Buildings currently account for over 40% of total UK energy consumption and a similar percentage of the UK CO2 emissions.

We need to get better at making our buildings more energy efficient.

New buildings

The building regulations set minimum standards for the performance of buildings, with Part L specifically regulating the conservation of fuel and power. The building regulations are becoming increasingly more strict, with a long-term goal under the Energy Performance of Buildings Directive to move towards ‘nearly zero energy buildings’.

Key criterion described in Approved Document L include:

  • The designed carbon emission rate must not exceed the Target Emission Rate (TER) for a notional building of similar type, size and shape.
  • Fixed building services should achieve a reasonable standard of energy efficiency. This is intended to prevent inappropriate trade-offs between different elements of the building. Minimum limiting parameters are set for key components of the building fabric to ensure that this is the case.
  • Solar gains should be limited.
  • Air-permeability testing and appropriate commissioning of building services systems.
  • Provision should be made for energy efficient operation by providing the building owner with information enabling them to operate the building in a way that uses no more fuel and power than is reasonable.
  • Higher standards can be achieved through schemes such as BREEAM, Passivhaus, the Code for Sustainable Homes, Leadership in Energy and Environmental Design (LEED) and so on.

However, there is significant evidence to suggest that buildings do not perform as well when they are completed as was anticipated when they were being designed. The difference between anticipated and actual performance is known as the performance gap. Findings from studies over the last 20 years have revealed that actual energy consumption in buildings is often twice as much as predicted and can be up to 5 times higher than calculations carried out for building regulations compliance.

Offsite manufacture, with closely monitored factory fabrication of the whole building envelope in a controlled environment, means that building performance is not compromised by poor workmanship on site which is where most of the problems with conventional build systems occur.

Air Pressure (AP) testing and U-Values

  1. Air Pressure Testing (also know as air tightness, air leakage or air loss)

The Air Tightness Testing and Measurement Association (ATTMA) defines ‘air leakage’ as the ‘…uncontrolled flow of air through gaps and cracks in the fabric of a building. It is sometimes known as infiltration or draughts. Air leakage is not to be confused with ventilation, which is controlled airflow in and out of a building’.

In essence, it says that losing warm air from a building increases the energy requirement the building needs to provide an ambient temperature for the occupants. Higher energy requirements increase the cost of running the building and has a detrimental effect on the environment; so minimising air leakage, in a world where the cost of fuel is ever increasing, saves money.

Building Regulations require a minimum Air Permeability reading of 10m3/m2/hr @ 50 pa. Standard Timberworks buildings achieve between 2-3 m3/m2/hr and can be designed to achieve readings less than 1m3/m2/hr for passive house. For comparison, standard AP measurements of new build properties in the UK are generally between 5-7m3/m2/hr.

Controlled and closely monitored workmanship in a factory environment lowers the air permeability

  • U-values or Thermal transmission and EPC’s

The U-value of a building component is the rate of transfer of heat through a structure (which can be a single material or a composite), divided by the difference in temperature across that structure. The units of measurement are W/m²K. The better-insulated a structure is, the lower the U-value will be.

Workmanship and installation standards can strongly affect the thermal transmittance. If insulation is fitted poorly, with gaps and cold bridges, then the thermal transmittance can be considerably higher than desired. Thermal transmittance takes heat loss due to conduction, convection and radiation into account. Again, controlled and closely monitored workmanship in a factory environment and the use of quality materials and components lowers the u-value of the building superstructure, and saves running costs.

Timberworks -u-values Vs Part L Building Regulations Requirements (2020)

 Timberworks U-values  (w/m2K)Part L (Building Regs.) U-values
Wall0.18 – 0.220.3 W/m2k
Roof0.12 – 0.150.15 W/m2k
Ext. doors and windows0.8 – 1.21.6 W/m2k

* By using alternative materials in our panels can improve u-values still further

Low Air permeability readings combined with low U-values results in highly energy efficient buildings  and is reflected in the Energy Performance Certification (EPC) that each building now must have.

How does this compare?

In 2019 only 1% of all new builds achieved an EPC of A (Source; Ministry of Housing, Communities and Local Government)

To date, Timberworks have not built a building with an EPC of less than A, and a number have achieved A+.

Our buildings are extremely energy efficient!