Internal insulation to eliminate damp.... Lots of questions!

[RWhites]

Hi all.
I've been lurking for a while, but never posted until now. I'm about to undertake a fairly major DIY project, and I'm wanting to get some expert opinion on a few issues....

The underlying problem that I'm looking to address is a damp problem in an upstairs bedroom. The major damp issue is on one elevation, but also happens to be a wall where there is a full-width, full-height set of wardrobes - which I imagine are blocking airflow to the wall pretty well. The room has 3 external walls.

The house is constructed of red brick, with a cavity, and there is polystyrene-bead cavity insulation. The wall is rendered to the outside, but the render is in very poor condition and needs replacing fairly soon (financial constraints prevent this for now). The house is in an exposed position, and the main dampness inside corresponds with the part of the house that catches all the weather on the outside - prevailing wind and rain are pretty consistent here.

I've read that cavity wall insulation should never have been installed in a house of this type in such an exposed location, as it acts as a 'bridge' for moisture when under high wind load - but I guess there is little that can be done about that for now, I bought it like this!

I am unsure whether the dampness is purely condensation, penetrating damp, or both. (There was active woodworm in this position in the house when we bought it a few years ago, so I'm inclined to think there is definitely some penetrating damp).

The plan in my head is to remove all existing plaster, then build a 50mm metal-framed stud wall internally, immediately adjacent to the brickwork(on all 3 external walls), then in-fill between the studs with 50mm kingspan and clad the whole lot on the room-side with insulated plasterboard (25mm insulation on 12.5mm board). The room is not large, but I'm prepared to lose the internal space as it is my toddler's bedroom, and eliminating the dampness is more important than the space. I will also be removing the ceiling and insulating that while I'm at it.

My main questions are these:
Do I need to leave an air-gap between the stud wall (complete with in-fill insulation) and the brickwork? My current plan leaves no gap to speak of.
Do I need to incorporate an additional vapour barrier somewhere - I guess immediately adjacent to the brickwork?
I'm currently thinking I should incorporate a vapour barrier... is there a reason I shouldn't do so?
Is 'vapour barrier' just a posh way of saying 'big sheet of plastic'? Or are there some overpriced 'breathable' things I should be considering?

I think that covers it for now....! Any input will be gratefully received.

Many thanks in advance.

 

[GraftingTerry]

Id start by saying until you are able to address the underlying render issue then your attempts to solve the problem may prove futile - isolating the damp may well just lead to it smelling in the long term. That being said, id go for gyplyner metal and thermal board on the face (provides integral vapour control), this should fix the internal issue and minimise the loss of room.

Theres a hundred different boards to choose from, but i find this one to provide the necessary vapour and thermal properties.

http://www.insulationplace.co.uk/British-Gypsum-Gyproc-Thermaline-Plus-2400x1200x35.html

 

[RWhites]

Having thought about it some more, I reckon that most of the dampness is condensation. I'll be borrowing a damp meter soon that I hope will help determine accurately.

However, my questions at the end of the first post remain.... can anyone help?

 

[mointainwalker]

I'll be borrowing a damp meter soon that I hope will help determine accurately.

Can this tell the difference between the two, then ?

Do I need to leave an air-gap between the stud wall (complete with in-fill insulation) and the brickwork? My current plan leaves no gap to speak of.

No gap necessary if you use insulation board.

Vapour barrier is necessary, plastic sheet is fine, but it should go between plasterboard and insulation.

 

[RWhites]

I'll be borrowing a damp meter soon that I hope will help determine accurately.

Can this tell the difference between the two, then ?

Do I need to leave an air-gap between the stud wall (complete with in-fill insulation) and the brickwork? My current plan leaves no gap to speak of.

No gap necessary if you use insulation board.

Vapour barrier is necessary, plastic sheet is fine, but it should go between plasterboard and insulation.

Thanks for your input.

I plan to hack off some plaster in the affected area before using the damp meter - both against bare brick and damp plaster - if the brick reading is high, then I reckon I've got a penetrating damp problem, but if low, I'll just conclude it is mostly condensation. Also, if the plaster is wet / damp rather than dry I guess that is a good indicator....

 

[sharpener]

We had a similar problem in a stone barn conversion, where the gable end wall had penetrating damp and there was a small amount of black mould on the bedroom wall. When we bought it the structural survey recommended dry lining with a cavity made using e.g. plastic waffle spacer sheet ventilated top and bottom.

What we did in the end was to wash the wall with Jeyes' fluid and put up horizontal tanalised 2 x 2 battens, with 50mm breathable sheepswool slab insulation in between held in place with polypropylene geotextile (available in smaller quantities than breather membrane), then vertical 2 x 2 studs and finally foil backed plasterboard and skim coat. The cavity has Mapvents every 1.5m at the bottom and is exhausted at the top to a whole-house MVHR system - but if we hadn't been installing that we would have just put another row of Mapvents at the top.

A year on the bedroom wall is about 2 deg C warmer to the touch and there has been no problem with condensation, smells, damp or mould growth.

HTH

 

[JohnD]

a damp problem in an upstairs bedroom. The major damp issue is on one elevation, but also happens to be a wall where there is a full-width, full-height set of wardrobes

This is typical of condensation. If you can ventilate the space behind the furniture to the outside it will stop.


tape a piece of clear plastic tightly to the wall.

See of water forms on the room side (condensation) or on the wall side (penetrating)

Does anyone drape wet washing around the house or over radiators?

 

[RWhites]

This is typical of condensation. If you can ventilate the space behind the furniture to the outside it will stop.

tape a piece of clear plastic tightly to the wall.

See of water forms on the room side (condensation) or on the wall side (penetrating)

Does anyone drape wet washing around the house or over radiators?

Thanks for the input. I've not got hold of the damp meter yet, but I'm becoming increasingly convinced it is just condensation. I've taped a piece of plastic to the wall anyway to see if it is penetrating.

Of course the wardrobes aren't in place any more, so it all seems much better... and they won't be going back in that position anyway after the re-furb.

On the wet washing front... of course we do!! I know I know, but try telling the missus! On a serious note, this house is not what you would call 'unventilated', so whilst I accept the argument in part, the washing is a small issue in the great scheme of things. Having said that, as I work my way round the house with new windows, insulation etc, it will gradually improve from an 'unwanted ventilation' point of view... and then I'll be more mindful of too much moisture in the air....!

 

[mointainwalker]

the washing is a small issue in the great scheme of things

No it's not. There are likely to be several kilos of water in that washing and it's going to be distributed around your house as it dries..

Stopping this practice would the easiest, single most-effective thing you could do.