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Building envelope thermal insulation

Thermal insulation is an important technology to reduce energy consumption in buildings by preventing heat gain/loss through the building envelope. Thermal insulation is a construction material with low thermal conductivity, often less than 0.1W/mK. These materials have no other purpose than to save energy and protect and provide comfort to occupants. Of the many forms, shapes and applications of thermal insulation, this section focuses on those that are commonly used for building envelopes– i.e., floor, walls and roof, and have potential for South-South technology transfer. These include industrial insulation products and the application of natural elements as thermal insulation.

See also 'insulation in buildings' for other insulation options in buildings, such window and door insulation.

Introduction top

Industrial insulation products are largely classified into three groups – mineral fibre, cellular plastic and plant/animal derived.

Mineral fibre products include rock wool, slag wool and glass wool, which can be sourced from recycled waste. These materials are melted at high temperatures, spun into fibre and then have a binding agent added to form rigid sheets and insulation batts. If removed in appropriate conditions, mineral fibre can be reused and recycled at the end of its life.

Cellular plastic products are oil-derived and include rigid polyurethane, phenlic, expanded polystyrene, and extruded polystyrene. The products are available as loose fill, rigid sheets and foam. In the past, the production process involved ozone depleting agents, such as HCFCs. However, the production process has switched to using neutral hydrocarbons. As such, when sourcing cellular plastic insulation products, it is important to ensure the specified products have production processes that do not use ozone depleting agents. Cellular plastic products can be recycled but it is a cumbersome process. It is more suitable for cellular plastic products to be incinerated for energy recovery at their end of life.

Plant/animal derived products include cellulose fibre, sheep wool, cotton, and flax. These products have low embodied energy, as the materials can be sourced from renewable raw materials. The products are in the form of fibre, batts or compressed board. Their production involves chemical treatment to ensure appropriate properties, such as fire resistance and no vermin infestation. As such, at the end of life, it is difficult to use it for energy recovery through incineration.

Building envelope thermal insulation is a proven technology that contribute to energy efficient buildings. Two new trends have recently been observed in the development of thermal insulation – the development of phase change materials (PCMs) and innovative use of raw natural elements as thermal insulation.

Phase change materials (PCMs) work based on the latent heat storage principle. “When temperature rises, the temperature of a latent heat store does not increase but the medium changes from one physical state to another, and by this means it stores energy. Therefore the take up of energy cannot be detected by touch. The temperature only rises detectably after a complete change of phase has taken place. When a change takes place, the latent heat involved is equal to the heat of melting or crystallisation of the storage medium. The advantage of PCMs is that large amounts of heat or cold can be stored within small temperature ranges.” (Hausladen et al., 2005).

Because phase changes between solid and liquid, PCMs (such as paraffin) have to be encapsulated prior to use. Paraffin-based PCMs have melting points ranging from 24 to 26°C and are mostly used to prevent heat gain in hot weather conditions (Hausladen et al., 2005). Encapsulated paraffin PCMs are mixed with mortars applied on building envelopes. Used in combination with night cooling strategies, PCMs can be effective in preventing heat gain through the building envelope. At present, PCMs are at the research and development, and test bedding stage. PCMs are promising technologies because they are lightweight, easy to apply and blend in well with conventional construction methods.

The second development trend of thermal insulation is the innovative use of raw natural materials as thermal insulation. An example is the use of untreated straw bales as insulation. In order to overcome a firehazard issue, straw bales are sandwiched between fire-resistant cladding materials, such as metal-based cladding, or glass panels to create aesthetic effects by making straw bales visible. Another natural element used as thermal insulation is air, which has a thermal conductivity of about 0.025W/mK. Its application is often found in the provision of an air gap in cavity wall construction to enhance thermal insulation performance (see figure 1). Use of air gaps is not sufficient for buildings in temperate regions, but could be sufficient for buildings in mild climate conditions.

illustration © climatetechwiki.org

Figure 1: Air gap used in conjunction with insulated timber-brick wall.

Feasibility of technology and operational necessities top

In developed and industrialised countries, building codes include requirements to safeguard minimum acceptable insulation levels for building envelopes, and thus provide the opportunity for deploying the application of thermal insulation technologies. However, this is usually not the case in many developing countries, especially least developing countries and remote rural areas. Therefore, a critical factor leading to large scale implementation of thermal insulation in these countries is to put in place supporting policies, both incentive and mandatory measures.

In addition, the cellular plastic production process mentioned earlier involved the use of ozone depleting agents, such as HCFCs, which have switched to using neutral hydrocarbons. When sourcing cellular plastic insulation products, it is important to ensure that the specified products with production process are not associated with ozone depleting agents. It is more effective if local regulations are in place to ban products with production processes associated with ozone depleting agents.

The application requirements of most building envelope thermal insulation products include appropriate detailed design, good workmanship and appropriate product selection, handling and installation methods. Therefore, capacity building, such as workshops to train design professionals and construction work forces in these areas are required.

Building envelope thermal insulation products are used in association with the construction details of floors, walls and roofs/ceilings for new building constructions and for retrofitting existing buildings.

Unlike the straightforward process of incorporating building envelope thermal insulation in new buildings, when retrofitting existing buildings it is crucial to identify suitable locations to include thermal insulation. The key locations are:

  1. Roof: to insulate with rigid boards or quilt between or under rafter or joist level.
  2. Roof space (in temperate regions): to provide ceiling with rigid insulation-backed plaster boards.
  3. Solid masonry or concrete walls: to insulate on the external with rigid boards then covered with water-resistant cladding materials; and to provide internal lining with rigid insulation-backed plaster boards.
  4. Cavity walls: to inject with loose-fill fibre; and to provide internal lining with rigid insulation-backed plaster boards.
  5. Concrete floor (in temperate regions): to insulate with rigid board under new screed and floor finish.
  6. Raised timber floor (in temperate regions): to insulate with rigid board or quilt between or under floor joists (XCO2, 2002).

