Moss

14.24

Log wall sealed with moss.

14.24

Log wall sealed with moss.

Moss has been used to seal joints in timber buildings for hundreds of years: between the logs in log constructions, around doors and windows and in other gaps (Figure 14.24). The moss has to be used as soon as it has been picked, because it hardens and loses its elasticity as it dries out. It can be boiled before use to reduce the amount of substances subject to attack from micro-organisms. But at the same time, natural antiseptic phenolic compounds found in some mosses can be lost.

Moss stops air penetration when compressed, and it is very hygroscopic. It can absorb large amounts of damp without reaching the critical level for the materials next to the moss.

14.10 BOG PEAT

Two types of moss are especially good in construction: Hylocomium splendens and Rhytriadiadelphus squarrosum. The latter is considered best, as it can last up to 300 years as a sealing material in a log wall without losing its main functional properties.

Peat has been used a great deal as an insulating material and moisture regulator in its natural state or as processed loose material, granules, mats or boards. These days, insulation products of peat are again being produced in Sweden.

Peat usually consists of decayed brushwood, plants from marshes, algae and moss. For building, the most important peat is found in the upper light layer of a bog and has not been composted. Older, more compressed and composted peat from deeper in peat bogs can be used in certain circumstances, but it has a much lower insulation value. Totally black, dense peat is unusable.

There is very little risk of insect and fungus attack in dry peat, as long as it is not built into a damp construction. Peat contains small quantities of natural impregnating toxins such as alcohol. It also has a low pH value (3.5-4), so it retards the spread of bacteria and protects against fungus.

The availability of peat as a resource is quite large but very regional. It is a semi-renewable resource, in the sense that new peat is continually but very slowly being formed from decaying vegetation. Extracting peat easily destroys a wetland environment, as well as releasing large quantities of methane CH4, which is a very potent greenhouse gas.

Peat products can have a long lifetime, but acids in the peat can attack fresh cement mortar. In the indoor climate, peat regulates moisture well. Waste peat can be used directly for soil improvement or combusted for energy production.

Peat blocks are based on peat rich in moss and can be cut from bogs as blocks, dried and used as thermal insulation. It is easily trimmed by sawing for building into walls.

Peat loose fibres are made from dried, ground peat with a little lime added (about 5%) and can be used as loose thermal insulation in floor construction and walls. They are usually blown into the structure in the same way as other loose fill materials.

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