HEAT INSULATION FOR A GREEN BUILDING
In our climates, whether we build new buildings or undertake renovations, seeking the maximum possible reduction in heat loss (thermal efficiency) is one of the main points to take into account in the green building approach. This reduction in heating requirements, absolutely necessary in light of economic, demographic and environmental indicators, is achieved by a three-pronged approach – “sobriety, efficiency and renewable energies.” In relation to the current trend of increasing energy needs, this approach will enable us to reach the “factor 4” objectives (commitment by western governments to reduce their CO2 emissions by a factor of 4 by 2050), by acting on three levers in a precise order, which is implemented as follows in the construction industry:
• First of all sobriety: Through architectural design that will save space (to be built and heated), reduce heat-loss surfaces, capture and manage free sun heating in winter, protect from the sun in summer. This sobriety in design is backed up by sobriety in use, which is also a major factor in reducing consumption.
• Then efficiency: Through a building envelope that drastically reduced heat loss in winter and avoids over-heating in summer, which also makes use of the thermal properties of materials, with equipment suited to needs.
• Lastly and lastly only, the use of renewable energies: As an addition to heating and hot water systems.
The efficiency of the building envelope is depended on three factors: Fully insulated walls, limited gaps in insulation (thermal bridges) and limited parasite air passages. Full insulation is a result of the project design phase: while limiting thermal bridges depends on the choice of construction systems and airtight seals are instantly associated with the quality of deployment work. Efficient insulation should dramatically reduce energy needs, at least within the range of the “factor 4” objectives.
In the conditions of use of the building, materials are often subject to aggressions or unplanned nuisances: Subsidence, damage by rodents, insects, humidity, loss of resilience after flooding, etc. If in theory all materials have a “guaranteed” durability, their sensitivity to all these situations is highly diverse and their real durability, like their performance, depends on the type of construction system in which they are used and the quality of the deployment work.
For really efficient green building insulation, we must choose both the suitable material and use it so as to ensure its resistance over time alongside that of the other elements of the wall associated to it. To know if a material is suited to a particular use, we need to see its full technical documentation which specifies the recommended methods of use. Sustainable insulation is also adapted to the building life cycle. The different sensitivities of insulation material to damage that can affect their durability are:
• Sensitivity to compression
• Sensitivity to rodents and insects
• Sensitivity to humidity (water and water vapour)
Insulation for clean and safe buildings
To have safe green buildings, insulation materials and walls must also have good fire resistant ratings. The fire resistance properties of construction materials are very unequal and light, aerated insulation materials, along with certain sealing materials (membranes) and finishing materials (paint, curtains, etc.) are sensitive materials. But their fire resistant properties are far from being the main factor for insulation materials as they are never left uncovered. The properties of the wall and above all its facing that should be considered from this point of view. In effect, fire resistance and the preservation of mechanical properties of walls featuring inflammable insulation materials are above all dependent on the properties of the facings and structural elements.
The choice of facing materials is therefore essential and determines the fire resistant capacity of insulation materials and walls. These insulation materials must be clean. This type of insulation must enable clean buildings, both for residents and the people who build them.
Pollution associated to such materials and in particular insulation materials may be of several different types:
• Moulds and pathogens, responsible for infectious diseases and/or allergies;
• Particle substances and microscopic fibres in suspension in the air, which can be inhaled and may cause serious illnesses: Silicosis, lung cancer, etc.
• Gaseous substances often emitted by organic materials resulting from petroleum chemistry, present in certain insulation materials, but also in glues, additives, manufacturing agents, finishing and decorative products such as styrene, toluene, benzene, formaldehydes, organic chlorine compounds, etc., known under the generic term of volatile organic compounds (VOC); they are increasingly subject to regulation, especially since the REACH European Directive;
• Heavy metals responsible for intoxication such as lead, but also wood treatment products (copper, chrome, arsenic) are today much less frequently used;
• Ionising and non-ionising radiation.
Choice of low-environmental impact materials
Insulation in a green building must use materials with a low environmental footprint. Life cycle analysis (LCA) is therefore the basic tool used to quantify the impact on the environment of a material, a service, or a building. This codified and managed approach (ISO 14040 standard series) unfortunately remains a matter for specialists, because in trying to be exhaustive, it has become complex and onerous.
