Mos

Okay thank you

I've read the appendix on the simple payback method. The above calculation does use a SAP-based method. This is what Part L appendix says on simple payback method: The marginal additional cost is the additional cost (materials and labour) of incorporating, for example, additional insulation – not the whole cost of the work. The cost of implementing the measure should be based on prices current at the date when the application is made to the building control body and be confirmed in a report signed by a suitably qualified person. The annual energy savings should be estimated using the Standard Assessment Procedure. I just need to get an energy assessor or quantum surveyor to sign the calc off.

FYI to add... the 15 year payback rule is not based on a 'whole dwelling' calculation so it should not require a SAP-type assessment. Part L specifically says that this relates ONLY to the material and labour cost (ex VAT) of upgrading the thermal element in question... in my case only to the external wall upgrade. Here is the calc for anyone interested: 62.5mm insulated plasterboard. Material and labour cost of element: £11,160 ex. VAT Fabric: solid brick, 215 mm (2 leaves), uninsulated; typical U-value from SAP tables ≈ 2.20 W/m²·K U-value after wall upgrade: 0.27 W/m²·K Improvement (ΔU): 1.93 W/m²·K Current gas energy pence/kWh (as per BEIS): 6.3p/kWH kWh saved/yr: ≈ 9,264 kWh/yr £ saved/yr @ 6.3p = 9,264 × £0.063 ≈ £584/yr >19 years to pay back initial costs.

Adding further insulation would not reduce the floor area by greater than 5% unfortunately. So I only have the simple payback clause to hang on to. Surely this clause is in Part L to enable some economic flexibility with homeowners like myself ... when I raised the fact that 62.5mm plasterboard would exceed the 15 year payback to the BCO, she asked me to send her calculations, which I did. It sounded like she was not familiar with this clause, and when I prompted her for feedback nearly a week later she replied "Insulation is insufficient. I need access to all documents to show where your interpretation is not correct." I literally copy and pasted extracts from Part L to support my case regarding the payback clause. Still waiting for her reply... to me it looks like she is deliberately trying to "prove me wrong" despite me citing word for word the document to her. I've now instructed an energy performance consultant to try to communicate with the BCO on my behalf to understand (1) what she wants exactly and (2) if a letter outlining the overall thermal enhancement would suffice. I may also get an quantitive surveyor to validate my simply payback calculation (which I got using chat GPT, which has been quite good at helping me). SAPs are not a formal requirement for renovated properties, they are only a requirement in new builds. They are not listed as a requirement in Part L. She has requested one, but according to the energy consultant, this is incorrect as a SAP on an old dwelling will always flag up issues and they are only appropriately applied to new builds. If anyone has further advice, particularly regarding the simple payback clause, I would much appreciate. I am in a desperate position and being inaccurately forced to add another layer of insulation over the existing would cost me thousands. Thanks

Hi I am currently extending and renovating our end of terrace house. The external wall construction is made of solid brick (2 leaf) with no cavity. The party wall is made from 4-leaf solid brick with no cavity. As I have removed the old internal render, this has triggered the requirement to thermally upgrade the external walls as per Part L. I have two issus raised by a very difficult building control officer, below: 1. PARTY WALL: the officer seems to be convinced that the party wall requires upgrade to meet the 0.3 u-value target stated for external walls. However Approved Document L, section 4, table 4.2 (Limiting U-values for new thermal elements) states a u-value of 0 for party walls in NEW thermal elements. It does not refer to party wall u-value requirements in renovated walls. However in the same document, section 4, table 4.3 (Limiting U-values for renovated or retained elements)... this table lists u-value recommendations to existing thermal elements. A thermal element, as defined in page 76 is: “a wall, floor or roof… which separates a thermally conditioned part of the building from the external environment (including the ground)”. It assigns a u-value of 0.30 W/m²K to external wall upgrades. A party wall u-value for renovated or retained elements is not listed, and a party wall does not represent a thermal element by definition according to Approved Document L (as it is a heated space between two dwellings). Therefore, there is no stated requirement that exists in law to thermally upgrade existing party walls during renovation. However, the BCO seems adamant and as yet has not been able to provide evidence to refute this. 2. EXTERNAL WALLS: Part L states that a u-value of 0.3 should be achieved when upgrading external walls in renovated properties. This would require using 62.5mm insulated plasterboard. However this would come at a hefty cost to us. As such, I have used the following clause in Part L to justify using a thinner insulated plasterboard (37.5mm): Approved Document L, (vol 1, 2021 with 2023 amendments) section 4, states the following (page 26): “4.13 If achieving the u-value in Table 4.3, column (b) either: 1. is not technically or functionally feasible or 2. would not achieve a simple payback of 15 years or less then the element should be upgraded to the lowest u-value that both: 1. is technically and functionally feasible and 2. can achieve a simple payback not exceeding 15 years. Generally, a thermal element once upgraded should not have a u-value greater than 0.7W/(m2·K).” I have provided the BCO with a calculation that shows using 62.5mm insulated plasterboard achieves a u-value of 0.27 BUT it would take approx 19 years to pay back the cost on material and installation. As such, we have gone ahead and applied internal wall insulation with 37.5mm which achieves a u-value of 0.67 (within the 0.7 backstop mentioned in the document)... which is the most practicable and economically justifiable option for us. Again, she is very stubborn on this and says she will need to go back to the document and dig up evidence to show why this would be non compliant. As yet, she has not provided this information and I now feel she is trying to frustrate the process. I would be grateful for any advice and thoughts regarding the above. We have not yet applied any drylining to the party wall as I do not know what the outcome with the BCO will be, but I have already insulated the external walls with 37.5mm plasterboard and do not want to remove this as it would cost a fortune. Thanks Mike