Low Energy House - What is Urethane Insulation?
Urethane insulation boards can achieve very low U-values with a minimum of material thickness. PUR can provide reliable long term energy savings for houses and meet the current and future requirements of the Building Regulations and the Code for Sustainable Homes
Rigid urethane is a term that covers several products incorporating Polyurethane (PUR) and Polyisocyanurate (PIR) . Most rigid urethane insulating products are manufactured from a mixture of the two materials to combine the chemical benefits of both.
Polyurethane (PUR) insulations are manufactured by chemical reaction between polyalcohols and isocyanates.The mixed components give off heat when they react and form a rigid thermosetting polymer. The heat given off evaporates a volatile liquid blowing agent contained in the mixture which produces a network of small bubbles in the material. The gas from the blowing agent remains in the cells and serves to improve the thermal performance of the material.
The foam can be cured to create one of two forms of the product. It can be manufactured by a continuous process to create thin sheet material which is laminated with various facings and cut into boards. Alternatively, it can be made into foam blocks to be cut into pre-determined shapes.
Polyisocyanurate (PIR) Production
Polyisocyanurate (PIR) is produced by the same manufacturing process as that used in the manufacture of polyurethane (PUR) but different ratios of the components are used. As a result, isocyanurate is formed which gives the material greater heat stability. Polyisocyanurate (PIR) is similar to polyurethane but can contain long strand glass fibres within the PIR core which is formulated to give off less dense smoke in fire.
Polyisocyanurate (PIR) insulation products exhibit increased fire performance, reduced combustibility and higher working temperature limits. When incorporated into building products they can meet some of the most demanding fire performance requirements.
Urethane Insulation - Blowing Agent
In order to comply with EC regulations, blowing gases should be CFC and HCFC free (zero ozone depletion potential) and have low global warming impact. The most common blowing agent used in this type of insulation production is pentane. Pentane is a hydrocarbon which has similar properties to those of butane and hexane. It is the most volatile hydrocarbon that is a liquid at room temperature. There is a slight risk that over time the blowing agent may escape and be replaced by air. In order to help eliminate this risk, as part of the manufacturing process, the rigid boards are faced with, gas tight, aluminium foil or glass tissue.
Urethane Insulation Boards
Urethane insulation boards are mainly used to insulate flat and pitched roofs, to partially fill cavity walls, as under-floor insulation in dwellings and in foamed composite panels. They can be used as a laminate with gypsum plasterboard to produce dry-lining wallboard.
Thermal Performance of Urethane Insulation
Rigid urethane insulation products offer good insulating properties due to the very low thermal conductivity of urethane foam. Heat passes through the board at a very slow rate which allows relatively thinner, lighter, less costly, roof, wall and floor construction.
Urethane insulating boards can achieve very low U-values with a minimum of material thickness. They can provide reliable long term energy savings for houses and meet the current and future requirements of the Building Regulations and the Code for Sustainable Homes
Urethane Insulation - Foil Facings
The reflective foil, if installed correctly, can also act as a radiant barrier that adds greater thermal resistance to the insulating core. The low emissivity facings improve the thermal performance when positioned next to an un-vented airspace. This makes the material particularly effective when it is used to partially fill cavities in external walls.
Thicknesses of Urethane Insulation
Urethane foam is mainly available in board form but can also be spray applied on site in domestic projects. Urethane boards are lightweight and exhibit very good insulating performance. Boards to insulate walls and floors and roofs are available from 50mm to 200mm thick. Multi-purpose PIR insulation board, that has been developed to provide convenient solutions for the elimination of localised thermal bridging, comes in thicknesses ranging from 12 to 45mm.
Physical Qualities of Urethane Insulation
- Compressive Strength
Rigid urethane insulation provides a high level of compression and sheer strength.
- Water Resistance
Moisture has a minimal effect on thermal performance. The water vapour permeability of rigid urethane insulation is low; it is also enhanced by the metal facings which act as a moisture barrier.
- Material Resistance
Rigid urethane foams are resistant to fungus and mould growth and will not sustain vermin.
- Heat Resistance
Rigid urethane can withstand constant temperatures up to 75 degrees C but are combustible.
Rigid urethane is a combustible material producing high volumes of smoke in fire. Polyisocyanurate (PIR) insulation products exhibit increased fire performance, reduced combustibility and higher working temperature limits. Insulation materials are rigorously tested to British Standards and fire performance data, to meet the requirements of building regulations, is generally available from manufacturers.
Rigid urethane is dimensionally stable and can be cut accurately to achieve a snug fit in situations such as between rafters where airtightness will be improved.
Rigid urethane is non-biodegradable. The waste material can be put back into the manufacturing process for re-use.
Thermal Performance of Urethane Insulation
The thermal conductivity of rigid urethane foam is usually within the range 0.023 to 0.019 W/m K at 10 degrees C. The thermal conductivity of rigid polyisocyanurate foam is usually within the range 0.025 to 0.023 W/m K at 10 degrees C.
In the UK, when comparing the thermal values of insulating materials, it is important to remember that the best performing material is the one with the lowest thermal conductivity value
About Urethane Insulation - Rigid Urethane Insulation - (PUR)