Do I need to carry out extension and insulation upgrades at the same time?

1 July 2021
by john biggs

I am planning an extension and wish to use the facility provided by Building Regulations Part L ‘Whole Dwelling calculation method’ clause 4.6. The area-weighted U-value of my extension is worse than required, due to the amount of glazing incorporated. At the same time I intend to upgrade the roof insulation to the existing dwelling and this U-value gain would outweigh the shortfall in the extension. My question is whether I have to carry out both the extension and the insulation upgrade at the same time, or can I proceed with the insulation upgrade prior to commencing the extension at a later date?

2 Answers

  1. Jen Grimble says:

    Hi John,
    Thanks for your question. I have asked one of our experts for comment and will get back to you as soon as possible.

  2. Nigel Griffiths says:

    Hi John,

    Yes you can upgrade your roof insulation at any time and commence the extension at a later date. The only benefit of doing both at the same time might be a slight reduction in costs. It’s not clear from your message what the roof insulation entails – if it’s just top up of loft insulation then this is not a difficult task but if the roof is being substantially altered and scaffolding is required then the saving would be more significant.

    Best regards – Nigel Griffiths (Build It Sustainability Expert)

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