The talented Hewitt Studios, designers of the Straw Bale Café shown previously on TreeHugger introduce their latest, The Limpley Stoke Eco House, (near Bath, England) telling us:
The project provides a model for sustainable and responsible family home; it achieves ‘zero-carbon’ energy in use, makes extensive use of local materials and has a low-impact form, one which is respectful of its neighbours and surroundings, whilst allowing its users to enjoy the truly stunning location. The dwelling was designed with best sustainable practice in mind - a low-carbon dwelling that meets the criteria for the Code 5 in terms of energy use.
According to the architect, in the Code for Sustainable Homes, this means "all carbon emissions from heating are eliminated (but not from lighting or appliances)."
Now I find the whole idea of Net Zero Energy and Zero Carbon confusing (and that table is little help), given that it says nothing about how the building is built, whether it is insulated with baby seal fur, or how many acres of semiconductors are parked on the roof, or what's making the electricity that is brought in from the grid. There is a lot more to green building than just being a power plant. (Although the Living Building Challenge people are trying to fix this) That's why this house is so interesting; it goes way beyond that.
The Limpley Eco House builds on the concept of the low carbon dwelling. Recently I showed the New American Home, a "green" and "sustainable" model home in Las Vegas that was built out of stone, stucco and a couple of acre-feet of polyurethane foam insulation. Foam has a really huge embodied energy; for a given R-value, 46 times as much as glass fibre. Many people will say that doesn't matter, that the carbon savings over the life of the building are what matters most. This is true, but that doesn't mean we shouldn't be trying to use materials with low embodied carbon and energy. Which is exactly what Hewitt Studios is demonstrating here, using a mix of active and passive sustainable technologies:
Carbon sequestering construction materials, chiefly timber; were chosen as the primary structural and cladding material. Only certified timber from sustainably managed forests was used as it is reusable, recyclable and easily disposable (as biomass fuel). All the concrete used contains pulverised fuel ash (a waste product of coal-fired power stations).
Straw insulation; This is made from abundant renewable UK materials and gives excellent thermal insulation and thermal inertia, combined with negative embodied carbon. The straw panels are also breathable, encouraging moisture to escape from the fabric, maintaining air quality and avoiding issues with condensation.
There is a lot to love in this 3121 square foot house that looks a whole lot bigger.
Natural purge ventilation; at certain times of the year it is more thermally efficient to bypass the MVHR. The prevailing SW wind direction flowing over the rear of the roof can draw stale air out of the open clerestory windows and encourage fresh air in along the front of the building if so desired.
Seasonal solar gain; projecting pv brise-soliel protects the glazing on the lower floor from the high summer sun (preventing overheating). However during the winter the lower sun can enter directly into the space, providing thermal gain when it is most required.
Thermal mass; the lower ground floor concrete slab acts as a heat sink to regulate temperature within the space. During the summer it absorbs heat, preventing the internal temperature from rising too quickly. In the winter it stores heat from the direct sun that shines upon it, slowly releasing it overnight.
Ecology / Biodiversity; we have sought to protect and improve wildlife habitat and site biodiversity. To this end we have installed a biodiverse sedum roof, areas of species rich grassland and planting, a native woodland habitat (inc. “Beauty of Bath” orchard trees), an edible herb and vegetable garden, as well as with bat and dormouse boxes.”
Wait, there's more: Rainwater harvesting, electric vehicle charging, a big mechanical ventilation and heat recovery system (MVHR). It all adds up to a house that, while some will complain is a big big for true sustainability, demonstrates some of the most important principles of good green design that go way beyond insulation and solar panels. More at Hewitt Studios.