Building Regulations

in the UK, Building Regulations 2010 set minimum standards for building work, including retrofitting. You can download a copy of the Building Regs from the government website -

https://www.gov.uk/guidance/building-regulations-and-approved-documents-index

It's worth reading the early chapters of the "Manual to Building Regs" document which succinctly explain the process, including whether you may need to notify Building Control of your project. Regardless of whether your project is notifiable, or even if you're carrying out the works yourself, you should still follow the Building Regs. Otherwise you risk a situation where a future building survey discovers substandard levels of insulation which could affect the value of the property.

Approved Document L, Part 1 includes requirements for thermal performance which encompasses insulation. These requirements aren't as stringent as some other standards you might have heard of (e.g Passivhaus - for more info see our Benchmarks page) and it should be remembered that they are a minimum standard that's intended to strike a balance between the cost of the work and the performance of the final construction. There's no harm in providing additional insulation beyond what Building Regs require, but the cost-benefit ratio may diminish if you add significantly more insulation than is required.