Portcullis House is located on the corner of Bridge Street and Victoria Embankment, just across the street from Big Ben (Address: Bridge St, Westminster, London SW1A 2LW). The building type is divided between office and assembly as it is occupied by 210 members of Parliament and their 400 staff.This government building reaches to 6 stories and comprises of a total of 23,000 square meters or 215,000 square feet (About 36,000 s.f. per story).Design was accomplished by architects at Michael Hopkins & Partners and engineers working at Arup, and construction was completed on 18 August 2000.

Project Basics

Portcullis House

The design team’s primary goals were to design an ultra-low energy building whose systems were integrated with the structure, and to design a building that would fit into the site’s context, which includes important landmarks such as New Scotland Yard, Big Ben, and the Palace of Westminster.The construction of Portcullis House was complicated by the reconstruction of Westminster Tube Station which is located directly under this site. In order to complete the project in a timely manner with the setback caused by the underground construction, the designers chose to rely on prefabrication. This choice was also ideal because of the minimal space on the site, and budget was obviously not an issue.The project cost £235 million, qhich was well above the initial budget of £165 million. About £4 million of the inflation is due to client variations, and £10 million were added through the late completion of projects underneath.

Background & Context

The economics of the project caused much controversy. In fact, it is often seen as a pretentious waste of taxpayers’ money. Perhaps that has something to do with the imported fig trees in the courtyard that cost a bundle, or the less-than-satisfactory energy performance of the systems.What has yet to be seen is the long-term payoffs of the building’s cost. It could very well be a wise investment.

In mass, the Portcullis House is a six-story square doughnut with a central courtyard/atrium and vertical circulation in each corner. On the ground floor are shops and the entrance to the underground station on the street side, while the building’s main entrance is on the river side. Also on the ground floor is access for the underground tunnel to the Palace across the street.The upper floors are populated with offices around the perimeter, off a corridor that looks over the courtyard/atrium (see images).As mentioned before, much of the building was prefabricated including the slabs, floors, granite columns, fenestration, services risers, and the entire roof (including the plant rooms and services distribution). The facade was specially designed to be blast-proof, and the building as a whole was designed to last 120-200 years.

The Design

Low energy heating and cooling is accomplished with 13 natural ventilation towers. Fresh air is brought in through vents under the windows. The hot air rises to the top and is then directed either to be cooled or directly to the offices. In the winter, this air is heated by solar radiation while during summer months, the air is cooled by extracted groundwater from two boreholes sunk into a chalk aquifer. Water is extracted and stored in buffer tanks.Whatever the time of year, the conditioned air is pumped down the sides of the building into the floor void of each office, as shown in the diagram to the right. Each vent can be manually controlled by that office’s occupant(s).The high-tech cladding is integrated with the mechanical ventilation system by way of a ventilated cavity behind the outer glazing.

Key Design Strategies

Because of the lack of underground space, the mechanical systems had to be sized to fit on the rootfop. The fourteenth chimney is actually a flue for the mechanical systems, which were designed like those on a submarine in order for everything to function in such a confined space.Some groundwater is stored onsite in a greywater tank for toilet flushing, but excess is discharged to the sewer.The Portcullis design team chose wavy precast concrete ceilings to increase the building’s thermal capacity, and high admittance surfaces to allow cooling using that thermal mass.The building skin is designed to let adequate light in thru the central atrium and windows with light shelves in each of the offices. Electrical lighting is mostly limited to compact fluorescents on a Delmatic auto-dim system that responds to the daylight.

The energy use goal was 90kWh/m/y (for the offices), and target CO2 emission was 750 tonnes/year. According to the Parliament: “All electricity consumed on the parliamentary estate has come from renewable sources since 1 February 2007, therefore there will be no carbon emissions resulting from electricity consumption in future. This has contributed to the reduction in carbon emissions for the year 2006-07.”

Portcullis House is said to use one-third less energy and emit about 2,600 fewer tonnes of CO2 than a conventionally air-conditioned building, but is that good enough?

Validation

Asking one author passionate about low-carbon design (http://inpicenum.com/2007/06/12/portcullis-house-emissions-pass-or-fail/) reveals these results:“Ignoring the figures for 2006-7 because of uncertainty about the source of electricity, let’s look at 2005-6. For that year, Portcullis House used 7,230,601kWh of energy and emitted 630.2 tonnes of carbon. They don’t specify a breakdown for fossil fuels and electricity. Doing a bit of math, the figures look like this:

So the building uses 50% more electricity and 60% more gas than a crappy 1990’s air conditioned office block. But this isn’t a standard air-conditioned building! This is state of the art Green and it’s gone wrong somehow.”

To get to the figures in the chart: “First, convert the carbon to CO2 (multiply by 44 and divide by 12) to get 2310.7 tonnes. So now we know how many kWh they used in total and what their total CO2 emissions were. Using carbon intensities for mains gas (0.19kgCO2/kWh) and mains electricity (0.422kgCO2/kWh) and a little excel magic, we get a solution for annual electricity and gas consumption. The total floor area you get by working backwards from the figures in the P.A. (7,230,601kWh divided by332 kWh/m2 gets 20,712m2).”

Portcullis House has attracted a few awards, including the 2001 Timber Industry Award for the use of timbers in the atrium and the coveted Stirling Prize in 2002.

When put to SBSE’s Regeneration-Based Checklist, Portcullis scores a final +75. This is based on a -750 for polluting some air and water, dumping untreated waste, being built mostly of virgin materials, and importing energy; and a +825 for recyclability (once its 120-yr-life ends), use of daylight, use of passive heating and cooling, ability to create pure indoor air, neighborliness, and beauty (in context).

Subjective Performance Studies

Not open to the public. To visit, check the website for London’s Open House Saturday tours: http://www.openhouse.org.uk/public/talkstours/architecturetours.html

How To Get There

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