House proud - a sustainable home in the Rocky Mountains

Wood Focus magazine
,
20 May 2012
Alan Moffat's house

More than 2,500 metres up in the Rocky Mountains of Colorado, USA, sits an environmentally friendly building designed with a lofty goal: to create a truly sustainable home, not only characterised by its ability to give back to the environment but to look good and be comfortable. Its owner, Alan Moffat, reports.

This was not a house built with sponsorship or unlimited funds, but with a view to help the environment in a small way and on a tight budget. Compromises had to be made, mainly due to local regulations and available funds, but the finished home is sustainable and efficient.

The process to build a sustainable home started in 2005 when my partner and I decided to build a home where we could not only live economically and sustainably, but also run my partner’s business from without impeding our social life. A lot of research was done up front on the types of systems that could be used, the materials available and what potential there was to recycle. Along the way there were disappointments, false starts, highs, lows and a number of misunderstandings.

The final design – an interpretation of a Swiss chalet – was a collaboration between myself (floor plans and eco-systems) and Stan Powers of Linwood Homes, which provided the structural work and the timber for the build.

A place to call home

The house is located on a 35-acre hillside plot about 72 kilometres west of Colorado Springs, 38.45°N on a site ideally placed to benefit from year-round solar gain. The house was orientated such that the longest frontage is slightly to the east of south, so it would receive maximum solar gain throughout the year but with construction features to limit overheating during the long, hot summers.

Designed to maximise space, the house uses a post-and-beam construction style where all of the materials in the structural build are wood. Beams are constructed from douglas fir, the frame and siding from western red cedar and walls from spruce/pine/fir (SPF ) walls, with 2”x15” solid SPF rafters.

Internally the walls and ceilings are either 1/2” or 5/8” gypsum, depending on location, with a plaster covering. All cavities are filled as follows: vaulted ceiling R45 (U=0.043), walls R21 (U=0.068), frame floors R30 (U=0.042), foundation wall R13 and the foundation slab has a U=0.079.

Exterior doors are made from R7.14 fibre glass with a U=0.124. The windows, of which there are almost 1,000 sq. ft. are double glazed Low E .33/.28 units with a U=0.330, while all internal doors are solid pine.

With so much glass positioned for maximum solar gain in winter, the risk of overheating in summer was very high. In order to reduce this effect, the roof overhang has been designed to provide shade for the living and sleeping areas, while the first floor deck provides shade for the lower floor office and study areas.

The energy study conducted on the finished home has given it a Five Star Plus Home Energy Rating Certificate with a HERS Index of 49. 

The systems

Grid-tied solar PV tiles

Choosing PV tiles instead of panels was an easy decision due to the aesthetic look and how they blend in with the concrete tiles. Although more expensive than panels, technology has raised the efficiency of the tile and they compete very favourably with PV panels. The set-up allows for feeding unused green electricity back into the grid to receive settlement payments at the end of each year, and as Colorado boasts 300 sunny days a year there is a likelihood of being in credit at year end. In addition, the system has been designed to have the capability for a wind turbine to be added at a later date if required.

Ground Source Heat Pump (GSHP)

Due to the nature of the top soil on the site, it was decided to have a vertical system installed. The pump chosen provides both heating and cooling, using environmentally friendly R410A refrigerant. It and has dual scroll compressor providing a heating coefficient of performance (COP) of 4.2 and cooling energy efficiency ratio (EER) of 21.7. With summer daytime temperatures regularly around 30°C, cooling is a necessity.

The system uses four bore holes each drilled to an approximate depth of 70 metres, with the inserted pipes stabilised using grout and linked externally before being brought into the house. At this depth the temperature is more constant and should not vary throughout the year, making the system more efficient. During the hot summer months the system, which is linked to a whole house ventilation ductwork, removes the warm air from the house and passes it across the heat exchanger providing heat to the hot water tank for free hot water and then returning the cooled air to the house for air conditioning.

Radiant floor heating

Radiant floor heating is an ideal partner to a GSHP because it does not require as much heat to warm a room as radiators, is more efficient and provides a more constant temperature because it does not rely on moving air to heat the room. The house has been designed for maximum control. It has been split into 12 zones including living, sleeping, working and garage areas with individual control of heating and cooling for each zone.

If the radiant floor heating requires a little extra help in winter, the air can be pulled from the rooms and added as a top-up to the heating system, or alternatively the installed log stove can be fired up using wood harvested from the site during the build.

This house is built from 75% renewable resources, it provides an estimated 60% of its electricity needs and can be extended to 100% if required, it is heated from a natural resource and is extremely well insulated to reduce heat loss. A lofty goal reached – almost.