How to choose thermal insulation for the house

There are many materials for insulating your home. Some of them, such as polystyrene or glass wool, we've known for years. Others, like jute, wool, hemp, cork, are new, natural materials that we hear more and more about these days. Things are changing worldwide, and in addition to the actual insulating characteristics of the material, new criteria are emerging. It becomes important how the material is produced, whether it is made from renewable materials or waste, how the carbon dioxide balance is or whether the material is recyclable. However, thermal insulation must meet certain conditions to be considered effective. Let's see which parameters are important in an insulation and how to choose the best natural thermal insulation.

Why houses need to be insulated

Thermal insulation of houses is necessary to minimise heat loss in winter and prevent heat from entering in summer. As well as increasing comfort, this means reducing the energy costs needed to heat or cool your home.

Insulation can be done during the construction of the house. About passive houses built to reduce energy costs down to 90% we have just learned. But there are also special materials used in the construction of houses that reduce heat loss. For example Thermibloc from France has created a building material from mineralised wood chips into which thermal insulation materials can be embedded. This material is in the form of blocks, similar to BCA. So the house will have ready insulated walls from the moment of construction.

Also in the range of building materials that also have insulation purposes are thermal insulating plasters. Their manufacturers claim that when they are used the walls are better thermally insulated. There are, however, opinions that they are not very effective and much more expensive compared to traditional insulation methods (e.g. mineral wool).

All types of houses, whether concrete, brick or BCA, need thermal insulation. Wooden houses also need insulation, although wood is a good thermal insulator. Round log houses or rectangular need insulation at structural joints between elements. Timber-framed or prefabricated houses need insulation at the roof, between rafters, in the attic, between the layers forming the walls.

Parameters according to which thermal insulation is chosen

Thermal insulation materials, natural or not, are chosen according to performance, and this is determined by several parameters:

• thermal conductivity - determines the ease with which heat passes through the material. The lower it is, the better insulator the material is. It is also called the lambda value (λ) and is expressed in W/mK;
• thermal resistance - this is the parameter that relates conductivity to the thickness of the insulating material. The resistance value is given by the ratio of the thickness of the material to its thermal conductivity. Thermal resistance is therefore inversely proportional to conductivity and the higher the thermal resistance, the better the insulation material. Unit of measurement: km²/W;
• Thermal diffusivity - is the ability of a material to conduct heat relative to its storage (e.g. metals transmit quickly, wood slowly). For insulators this parameter should have a low value. Unit of measurement: m²/s
• density - a high density material has a high total weight which means it has low thermal diffusivity; kg/m³
• vapour permeability - measures the ability of a material to allow water vapour to pass through it. Thermal insulation must be vapour permeable. Wood-frame houses have an even greater need for insulation materials to allow moisture transfer. Otherwise mould will develop and the next step is wood rot, which affects the strength structure.

A newer criterion, but increasingly taken into account, is the carbon dioxide balance. It is also known as bound carbon. It is not a criterion related to insulation performance but to the gases that lead to global warming. It is a ratio showing how much carbon dioxide was released into the atmosphere during the production of the insulation material compared to that absorbed by the raw materials from which it was made. In this respect, insulation produced from renewable plants has a positive balance.

Natural thermal insulation

The most popular natural materials for insulating houses are wood fibre boards, wood fibres, sheep's wool, hemp, jute, cork, recycled cellulose. There are others - seaweed, straw, corn cobs - but they are used occasionally. But the others have become industrially manufactured insulation products and are easy to use.

Wood fibre boards and independent fibres

Insulation is the result of using waste from the wood industry. The fibres are obtained by a chemical process that partially removes lignin, the substance that stiffens wood. The result is a kind of wood wool that can be used as individual fibres or pressed into slabs.

Wood fibres are used to insulate hard-to-reach places and need special installations and specialists to fit them. The plates are mainly used for external insulation because they are more rigid and can be easily fitted. This stiffness also means that they can be combined with other natural materials in the form of mattresses (hemp, wool) to make them stiffer and easier to fit.