For a construction material, an LCA seeks to quantify its cost to the environment, ideally at each stage of its life: Manufacture, transport, deployment, maintenance and end of life. Such an approach therefore enables us to calculate what the material consumes (fuel, coal, water, renewable and non-renewable raw materials, etc.) and emits (pollutants affecting soils, air, water, etc.). Such matters are subject to eco-assessments, LCA, impact studies, etc.
For the choice of eco-insulation materials, the most commonly used environmental indicators are the CO2 assessment and grey energy. Other indicators are used to check that a material that has a good score on the initial criteria does not present serious drawbacks on the others. Take the example of asbestos, which according to the CO2, grey energy and resource scarcity indicators, would have been an eco-material … except that on the toxicity indicator the result is disastrous.
The main environmental assessment indicators are:
• Human toxicity
• Photochemical ozone formation
• Energy consumed
• Water consumed
• Depletion of natural resources
• Inert waste formation
• Radioactive waste
• Greenhouse effect
• Aquatic eco-toxicity
In general these are expanded polystyrene, extruded polystyrene and polyurethanes. These insulation materials are produced by the oil industry, most often from one or more by-products of the refinement process. The fact that they are most commonly produced by recycling materials considered to be petrochemical waste (like naphtha, used as a base for polystyrene), does not automatically make them acceptable for a coherent green building approach. Reasons:
• Their production is energy-intensive, produces vast amounts of CO2 and pollutes natural environments (air, water, stratospheric ozone, etc.).
• In the usage phase, even though the most toxic products for the environment and human health have been banned, synthetic insulation materials still pose many problems of VOC emissions and are for the most part highly toxic in the event of fire.
• At the end of their life, no recycling channel is sufficiently organised to ensure the separation of components and/or their elimination without risk to health and the environment.
Nonetheless, all synthetic insulation materials cannot be lumped together in the same class. Polyester fibres are comparatively a good choice (although still limited). Their production generates pollution and is energy-intensive, but their use does not present any notable risks for human health. The fibres are naturally stable and do not release VOCs or toxic gases in the event of fire. They can be reused at the end of the building’s life.
These are mineral wools, cellular glass, glass foam, expanded glass, expanded perlite, expanded vermiculite, expanded clay, pumice stone, pozzolana and mineral foam. These insulation materials are made of mineral raw materials (silica, clay, volcanic rock, etc.). They can also include certain products of recycling (glass, blast furnace coke, etc.) In an industrial process where various additives are generally integrated, the raw materials are transformed into fine fibres, rolls, panels, expanded granules, etc. with very variable properties.
Their production uses raw materials that are often abundant in the Earth’s crust, but the high-temperature manufacturing processes are energy-intensive and produce CO2. In the usage phase, products offer varying degrees of stability depending on their textures and densities. At the end of the building’s life, the possibilities of reuse or recycling depend greatly on the nature of these products and above all those associated with them. Mineral insulation materials can therefore only be used for green building applications according to their own properties.
Vegetal and animal origin insulation material
The main vegetal insulation materials used are made of wood or agricultural products. They are commonly used in green building construction and their use is rapidly growing, for several reasons:
• The resource is renewable and greatly abundant;
• As they fix CO2, they have the best carbon balance of all insulation materials and are not energy-intensive, except for dense industrial products;
• Free of specific additives, they are clean for residents if correctly deployed to prevent any abnormal risk of humidity, i.e. in airtight and watertight walls that perspire;
• Their fire-resistance properties are satisfactory compared to preconceived notions;
• At the end of the building’s life, they can be reused or valorised as fuel or for some as compost.
But not all vegetal insulation materials are ecologically sound. Cotton wool, for example, when produced from native fibres, is the product of an agricultural industry based on intensive mono-culture that is extremely polluting for soils, destroys food crops and the autonomy of producing country populations. The situation is obviously not the same for recycled cotton.
Animal-origin insulation materials are mainly made of hair such as sheep’s wool, bird feathers and duvets. They are the only thermal insulation materials produced naturally as such. In theory, all animal hairs and feathers could be used to produce insulation materials. But in the current economic context, the resources must be sufficiently concentrated and/or organised.
Insulation of external walls
In a building, the wall is the separation with the most contact with the outside, therefore with the most heat exchange possibilities. It is also the most mechanically strained (supporting ceilings and roof, resistance to natural elements such as wind, seismic events, etc.) and the most complex, as it features almost all the passages between inside and outside (doors, windows, etc.). Walls also represent the largest volume of materials. It is therefore not surprising that a building is often referred to by the materials used to build its walls: A stone house, a brick wall, a straw house, etc., i.e. a house with walls built using these materials.
