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Condensation on inside of external brickwork inside cavity


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I am almost at the stage of putting insulation in between the timber stud work that is up against the external brick walls. We have a sizeable cavity space due to requirements of structural engineering specs but I've just noticed some serious condensation on the brickwork directly underneath the box gutter. Ok it was after the recent cold weather we've had and the property isn't totally airtight yet so its' pretty cold inside as well but is this normal? and will it stop once the cavity is closed up with this insulation between the stud work and plaster boarding on top?

I don't know if it's anything to be concerned by and therefore easier to rectify now before covering up.

I will attach a photo.


Edited by ashthekid
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Ventilation is always good, ideally don’t build your inner walls and insulation etc while the brickwork is wet through, but once your inner skins are up there will be little to no moist air hitting the bricks and the space will be much warmer anyway.

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A few comments, yes the brick wall will continue to pick up condensation but only in very cold weather. 

I would use sheet insulation packed off the bricks by 25mm with say 25mm EPS then insulate as you plan , a full layer of 50mm would work best I think.


a vapour barrier is totally crucial ON THE WARM SIDE OF THE INSULATION.


bit advanced but I worry about this https://readinguk.org/draughtbusters/lead-pumping/  


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There is a sizeable cavity between the exterior brickwork and the beginning of the stud wall - approx 20-30cm - this was required by structural engineer because the brick wall is so old.

Does that cavity size make a difference?


And where exactly would you put the vapour layer?

If the order is: brick wall, 20-30cm cavity, timber stud work with 100mm PIR in between studs, 9-12mm ply, 20-25mm PIR, 19-25mm batten, 12.5mm plasterboard.


I'm assuming before the ply goes on?

Is the ply important?

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