Alternatives to aircrete blocks

So you are going to start building your new house or property. The energy assessor has approved the design. The Architect has allowed for aircrete blocks.

But.…The merchants and suppliers have run out of all aircrete blocks. Again.

There are alternatives to aircrete blocks. Yes, the thermal performance will not be quite as good, but there are other energy balances to be consider.

1. Try and find a concrete block (to suit your needs for structure and acoustics) and look for a thermal conductivity (or lamda) value of 0.28 W/mK or less. This is considered ‘ultra-lightweight’ by the Concrete Block Association. Example below:

2. Get the manufacturer of the insulation to calculate your ‘U’ value as they want to ensure you get the best result. So if full fill insulation, try Knauf Insulation or partial fill, then register with Celotex and use their online U Value Calculator.

3. Ask the energy assessor (SAP or SBEM assessor) to review their Thermal Bridge Details using the Concrete Block Association



4. This will help prove less heat loss at the junctions depending on type of insulation used. Extract below of figures:



5. Not passing still? Check what is used for extract ventilation. Try the Greenwood Unity CV2 Continuous extract fan. It is a low velocity, continuously running extract fan with a boos, but low energy.

6. Not passing, let us know and we can help point you in the right direction.

More on Thermal Bridging

Here are some recommended guides and websites to obtain enhanced details for thermal bridging.:

  • Knauf Insulation when used with aircrete blockwork (lamda <0.19 W/mK) or timber frame construction.
  • Aircrete blockwork – for full fill and partial fill solutions.
  • Concrete Block Association – For blockwork of all density values for partial and full fill insulation.
  • LABC Details – Check out these by LABC
  • Xtratherm Insulation – lots of details including a handy calculator.
  • Besblock – They have lots of details, scroll to the bottom of the page and this handy summary is also very useful.
  • Celotex – Steel frame and masonry solution using their insulation. You need to login to access.

Need a bespoke calculation?

Low Carbon Box will research the best available option. If the detail is not currently available and we believe we can improve on this, then we can provide a bespoke thermal bridge detail.

Just get in touch.


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