Extension & Conservatories

extensions & conservatories

Building Regulations L1B 2015

Legal Requirements (Building Regulations Part L1B)

...  all extensions to existing buildings have to comply with the "Standards for new thermal elements" set out in Table 2 of Part L1B of the Building Regulations  ...  

table 2Table 2 sets the upper limits (worst case) for the u-values of the envelope of the extension. These u-values are sometimes refered to as the 'elemental backstops'.


...  an 'extension' to a dwelling is deemed to be a 'conservatory' if the glazing area of the extension is greater than or equal to 25% of its floor area  ...

Conservatories, as well as complying with the 'Standards for new thermal elements', requires a further calculation (CompSAP) to demonstrate that the heat loss of the conservatory is less than or equal to the heat loss from a 'notional' extension of the same dimensions.

Calculation Methodology (CompSAP)

The energy calculation undertaken for a conservatory is referred to as a CompSAP (Comparative Stanadard Assessment Procedure).

In other words to achieve Part L1B compliance for a conservatory we need to do the CompSAP calculation.

Outline of the CompSAP process

 Setup Stage (we set up the job on our computer and produce a Fee Proposal & Contract)
  • The client request us for a CompSAP and gives us the address of the property along with contact details of the Agent and the Payer.  
  • We set the new job up on our computer system and produce a Fee Proposal, which is sent to the client via email.
  • Once the client has accepted the Fee Proposal (via return email) we proceed to the Design Stage.
  • It is important to note that the Agent is our main point of contact throughout the whole process and ensures that all measures are taken to gain Part L1B of the Building Regulations.
 Design Stage (we consult with the Agent and produce a Final Report)
  • It is important that the CompSAP is undertaken before building commences. This ensures that any potential problems are addressed before building commences.
  • The data for this calculation is extracted from the working drawings and the design specifications.
  • If the CompSAP shows non-compliance with Part L1B of the building regulations then the Energy Assessor will consult with the Agent to discuss what changes are needed to achieve compliance.
  • You will then receive a Final Report which contains all relevant documents relating to this proposed Extension (Conservatory)
  • The Final Report should be passed to your Building Control body to be used as part of their monitoring process.
 Completion Stage
  • Once the Extension (Conservatory) is completed, and provided it complies to the specifications outlined in the Final Report, Building Control will sign-off the building project.


Pricing depends upon the complexity and location of the building. If you would like more information, advice or a quotation, then please call

Richard Owen on 01485 544757 or click here for contact information  >>>    Contact Us