Timber Sheet Materials

The 10-Minute Offer for Apartment Buildings

Investing in Apartment Buildings

Get Instant Access

Basic info is found in Chapter 10.

Timber products can be used anywhere in a building where surfaces need to be covered; as whole timber, as an ingredient in laminates and composites for sheeting, as natural rubber flooring or as cellulose for wallpapering (wallpapering is discussed in a separate section at the end of the chapter).

Whole timber can be used to cover roofs as shakes, shingles or planks (Table 15.7). As cladding it can be used as panelling or wattle,

15.16

Plants used for air cleaning In a combined office and apartment building in Nurnberg (Germany). Architect: Joachim Eble, 1997. Photo: Dag Roalkvam.

15.16

Plants used for air cleaning In a combined office and apartment building in Nurnberg (Germany). Architect: Joachim Eble, 1997. Photo: Dag Roalkvam.

15.17

Potted plants with air cleaning properties: (a) peace lily and (b) spider plant.

15.17

Potted plants with air cleaning properties: (a) peace lily and (b) spider plant.

and as flooring it can be used as planks, parquet or timber cubes. Sheets and boards are produced in forms including fibreboard, cork, chipboard and veneer. The first two of these have their own glue in the raw material which allows them to form the boards; the latter two need added glue. Today these synthetic adhesives are usually based on formaldehyde, polyurethane or phenols added in a proportion of 212% by weight. Laminated products are also made with chipboard in the middle and have a veneer surface; or a different type of plastic coating, sometimes finished to look like timber. Natural rubber flooring is a product made from latex extracted from the rubber tree (Ficus elastica) with added fillers, stabilizers, colour pigments, etc.

All types of timber, both softwood and hardwood, are used with few exceptions. Products made of chipboard have no particular requirements and can even be made from minced demolition timber. The substances used for glue in the production process and the impregnation materials used in external timber cladding can come from questionable sources (see Chapters 17 and 19).

Timber is often a local resource, and all surface materials made of whole timber can be made locally. Timber is treated best at small mills. It is clear that timber needs human attention, and there are limits as to how mechanized sawmills should be. In whole timber products, 50 to 60% of the trunk is normally utilized, while in particle boards and fibre-boards this is often more than 95%.

The energy consumption in production varies from product to product, but is generally low to moderate, with the exception of complicated composites rich in plastics, and some fibre-boards that need a high temperature drying process. The amount of energy needed in the production of natural rubber flooring is about half of the equivalent synthetic rubber products.

Since trees bind carbon dioxide from the atmosphere, all wood-based products store carbon in the finished buildings and for as long as they last. This represents a useful buffer against global warming.

There are generally few environmental problems relating to the production processes at sawmills or joinery shops. Wood dust can, however, be carcinogenic; this is particularly the case for oak and beech. Synthetic glues and impregnation liquids can pollute the working environment as well as the immediate natural environment, as effluent in either water or air.

Table 15.6 The absorbtion of formaldehyde CH2O by different plants with a total leaf area of 0.5 m2 during a day and a night (24 hours)

Species

Absorbtion (1CT3 mg/24 h)

Banana (Musa)

57

Ivy (Hedera helix)

48

Tri-leaf philodendron (Philodendron spp)

23

Spider plant (Chlorophytum comosum)

19

Devil's ivy (Scindapsus aurea)

Devil's ivy (Scindapsus aurea)

Table 15.7 The use of solid timber as surface materials

Species

Roofing

External cladding

Internal cladding

Flooring

Alder

x

Ash

x

x

Aspen

(x)

x

x

x1

Beech

x

x

Birch

x

x

Elm

x

Juniper

x

Larch

(x)

x

(x)

x

Lime

x

Maple

x

Oak

(x)

(x)

(x)

x

Spruce

x

x

(x)2

Scots pine

x

x

x

x

1 Not so hard-wearing, but soft and warm.

2 Increased wearing when painted or varnished.

1 Not so hard-wearing, but soft and warm.

2 Increased wearing when painted or varnished.

Timber is generally favourable in the indoor environment, having good moisture-buffering properties, but these are often eliminated by treatment with synthetic varnishes or vapour-proof paints. Untreated timber has good hygienic qualities. It proves to have far less bacterial growth on its surface than the equivalent plastic surface.

Softwoods can release small amounts of natural formaldehyde for some time after installation, but this is not known to cause problems for people with allergies (Englund, 1997). Cedar contains thujaplicines which are known allergens and should not be used internally.

Glued products can emit a wide range of gases into the indoor air. Glues of polyurethane (PU) and methylene diphenyl diisocyanate (MDI) can emit small quantities of isocyanates; while glues of urea-formaldehyde (UF) emit formaldehyde. Emissions increase with temperature and humidity. UF glues have little resistance to moisture and - if they become damp during transport, on site or when painted with a water-based paint - the boards will give off much higher emissions than a factory dry board. Cork products coated with polyvinyl chloride can emit volatile compounds associated with polyvinyl chloride.

Timber impregnated with heavy metals or creosote should not be used in greenhouses or on roofs, where rainwater passing over the timber runs into soil for cultivating food. Handling of creosote impregnated materials can cause eczema on the hands and feet even without direct contact. Bare skin has to be protected. Creosote can also damage the eyes, and cause more serious damage to health.

Durability is dependent upon the climate, the quality of the material and the workmanship, but is generally good as long as the timber is not overexposed to moisture (see Table 10.9). However, artificially fertilized and quickly grown timber is less durable. Timber roofing is not suitable for damp climates with large variations in temperature. As a result of expected climate changes, the risk of damage will probably increase in Northern and Eastern Europe during the present century.

Technically, all sheeting and boarding can be re-used when fixed in such a way that removal is simple. In practice, this is more viable with internal cladding. Exterior timber boarding panels or timber roofs are exposed to the elements and get worn out over the years, so there is often little left of value. There is also little potential for re-using wood-based boards, with the exception of carefully mounted high quality fibreboard and plywood. In theory, many of the more worn products can be ground for new production of particle board.

Solid timber and fibreboard that is untreated, or treated only with natural products such as linseed oil, can be burnt for energy recovery in normal boilers or composted. Glued products and products laminated with plastic materials have to be treated as special waste and incinerated in boilers with special filters. Impregnated products must be incinerated at especially high temperatures; and is often transported to cement factories where the oven temperatures are sufficiently high to break down most of the toxic compounds. This often implies long transport distances and is, from a purely energetic point of view, probably not worthwhile. Combustion residues must be specially taken care of. All wood waste, even though natural, can lead to an increase in the nutrient level of the water seeping from the tip.

Was this article helpful?

0 0

Post a comment