U is not enough
By julietm, Nov 21 2014 07:43PM
Bored of the tedium of barn conversion plans, I've gone back to basics and remembered some principles: natural, sustainable, renewable. The barn now has a new plan: to keep its environmental impact, in terms of construction and functioning, to an absolute minimum. All very eco-worthy but I'm only just beginning to realise what this means.
To start, it's all about U.
Turns out that the U-value of a building - a measure of its thermal efficiency - is the crucial thing in terms of sustainability. It's so important that it exists as a minimum standard in building regulations. Eco-warrior or not, if you have planning permission for a new build or conversion, you have to achieve the prescribed U-value. In practice, it's all about insulation; extraordinary thicknesses of the stuff - in the roof, walls and floor, with no drafty, heat-losing, single-glazed windows or doors. (Not like any house I've ever lived in is for sure.)
For me, U is not enough.
My personal eco-challenge is about the sustainability of the materials used and their impact on an old barn like this - in particular, on the capacity of its natural stone walls to 'breathe' and regulate temperature and moisture. U is not everything and here, in pursuit of a plan based on principle, we are way off grid.
There is the most extraordinary range of natural, sustainable building materials available as alternatives to the inherently unsustainable cement, gypsum and fibreglass that dominate the mainstream (still). Some are traditional, predating the mainstream. Others are modern innovations, a response to climate change concerns. Not only are these materials sustainable in terms of their source and manufacturing process, but they will also insulate and finish the barn's thick stone walls without compromising its breathability.
Best of all, the builders, who've never worked with alternative materials before, and building inspector, who's not seen such a mix in use before, are also up for the eco-challenge. (They are not blog readers, for sure, but thank you: Danny, Tommy, Bob, Andrew and Eifion, you are all awesome.)
Our ingredients for this stone barn conversion are:
• stone, slate and wood: re-using as much of the existing structure as possible and salvaging what we're missing from local, second-hand sources;
• lime: CO2 neutral and very traditional, for rendering, pointing and painting (limewashing);
• cork: insulating wall boards and an important component in a highly insulating plaster;
• hemp: another insulating plaster made entirely of British ingredients;
• glass: a recycled, 'exploded' aggregate, 'Glapor', capable of insulating and regulating moisture;
• wool: yes, that old stuff, between the joists and under floor boards to keep them cosy.
The barn floor is on its way. Within 24 hours of digging and filling to a U-calculated depth of 28cm, its thermal qualities have been noted, tested and found immediately preferable to any of the conventional understorey insulators available on the farm (straw, hay, discarded clothing etc) by the on-farm expert. Because, if anyone understands the value of U, thermal-seeking cats do.