 'Tenants want a ceiling,' he explained. 'It's a matter of perception.'
Innovation from experience
Other innovations have been brought in as the result of experience on earlier buildings. For instance, at Stansted, the cantilever beyond the outer row of columns has been extended from 750 to 1200mm, to the width of two complete floor tiles, making this a fully usable space.
The fire-escape stairs are put in at an early stage, and used during construction. At Gatwick, the stairs were precast, whereas at Stansted they are in steel with bolt-on concrete treads, which can be replaced. The handrails were in place from the start, obviating the need for temporary handrails. At Gatwick the raised floor had to be joined via a bracket to the transom of the spandrel panel. At Stansted, a dummy transom has been inserted at the level of the raised floor, simplifying construction.
Everything possible had been done to reduce unnecessary construction or maintenance costs. The building is orientated so that it needs solar protection on only one side. A 3D model is accessible via a website to ensure that everybody is working to the same drawing, and this includes clash protection.
While many of the developments have grown out of the construction process, and the close co-operation of the team members, others have resulted from post-occupancy surveys. On the Gatwick building, for example, it was found that the building users were not completely happy with the design of the wcs, so the layout was changed, and space stolen from elsewhere to make them bigger.
baa has refined its framework agreements. Instead of the original six architects, it now has three, with Pascall + Watson for example working on all terminal buildings, and Geoffrey Reid on all the offices. So the process can continue to develop with the same client. Geoffrey Reid is also thinking of marketing the knowledge gained to other, external clients. The dissemination of knowledge, which the Egan report identified asessential, seems to be under way.