Insulation Properties
is wool really a sustainable insulation?
For insulation values click here
Assuming that the question of designing in enough insulation has been dealt with the question is about what kind of materials to use. Here the issues are -
- moisture
- compressive strength
- is it self supporting?
- is it easy to fit?
- must it be fire resistant?
- must it also be acoustic insulation?
- is it vermin proof?
Moisture
cork is stripped from the cork oak tree about every 9 years
This is probably the first criterion because some insulating materials are not suitable for use if they are in contact with a damp surface (such as a wall which is partly below ground). These include wool, cork, mineral fibre (although fibreglass batts may be OK), and recycled paper fibre. Instead you can use foamed glass or suitable grades of polystyrene or polyurethane.
Compressive strength
Insulation which goes beneath a concrete floor slab or needs to support a roof finish must have the required compressive strength. These tend to be foamed glass, polyurethane and polystyrene.
Self supporting
In some situations (such as the normal cavity wall) the insulation needs to be self supporting over a certain distance so mineral fibre batts would be used rather than quilt.
Ease of fitting
This is most important because poorly fitted insulation regularly shows up as a problem. At its worst it can cause whole areas of a surface to have virtually no insulation value at all and possibly lead to interstitial condensation. Even very small gaps of a few millimetres can cause massive problems. See the article on the five main types of situation where poor fitting can happen.
Fire resistant and acoustic insulation
In many situations the thermal insulation may also serve as fire resistance and acoustic insulation. This is often a complicated matter which is dictated by the building regulations . Suffice to say that if you want to alter the type of insulation from that shown on the drawings which have received building regulations approval then you will probably need expert advice from an architect, building technician (or your building inspector if you are on friendly terms).
Vermin proofing
Problems with vermin have almost disappeared from the public conciousness because of the long history of building mainly with masonry walls and avoiding timber. There is something of a change taking place at present and if timber frame is being used then there needs to be design consideration for excluding vermin. The rule of thumb is that if you can get a pencil into a hole then a mouse can get in. Hence the size of the openings in air bricks. If mice get into fibrous insulation they can burrow for long distances and you may have no way of knowing the routes they are using, let alone controlling them. In theory they may be able to get right round the house. The points of entry in a timber house are likely to be around the sole plate or up through a suspended ground floor. It is worth checking the insulation you intend to use to see if it discourages rodents. For instance Warmcell has been tested and the boron fireproofing also discourages mice. Mineral fibre is a positive paradise for rodent nest building. If in doubt it pays to cover any susceptible areas with plasterer’s lath. This is galvanised expanded metal which will not allow mice through the openings.
Embodied energy
The plastic insulating materials like polystyrene and polyurethane have a high embodied energy but where moisture is an issue there is probably no alternative except foamed glass. Cellulose fibre, cork, hemp and wool have very low embodied energies. Mineral fibres are quite low but still about ten times that of natural materials. See a table of values here . It should be borne in mind that because insulation is mainly light in weight that its embodied energy in a building is a relatively minor factor compared with say masonry.
Sustainability
Cork, hemp, flax, mineral fibre and cellulose fibre are all in good supply and present little threat to the environment. At present hemp is mainly produced on the continent though there are plans to produce it in the UK.
Expanded polyurethane and expanded polystyrene are of course both oil based and cause considerable CO2 pollution in their manufacture.
Wool may cause concern because of the damage sheep do to the countryside and may also be a problem from a vegetarian standpoint as their rearing is intimately bound up with the meat market.
Health
There is a long history of concern over the use of mineral fibres (being inhaled by operatives) in the UK including some local authorities banning their use in the past. However, although many people find working with them unpleasant there doesn’t seem to be any firm evidence of health risks.
