Insulated slab

Mach Two

What is the correct method of putting insulated slabs on the interior walls of a house. The house is an old house. About 80yrs. The slabs are 12mm plaster board with 30mm foam backing. It is only the exterior walls that are being done.

Calahonda52

what is the wall construction?

Mach Two

Mass concrete. Approximately 45 cm wide.

Calahonda52

what is the internal and external finish on the wall?
any sign of damp?

Biker1

30mm of insulation on mass concrete walls=condensation and mould growth

BryanF

Biker1 wrote: »

30mm of insulation on mass concrete walls=condensation and mould growth

Really, can you back this up?

Mach Two

Sand plaster internal and external. Dampness on the walls. Walls facing east. So cold walls.

BryanF

If you have dampness you need more ventilation and heat. Or you have a leak. Figure out which of these are causing the dampness before drylining.

Biker1

Joseph Little is considered a leading researcher on the topic of condensation risk in buildings. https://passivehouseplus.ie/articles/insulation/breaking-the-mould-part-i
My own experience in the matter backs up his conclusions.

Calahonda52

Biker1 wrote: »

Joseph Little is considered a leading researcher on the topic of condensation risk in buildings. https://passivehouseplus.ie/articles/insulation/breaking-the-mould-part-i
My own experience in the matter backs up his conclusions.

The article to which u link is for a 215 hollow block wall, with 100 mm insulation.

This is very very different from a 450 mm mass concrete wall and 30mm insulation.

https://wufi.de/en/service/free-wufi-versions/ is required for an exact calculation

As you know the key issue is where the dew point occurs in the delta T line across the wall.

100 on 215 HB is going to have it on the inside surface of the block.
30 on 450 mass concrete, if a dry wall and not exposed to driving rain, will not be on the inside face

Biker1

While you are correct in saying the article was for hollow block and 100mm of insulation it also referenced the fact that all single leaf construction types act in a similar way.
Whether the wall is dry or wet or dry is only factor and as you say it is where the dew point occurs is the problem.

BryanF

What was the max Insulation dry-lining Thickness/ u-value figure that was mentioned in series?

Mach Two

Does that mean they should be glued rather than fixed by metal pegs.

BryanF

Mach Two wrote: »

Does that mean they should be glued rather than fixed by metal pegs.

No

Dudda

I'm sure you have reason for internally insulating but I'll ask anyway.... Can you externally insulate? I know it's more expensive but grants are available. Its a much better job and you can have a lot more than the 30mm which won't really make a massive difference.

Mach Two

I won't saw I can't externally insulate but would prefer internal. It would be very expensive to externally insulate I would think.

BryanF

Mach Two wrote: »

I won't saw I can't externally insulate but would prefer internal. It would be very expensive to externally insulate I would think.

But it’s a way better job.

Mach Two

BryanF wrote: »

But it’s a way better job.

I won't disagree with you as I have no experience of it.

Water John

A relative of the OH has one of those 1970s prefabricated houses, which I think are maybe single skin. Had it externally insulated a couple of years ago, mighty job. Would be away ahead of slabing if you have the funds.

Mach Two

I would also have to hardwall the inside of the walls as the condition of the walls is not great.

Out of curiosity. If insulating the outside walls is better does that mean that all new builds will be done in that manner.

Biker1

While it is not common place in this country at the moment, external wall insulation and an insulated slab would be my first choice if building again.

MicktheMan

Biker1 wrote: »

While it is not common place in this country at the moment, external wall insulation and an insulated slab would be my first choice if building again.

and?

why split your insulation?
why lose the thermal mass?
where's your air tight barrier?
why not just go with better ewi?

sydthebeat

Biker1 wrote: »

While it is not common place in this country at the moment, external wall insulation and an insulated slab would be my first choice if building again.

Not a good construction on a new build in my opinion.

Thermal mass is a valuable asset to regulate your internal temp.

upupup

Mach Two wrote: »

What is the correct method of putting insulated slabs on the interior walls of a house. The house is an old house. About 80yrs. The slabs are 12mm plaster board with 30mm foam backing. It is only the exterior walls that are being done.

I did this to my house 10 years ago and it made a huge difference to my house.My house was a built by the council in the 50s/60s,there are probably thousands built from the same plan.It is 450 mm mass concrete with 40mm cork stuck to the concrete wall.The cork was plastered and skimmed.It was cold but not damp but in very cold weather clothes would get damp but not the walls.

On every external wall I put up plastic, 50mm kingspan and slabs so I now have 450mm concrete-40mm cork-plaster-skim-plastic-kingspan-slab-skim.There are a lot of layers now!I'm very happy,cosy and warm with the job.

Calahonda52

Mach Two wrote: »

1: I would also have to hardwall the inside of the walls as the condition of the walls is not great.

2: Out of curiosity. If insulating the outside walls is better does that mean that all new builds will be done in that manner.

Hard wall is an excellent substrate for mould growth.

2: no for two main reasons
you can't ewi all builds, eg TF
standard ewi, without a proper rain shield, is not suitable for exposed locations

Biker1

When I said insulated slab i was referring to the foundation slab and not internal wall insulation.

sydthebeat

Biker1 wrote: »

When I said insulated slab i was referring to the foundation slab and not internal wall insulation.

makes much more sense

I fully agree, costs are a prohibitive factor currently though