Insulation parameters: thermal conductivity - 0.38; resistance - 2.5; density - 160 for boards and 50 for fibres. It is vapour permeable, so suitable for wooden houses.

Sheep wool

I have often wondered why Romanian shepherds throw wool away instead of finding a way to use it, and insulation seemed to me one of the best ways to use it. Studying more about wool insulation, I understood that wool goes through many operations and transformations before it gets there, which means labour and energy consumption.

The wool is collected, cleaned, washed and then pulled into thin mats of yarn. All this must be done without the use of dangerous chemicals (harsh detergents). To be made into insulation it is mixed in the proportion of 5-10% with recycled polyester adhesive and boric acid salts (in the proportion of 2-3%) for protection against pests. Wool insulation is available in rolls of various thicknesses.

Thermal conductivity is o.038; thermal resistance: 2.63; density: 23 and it is vapour permeable.

Hemp

Hemp is an industrial plant that has long been used as a fibre for natural fabrics. That used for fabrics is different from hemp used as a drug.

Hemp grows fast, reaching 4 m in height in 3-4 months. The leaves are large and shade the soil, so herbicides are no longer needed to protect the crop. This is why the hemp fibres obtained are free of dangerous chemical compounds. As with wool, up to 10% recycled polyester adhesives are added to hemp insulation. For fire protection, 5% sodium salts are added.

It is found in the form of rollers or mattresses of different thicknesses. Conductivity: 0.039-0.040; resistance: 2.5; density: 25-38; vapour permeability

Jute

Jute is an annual plant that is grown mainly for the fibres obtained from the stem. They are used to make string, rope, carpet yarn and sackcloth. Jute insulation has recently appeared. It's made from recycled jute sacks used to transport cocoa beans, and the idea was the brainchild of chocolate maker Ritter. Its emergence has a beautiful story, which you can find here here. Tests have shown that is the best summer insulationcompared to all products on the market.

Jute fibres are used to make insulation in the form of mattresses that are easy to fit, do not cause irritation and do not rot. The thermal conductivity is 0.038; the strength: 2.63 at 100 mm mattress thickness and density 34-40. It is vapour permeable.

Pluta

Pluta is actually the bark of an oak tree that grows in the Mediterranean area of western Europe and northern Africa. The bark is harvested when the trees reach 20-25 years old and regenerates so that after 9 years it can be harvested again. Such oaks live for around 200 years.

The main producer of cork products is Portugal. Natural cork stoppers of the highest quality are obtained from the thick bark and the thin bark is processed into granules. From these granules cork boards are made.

And plugs are made from the plates. Only 25-30% of a plate's surface area is used for plugs, the rest is waste. From these losses the idea of an insulation material was developed. The scrap is cut into thin strips and pressed. During pressing, suberin, a natural binder, is released, which holds the strips together to form slabs of different thicknesses.

Cork insulation has very good insulation properties, both thermal and sound insulation and vapour permeability. Conductivity 0.36-0.38 and density 110-120. Unfortunately I could not find any information about thermal resistance.

Recycled cellulose insulation

It's basically recycled newsprint. The newspapers are shredded very finely and mixed with sodium salts, which give them fire resistance, and non-hazardous organic substances (such as boric acid salts) for resistance to mould and insect attack. Insulation is similar to individual wood fibres, so they are applied using special installations that distribute them evenly in the tight spaces being insulated.

Thermal conductivity is between 0.38 and 0.40, thermal resistance is 2.63 and density 27-65. It has vapour permeability.

As you can see there are plenty of natural materials for insulating your home. And I haven't told you all of them, but especially the ones you can find in the country. For example Naturalpaint you can find 4 of the materials presented. It's hard to say which is the best insulation for your home because the factors on which the choice depends are many and varied. It is best, when deciding to insulate, to talk at length with your supplier about the advantages and disadvantages of each type and to tell them what you expect from the insulation of your home. This is the only way to make sure you won't be disappointed.