Passivhaus

Last week I went on an AECB CarbonLite course on understanding the Passivhaus standard, principles and methodologies.

It was a really good day for learning what the standard means and getting an introduction to the software. It's encouraging that there is also a standard for renovation, not just for new build. It's great that it's possible to build new houses to a high standard of insulation and airtightness with proper ventilation that will use 75% less energy for heating than a conventional new build. However, we can't build new houses quickly enough to replace all our existing houses and we probably wouldn't want to. Therefore, if we are to have comfortable homes that don't cost a fortune to run then it's important to renovate our existing housing stock to a high standard, so that they are warm, properly ventilated and with good air quality.

One issue I have is that all the emphasis is on the use of energy post-construction/renovation to heat the house; the embodied energy in the materials used is not considered. This is something that must assume more importance in future so that there is a reduced energy demand to produce construction materials and build houses.

This week I've been up to York for a meeting of a working group called Renewable Building TWG. A summary of the meeting will appear on the group's page.

The group exists to facilitate the development of the renewable building products supply chain in the UK and members come from agriculture; or are suppliers, distributors or manufacturers of renewable building products; or designers and builders; as well as Government and researchers from academia, SMEs and large companies.

Since the group formed, some members were involved in a demonstration project, 'The Renewable House', built at BRE Innovation Park, Watford (pictured here). The house used renewable materials to deliver a low cost, affordable house that meets Level 4 of the Code for Sustainable Homes through materials. Group members have also been involved in other projects such as the strawbale houses at Waddington referred to in my April blog. Other members of the group manufacture and supply products based on renewable materials such as sheep wool or hemp insulation, wood fibre boards and others.

How does your garden fare?

We have had some prolonged dry spells this year already, in central and southern England in particular. So how do you cope with dry spells in your garden?

In our own garden we try to keep water needs to a minimum; our water is metered and it just seems crazy to put high quality drinking water on the garden. You wouldn't pour bottles of mineral water over the garden, so why use tap water, which is of similar quality? We collect rainwater, but there is a limit to how much you can save in water butts, so we don't want to create a big watering need as this can take some time with a watering can.

Our main strategy is to have perennial plants in the garden, these are well established and their roots tap into underground water supplies. Plants in our garden have to be fairly tough anyway as there are mature trees in our neighbour's garden on our north boundary and they take quite a bit of the water.

In addition, we have not only one rainbarrel on each downpipe, but two in series, and if there was room we would have more on each downpipe. During a rain shower lots of water comes off the roof and into the downpipe - what doesn't go into rainbarrels just goes straight into the sewer system. Therefore, if we collect as much as possible it can be used to water the garden and it doesn't contribute to the flood risk created by excessive run-off of rainwater. Thanks to my former colleague, Phil Wildbore, for this bit of inspiration.

We never water the lawn in summer when it's dry. OK a well-tended green lawn looks wonderful, but grass is adapted to dry climates and actually survives a drought much better than some other plants. It will always come back when the rain returns, so just look after it well in other ways and it will reward you.

We do have some hard surfaces around our garden. By far the largest part of these is covered with gravel, rather than tarmac or paving. This is also a good strategy because gravel soaks up rainwater, which is then available beneath the surface for the beds and lawn. Where there are impermeable surfaces the rainwater will run off, be lost to the garden and contribute to localised flooding problems.

It's been illegal for some time now to put down new impermeable areas in your garden. I've noticed the impact of this in our locality as people are opting to have gravel drives rather than paved drives. Our drive is looking worse for wear after several years and at some point we will have to consider one of the new permeable surfaces to replace the present tarmac.

I'll keep you posted!