Using wood is one of the best solutions for energy shortage
Wood construction consumes minimal energy. Wood is light and easy to put together on site. Foundations are minimized. Transport and construction require less energy.
Wood buildings are more energy-efficient
Wood is a natural thermal insulator. Using wood helps to save energy over the life of a building, as its cellular structure provides outstanding thermal insulation: 15 times better than concrete, 400 times better than steel and 1 770 times better than aluminum. A 2.5cm timber board has better thermal resistance than an 11.4cm brick wall. Wood’s low thermal conductivity means 90% of the insulation value can be realized, with only 10% lost to thermal bridging. Timber structures from frame walls to CLT panels provide cavities for additional insulation materials to meet energy regulations. This means thicker walls and more insulation materials are required for steel, concrete, or masonry structures to achieve the same level of thermal resistance.
Therefore, wood envelope outperforms Chinese Energy Codes with the same cost compared to other envelopes, or the energy-efficiency of wood construction reduces the cost of meeting the codes.
Wood frame buildings are easy to insulate thermally
Unlike solid concrete or masonry structures, wood frame walls, floor joists, and roof joists inherently provide space for fibrous insulation, the most economical way to achieve better insulation. Application of mineral insulation is a standard element of any wood construction project. It is conducted with minimal additional labour or material expense and provides significant returns. Wood’s low thermal conductivity means 90 per cent of the insulation value can be realized, with only 10 per cent lost to thermal bridging. Wood structures can also be readily insulated on the exterior or interior if additional energy savings are desired.
Light steel frame walls also have cavities for insulation. But the high thermal conductivity of steel means only 50 per cent of the insulation value can be achieved. Extra measures are always required to reduce local energy loss and vapour condensation as a result of steel thermal bridging. It can also lead to ‘ghost marks’; dark vertical marks that appear over the framing on the interior surfaces of exterior walls, as a result of faster dust accumulation on cool surfaces.
An energy consumption field test by the Harbin Institute of Technology considered a wood building using 38 mm x 140 mm studs, cavity insulation and 30 mm of exterior rigid panel polystyrene insulation. This was compared with a brick building clad with 60 mm rigid panel polystyrene insulation. Harbin is an area which experiences severe cold.
The test measured the thermal transfer coefficients (K) of the walls as 0.244 for wood buildings and 0.526 for brick buildings. The timber building reduced coal consumption by about 50 per cent.
Wood frame construction outperforms Chinese Energy Codes with no additional cost
Wood frame buildings are generally rated as more efficient and economical than other construction types. They outperform all the relevant requirements for building energy efficiency in China with no additional cost.
JGJ 26 “Standards for Energy Design for Severe Cold and Cold Areas” requires buildings in Beijing to have thermal transfer coefficients (K) from 0.55 to 1.16. Typical wood frame walls can achieve thermal transfer coefficients from 0.3 to 0.5 depending on stud size, spacing and insulation materials.
According to calculations by Shanghai Xiandai Architectural Design Group, the effective thermal transfer coefficients of conventional wall assemblies with 38 mm x 89 mm studs, range from 0.46-0.49 and 0.37-0.40 with rock wool and glass fibre insulation, taking into account the thermal conductivity of the studs. These thermal transfer coefficients (K) can be further reduced to 0.3 or lower if 38 mm x 140 mm or wider studs are used for framing, or extra exterior insulation is applied. By comparison, steel, concrete, or brick walls would require extra and more expensive, rigid insulation panels in order to achieve similar insulation performance, and walls would be thicker.
- Thermal conductivity is the rate of heat transferred by conduction through solid materials subject to a temperature difference on each side of the material.
- Thermal transfer coefficient (U-value or K-coefficient) is a measure of heat conductivity through a building assembly, comprising a number of materials.
- Thermal resistance (RSI) refers to the resistance to conductive heat transfer through a material or assembly. It is the reciprocal of conductivity (1/K).
- A lower K or a higher RSI means better thermal or insulating performance.
- Thermal bridging refers to the higher thermal conductivity of a structural component, within the insulated assembly, providing a bridge for more rapid heat transfer through the assembly and thereby reducing the overall thermal performance of the assembly.
The energy-efficiency of wood construction reduces the cost of meeting the codes
All concrete, masonry, and steel frame structures need rigid insulation panels in order to meet China’s energy efficiency requirements. In Beijing, concrete or masonry buildings need additional 50 mm to 80 mm thick insulating panels. In Shanghai, they need 50 mm thick panels in order to meet the minimum energy requirements. By comparison, conventional wood frame construction using fibre insulation meets the requirements without additional insulation, using 38 ×140 mm studs in Beijing and 38 × 89 mm studs in Shanghai. A considerable saving can therefore be made.
If additional insulation is not used, steel and concrete buildings will consume much more heating and cooling energy. The dramatic savings in cooling and heating costs of wood frame building envelopes have been confirmed and praised by developers and property managers who have experience with these constructions in China. As one of the world’s largest countries, China is subject to extreme climate variations. The energy-efficiency of wood structures is beneficial in all climates, but particularly in China’s colder regions, where heating is required.
China is facing an energy challenge
China is experiencing rapid economic development. It has the world’s second largest energy consumption, exceeded only by the USA. In 2003 its total energy consumption was 1,68 billion tonnes coal equivalent. By 2010, according to a recent government estimate, energy consumption could exceed 3 billion tonnes a year.
This growth in consumption has led to energy shortages, which can hold back economic development. And, in spite of extensive domestic fossil fuel reserves, China has become one of the largest energy importers in the world. Improving energy efficiency and developing renewable energy supplies have therefore become a priority.
Energy production has a serious impact on the environment
China’s current energy supplies are heavily dependent on fossil fuels, which emit large quantities of CO2. Rapid economic development, accompanied by higher energy consumption and the use of fossil fuels, is presenting serious challenges to air, and water quality across the country.
Improving energy conservation and using environmentally friendly and renewable materials can reduce the impact of economic development and provide a better living environment for China’s population.
The construction and operation of buildings create greater environmental impacts than most people realize. Globally, buildings are responsible for 20% of all water consumption, 25%~40% of all energy use, 30%~40% of greenhouse gas emissions and 30%~40% of solid waste generation. Of the total energy consumed by buildings, on average 22 per cent is used during the construction phase and 78 per cent during the long-term operation phase. Estimates suggests that the building sector now accounts for about one-third of China’s total energy use and this is expected to grow in the future.
Currently in China, buildings are responsible for more than 40% of energy consumption. Almost 2 billion m2 of new buildings are completed each year, more than 80% of which are made of fossil fuel-intensive materials, constructed in an energy-consuming and polluting way, and performing with energy consumption per unit area currently two to three times higher than in developed countries. China has set ambitious targets and will work hard to achieve them.