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Scotstoun House, Edinburgh

Scotstoun House, Edinburgh

The adaptation and extension of a poorly performing but listed 1960's office building to provide a BREEAM Excellent and EPC A-rated building to meet the client's needs for the next 30 years.

Overview

In 1965 Arup Scotland purchased Scotstoun House at South Queensferry (near the just completed Forth Road Bridge). They demolished the 18th century house and in 1966 built a low, single-storey, pavilion-like office building at one end of the walled kitchen garden, with outlooks into the walled garden and over the lawns of the former house. A cottage and stable at the other end of the walled garden were converted into a plant room and a caretaker’s house.

Originally designed to house 60 staff, by 2005 100 people were working in the building and its cellular layout, adapted with much effort over the years, was inflexible and did not suit the way the company wanted to work. The space was cramped, poorly ventilated, had only one meeting room with limited facilities such as a staff kitchen; there was not enough room for printing equipment and a prefabricated structure had been tacked onto the building for archives storage. In the concrete and glass structure, the occupants were cold in winter and overheated in summer; with the window blinds down almost continuously to protect its inhabitants from glare, heat or cold, and with its wood-panelled partitions and ceilings, the building was dark and the fluorescent strip lights were on for 12 hours every day. Despite some affection for its growing status as a classic building of the 1960’s it was not a comfortable place to work, and did not provide a good image for Arup in the 21st century.

Arup Scotland commissioned haa design to evaluate their business, how they wanted to work and how they might work in 20 or 30 years time. While this was being carried out Historic Scotland spot listed the building as B Grade, covering the 1960s building, much of the interior furnishings, the walls of the kitchen garden, the cottage and outbuilding in addition to noting that the pavilion like setting of the building in an old park was something that should be preserved. 

Approach

In line with the recommendations from Historic Scotland Haa design proposed a simple addition connected to the south east face of the existing building, extending within the space of the walled garden. The height was carefully designed to complement the existing building and a clear link designed to separate the old and new parts of the building. The new addition provides 625sq. m of working space including meeting areas, break out spaces, core service areas and a new entrance. 

As recognized leaders in the field of promoting sustainable design, the aims to meet very high standards were there from the outset of the project. From the beginning, the project had specific aims of bringing as much natural light as possible into both the old building and the new extension, creating excellent air quality, cooling and ventilation through passive means throughout the whole building, providing a low-carbon source of heating and reducing energy bills and carbon emissions. After determining the overall plan, form and orientation of the building, extensive analysis of the existing building and modelling of air-flows, temperature variations etc., was carried out to detail the performance of the external envelope and refine the design, specify glazing and ventilation solutions and select low energy systems. The preservation of the external walls of the old building, the fenestration and the timberwork fitted internally into these walls (which came as part of the listing of the old building) defined certain parameters; equally new interventions, such as the opening up of the interior space of the old building and the introduction of more natural light, were appreciated by Historic Scotland for the degree to which this showed off the character and detail of the old building. A continuous dialogue with both Historic Scotland and the CEC planners led to both bodies buying into the changes proposed and gaining increased confidence in the approach of the design team and the solutions being proposed. For example Arup’s environmental modelling prediction of likely over-heating in one corner of the old building led to a proposal to change two fixed windows into opening French windows, but equally to the shortening by the design team of the link between the old and new buildings, to increase the flow of air around the building at that point.

preview scotstoun

In construction the need for new construction materials was reduced as the main structure and the external walls of the existing building were being retained and re-used. The extension utilised one of the existing garden walls, which was levelled and underpinned, and part of another one which was partly demolished, stored and rebuilt as part of the redevelopment. On site material was stored and crushed, and then used for granular fill across the site and under road bases. Some elements of prefabrication were used to reduce construction waste on site. Conversely, the nature of the old building and the materials that did have to be retained (walls, window format, timber, steelwork etc.) meant that only limited intervention in the old building was possible and close attention had to be paid to solar gain, heat build-up, ventilation paths and so on.

Many low-energy technologies were proposed during the design process but many of these were ruled out as not being cost-efficient for a building of that size, or compatible with the design. Rain water harvesting for example was rejected both on cost grounds and because the parkland surrounding the building provided the opportunity to install a swale to capture and disperse all water run-off, coupled with a sustainable urban drainage system for the external areas. Materials were selected on the basis of a Green Guide A rating. Natural, inert and recyclable materials were used throughout. The tone of the existing building was reflected in the choice of concrete, timber, steel and glass as the primary materials used in the new extension. A new aluminium capping to the old building is mirrored in the extension and in the choice of aluminium for the new windows, creating strong lines in a soft parkland setting. Lead was the one new material introduced, chosen as a softer material to tie in with the blue engineering brick on the exterior fringe to the old building.

