Beginner’s guide to Eco Building

Responsible selfbuilders are taking a more sustainable approach to their homes, using construction methods and materials which are kinder to the planet.

Timber frame house construction on site

A timber frame taking shape on site. This form of construction uses renewable materials and lends itself to high levels of insulation.

Increasingly, selfbuilders and renovators are adopting a more sustainable approach to construction, choosing methods and materials which are kinder to the environment and produce healthier homes in which to live.

The importance of concentrating on the fabric of a building can’t be overstated. Without first carefully considering the walls, roof, windows and insulation to be used, and the way these will work together, a house can never achieve its optimum performance in terms of energy efficiency and levels of comfort.

Passivhaus

One of the most popular models for achieving a low-energy home is the passive house, based on the standard set by the Passivhaus Institute in Germany. To build a certified Passivhaus you will need to meet a strict set of criteria for extremely low-energy buildings, which use around 90 per cent less energy than standard buildings in the UK. Eliminating the need for space heating and cooling is seen as the most cost-effective way to achieve a low-carbon building, rather than adding expensive renewables.

Passivhaus design focuses on a combination of air tightness and insulation, removing thermal bridges and maximising passive solar gain, together with installing energy-efficient glazing and a mechanical ventilation and heat recovery system. Simple, compact shapes ensure the external surface area of the building is reduced to further minimise heat loss.


Airtightness is a key consideration in a Passivhaus build.

To get a design certified, airtightness and commissioning tests need to be carried out on the finished house, but it is advisable to complete a design check before work begins to ensure that the design has the potential to meet the target. The Passivhaus Trust has some very good guides on the topic.

See SelfBuild & Design Guide "What is Passivhaus?"

Stylish Passivhaus

Gresford Architects Passivhaus in Berkshire

This new Passivhaus built on the site of a derelict water tower in west Berkshire, eschews the clichéd ‘hair shirt’ approach to sustainable living. The owners enthusiastically embraced modern energy-saving technologies and materials, using Passivhaus design principles to achieve excellent thermal performance. Gresford Architects and Ecology Building Society were both chosen for the project on the basis of their expertise in Passivhaus developments.

With its large windows and generous living spaces, the four-bedroom family house is a contemporary interpretation of the local historic timber-framed barns. While Passivhaus buildings typically face south, the new home is orientated to the west to take advantage of the rural views. The west-facing windows are large, with smaller ones on the east and north elevations to reduce heat loss. The southern elevation has large windows at ground floor level, opening onto a generous paved terrace area.

Gresford Architects: gresfordarchitects.co.uk. Ecology Building Society: ecology.co.uk

SIPs are becoming popular with selfbuilders because of their suitability for achieving excellent airtightness and high levels of insulation, as illustrated here with these SIPs supplied by sips@clays.

See SelfBuild Guide to SIPs

Natural materials

Choose natural, sustainable materials, such as wood and wool, over synthetic products and try to buy locally wherever possible. Ask any trades working on your house about the materials they plan to use, too.

Low VOC (volatile organic compounds) paints and stains are available which don’t emit toxic pollutants. Ordinary paints are manufactured from complex, synthetic chemicals, many of which can be damaging to your health or the environment. Natural paints and stains based on oils, simple minerals and plant products are free of polluting solvents and are available from a number of sources, including greenbuildingstore.co.uk.

Many homeowners are now also shunning carpets in favour of low-maintenance hard floor surfaces. Carpets can harbour dust mites, which induce allergies, and may have been treated with a variety of chemicals. If you decide to buy a natural wood floor instead then choose a product displaying the FSC mark (Forest Stewardship Council, fsc-uk.org) and seal it with an eco-friendly wax or wood oil.

Insulation

Without adequate insulation more than 40 per cent of heat will be lost through the walls and roof of a house, so insulating thoroughly can significantly reduce utility bills. Some insulation performs better than others, which makes calculating the thickness required to achieve a satisfactory performance more complicated.

Insulation manufacturers will usually quote the thermal conductivity, known as the K-value (or lambda) of their products.

This is a measure of the thermal conductivity of a material – how easily heat passes across it. A low value means the material conducts less heat and is a better insulator. The National Insulation Association has further details on its website (nia-uk.org).

Warmcel fills timber-frame panels completely, to a high density leaving no gaps or cracks that a cut insulation can create.

If you’re building a new home or extension don’t just comply with the current Building Regs requirements for insulation – these are a minimum guide and many people opt to double the quantities of insulation in their roof, walls and floors. Make sure that the products you choose are natural and environmentally friendly, such as Warmcel (warmcel.co.uk), a loose-fill DIY cellulose fibre insulation suitable for lofts and timber floors; Isonat (isonat.com), made from UK-grown hemp fibres and recycled cotton, or sheepswool insulation such as Thermafleece (thermafleece.com).

