Thermal Bridge assessment for Part L compliance
It seems a shame that due to restriction of competence to calculate thermal bridges for Part L compliance to only registered assessors, that it is very unlikely that these calculations will be carried out at all. There are only two registered Thermal Bridge assessors in the country.
The reality is that due to costs, clients are not going to pay for thermal bridge calculations and default values will be used in the majority of cases, leading to over-design and higher construction costs.
If we compare this to the PassivHaus certification process, I will model a project using the default PHPP values. I know from experience that if a project’s space heating is around the 15 kWh/m2A figure, if I calculate the thermal bridges, I will knock a further 1 or 2 of this. Therefore, if a building is already compliant, I may hold off on the thermal bridge calculations as an extra card to be played if a problem arises during the process. Or if a project is struggling to make the standard, I will go ahead and calculate the TBs.
Having done the Passive House Acadamy’s Thermal bridge calculation course, a two-day training regime, I am competent to calculate 2-dimensional thermal bridges, for the purpose of PassivHaus Certification. This process also generates Thermal Bridge data suitable for DEAP/Part L assessment, however, I am not allowed to use it as I am not a registered assessor.
It seems to me, that as a Design Certifier under BC(A)R, if I profess to be competent to carry out a thermal bridge calculation, in the same way that I am deemed competent to perform a U-Value calculation with third party accreditation, I should be allowed to. Without being allowed to, as per the current situation, it is reasonable to state that buildings are being over-designed by just under 10%, to compensate for the fact that clients will use default thermal bridge factors, rather than calculate and try to precisely reach compliance.