Insulating an undercroft

Discussion in 'Eco Talk' started by MattJG, Nov 28, 2017.

  1. MattJG

    MattJG New Member

    My 1930s house has a 3 foot tall undercroft which spans the space of the kitchen/diner. Roughly half of the houses flootprint.

    Our kitchen/diner is always a bit colder than the rest of the house and the (karndean) floor is colder which I suspect is due to the undercroft. We have an efficient and good sized radiator which ensures the room heats up but it takes longer than other rooms.

    What is the best way of insulating it?
    I am considering something like this and stapling to the joists under the floor in the undercroft.

    My only thought is around ventilation. I'm assuming the undercroft helps with airflow to the house to stop damp/condensation?

    I intend to replace the undercroft door and looking into cavity wall insulation for the exterior wall. We also have a trifold door leading out but it's recently fitted so I doubt it's causing significant heat loss.

    Am I on the right track with this idea?
  2. KIAB

    KIAB Well-Known Member

    I would look at sticking 100mm insulation batts between the joists, they are usually friction fitting, but can be held in place with string nail across joists, or use tile batten.

    Look at Rockwool slabs like their RWA 45 slabs or multi purpose slabs like Knauf Earthwool various thicknesses.
  3. Bob Rathbone

    Bob Rathbone Well-Known Member

    I agree with KIAB, use string and staples, cover the whole thing under the joists with a permeable vapour barrier letting the vapour flow into the undercroft. This will reduce condensation and stop draughts between the floor boards.

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