There is a wide range of technical possibilities to provide wall insulation for green buildings. The basic solution is to build insulating walls (assembled on wooden structures and built-up walls). In this family we have:
• Built-up walls with distributed insulation: Load-bearing clay bricks, cellular concrete bricks and lightweight concrete blocks;
• Externally-insulated walls: Rendered insulation without air gaps, insulation under cladding with air gap and built-up cavity wall;
• Internally-insulated walls: Insulation using rendered panels or blocks, insulation attached to wooden structure and insulation with built-up inner partition;
• Wood walls and wooden frame: Insulated solid wood walls, with a wooden frame and dry insulation filler, lightweight concrete fillers and wooden frames with straw bale filler.
Walls with distributed insulation or clay bricks are built using load-bearing blocks that are self-sufficient from a thermal standpoint in most cases. They are made of lightweight materials: Porous clay with multiple perforations, cellular concrete or light granulate bonded by a cement (stone, expanded clay, etc.). It is possible to do thermal correction on built-up walls by:
• Laying thin insulation on the inside and/or outside;
• Applying an insulating rendering on the inside and/or outside;
• Applying a low-effusivity interior cladding.
There are three main types of floors, depending on their position in the building and their thermal function between the living areas and the outside:
• Ground floor surfaces in direct contact with the soil, or floors over an earth platform: High inertia floors (insulation under slab), medium inertia floor (insulation under screed) and low inertia floors;
• Floors separated from the ground by a non-heated empty space (flooring on non-heated space). This space can be the exterior environment (house on pillars or piles), a temperate environment (crawl space) or a buffer space (cellar, underground, non-heated floor, etc.): Insulation of existing slabs, wood and concrete floors;
• Intermediate floors between lived-in and heated levels.
The design of floor-level insulation over solid platforms is done according to several main criteria:
• The desired level of inertia
• The thermal function of the floor (passive or active with heated flooring);
• The type of interior covering desired (tiling, concrete, bare earth, wooden parquet, linoleum, etc.).
In all cases, the risks of capillary rising and of thermal bridges must be managed attentively.
In a new green building construction project, the most logical systems from a thermal, economic and environmental viewpoint are in general wooden structure floors, on which the desired inertia can be applied for interior areas with a dry or wet screed. In addition, the thermal limitations for floors between heated levels are often subject to acoustic comfort requirements that must be taken into account. The floors of attics, unheated roof spaces must be taken into account in roof insulation.
Roofs are extremely important components in the construction of a green building. They help to control the air flows and humidity in a building and also insulate it from exterior temperatures. In most old buildings, the protective function of the roof did not include the thermal insulation role so to speak, which was done on the last floor level, the attic floor. They were referred to as cold roofs.
Today, it is rare that the two functions of protection and insulation are not merged in order to make the whole volume of space under the roof and inside the walls inhabitable. But this gain of space comes with a new role for the roof as an exterior separation. From a thermal management viewpoint, roofs are opaque walls which, for a given surface area, present both heat losses in winter and the risk of overheating in summer.
This tells us that it is the separation that must receive the highest level of insulation, both to prevent the loss of heat in winter and to prevent its entry in summer. Insulating the roof should therefore take into account not only the thickness of the insulation material, but also its density (transmission inertia) and all the thermal bridges and air leakage points. The massive use of wood in any construction approach for its mechanical properties has already helped to reduce thermal bridges due to its relatively low conductivity.
To remedy the effects of transmission inertia on the roof, the first actions to take are in construction:
• A low-capture covering (plant roof)
• An air gap under the covering, sized for a real thermal draft, which depending on the gradient, may represent wide spaces (over 10 cm for a 30% gradient) and specific fittings for the entrances and exits of the air flow;
• A high-inertia interior cladding (ceiling).
The plant roof or green roof is a major ecological benefit for sustainable constructions. It brings together all the benefits of a sustainable construction. Installed on terraces or flattish roofs, a green roof is part of a sustainable development approach as it proposes natural building insulation. In the urban context, a green roof helps restore biodiversity. This solution also offers strong perspectives in terms of biological filtration and cleansing of rain water. It also captures rain water and limits rain water run-off in pipelines. Green roofs in an urban environment also help to reduce CO2 content in the air, while capturing the main culprits of pollution (atmospheric dust and pollen).
