Celcon Aircrete Blocks

Celcon manufactures a wide range of quality aircrete products, available in a variety of grades and dimensions, and all conforming to BS 6073. This is the excellence of Celcon aircrete.

Celcon Blocks Thermal Mass

Due to their thermal mass Celcon blocks have the ability to store and radiate heat back into a building. This helps your house act as a storage heater, absorbing heat and radiating it back into the building when the temperature drops. This reduces any dips in temperature during the winter and peaks in summer creating a comfortable environment.

Range of Celcon Blocks

The range of Celcon products all with excellent thermal properties means that Celcon can offer blocks for foundations, cavity walls, solid walls and beam and block floors that satisfy the energy efficiency requirements of Building regulations.

Energy Conversation Requirements

The current energy conversation requirements set out in Approved Document ‘L’ to the Building regulations (England and Wales) and Technical Standard J (Scotland) incorporate amendments which were focused not simply on changes to the U-value requirements for each part of the building’s fabric, but also on the building as a whole.

On the 13th September 2005 the ODPM and DEFRA released an interim or Draft Approved Document L (energy efficiency) of changes which came into effect on 6th April 2006.

The most significant differences for dwellings from the previous Part L document (which came into effect 1 April 2002) are:

a.      only ONE method of compliance (SAP). Target U value and elemental approaches are now longer permitted for new dwellings.

b.      once built, Mandatory Air tightness testing (for all but a few cases)

c.      no more 'worst' cases covering multiple units - information will be                                               required for each individual dwelling; an example of a completed Checklist is given  in L1A

The Reasons for Change

Roughly 46% of the UK carbon dioxide (CO2) emissions are produced by the energy consumption of buildings, including the operation of associated building services. This is an area where new legislation can have an impact, and consequently these pressures have filtered through to those sections of the national Building regulations that deal with the Conservation of Fuel and Power. In arriving at the amendments the following important areas were considered;

  • Reduction of CO2
  • To retain or improve design flexibility
  • Reduction of Technical Risks
  • Avoiding excessive costs

The Main Changes

  • U-values for all building elements have been reduced
  • The method for calculating U-values has changed. This means that, for the same construction, a slightly higher (worse) value is produced
  • Tighter control of heating and hot water components and commissioning of these systems
  • Boiler efficiency is now an integral part of all methods of compliance
  • Improved guidance on the control of air leakage and cold bridging outlined in a separate document, providing robust construction details
  • Measures included addressing the overall performance of heating, lighting, air conditioning and mechanical ventilation systems
  • New requirements for both internal and external lighting

Future amendments are already under consideration regarding aspects such as the control of overheating in well-insulated dwellings.

Thermal Bridging, Air Leakage and Condensation

Whilst these issues were not ignored before, the changes to Approved Document ‘L’ have now addressed them in more detail.

The previously published Building Research Establishment document BR262 “Thermal Insulation: avoiding risks” 2002 Edition continues to be relevant. It gives comprehensive data with accompanying diagrams on constructional details for the overall building, floors, walls, windows and roofs. To supplement and extend this guidance additional material was released at the same time as the revised Approved Document ‘L’. Under the title “Limiting thermal bridging and air leakage: Robust construction details for dwellings and similar buildings”, its purpose is to help meet the energy efficiency aims of the revised Approved Document ‘L’ without introducing any inherent or potential risks associated with such aspects as interstitial and surface condensation and with undue air leakage, both inward and outward.

These details were drawn up for dwellings and buildings with a ‘domestic internal environment’. Special situations such as drying rooms and swimming pools are not covered and will need special consideration. They are based on existing industry practice and could be achieved with the skill available on site. For walls, the details cover U-values in the range 0.35 to 0.47 W/m²K. Where U-values lower (better) than 0.35 W/m²K are to be used these details can be assumed not to increase the risk of greater air leakage or thermal bridging although it should be ensured that the thicker insulation levels needed do not compromise the 'buildability' aspects in any way.

Using the Robust Details

Four types of wall construction are covered in the document:

  • SOLID WALLS with external insulation
  • CAVITY walls with
    • a fully filled cavity
    • a partially filled cavity
    • an internal surface insulation

For each wall type, details are shown for a wall junction with:

  • Roofs – pitched and flat
  • Floors – timber and concrete – solid and suspended ground floor – intermediate levels.
  • Separating / party walls

On each detail, because the thickness of insulation material required will depend on the thermal properties of the material to be used, a thickness is not given. Instead, wherever it is critical a minimum R value is quoted:

R = t/l


t  = the thickness and
l = the thermal conductivity of the insulant

Note that any type of masonry material or insulant may be used if it is suitable for the intended purpose. Generally, where a Celcon block is to be used a lesser thickness of added insulation will be needed.

For simplicity throughout the Robust Details, all the cavity constructions have been shown with a brick outer leaf. However, an external finish of render, tile hanging or weather boarding can be used on other types of masonry suitable for the purpose.

Other Information

Where construction details or applications fall outside the scope of BR262 or the Robust Details, the BRE paper IP 17/01 ‘Assessing the effects of thermal bridging at openings’ may be used.

This information has been sourced, reviewed and adapted from materials provided by H + H Celcon.

For more information on this source, please visit H + H Celcon.


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