Take care to eliminate cold bridging at junctions and around openings

Take care to eliminate cold bridging at junctions and around openings, design airtight detailing to prevent air leaking through the structure, and consider how the house will be ventilated if it is totally sealed.

See SelfBuild Guide to Home Insulation

Heat

One of the most important elements of any ‘green’ house is actually free. Orientation of the building on its site – ideally facing between south-east and south-west – and the sizing and placement of windows is critical to maximise passive solar gain from the sun’s rays.

Solar water heating systems use solar panels, called collectors, which are often fitted on roofs. They collect heat from the sun and use it to warm water which is stored in a hot water cylinder. A conventional boiler or immersion heater can be used to make the water hotter, or to provide hot water when solar energy is unavailable.

The cost of installing a typical solar water heating system is £4,000 to £5,000 (including VAT at five per cent for a 3.6-sqm system). Savings are moderate – the system can provide most of your hot water in the summer, but much less during colder weather. You may be able to receive payments for the heat you generate from a solar water heating system through the UK government’s Renewable Heat Incentive (RHI). A competent accredited installer will be able to assess your home and help you choose the best set-up to meet your needs.

Installing ‘slinkies’ for a ground source heat pump system. (griffithsaircon.co.uk)
Ground source heat pumps use pipes that are buried underground to extract heat from the ground, which is then used to heat radiators, underfloor or warm-air heating systems and hot water. Installing a typical system costs £10,000 to £18,000 and running costs will depend on several factors, including the size of your home and how well insulated it is.

Air and water source heat pumps use similar principles to ground source heat pumps to extract heat from air or water instead of the ground. They can be fitted outside a house and generally perform better at slightly warmer air temperatures.

A wood-fuelled biomass boiler could save you up to £960 a year compared to an old electric heating system or boilers.

Biomass boilers for homes are fuelled by clean, renewable wood pellets, wood chips or logs. (energyclever.com)

An automatically fed pellet boiler for an average home costs from £8,000 to £15,000, including installation, flue, fuel store and VAT at five per cent. Manually fed log boiler systems can be slightly cheaper.

Green Deal

The Green Deal allows homeowners to make improvements to existing properties with no upfront payment. The expected financial savings must be equal to or greater than the costs attached to the energy bill, and a range of renewable technologies are available, including solar thermal, solar PV, biomass boilers, ground and air source heat pumps and micro-CHP.

All work is carried out and checked by accredited installers and the loan is paid through the savings made on your energy bills. If you move house then the new owners will take on the payments. Visit gov.uk/green-deal-energy-saving-measures for further details.

Electricity

Renewable energy is generated from natural resources such as the sun, wind and water, using technology which ensures that the energy stores are naturally replenished. Instead of buying all of your energy from suppliers, you can install renewables technology (also called micro generation and low-carbon technology) to generate your own.


Solar PV (photovoltaic) cells generate electricity directly from sunlight and, like solar thermal, PV panels are best sited on a south-facing roof slope. Solar electricity is green, renewable energy and doesn’t release any harmful carbon dioxide or other pollutants. According to the Energy Saving Trust (energysavingtrust.org.uk) an average domestic solar PV system is 4kWp and costs around £6,200 (including VAT at five per cent).

Following the closure of the Feed-in Tariff scheme to new solar PV system applicants in March 2019, the government is introducing a Smart Export Guarantee. This will require most suppliers to offer something for your exported electricity. In the meantime, some companies are already offering export payments to their customers.

Water recycling

One big advantage when you are building your own home is that you can install a water collection and distribution system for the garden while you have mechanical diggers on site. Rainwater harvesting promises savings of 50 per cent or more on average water consumption, and popular roof coverings such as concrete tiles make excellent collection surfaces.

Water from the roof is collected via guttering and downpipes through a filter and into a storage tank, which may be buried in the garden or installed in a garage or basement. From here the water is pumped to the point of use, and if there is insufficient water then the system automatically switches to mains supply until rain refills the tank.

With a little extra investment, rainwater can be used inside to feed WCs and washing machines.

Installing a domestic system is more straightforward in a new-build home, but with some alterations to down-pipes and interior plumbing, a system can be added to existing houses. Visit rainwaterharvesting.co.uk for further details.

The chart shows a rough breakdown of water use in a typical household. It also illustrates how much is harvestable (diagram from marshindustries.co.uk)

Grey water – the waste from baths, basins and showers – can be filtered and recycled for toilet flushing, the washing machine and outdoor use, saving up to 60 per cent on bills.

Promoting sustainable building

The Association for Environment Conscious Building is a network of individuals and companies with a common aim of promoting sustainable building. It brings together builders, architects, designers, manufacturers, housing associations and local authorities to develop, share and promote best practice in environmentally sustainable building.


This Beginner's Guide to Eco Building is from the February 2020 issue of SelfBuild & Design magazine.

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