Tag Archives: construction detail

What changes are in store for the April 2014 Part L Document?

HCD group – Changes to the Building Regulations Approved Document Part L

Scheduled for April 2014


What changes are in store for the revised Part L documents this April?

In an effort for the government to demonstrate a reduction in carbon emissions for the United Kingdom the new revision for Part L of the Building Regulations will be released in April 2014.   These changes are intended to make a step towards a potential zero carbon new build house in 2016 and extensions in 2020.   Generally speaking, the changes are targeting a reduction of 6% in CO2 emissions for new build houses and 9% in non-domestic buildings this time around.

This modest increase in thermal properties, rather than the projected more significant step, is a deliberate act by the government to easy the change on the economy.   Their figures suggest that these changes would result in a 1.2% construction cost increase.   Reality suggests that the increase is more likely to be significantly higher at around 8-10%, which will actually be quite a hit on the construction economy.


So what are the changes and how will they impact on design?

For new build houses all of the external fabric elements have had their U-values improved.   Typically, walls will be 0.18 W/m2K, floors & roofs will both be 0.13 W/m2K and windows/doors/rooflights 1.4 W/m2K.   Limiting standards, the lowest any element can be, remain the same as current levels.   One point is clear with the revised figures is that a specification will pass if within the typical U-value targets and the updated 2012 SAP (Standard Assessment Procedure) calculation system will also pass at these levels, which was not always the case.

The revised Part L bases its standard pass rate without the use of renewable energy though, allowing any introduction to be an improvement on the basic provision against carbon emission reduction.   Compensation against reduced U-values can be tackled with the introduction of renewables, for example.

Party walls have been reviewed after evidence was found to support the argument that they act like chimneys drawing warm air from the spaces out through the roof.   As a result U-values have been applied here too with an option to provide a solid wall with block laid flat construction, though this method is likely to require attention to combat noise transfer.   A full filled insulated cavity party wall is the best solution providing it is sealed at all exposed edges.

Fuel factors are a new element within the overall assessment.   This set of figures provides a pre-determined factor against which type of energy is being used within the building.   Gas is the preferred and best option while electricity gets hit the hardest.   Be careful when installing heat pumps that require grid electricity to run them.

Efficiency of installed equipment, such as fan system for heat exchangers in passive houses and all lighting units, have been improved.   This will have an impact on fan systems in particular with manufacturers needing to improve the efficiency of their products to avoid duct sizes increasing.

These principles are the same for extensions to existing dwellings, though the required U-values are not as low as new build.

Again, U-values to external elements have been improved for new non-domestic buildings but the most notable change is the reduction in air permeability.   This means that connection details and then the construction of those details needs to be carried out with more attention in order to achieve the requirements.   As with housing, renewable energy is not included in the basic specification level allowing these to be added as an improvement or as part of a compensation for reducing performance of other elements.

Both for domestic and non-domestic new builds a report has to be provided that demonstrates a consideration of high efficiency alternative systems, such as renewables, district heating or heat pumps perhaps.   A simple statement is required to explain why more efficient systems have not been employed but there is no method to enforce or challenge the report.

Extensions to non-domestic buildings have retained the current requirements for U-values.   However, renovation of existing thermal elements will now require consideration at building regulations and will have to meet the current standards.

In summary, there are general improvements to all external elements in terms of thermal efficiency that targets a reduction in CO2 emissions by 6% for domestic buildings and 9% for non-domestic and a new SAP calculation for domestic buildings; the 2012 system.   These all come as a stepping stone towards a projected ‘zero’ carbon level for both domestic and non-domestic by 2020.   Watch this space for the next set of changes in two years time, we might have only just got used to these changes by then.

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Why do we still build with masonry?

We are in the 21st century and still using a 200 year old technology to build our houses. Why?  With a number of alternatives available today we are going to ask why they are not used very widely.

In the UK bricks have been made and used in housing construction for decades. The clay used is a natural material that is easily extracted and processed to make bricks. Built as a cavity wall with insulation between we have now developed this technology to the Nth degree.

There are other technologies used in the construction industry; such as timber or steel frame, pre-fab systems and composite structures. Sometimes other constructions or objects are used to form spaces and houses like shipping containers. There are also products likeDurisol or Beco Wall Form that provide ‘lego’ style concrete filled wall construction.

So, why do we still use bricks (or masonry) and is there anything wrong with this technology? It’s a well known craft that has been passed down through generations. Where it has been developed into cavity walls and adding insulation it is quite a successful composite construction: it keeps the weather out, provides security. It’s a great method of construction that has been proven over decades.

Why aren’t other technologies used? Timber frame has been used to some extent in this country. However, it has suffered because of a combination of climate and poor weather protection or breathability. Steel framing has been used widely in industrial and commercial construction and probably becomes more efficient in larger buildings and multi-storey.

Technology has made major break throughs of recent years with the consideration of allowing composite construction and buildings as a whole to breath. This allows trapped moisture, a significant issue in the UKs climate, to escape without compromising the buildings integrity. Ironically, early masonry construction (circa 19th century) naturally allows the construction to breath. Sure, there was little insulation in a solid masonry wall between 450-600mm thick. But the combination of thick solid construction that water would find difficult to penetrate, lime mortar and plaster work with non-plasticised paint these construction methods were almost perfect.

There is a tradition of brickwork in this country. True the brick type does vary across the country. In some parts a vernacular stone is found and used extensively. The planning system often asks for in keeping appearances in building finish. These are all significant limitations.

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Vapour barrier or breather membrane?

Bizzy Blue Design Ltd has reviewed the various terminologies to understand the correct usage and application of this often misunderstood technology.

Understanding the different applications for these products could mean the difference between a high performance building and a damp one that would be very difficult to put right without starting again.   We have investigated their applications and understood their respective performance values to become better educated towards their specification.


  • Vapour Barrier (or Vapour Control); withstands vapour pressure and minimises gaseous vapour penetration
  • Breather Membrane; water resistant and vapour breathable


  • Vapour Barrier; applied internally to walls, roofs or exposed floors.
  • Breather Membrane; applied externally to exposed structures.

We understand that the principle of using a vapour barrier is to control and reduce the amount of gaseous water vapour within a building and prevent it travelling through an insulated external or exposed structure where risk of interstitial condensation may occur.   The vapour barrier is applied internally to minimise vapour penetration into the insulation layer.   A breather membrane is applied externally to act as a barrier to water from the outside whilst also allowing the structure behind to breathe away any water vapour within it.   Using both products together as part of a composite structure will act to minimise water vapour penetration from inside the building and through the insulated structure, while allowing any vapour to escape externally and resist water penetration from the outside.

A traditional masonry cavity wall would not require a breather membrane as the external skin would act as the breathable layer and would control the level of water penetration from the outside.   A breather membrane would, however, be applied to a timber framed external wall that then has a masonry outer skin as this would protect the timber from any water within the cavity.

This theory works perfectly and logically on any external element (wall, roof or exposed floor) in contact with external air.   However, exposed floors, such as a ground floor where there are no basements, need to be treated in a different manner.   Where the ground is the external substance you are dealing with ground water pressure and this should be resisted by a Damp Proof Membrane or water proof tanking system.   Depending on where the floor insulation is positioned, a breather membrane can then be applied over the insulation to allow any water vapour or moisture to evaporate into the heated space above.

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