More About Sustainable Maerials

Materials for the SEED Houses have been carefully selected with sustainability as the primary criteria.


The use of timber has many environmental advantages. Unlike metals or quarried products, timber is a renewable resource. Forests provide important habitats, trap air pollution, emit oxygen, reduce soil erosion, and reduce flooding by slowing run-off into watercourses. Forests are also a vital carbon sink –
an average tree absorbs 9.1 kg of CO2 per year, as much as that emitted by a car traveling 11,000 miles. This carbon remains locked up in the wood until it is burnt or allowed to decompose meaning that timber building can contribute to carbon sequestration and to reducing the impacts of climate change. Compared to many other building materials very little processing is needed to prepare timber for use as a building material and this means that wood intrinsically has low embodied energy. Wood has very low toxicity and has good moisture handling abilities; it is also very durable when carefully used. The oldest timber building in the UK is an 11th century church in Essex.

There are disadvantages to using timber however, irresponsible forestry practices cause serious  environmental problems worldwide and the transportation of timber over long distances adds greatly to energy costs. SEED insists that the timber used in our buildings is sustainably produced and produced as locally as possible. All our timber is certified by the Forestry Stewardship Council (FSC), which is an independent environmental auditing body, who promoting responsible management of forests by issuing  certificates for responsibly and sustainably produced timber and timber products. In addition to this, all the structural timber for our projects is Spruce, a timber species which has until now been considered of limited value for construction, but which is very abundant in mature forestry in Wales. For finishing materials we use more durable timbers, namely Larch for the rain screen and Douglas Fir for joinery.

Warmcel cellulose insulation is a loose fill insulation that is made in Wales from recycled newspaper and treated against fire and vermin using naturally occurring mineral salts. Warmcel provides a good level of insulation with the added advantage over batt insulation of being blown into the structure, filling the voids entirely and avoiding gaps where cold spots could occur. Warmcel also has good acoustic qualities and we are anticipating very good results from acoustic testing.


The choice of roof material reflects a sanguine approach to sustainablility. Despite the high embodied energy of steel,when the thinness of the product is taken into account the embodied energy per m2 is around half of that of clay tiles . In addition to this, the lightweight nature of steel roofing means that less material is required to form the structure of the roof.


The choice of membranes has been carefully considered to provide a fully breathable wall structure. Following the 5:1 outside to inside rule we are using Tyvek Reflex as the outer breather membrane and Tyvek SD2 as the inner airtightness/vapour check membrane. Condensation Risk Analysis has shown that there is no risk of interstitial condensation while trapped moisture is allowed to escape from the wall structure and internal condensation is avoided.


Glass is made from naturally accruing sands but has high embodied energy. We have used high specification low E-argon filled double glazed units to maximizes the thermal properties and long term performance which is much better than acrylic alternatives.


Synthetic paints and coatings pose known health risks and are environmentally damaging. The use of natural paints is safer for the environment and human health. Many ingredients are from renewable sources and they allow natural substrates to breathe.