Forestry Commission Scotland:10/10/2007'Sustainable and Exemplar' offices.
In December 2004, HRI-architects, in association with Hurd Rolland Partnership, were appointed to design the new Inverness Forest District offices for the Forestry Commission on their site at Tower Road, Inverness.
The design brief was developed to 'provide new office accommodation that fulfilled the ideals of providing a sustainable and exemplar building that has an emphasis on local timber use'. This brief was interrogated to see how sustainability could be applied in this situation taking into account site parameters, the nature of the clients business, and the ideals of reducing energy consumption both as a finished operating building but also as a method of procurement.
The brief also called for an exemplar approach to the use of timber. This needed to be contextualised to identify ways in which timber might be used, expanding tried and tested methods of construction in perhaps new and innovative ways or as a test bed for new approaches and materials.
A wide variety of sustainable options were considered and from this palate the following were developed in the context of 'pragmatic sustainability'.
- Use of home-grown timber from well managed forests.
- Restricting the 'road miles' of materials and people where possible to reduce energy consumption.
- Re-cycling of rainwater for toilet flushing.
- Bio-mass heating.
- Maximise the solar heat gain.
- Minimise heat loss by enhanced levels of insulation.
- Use natural rather than 'manufactured' insulation products.
- Filtration of excess rainwater to minimise the impact on the local surface water systems.
- Natural 'passive stack' ventilation system rather than electrically powered ventilation systems.
- Reduce the use of unsustainable materials such as steel, concrete, aluminium, and treatment of timber.
- Reduce maintenance costs by good design and careful specification.
Exemplar use of timber was defined as follows;
- Use of locally grown hardwoods for finishes.
- Use of locally grown softwoods for the structure.
- Use of locally grown softwoods for external cladding.
- Use of locally grown softwood, locally manufactured board products.
- Avoiding the use of unsustainable chemical based treatments to timber.
- Use natural methods of modifying timber to enhance its performance and thereby open up new opportunities for timbers not normally used for cladding.
- Using timber in unusual or demonstrative ways.
Timber structure.
The timber for the structure is Douglas Fir. The design also called for some timbers to be 12m long, sizes that are difficult to obtain from the homegrown stock. But the Forestry Commission were able to identify and supply suitable timbers from their stands at the side of Loch Ness, near Fort Augustus.
The timbers were successfully felled, trimmed and transported to a sawmill at Kirriemuir. When cut the Commission appointed a TRADA approved visual grader to identify the stress grade of the cut timbers. The timber was of a much higher grade and quality than expected. The 'green' timber was air dried on site.
Careful detailing and cutting of the timber was essential. To achieve this, the structure was drawn on CAD and a fully dimensioned cutting schedule was prepared to assist the joiners to prepare the timber and assemble the frame. This attention to detail proved beneficial in practice, since this and careful setting out allowed the frame to fit together accurately.
Secondary structure (floors, walls and roof).
JJI joists were chosen for the floor, wall and roof secondary timbers manufactured locally by James Jones & Sons of Forres. These joists comprise a top and bottom flange of C24 Spruce from Scandinavia and a 9mm thick web made of Oriented Strand Board (OSB) manufactured from locally grown spruce and formed at the Nexfor plant at Dalcross. These part local products were ideal for the spans involved being structurally efficient, easy to handle, and the slender web reduces the effects of 'cold bridging', thus enhancing the thermal efficiency of the fabric.
Cladding.
Un-treated larch from the Forestry Commissions own woodlands at Fort Augustus was selected, and by careful selection, good detailing and a protective design (use of large overhangs) allows a home grown product with natural durability properties to create a distinctive but simple cladding effect on the gables and soffits of the roof overhangs.
Locally grown Scots Pine from Culbin Forest was selected for a natural impregnation process using furfuryl alcohol which modifies the timber to enhance its dimensional stability, durability, insect and beetle resistance and at the same time produce a pleasing warm colour to the timber. This process allows a timber that would not normally be considered as a cladding material to be used in this way with a 30 year guarantee.
Rainwater harvesting.
A 6000 litre underground water storage tank takes water from the roof and returns this to the toilet cisterns thus reducing the amount of water taken from the public water supply.
Passive stack ventilation.
Much energy is consumed in commercial buildings in ventilating a building. This is often increased by the use of air-conditioning. By means of the double height open plan space natural convection currents are created that circulate the air and sensor controlled 'windcatchers' on the roof open or close the dampers to allow excess heat to be released or introduce cool fresh air to the work space when required.
Bio-mass heating.
A locally sourced wood chip fired boiler was seen as the most appropriate method of heating the building with comparatively low road miles and supporting local businesses, the local Forestry wood school and using a timber product.
Underfloor heating.
To create a uniform heating system, underfloor heating was selected for the ground floor. This method works more effectively with the passive stack ventilation system than radiators.
Heat Gains versus Losses.
Unnecessary heat loss from the building is essential. To achieve this high levels of insulation have been specified using natural insulation formed from crushed volcanic rock that exceed the requirements of the Technical Standards by an average of 31%. The orientation of the building allows the South-West facing façade to absorb heat from the sun. People and electronic equipment added heat to the building. The high levels of insulation minimises heat loss, and the heat gained from the sun, people and equipment are then balanced closely creating a building that is comparatively very inexpensive to run.
In essence, it remains the aim of the client, Forestry Commission, and the designers to develop ways in which sustainability can be promoted using a 'pragmatic' approach without compromising good aesthetic design and the desire to create a very pleasant working environment. By this we mean that cognisance of the site, geographic location and costs are balanced against the principles of sustainability avoiding the obvious pitfalls of over specifying materials and technology that is simply not necessary. Research into materials and their careful use to minimise maintenance; making the building air tight and thermally efficient; ensuring good use of natural light and minimising energy consumption are easily achievable without the use of expensive and often gimmicky equipment and will do more to promote the ideal than the pursuit of an overly ambitious techno-solution.