Performance

The whole building is separated into 10 zones for heating and fresh air control, with a target temperature of 21°C. Hot water, from a tank, heated by the biomass boiler in the plant room is pumped through pipes that run around the perimeter of the old building. Ventilation is entirely natural throughout the whole building, with new manual winding handles fitted to the ‘hoppers’ at the top of the old windows, and the louvers in the clerestory of the central core and in the link area designed to open automatically when temperatures exceed settings by 2°C. The only mechanical air-cooling in the building is in the print room and communications room.

An integrated control system monitors the energy performance of the entire building. This system can identify leaks, highlight wastage, and provide detailed performance analysis. The internal and external environments are comprehensively monitored for temperature, relative humidity, carbon dioxide and light levels. The system includes a weather station, the output of which is used to validate the original modelling of the daylighting against measured values.

Insulation has been increased in the old building through replacing all the old Crittall single-glazed windows with like for like double-glazed alternatives. Due to height and load restrictions above the ceiling in the old building (which received a completely new roof) thermal mass has been added to this part of the building through the installation on the upper surface of the tongue and groove boarding of a 5mm layer of Phase Change Material (PCM). When the room temperature increases the PCM melts and absorbs and stores heat. It releases the heat when the temperature drops in the evening and overnight and the material returns to solid. Not used before in an office situation, this provides additional thermal mass that is purportedly equivalent to 150mm of concrete. In addition to the light coming into the building through the new clerestory windows around the new core, over 70 solar tubes (sun pipes) are fitted into the new roof to bring natural light directly into the working areas. Suspended low-energy fluorescent lighting is triggered to come on when natural light levels fall below 400 lux.

The cottage building was refurbished to provide showers, drying racks and lockers for the use of those cycling to work, and the existing meeting room upgraded. The new biomass boiler (a mandatory requirement from the City of Edinburgh Council) and a storage unit for the biomass pellets were inserted in the old plant room, along with a back-up gas boiler. The pipes from the boiler to the office building use the same trench as the 1960s boiler.

The continued monitoring that takes place confirms that the PCM in the ceiling of the old building is functioning as designed. There is some feeling that the clerestory louvers in the central core of the old building were over-designed, i.e. have more ventilation capacity than is required. Arup have validated the accuracy of the original model that predicted yearly energy usage and demonstrated that the daylighting scheme is saving 60% of the electrical energy for lighting annually compared with the previous building. Modelling also predicts that heating costs will be reduced by 30%. The project was subject to the 2008 Scottish Technical standards for energy usage, which were not only achieved but significantly exceeded. The refurbished building achieved a BREEAM Excellent rating and EPC A-rating, an outstanding achievement considering the restrictions imposed by the original building.

 

Lessons

Haa design’s previous relationship with Arup and the shared vision between haa, the Arup team in Edinburgh (as client and engineers and as BREEAM facilitators) clearly put the project on a good path from the outset. This particularly applied to the overall vision of sustainability that was shared between the Arup offices in Edinburgh and London, and the depth of Arup’s knowledge about sustainability and their commitment to it at a fundamental analytical level. haa design have also been designing sustainable buildings for over 15 years, and have detailed knowledge of the BREEAM process, having used it as it has developed over the years. Their approach is also to create sustainable buildings designed around first principles, and then integrate appropriate technology. The development of a close working relationship with the contractor and the detailed discussions that took place to understand key construction elements and building sequences played a significant part in the completion of the project on time and on budget.

The extent to which Arup were able to model the new building prior to proposing solutions for heating, lighting, ventilation, etc., contributed greatly to the design of those solutions, which has attested by the monitoring of the building’s performance once it was in operation. The particular attention at that time being focused on sustainability by the planners at City of Edinburgh Council and the standards they were asking of developers reinforced what the team themselves already felt, and the proposals that addressed sustainability became integrated into the development and became part of the planning consent.

Historic Scotland’s listing of the building clearly reinforced the retention and renovation of the old building as part of the ultimate solution for meeting the client’s needs on that site and avoiding a 100% new build option, together with the retention of much of the existing fabric. This starting-point also acted as a major driver to the solutions ultimately developed in reaching the BREEAM Excellent rating and the EPC A-rating, in that the limitations imposed by the old building demanded more innovation in developing insulation, ventilation, heating and lighting solutions, and ultimately the design for the total new building.

Links

ARUP

haa design

 

Resource Efficient Scotland supported the preparation and presentation of this case study for the Retrofit Scotland website.

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