For both new construction and retrofitting existing buildings, it is important to understand and provide the conditions for thermal insulation products so that they can achieve their expected performances over their life span.

  1. Mineral fibre products are available in batts, rolls and loose. They can be applied in off-site and insitu construction. Due to the open structure, the products are air and vapour permeable, which can reduce their thermal insulation performance. It is, therefore, necessary to provide foil backing and good workmanship to prevent the product from being exposed to vapour and water. This can often result from condensation occurring between the external wall panel/layer and insulation layer, and/ or leaking water pipes that are built inside the wall.
  2. Cellular plastic products are considered to be long-lasting materials. The products are not susceptible to decay or vermin infestation. Besides rigid sheets, cellular plastic products can be in the form of foam, which is applied to the building envelope through spraying. Spray foam insulation is applied as liquid, using a hose and spray gun. It is a combination of two substances that blend upon contact, and after a few seconds become a thick foam. The insulation can be sprayed after electrical and plumbing services are in place, as it expands during curing, sealing all gaps.
  3. Plant/animal derived products are most susceptible to vermin infestation. Although chemical treatment is often provided in the manufacturing process, the chemical treatment can leach out if the products are wet or exposed to high humidity conditions. Preventive measures include provision of backing, good workmanship, and avoid applying the products in wet and moist conditions.

Good detailing and workmanship to prevent air leakage are crucial for all types of building envelope thermal insulation. It is important to pay additional attention to detail, when installing insulation materials at the electrical outlets and wiring inside walls, cutting and shaping the insulation materials to tightly enclose with the wall frame.

Furthermore, as an overall quality control measure for building in extreme climatic conditions, it is recommended to have building envelope commissioning with attention paid to thermal insulation, especially in larger-scale buildings.

Status of the technology and its future market potential top

Building envelope thermal insulation products have been widely used in temperate regions. In many developed and industrialised countries, thermal insulation is a regulatory requirement for energy efficiency and occupant health purposes, which provide a fairly constant market for the thermal insulation manufacturers. The market for building fabric thermal insulation products is not as large in hot and humid tropical regions, where natural ventilation, not air-tightness, is a more appropriate strategy for thermal comfort. In this context the use of thermal insulation is not extensive, and the use of an air gap in the cavity wall for the west facing façade to prevent heat gain from hot afternoon sun is found to be sufficient. Roof insulation, however, is applicable in all climate regions, including the hot tropical bell. In the Caribbean, for example, roof insulation has generally been accepted as a “proven energy conservation solution” with mineral (glass) fibre generally the lead product.

How the technology could contribute to socio-economic development and environmental protection top

The primary contribution of building envelope thermal insulation is to provide thermal comfort to its occupants. This supports healthy living environments and better productivity at workplaces.

Thermal insulation reduces unwanted heat loss or heat gain through a building envelope. This, in turn, reduces energy demand for cooling and heating of buildings, and thus is a mitigation measure to reduce GHG emissions.

Large-scale implementation of thermal insulation has also been proven to be an economic stimulus. In the European region alone, there were nearly 12,000 companies, with a total of 400,000 employees, operating in the value stream derived from cellular plastic products (ISOPA & Polyurethanes, 2009). There are ample business and job creation opportunities for developing countries, if successful North-South and South-South transfer programmes for building envelope thermal insulation are in place.

Financial requirements and costs top

Financial requirement for building envelope thermal insulation includes the costs of the products and their installation.

The product and installation costs of thermal insulation are computed based on per unit of area and per unit of thermal conductivity value. The installation cost for loose fill products are lower than that of other insulation products, because it is easy to install. However, due to the lack of additional protection from moisture and vermin infestation, long-term durability is a consideration.

Maintenance costs for thermal insulation products is low and not even required for cellular plastic products. In the case of mineral fibre and plant/animal derived insulation, if the products do not perform as expected due to increased thermal conductivity caused by moisture or vermin infestation, replacement is required.

For naturally-ventilated buildings in mild climatic conditions, roof insulation and west-facing wall insulation are the most effective methods of preventing heat gain through the building envelope, and thus have better return on investment compared to applying insulation to the entire building envelope.

Use of straw bales and air gaps (in cavity walls) incur insignificant cost, except for the thickness of the wall. However, long-term performance is an issue to look out for. In developed and industrialised countries, mineral fibre products are cost competitive compared to cellular plastic and plant/animal derived products. However, in developing countries and rural areas, plant/animal derived products are more cost-effective, because of the higher availability and accessibility of these raw materials. Cellular plastic products are rigid, stable and performed well in the long term. They require the least maintenance cost.

References top

Hausladen G., Saldanha M., Liedl P. & Sager C. (2005). Climate Design: Solutions for Buildings That Can Do More with Less Technology. Munich: Birkhauser.

ISOPA & Polyurethanes (2009). Fact Sheet: Saving Energy in Buildings through Thermal Insulation with Polyurethane. [Online]: www.isopa.org/isopa/uploads/Documents/documents/Energy%20Saving%20in%20B...

XCO2 (2002). Insulation for Sustainability – A Guide. [Online]: www.pu-europe.eu/site/fileadmin/Reports_public/sustainability_a_guide.pdf