Dry lining over dry lining

NickTellis

Builder is going to be putting 50 mm Kingspan drylining over existing 30 mm polystyrene drylining on all interior "outer" walls. Anyone know of any problems doing this? I'm a bit concerned about interstitial condensation as the cavity has just been pumped also.

Poor Uncle Tom

How wide is the cavity that has just been pumped? Is it a standard 100mm blockwork leaf either side of the cavity? is there any stone or other vineer outside the outer leaf?

NickTellis

Yes, standard 100 mm blockwork either side of a 100 mm cavity. There is only the new render on the outer leaf.

Poor Uncle Tom

As a very rough guide in this case putting any more than half the width thickness of cavity insulation onto the inside of the wall could most likely lead to interstitial condensation. In this case probably behind the 50mm inner insulation.

NickTellis

Poor Uncle Tom wrote: »

As a very rough guide in this case putting any more than half the width thickness of cavity insulation onto the inside of the wall could most likely lead to interstitial condensation. In this case probably behind the 50mm inner insulation.

B****x.
Beyond leaving the windows open 24/7 is there any practical way to combat this?

sydthebeat

do you know why the original 30mm polysyrene was put in in the first place?

Is it a case of a cavity wall built with no insulation, and then a decision was made subsequent to dryline?

If you have a 100mm cavity pumped and then a 30mm polystyrene internal insulation layer, id say you have enough. id put the money you are now not spending into making sure you dwelling is properly air tight and ventilated. Pay for an air tightness test and report and take remedial action.

NickTellis

Original dry lining was put in (by previous owner) as the cavity was empty. Money has already been spent - the 50 mm boards are currently sitting in the living room waiting to go up next week...

Poor Uncle Tom

NickTellis wrote: »

Original dry lining was put in (by previous owner) as the cavity was empty. Money has already been spent - the 50 mm boards are currently sitting in the living room waiting to go up next week...

NickTellis wrote: »

Builder is going to be putting 50 mm Kingspan drylining over existing 30 mm polystyrene drylining on all interior "outer" walls. Anyone know of any problems doing this? I'm a bit concerned about interstitial condensation as the cavity has just been pumped also.

The horse and the cart are the wrong way around.

Putting the extra insulation on the inside will cause you extra problems with ventilation and heating and continually balancing both to keep the air moisture content low inside the house. It is not impossible but you are making things hard for yourself. Providing a good MHRV system will help and manually checking walls and windows for condensation daily will also help.

sinnerboy

Can you get a credit note for the insulated boards ? I would try rather than press on regardless .