Tenement flat - stop draught behind lath plaster wall

[rarara]

Hi, to cut a long story short I have a top floor tenement flat, with a couple of rooms (kitchen, wc) protruding from the main building. The kitchen in particular is pretty cold, particularly when blustery. I thought the main reason was the lack of loft insulation in the protruding part of the flat (seperate loft space with no access until now).

I have bought some rolls of knauff and will insulate shortly, but I noticed yesterday when taking a socket off one of the walls that there is a draught (behind the lath + plaster) that would cut you in two.

1) Will loft insulation be of limited benefit while this wall is acting as a big heat sink?

2) Is there any way to limit this airflow?

I understand that there should be an air-gap between the plaster and the sandstone wall on the outside to prevent transfer of moisture. I am presuming that there is a gap at the top/loft which is allowing wind to whistle down - can this be blocked even partially, to still allow the gap to exist but prevent it being so cold??

 

[Alastairreid]

The lath will be unlikely to extend into the loft it would normally finish at ceiling level.

The external walls will be cold, the only real remedy would be to line the walls with an insulated plasterboard.

 

[JohnD]

if it is your own flat, best result would be to tear off the L&P and reboard with a bonded insulating plasterboard, plus extra insulation board in the cavity (spaced away from the stone or brick).

Celotex or Kingspan is suitable, with the shiny metal foil. You will not know what thickness to use until you have the L&P off and measure the gap.

You will have quite a bit of dirt, and redecoration to do, but old L&P is usually cracked and loose, and you will have a nice smooth wall to make future decorating easier. For best results have a plasterer skim it, it will not be expensive.

Do any plumbing or wiring while the wall is open, even if you just run some plastic conduit for future use and put some blanked-off boxes in. Phone, TV and alarm cables, not just sockets, in separate conduits.

 

[rarara]

The idea of tearing down the wall isn't appealing as it is in decent condition and I have only recently had the ceiling repaired/replaced

The real issue I am trying to address isn't so much the fact there is a gap, but more the problem with the air movement. When it is below zero and frosty I never notice the room as cold as when there is a breeze. How does the air get into the space - at its highest point under the gap in the eaves?

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• rarara
• 2 Mar 2015
• 1

 

[Alastairreid]

Are there external wall vents nearby?

 

[rarara]

there is the vent where the boiler exits - it is on that wall. looking from another room there is approx 1/2 to 1" cap between the core and the vent pipe on the outside

 

[Alastairreid]

There should not be a gap between the flue pipe and blocks, it allows carbon monoxide to enter the cavity.

Are there any other vents on that elevation which would allow the cavity to air.?

 

[rarara]

Looks like this...

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• rarara
• 2 Mar 2015
• 1