Beneath I outline some of the sustainability features of Shawm House. Within the confines of a constrained budget, limited resources, and a time frame tried to consider as holistically as possible the environmental impact of the house. By no means perfect it was a good first attempt of which I am fairly proud. There are certain products, details, and build ups that I would change if I could start over but then again when is a perfectionist ever satisfied...
Shawm is built with Passivhaus principles. Passivhaus does away with the need for any space heating system relying on a highly insulated fabric, air-tight construction, mechanical ventilation with heat recovery, and 'passive' solar gain through southerly building orientation. Unfortunately the site on which Shawm is built is oriented principally to the north removing the opportunity to capture the passive solar element. However, in line with good green energy principles, i.e. reduce demand first, the same principles are still employed to lower space heating demand as far as possible. Thus the building is super-insulated, extremely air-tight, and mechanically ventilated.
A 'fabric first' approach was taken in designing and constructing Shawm i.e. we invested heavily in creating a super-insulated structure, minimising wherever possible any thermal bridging (points of poor insulation or conductive paths through the fabric). The wall build ups changed at certain points through the building; it was important for example in the existing solid masonary stable block to use a vapour-open build up allowing the fabric to 'breather'. And whilst for spacial reasons the u-values (indicator of how well the fabric conducts heat) could not be quite as good in the existing stable block, in the new-build they were very low indeed (0.12 in the floor and .13 in the walls and roof). Maintaining this approach the glazing through the property is triple glazed.
Avoiding the uncontrolled 'leakage' of warm air from a building is key to passivhaus and low energy building practice. Shawm employs a number of methods to ensure that the building is as 'airtight' as possible. Employing a build up a Icynene, a spray foam insulation across the walls and roofs of the structure provides a first layer of airtightness. The foam expands into every nook and cranny of the building sealing and small gaps in the fabric. Internal of that is a continuous air-tight layer made up of a seamless membrane layer with all junctions being taped and sealed, employing tapes, specialist grommet type products, foam, and mastic. Shawm achieved an airtightness value of 0.36 ach/h@50pa which is extremely good, particularly for a building that incorporates a conversion element.
Given all the benefits of timber frame - emboddied carbon, offsite construction, speed of build, ease of insulation - I struggle to comprehend why anyone would build in masonary over timber frame. The creation of timber frame open panels is so straightforward that we fabricated the entire frame inside a redundant former hay shed on site, later demolished, and walked the individual panels onto the slab. It was a frustration but we made the decision to use imported timber to construct the frame, the quality of UK timber supply just being of such poor quality.
Local and low carbon materials
Wherever possible we tried to use local and low carbon materials. We had hoped to use Cemfree but unfortunately it wasn't quite available at the time; instead we used an 80% PFA replacement instead. The larch, used extensively on the roof and walls of the two new buildings is locally sourced from just north of the Scottish border. The stone to the front facade of the two buildings and the landscaping is sourced from a local quarry in Alston, 40 minutes south of the site. Perhaps one of the most rewarding elements of the build has been the harvesting of timber from our own woodland - a dozen or so mature birch and beach trees, and ultimately turning into into furniture for the property. Real Wood Studio a small collective in Jedburgh, Scotland, offered a service to fell, mill, kiln, design and produce, taking our resource all the way from tree to furniture.
Having reduced demand as fast are possible, not only by building with Passivhaus principles but also using LED lighting throughout and energy efficient appliances, the final piece of the sustainability package for Shawm was to integrate renewable energy technologies. Through the winter space heating and domestic hot water is catered for via a small biomass pellet boiler. Generating electricity all year round and providing domestic hot water via solar switch technology. Having chosen to keep the PV array off the main roof for aesthetic reasons we used high power black on black SunPower modules to get a higher output out of a smaller array. Finally rainwater falling on the building roofs is stored and pumped around the building for non-potable uses.