Insulating victorian rear addition roof

Discussion in 'Eco Talk' started by jambo_sana, Dec 1, 2020.

  1. jambo_sana

    jambo_sana New Member

    Hi all!

    We pulled down a few ceilings today and this gave me a good look at the roof in the back room of our vicorian rear addition. This part of the house has a low, sloped roof with no loft space.

    This is what it looks like:


    Now, there was no roof insulation there before, and given that it also has 3 external walls, it has always been pretty chilly.

    I was wondering if it's possible to add insulation without decreasing the height of the room substantially. The spot where the ceiling is horizontal should be easy enough - we can add rockwool insulation above the ceiling plasterboard.

    For the sloped part of the ceiling, I was wondering if it's possible to:
    - add 50mm rigid insulation board to the 10cm rafters, leaving a 50mm ventilation gap
    - attach a 27mm insulated plasterboard to the rafters

    I know this doesn't give a great deal of insulation, but I'm operating on the principle of something is better than nothing. We really don't want to sacrifice height - it's a very pokey room already.

    Does this make sense, and would this provide enough insulation under the rafters to avoid cold bridging and condensation issues?

    Also, does this leave enough ventilation under the roof?

    Thanks all - I would appreciate any insight into this, and maybe experiences from someone who has a similar room.
  2. Bobby Dazzler

    Bobby Dazzler Active Member

    I think your work should be subject to BC regulations because you're replacing most of the ceiling.

    But to answer your questions, your proposal should provide enough to avoid cold bridging and condensation, but it might not meet BR

    Use loft ventilation trays to maintain ventilation where your rockwool will meet the roof.

    And add a vpm immediately above the plasterboard. Polythene sheet stapled to the rafters will suffice.
  3. jambo_sana

    jambo_sana New Member

    Thanks very much - that's helpful. My plan was for the foam insulation to extend a bit above where the rockwool would meet the roof, hopefully preventing the wool from meeting the roof and making sure there's no gap there.

    I've been in touch with BR and they said it wouldn't need to meet insulation regs in this case, but we'll re-do the whole back of the house in a year's time and that will - but until then, better something than nothing.

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