Building Materials

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The different types of building systems, such as straw-bale construction and Structural Insulated Panels, are discussed in Building Systems. Below is a more general discussion on materials, such as reclaimed beams and eco-cement. There are separate pages for specific aspects of the materials of construction, such as Paints & Finishing Materials and Insulation (see bottom of page).

The fabric of a building will make a large difference to its environmental credentials. Bricks, for example, have a lot of embedded energy in them: their clay has to be dug from the ground, shaped and fired at a very high temperature. Transportation to the construction site and the need for cement to stick them together just makes the whole situation worse. I would suggest that a house of bricks would never reach true C-Zero status (carbon neutral), unless it could actually reduce the amount of CO₂ in the atmosphere during its occupied lifespan by enough to make up for all the CO₂ emitted to make the bricks in the first place.

Building materials do not feature particularly highly in the Code of Sustainable Homes, as the code mainly concentrates on the running of a home and not the construction of it. Under the code, C-Zero can be achieved with little reference to the embedded energy of the building fabric. However, the related Green Guide to Housing Specification and Green Guide to Specification, which includes non-domestic situations, contain eco-ratings on most building materials around, based on the full life-cycle analysis of each one. These are extremely good and cost between £40 and £50 - available from the Building Research Establishment.

Windows and doors should be made from wood rather than plastic (uPVC), as the wood will last a lot longer if maintained and takes a lot less to manufacture. Almost all windows and doors will be made with FSC approved timber, but it is always worth checking. Try to avoid anything from rainforests, even if it claims to be sustainably logged; any logging in rainforests upsets the delicate ecosystem and leads to significant loss of habitat. It is always best to use double-glazing systems, but beware those with evacuated or argon-filled glazing units, as they usually leak and revert back to normal double-glazing quite quickly. Please see the insulation article for more information on windows.

Portland cement is one of the worst culprits in the building game, and one of the most abundant. In 2002, a quarter of a tonne of the stuff was manufactured for every single person on the planet. Producing a tonne of CO₂ for every tonne of cement, it is no surprise that it accounted for 5% of all greenhouse gas emissions in the EU and 10% in China. But Portland cement can largely be replaced by waste materials.

Fly ash is a waste product from coal-fired power stations and can be used as a substitute for Portland cement in concrete. It can be used to replace more than 60% of the cement and actually improves the characteristics of the concrete. Blast furnace slag and rice husk ash can also be used to a lesser degree. It is tricky to deal with at higher substitution levels, but should be available as pre-cast or ready-mix, cast in-situ options. A good choice if you can source it.

Similar substitute cement can be used as mortar to glue bricks together. There is also an eco-cement, using magnesite instead of limestone as the base, which requires much less energy to make and can incorporate waste materials more easily. There is also MSWIA cement, which is basically traditional Portland cement that has had 50% of the limestone used to make it replaced with municipal and industrial waste.

Lime mortar and concrete are also good alternatives to the Portland varieties. Lime is made by burning limestone at much lower temperatures than needed to produce Portland cement, so has less impact on the environment. It also absorbs CO₂ whilst setting, is vapour-permeable and flexible. It can be used for new buildings as well as old, the concrete (limecrete) is suitable for footings and foundations, and although it usually sets at a slower rate than Portland, it can rapidly achieve suitable strength characteristics for the construction of even large buildings. St. Astier is the best place to get the necessary advice about the best lime products for your project, as they are the people who make the stuff. Cost is a bit hard to pin down, but hydraulic lime appears to be about four or five times the price of Portland cement.

A variation on limecrete is hempcrete. This is lime mixed with chopped hemp as aggregate and a little Portland cement to help the setting process. Hempcrete has very good thermal properties, is airtight due to being flexible, is light (so foundations can be smaller), fairly soundproof, fire- and pest-resistant and vapour permeable. It is not very strong, though, so usually needs to be used with a supporting frame (such as timber or steel) and is not appropriate for foundations. Application is usually by pouring into shutters or spraying and can be used for walls, floors and roofs (as insulation only: the u-value for a 250mm thick block is between 0.27 and 0.11 W/m²K). See Tradical for more information and where to buy (under the Partners section). Construction with hempcrete appears to be a bit more expensive than standard methods, largely due to the supportive framework required. In itself it does not appear to be that expensive.

Womersleys have a great range of lime and general eco-friendly mortars, plasters, paints and traditional buildings materials. Lots of technical guides too, which are useful.

Reclaimed materials are a good idea where possible, but cost, quantity and condition can all cause problems when trying to build an entire house or extension with them. Sourcing reclaimed materials is best done locally, so a good place to start is Salvo, which has a directory of salvage and reclamation yards, a listing of architectural items for sale and a list of demolitions where low value aggregates and scrap can be sourced.

A friend of a friend in Bristol once tiled his house with old vinyl records, which may be a bit extreme but does demonstrate what is possible with a little imagination

If using steel joists make sure they have a high recycled content. They often contain only 15% recycled steel, but they are available at over 90%, so ask around. Also, be careful if using steel joists in external walls as they can act as a thermal bridge and lower the thermal rating of a building; there is specialist insulation available to counter this where unavoidable.

Aircrete or Thermalite blocks are pretty good for building the walls of standard residential buildings: they have adequate strength, are easy to use and have good thermal properties. However, if you want to combine thermal efficiency with sustainable construction, it may be better to go for more timber, straw, hemp or other ‘organic’ construction materials than Aircreate, as it is manufactured from mineral bases (mud ‘n’ rock, more or less).

Flooring is a big subject, but again, reclaimed boards are good. The actual construction of the floor will depend on the overall design of the building, but on ground floors thought should be given to underfloor insulation and heating. If using a concrete floor, consider using hempcrete or concrete with recycled aggregate content and eco-cement. The latter can shine up a treat for a decorative finish, especially if the right recycled aggregates are chosen, but if you want a floor covering consider screeds containing recycled glass (instead of sand), hempcrete  or bamboo. Suspended wooden floors can be great and reduce the use of concrete, but the need for ventilation can make insulation tricky and give underfloor heating all sorts of problems.

Sedum roofing is one of the best types of growing roofs around, as it is drought resistant, low maintenance and has pretty flowers. However, you could use more or less anything to make a living roof, such as grass, wildflowers or liverwort (possibly). Living roofs are good for flat or low pitched roofs, but not really for standard pitches.

You will need to make a solid roof structure, such as wooden board, then cover that with roofing felt (or similar). Then goes a drainage blanket (a bit like shallow rubber egg boxes), geotextile filter layer (like a blanket - keeps the soil and roots out of the drainage blanket), soil and sedum. It is good for ‘sustainable drainage’: it helps prevent flash flooding caused by urbanisation. It also gives some insulation, especially keeping the heat out in summer. The drawback is that it tends to be a bit heavy and you may need to strengthen the roof timbers. Cost is tricky, but an average 3 bedroom house may need around £3,000 to install, once you have the framework and support boards in place. A good place to start investigating your particular project is EverGreen Roof Gardens.

What to do

Find out a lot more before you build a whole house! In the meantime, consider hempcrete (especially to pour for ground-level floors), reclaimed materials and creative flights of fancy.

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