Best way for me to create a warm and dry loft space...

Discussion in 'Floors, Stairs and Lofts' started by WetWilly, 17 Dec 2016.

  1. WetWilly

    WetWilly

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    Hi,

    Background
    We've recently moved into a 1980's built bungalow.

    The loft is a standard truss design extending about 10m in length.

    There is a layer of non breathable old type felt below the roof tiles. The loft is ventilated on one side by a full length trench vent. On the other side, the same style vent has been covered by a flat roof extension. To compensate, tile vents have been installed in the main roof and soffit vents in the flat roof. However, this side suffers from heavy condensation on the underside of the roofing felt.

    There is roughly 300mm of mineral wall type insulation on the loft floor. It has been boarded over in the centre for storage.

    What we want...
    We want to make this a warm loft. We run a business from home and have always kept our stock in the loft. This wasn't a problem in our old house. The loft was great. But here, the items are becoming cold (brittle) and worse, damp. We would like to convert to a warm loft area.

    The idea
    Based on the construction of our old loft, we would like to insulate on the rafters, leaving 50mm+ space behind for airflow. This would be done with foil backed Kingspan or similar. We would seal with tape. And remove the mineral wall insulation from the joists to allow heat up into the loft.

    Would this work?
    Does this sound like a good idea? We are very concerned about the condensation. The answer to that seems to be more ventilation, but because we want a warm loft, we would rather try and control it using the Kingspan as a vapour layer and of course, to further protect our items. Would condensation form on the 'warm side' of the Kingspan?

    Basically just looking for any type of advice you can offer. Have read so many conflicting opinions on what to do, I just don't know.

    Thanks!
     
  2. freddiemercurystwin

    freddiemercurystwin

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    You could introduce a continuous ridge vent system, on the flat roof side a tile vent at low level between every truss, insulate under the truss rafters to ensure there's an adequate air gap with your kingspan. Effectively how a loft conversion would be insulated.
     
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  4. WetWilly

    WetWilly

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    Hi. sorry for being an idiot. Can you elaborate what you mean?

    I think you mean put a vent the entire length of the loft on the flat roof side of the ridge tiles? So this sits behind the Kingspan in the 50mm+ gap? Then a tile vent in every truss gap? There are 15 truss gaps on each side.

    Cheers.
     
  5. freddiemercurystwin

    freddiemercurystwin

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    Yes if want adequate ventilation. Unless you have some other means of achieving the ventilation?
     
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  7. WetWilly

    WetWilly

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    What I was thinking, but I don't know if sufficient, is to leave the 50mm gap behind the Kingspan going up to the top ridge, and then leave a gap there too, for the air to flow over the top of my 'insulated box' down to the hidden eaves that will be well ventilated. Ridge vent does seem like it would work well there too if I can do it. Does the insulated box need to be ventilated at all? Or just all around it.
     
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