If being eco-friendly is particularly close to your heart, and there is some building to do on your house, dont worry, we can tell you which form of wall construction is best ecologically.

For many years, the external masonry cavity wall, two skins of brick or block with a space in between, has dominated domestic construction. The cavity has two functions: preventing damp and providing insulation. Nowadays, cavities are filled with thermal insulation to meet, or exceed, the current building regulations (100mm of insulation until next years revision). The regulations allow cavities up to 300mm (12) wide using conventional wall ties and many low-energy houses now have insulation up to this thickness.

Brick, stone and concrete have high thermal mass, which means that heat can be absorbed, stored and released depending on the temperature. This provides a fairly constant internal temperature and is suitable where the home is more or less constantly occupied. It is now thought that providing thermal mass within a house will be increasingly important, as the climate gets warmer. The modern practice of dry-lining the inside face, by fixing plasterboard sheets to it, is discouraged because it is difficult to seal against drafts, and it effectively prevents the internal masonry leaf from having any useful function as primary thermal mass. Instead, traditional plaster or render should be applied straight on to the wall. Floor joists should always be supported by steel hangers and separate lintels provided for each leaf of the cavity, to prevent cold bridging. Cavities should be closed at openings by timber or rigid insulation fill, the inner leaf should not be returned in masonry as this would be another cold bridge.

Masonry materials

Walling of earth from the site, cob, or stabilised earth blocks, would be the best ecological choice or a masonry wall, for embodied energy and health reasons. Fired clay bricks, however, make an attractive, durable and low maintenance outer skin, but they must be laid in a lime-rich mortar, so they can be reused in the future and also to minimize any cracking problems. Second hand bricks are the best choice, if not, new bricks should be sourced as locally as possible. It is presently difficult to avoid the concrete block; it is best to choose those now made using recycled and secondary aggregates or those using cement replacements such as PFA. In the rest of Europe , the more environmentally friendly hollow clay blocks are universal these are now being imported to the UK and some are now being manufactured here. Another low-impact material is sand lime brick autoclaved at lower temperatures than clay brick, and hence having a lower embodied energy. Most Dutch houses are constructed using pre-cut sand-lime panel blocks a fast and environmentally sensible practice that has unfortunately yet to reach us.

Insulation Materials

Cavity walls can be insulated using a fully filled loose material, such as blown glass wool or rock wool, or poured perlite beads. Filling with these products is best done after the walls are constructed, to avoid the constructional and energy conservation problems associated with trying to insulate a wall as it is being built. Rigid insulation boards made of plastic foams such as urethane and phenolic foam offer thermal benefits (less thickness for the same insulating value) and now have zero ozone depletion potential, however, they must be installed properly without gaps to ensure air tightness.