Timber Materials

Basic info is found in Chapter 10.

Timber has many good climatic properties both in its solid state and in a shredded or particle form. Log walls have covered all the climatic functions in Scandinavian dwellings for hundreds of years; timber is wind-proof, it is a good regulator of moisture, and it has a reasonable insulation value. However, even thick log walls do not quite fulfil present insulation standards, which can only be reached by adding extra insulation on the outside. A good insulation value can also be achieved by sufficiently thick massive wood elements (see Chapter 14). This is particularly so where the timber is joined with dowels rather than glue and small air spaces between the boards add insulation value; the boards can be grooved to increase this effect.

When timber is reduced to smaller dimensions, it will gain even better qualities as thermal insulation. Sawdust, shavings and woodwool are available from all timbers. These can be used directly as compressed loose fill. In Sweden, Finland and inland Norway this was the most widespread form of insulation in framed building up to the 1950s. These materials are also made into sheets, slabs and building blocks by adding cement or glue. Woodwool cement boards are much used as acoustic ceilings and baffles. Sawdust, wood shavings and chips can also be used as a lightweight aggregate in earth construction. More finely shredded material, defi-brated wood fibres, provides a basis for highly insulating products, either as loose fill or as glued matting and boards. In some board products the wood particles themselves provide the

Table 14.7 Acclimatizing qualities of wood products

Materials

Composition

Areas of use

Massive wood constructions1

Untreated timber

Thermal buffering, moisture buffering, sound insulation, thermal insulation3

Timber panelling and flooring2

Untreated timber

Moisture buffering

Cork, loose fill and boards

Granules of cork oak. Boards are glued with bitumen, gelatine etc.

Thermal insulation, moisture buffering, sound insulation

Sawdust and wood shavings, loose fill

Wood particles, possibly with whey, soda etc. added

Thermal insulation, moisture buffering, sound insulation

Woodwool cement

Woodwool, sodium waterglass, cement, water

Thermal insulation, moisture buffering, sound insulation

Wood fibre, loose fill

Defibrated wood fibre, ammoniumphosphates, possibly borates

Thermal insulation, moisture buffering, sound insulation

Wood fibre matting

Defibrated wood fibre, glued with starch or polyolefins (melted), additives4

Thermal insulation, moisture buffering, sound insulation

Porous wood fibre boards

Defibrated wood fibre, glued with lignin, polyurethane bitumen etc., additives4

Thermal insulation, moisture buffering, sound insulation, wind barriers

Hard wood fibre boards2

Defibrated wood fibre, glued with lignin, phenol formaldehyde, polyurethane etc, additives4

Vapour retarders, air barriers

Cellulose fibre, loose fill

Recycled cellulose fibre, borax, boric acid

Thermal insulation, moisture buffering, sound insulation

Cellulose fibre, matting

Recycled or virgin cellulose fibre, glued with polyolefines or polyesters (melted), additives4

Thermal insulation, moisture buffering, sound insulation

Cellulose building papers and sheets

Recycled or virgin cellulose, sheets are laminated with polyvinyl acetate etc., possible additives of latex, bitumen etc.

Vapour retarders, air barriers, wind barriers

Discussed in Chapter 13, Structural materials. ! Discussed in Chapter 15, Surface materials.

Depending on construction method. * See page 280.

Discussed in Chapter 13, Structural materials. ! Discussed in Chapter 15, Surface materials.

Depending on construction method. * See page 280.

glue, lignin, during the process when the boards are manufactured under heat and pressure. Defibrated wood fibres are also used as a basis for cellulose products, see page 289.

The bark of some trees can also be of use as a climatic material. Bark from cork oak provides high quality thermal insulation. Bark from birch has been one of the most common waterproofing materials throughout history, especially as an underlay for roofs covered with turf.

Extracts from both coniferous and deciduous trees can also be used for waterproofing and impregnation.

Sustainable forestry and replanting schemes ensure that timber resources are renewable. Many of the products are even based on waste such as sawdust and wood shavings. However, some of the glues, flame retardants and fungicides used have a doubtful environmental profile.

The energy use in timber production processes varies a lot from product to product, but it is generally much lower than similar products in other materials. Exceptions include wood fibreboards that require high process temperatures, and woodwool slabs which comprise a high proportion of cement.

Pollution arising in the different levels of production, usage and waste is relatively small. In this picture, the ability to store carbon should also be accounted for.

Timber-based climatic materials can generally be considered as durable and stable. If treated with care, the denser board, block and slab products can be re-used. This is, in principle, also the case for loose fills that can be sucked out and used in new constructions. Pure wood can be recycled as raw material for the production of particle boards and even for certain wood fibre products.

All timber products can be recycled for energy. This potential is somewhat reduced in the case of products containing cement or where fire retardants have been added. Glued products and products treated with fungicides, flame retardants and similar, often require combustion in furnaces having high quality flue gas cleaning. This is unnecessary for pure timber products. These can also be composted, as long as the process is controlled to avoid potential eutrophicating effluents.

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