The green roof technique can also insulate the building naturally. The mix of earth and rooted plants on roofs produces an airtight and watertight roof but which can also resist wind and fire. For the past few years, the practice of creating green roofs is a de facto part of current sustainable construction practices, the architectural version of the sustainable development philosophy. Green roofs can in effect protect the insulating membranes from UV rays and solar thermal radiation. This natural protection means we can hope the insulating membrane may last from 30 to 50 years.
Picture window insulation
Picture windows are special points in the envelope of the green building as they have multiple functions. From a thermal viewpoint, they are both and alternately sources of heat capture and loss depending on their orientation, the time of day and the season. But they must also provide views of outside, enable people to go in and out (sliding doors), let light in, air in and out at certain times, etc. All these functions make them highly technical components, for which thermal performance must go alongside the other functions we expect of them.
Heat losses from picture windows are caused by two factors: The intrinsic quality of the windows and the quality of their installation. In terms of picture window dimensions, the whole idea is to use as few surrounding frames as possible for a given surface area of window, i.e. prefer large panes and increase the size of picture windows rather than their quantity. As in relation to two small windows, one large window of an identical surface area:
• Loses less heat as it features more glazing and less frame
• Captures more heat because in picture window only the glazing can do so
• And costs less in frame costs and masonry.
OTHER LIGHT MATTERS IN A GREEN BUILDING
Plumbing and electricity in a green building
Plumbing is also another important element in comfort, savings and safety in a green building. Its installation is a necessary step in construction. Water is effectively necessary for the comfort of the inhabitants, both for hygiene and drinking. Faced with the challenge of preserving the environment, specialists are slowly succeeding in designing eco-friendly plumbing. This must be designed in such a way to generate as little grey energy as possible and must be coordinated with the rest of the home.
The plumbing materials in a green building must be manufactured using processes that respect the environment. Manufacturers try to use as little carbon as possible and improve the heat insulation of components, to limit heat loss. Specialists are also making efforts in matters of water saving, environmental respect and septic tanks. It is important to maintain plumbing or to change it regularly, to avoid it becoming toxic both to the environment and to human health.
Polyethylene pipes are made of recycled plastic. They are interesting from a sanitary viewpoint, and especially in environmental terms as they are made from recycled products. Unfortunately, they are not very resistant and have difficulty in supporting heat and high pressure. What is more, the use of plastic piping for central vacuum cleaning systems, the cold air inlets for chimneys and gas heating systems, may contribute to reducing draughts in the family environment.
PVC pipes represent a big shock for the environment. The consumption of grey energy in their manufacture is high, their elimination can also cause problems and their reliability is not impressive. PVC becomes brittle under freezing temperatures and its leaktight properties will deteriorate after around thirty years underground but after only 10 years in the sunlight. PVC is produced using oil and salt. It contains plasticizing agents that are hazardous to human health, notably phthalic ester. Also used in its composition are stabilisers based on toxic heavy metals, fire-retardant agents made of chlorinated paraffin which are harmful to health, or antimony derivatives, which are reputedly carcinogenic. These substances also create problems during their production and elimination.
In a green building, the right choice in tap fittings can make substantial water savings, such as:
• Mixer taps: Enable considerable hot water savings, therefore of power used to heat the water;
• Thermostatic tap: With a conventional shower tap, a large quantity of water is lost when adjusting the temperature. With a thermostatic tap, you control the desired temperature on one side using the indications on the appliance, and on the other side the desired water pressure.
• The flow reducer: This is installed on a shower head at the base of the pipe and can reduce the water flow by half, while maintaining the same spray pressure;
• Aerator: It is installed on a tap. It prevents leaks and reduces the water flow while maintaining an identical pressure compared to a non-equipped tap. The water volume is reduced by compensated for by air.
It is fully possible to produce your own electricity with ecological production methods, through photovoltaic power, wind turbine power or hydraulic power. It is also possible to select environmentally-friendly electricity from suppliers. The liaison committee for renewable energies and WWF-France have created the EVE mark (Environmental Green Energy) so that consumers can choose between the different suppliers of ecological energy. The idea is to supply, in a fully transparent manner, electricity that is produced in respect of the environment and to promote the development of renewable energies. For its part, Greenpeace has launched its green offer comparison tool, Ecolo Watt.
Plastic plays a major role in high tech and is often taken for granted. The plastics used in making electric components in an installation must be specifically suited to satisfy the conjoined needs of electrical safety and fire safety. The durability of the plastic parts of electrical components enables such products to have a long useable lifetime.
