Building an extension is probably the nearest we will ever get to building our own house from scratch. What do we want from it, apart from extra space? How radical can we be?
There are many aspects to an eco-home. I will set out below some of the challenges and aspirations, though we have at this stage done no calculations to see what is feasible given the orientation and position of the house in relation to its neighbours, and the location of its garage on the south side.
Together with passive solar heating, insulation is the cornerstone of the PassivHaus standard of building. We probably can’t aim for PassivHaus because of the existing portion of the house, but we may reach the next stage down, EcoPhit.
A house has to be insulated against temperature leaks into or out of the building: this is easy with a new build but harder to apply to an older house. In particular, 1960s houses are built on concrete as ours is, and there is little headroom in the house to add a layer of floor insulation without excavating the concrete (a bit and messy job).
Current heating is by means of an oil-fired boiler and distributed through microbore piping to radiators in the house. Hot water is obtained by the same method, and there is an airing cupboard containing an immersion tank in the tiny bathroom.
Oil is expensive and inefficient, and requires a tank in the garden to store the oil. This tank is badly rusted and in danger of leaking (which could cause serious environmental damage) and although the radiators look fairly new, the piping needs replacing. There is gas to the house (though currently unused) and the conventional route would be to install a gas boiler and replace the piping.
But we’re examining an altogether more radical options. The house has several chimneys currently not in use, and we are very used to woodburners, and we have a supply of wood. Installing a highly efficient Burley (link) woodburner in the lounge will enable the heating of a good portion of the house. A masonry Ecco stove (link) installed more centrally will store the heat from burning wood and release it gently, creating convection currents throughout the house.
These are fine but expensive options. I justify the expense buy not replacing the boiler, ripping out the pipes and the rads and relying entirely on woodburning. But is this sensible?
One of our plans is for a electric backup headers: we are just hoping this will be enough, and that we are not mad to rip out the conventional water-based heating system.
The house needs rewiring, which can’t be done until the electrician can be given plans for the extension.
The same electrician can install solar panels, which would be a logical decision if we are relying partly on electricity for heating. A solar collector for hot water will also be a good plan. But some people argue, why install panels with high embodied energy when you can simply sign up for a renewable electricity provider? I suppose the answer is, because if we have our own system we can trust it. If we generate it ourselves, we know it’s renewable.
Solar technology is undergoing a revolution as batteries are coming available to store the electricity during the times when the sun isn’t out. We’ve been glued to the latest videos featuring the Tesla (name? link?). But we haven’t dared ask how much it will cost.
Hand in hand with insulation goes ventilation – because a house that could not evacuate the stale air within it, or provide cool air in summer, would be unhealthy and uncomfortable. The trick is to ventilate without losing heat in winter.
The PassivHaus model relies on mechanical ventilation with heat recovery. This requires pumps and filters that need servicing, and some people don’t like the uniform atmosphere this creates, finding it rather artificial. This is of course a matter of opinion. MVHR needs pipes to be installed throughout the house so this is the right time to be planning it.
There are other forms of ventilation that require the house to be correctly designed in order to work, and for the air flow to be mapped. Some books say you have to have insulated walls but porous ceilings for it to work. Others refer to stack ventilation, which is the vertical movement of air from floor to ceiling in a building.
We still don’t know enough to know which is best applied to our situation.
Minimising our water use is another environmental goal, and while we’ve got diggers creating an extension, we may as well dig the garden and install an underground tank. The tank will store rainwater that drains from the roof of the house, but it’s what we do with the water that isn’t clear.
The obvious use is for watering the garden. But wouldnl’t it be nice to flush our toilets with it, and wash our clothse and dishes? This requires planning and extra piping.
So what happens if you hook up your toilets to the underground tank, and then run out of water during a dry spell? One solution would be to link the tank to the mains which would only need to top it up if the rainwater level falls below a given level.
But we wonder whether this will work, and how much maintenance it will need. What are the things that can go wrong?