air tight regulations

Yianni Spanos on what the recent revision to Part F of the Building Regulations will mean for the construction industry… 

One of the challenges for achieving low energy buildings is to significantly improve their air tightness. Ventilation provisions within the new Building Regulations Part F have been increased for commercial buildings and dwellings with a recommended design air permeability tighter or equal to 5 m3/(h.m2) @50Pa.

Focusing on construction, achieving an air tightness target of 5 m3/(h.m2) is not a difficult task. For many years specifiers have demanded significantly better standards of air tightness in quality buildings to ensure that the occupants enjoy a satisfactory state of comfort and well-being. For air-conditioned buildings, and buildings which aim to be low energy, a maximum air permeability standard of 3 m3/(h.m2) has been set by many building owners and operators.

The major benefits of tighter air tightness standard are far better control, fewer staff complaints and improved energy efficiency. Equally, many clients in the retail sector have adopted lower air tightness standards than required by the Building Regulations, such as 2 m3/(h.m2) for new build projects. Even extensions to existing buildings can routinely achieve an air permeability target of 3 m3/(h.m2).

In this regard, under normal practices for mix-mode and air-conditioned buildings, superstores, museums and storage, mechanically ventilated dwellings, factory and warehouses, the air-tightness should is expected to be better than 2010 amendments. Special consideration should be given to the design of naturally ventilated dwellings, schools, hospitals and naturally ventilated offices, when best practice for those type of buildings can achieve 40% - 60% better air tightness level than the new Part F standards.

The path to routinely achieving air tightness targets is as follows:

• Specify the air tightness target at a very early design stage;
• Specify the air seal line at a very early stage. The inside surface of the structure is usually the airtight surface. The airtight surface should be brought inside rooms which will be ventilated to outside, such as boiler rooms, plant rooms, electrical switch rooms and lift shafts;
• Require air sealing detail drawings from the architect or design and build contractor;
• Consider specifying an air tightness consultant to review drawings;
• Specify that air tightness testing be undertaken by an independent organisation  which is a member of ATTMA, the testing organisation for the British Institute of Non-Destructive Testing;
• In liaison with the testing organisation, specify all aspects of the air tightness contract process. Where necessary, specify penalty charges for failures not rectified in a reasonable time-scale;
• Consider specifying an air tightness consultant to inspect the building during the construction process;
• Clearly communicate the requirements to all design and construction parties.

What main contractors and subcontractors need to do to ensure they're not caught out by the changes?

Specialists should have an early involvement and provide support to the contractors in the design and project management process. In some cases, advanced solutions may be required to meet the targets of the 2010 amendments, especially for construction solutions for which it was challenging to pass the 2006 amendments. It also vital that the project management fully understands and ensure co-ordinations of different trades with aspects of the external façade, and especially when structural supports, or building services, pass through a ‘perforated’ façade and external building elements.

With regard to ventilation systems, reference should be made to a new ‘Domestic Ventilation Compliance Guide’ for guidance on installing, inspecting, testing and commissioning ventilation systems in dwellings. For mechanical ventilation systems installed in new dwellings, air flow rates shall be measured on site and a notice given to the Building Control Body. This shall apply to intermittently-used extract fans and cooker hoods, as well as continuously running systems. In addition, the owner shall be given sufficient information about the ventilation system and its maintenance requirements so that the ventilation system can be operated to provide adequate air flow. All fixed mechanical ventilation systems, where they can be tested and adjusted, shall be commissioned and a commissioning notice given to Building Control Body.

What impact the changes will have on finance and profits?

Under Part F 2010, the contractor should have a greater focus on ensuring that the design is delivered according to correct specifications by specialists. Over the last four years, air-tightness levels were in many cases 50%-60% better than Part F 2010 at no additional cost. It is expected therefore that changes will not have an impact on profits when the design follows a proven assessment routine.

Although these changes will not have a fundamental effect on finance, as well as setting out physical performance requirements performance specification for building envelopes, procurement will need to ensure that contractors have the calculation competences and accredited details needed to secure the required air-tightness levels. Projects with many on-site design variations could be subject to greater misalignment with the expected air tightness results and a greater risk to the contractor team charged with delivery.

Dr Yianni Spanos is Associate Director at Capita Symonds.

let's get down to earth...

Malcolm Richards (right) on how rammed earth construction techniques can be used to reduce the energy used in constructing buildings...

Whilst initiatives such as photovoltaics and geothermal energy will help to deliver longer-term energy efficiency benefits, it is clear that they could be usefully supplemented in the more immediate future if the embodied energy in construction materials were reduced.

Research has shown that about ten percent of global CO2 emissions result from cement production, so cutting our dependency on this and other kiln-fired components, such as bricks, could make a big difference.

For some time now I’ve been studying the use of ‘rammed earth’ construction. Rammed earth is based on the compaction of graded soils into formwork to produce an unfired environmentally friendly building material. Rammed earth materials can be also sourced and produced locally, negating the haulage and storage impacts of kiln-fired masonry components and mortars.

Walls produced using rammed earth contain less than one twentieth of the embodied energy of traditional cavity walls. They are more easily returned to the ground when no longer required so the material is borrowed, not stolen. Earth walls have a high thermal mass and act as a heat sink, absorbing heat energy through the day and releasing it into the building as temperatures fall at night. Experiments have shown that rammed earth can actually reduce warm daytime temperatures by 4 or 5 degrees C - equivalent to some cooling systems. At the same time earth buildings stay warmer in cold climates, with internal temperatures unlikely to fall below 140C when occasional external sub-zeros are experienced. Given that half the energy generated in Britain is used to heat or cool buildings, the potential to reduce energy consumption makes earthen buildings an important environmental initiative.

Earth walls control humidity levels within buildings by absorbing excess water vapour and releasing it back when the environment is drier. They also have good sound absorption properties and absorb volatile organic chemicals from the atmosphere, potentially eliminating sick building syndrome. In addition to the normal applications, rammed earth can also be useful in disaster areas as it can be rapidly built using indigenous materials and local labour that requires little training.

Earthen architecture is gaining strength in many parts of the world, including Europe, Australasia and the Americas while building codes for the material are also now being developed, including new seismic design regulations in New Zealand.

Rammed earth is a material that minimises energy input in the construction phase, makes an input into energy consumption and can be returned to the ground when no longer required. It is a material with a viable future and one that won’t (ahem) cost the earth.

Malcolm Richards is a Director of Structures at Capita Symonds.