Doors and windows for green buildings
Doors and windows seal a building and therefore must respect very strict criteria. Entrance doors must protect against humidity, freezing, heat and noise. They must also provide safety, durability and energy efficiency. As many of their customers do not trust conventional doors made of wood, manufacturers use aluminium and PVC for the structure, with low-quality insulating foam fillers. This type of door is highly criticised for environmental reasons and traditional wooden doors are to be preferred.
Today there is a vast range of durable and efficient solutions made of plastic materials for doors that are easy to maintain. Despite their low weight, plastic doors are extremely durable. In fact, the spreading use of plastic door products has validated their strength, their energy efficiency and their acoustic value.
Entrance doors with a plastic foam core may inhibit noise and add insulation value, which can help reduce heating and cooling needs. Sealing foam can also be used to draught-proof windows, doors and thresholds, to seal out undesirable air draughts. From an ecological viewpoint, solid wood is the most suitable material. This is because a solid wood panel made of three or four crossed laminated sheets is strong and guarantees good thermal and acoustic insulation.
Windows are a building’s weak points in terms of thermal insulation, including for the green building. In winter, south-oriented windows capture more heat than they lose. Some are partisans of single glazing for south-facing windows, which favour solar contribution to heating; others prefer insulating glazing that reduces heat loss. Before making a choice, both the glazing and frames must demonstrate good thermal performance. However, a multiple-opening window features two panes that are only separated very rarely (for cleaning), which improves insulation. A double window comprising two panels that open separately. They allow good thermal and acoustic insulation.
Vinyl windows and glass doors enables less electricity to be used for heating and cooling a house or larger building. This energy efficiency helps reduce greenhouse gas emissions from power stations. Also the low maintenance needs of vinyl windows and glass doors eliminate the need for paint, tinting, thinners and paint removers, which harm the air quality.
Staircases are essential elements in a construction and must satisfy very specific standards in terms of safety. In buildings, staircases that present a certain risk are usually built with heavy materials (in general concrete). The joins between the steps and the stringer, the core or the wall, as well as those between the stringer and the planks, should systematically be acoustically treated, which will considerably limit the propagation of noise in a wooden staircase.
As an eco-material, local wood should be tested for its durability properties. A hard wood such as oak will resist for at least 80 to 100 years, but thin steps made of tender wood are to be avoided. For green buildings, wood is naturally recommended.
Terraces and balconies
Like roofs, green terraces and balconies are becoming an important component for the green building approach. A terrace designed in the spirit of a garden would create a genuine micro-ecosystem, where birds and insects can thrive. Without neglecting the aesthetic aspect or the original motivations, a terrace can also become a kitchen garden. Fruit and vegetables to hand can accompany delicious meals cooked in the kitchen. To achieve this, the space needs to be optimised, and water and utility use regulated. A bin to recycle natural waste (peelings, weeds, branches) will be needed to create green compost. This will rapidly be reused to cover the soil or for compost mixed with soil after long decomposition.
The components of a green terrace are: Vegetation, cleaning plants and shadow plants. They should be set out to reduce heat spots, as recommended by the LEED certification. Different materials are to be used to make such spaces. You will need to identify the purpose and intended use, the assemblies and arrangements necessary. The architecture should therefore be used, not only by the materials that it represents, but also by its volumes, forms and styles. Architecture and landscape are capital factors to succeed in fitting out terraces and balconies.
AIR QUALITY INSIDE A GREEN BUILDING
A building built in a sustainable development approach also takes into account the long-term and short-term health of its occupants. For this reason, green buildings should fully integrate measures intended to improve interior air quality into their design.
These constructions can result in the selection of materials that do not liberate toxic compounds, not dangerous chemical substances. The adjustment of ambient conditions in terms of ventilation, temperature, humidity and lighting is also to be improved. Healthy interior environments not only ensure the well-being of the occupants, but also guarantee their satisfaction and stimulate their productivity.
GREEN BUILDING – Ecological construction
GREEN BUILDING – Components
GREEN BUILDING – Environment and climate
GREEN BUILDING – Certifications
SUSTAINABLE DEVELOPMENT AND THE ENVIRONMENTAL FOOTPRINT
GREEN BUILDING – Green installations
GREEN BUILDING – Eco-technologies and practices
GREEN BUILDING – Zero energy home and economic aspects