Structural Protection Of Exposed Components

19.1

Protective principles for outdoor use of timber (balconies etc.); a-b: Exposed tangential sides; c-d: Exposed radial sides, but the pith and the juvenile wood will make the wood shake and deform; e-h: Exposed radial sides without pith. Source: Trainformation, Sweden.

19.1

Protective principles for outdoor use of timber (balconies etc.); a-b: Exposed tangential sides; c-d: Exposed radial sides, but the pith and the juvenile wood will make the wood shake and deform; e-h: Exposed radial sides without pith. Source: Trainformation, Sweden.

19.2

Protective splicing of vertical panelling. Type (a) and (b) are highly protected while type (c) will easily shake and crack, especially around the nails. Source: Tratek, Sweden.

19.2

Protective splicing of vertical panelling. Type (a) and (b) are highly protected while type (c) will easily shake and crack, especially around the nails. Source: Tratek, Sweden.

If buildings have been constructed with materials so that air circulates easily, and keeps them dry, then fungus will not attack.

All types of timber should be used in a way that allows movement to take place; otherwise splitting and gathering of moisture will occur. The heartwood side, which is generally the least moisture absorbent, should be on the outside (Figure 19.1). Moisture is usually most quickly absorbed at the ends of the timber. The end grain must therefore be protected. Exposed ends of beams can be cut at an angle or preferably covered.

Panelling should be well ventilated. The more exposed a wall is to driving rain, the wider the air gap behind the panelling should be; this is usually 5 cm in very exposed areas, and about half that in normal inland situations. Horizontal battens fixed directly to panelling should have a sloping top side, or be mounted on a vertical batten system against the wall. The distance of the panelling from the ground should be at least 20-30 cm.

The bottom end of vertical panelling should be sawn at an angle so that drops are formed and let off on the outside face of the timber (Figure 19.2). The root end should be pointing downwards as it contains more heartwood. Water may collect in the joint between the two layers of vertical panelling. Along the coast where there is plenty of driving rain, this often results in rot, as drying periods can be very short-lived. On the coast, panelling should therefore be horizontal. This also gives the advantage of less exposed end grain. Rot usually occurs at the bottom of the wall, and with horizontal panelling it is quite easy to remove and replace a few planks; with vertical boarding all the planks would be affected.

In particularly damp areas, the colour given to the surface can also play a part. A dark ochre colour can reach a temperature of up to 40 °C higher than a white surface in sunny weather. This can be a significant factor for drying times. In damp places where, even during the summer, there are only short periods of sun between showers, the drying time needs to be as short as possible. However, if the temperatures get too high, splitting or cracking can occur, which can also increase the intake of moisture.

Combinations of wood with metal, lime and cement-based mortars and concrete can cause problems. Condensation can occur around metal components, while in combinations with cement and lime, alkaline reactions can arise which increase porosity and moisture absorption in the timber.

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