Correct way to insulate single skin wall please.....

[Keith9534]

We have a single skin porch on the side of the house.

Its constructed on the front and rear faces of brick. The side wall, which is against the neighbours wall with a 12" gap, is high density concrete block.

I removed the plasterboard which was batterned to the wall with a small air gap as they had mould growing on them . The rear face of the plasterboard was clean. The actual boards were damp as they crumbled easily when taking them off.

My question:

What is correct when re-fitting the porch?

Do I put a membrane against the wall, then insulate with double foiled celotex and then fit a vapour barrier under the plasterboard ( the alternative being foil backed plasterboard )

OR

Do I fit double foiled celotex to the wall, a vapour barrier and then plasterbaord.

Or

Do I fit double foiled celetex to the wall, tape the seems and then plasterboard.

I have read lots about allowing the room to breath, etc, but am confused about the correct way to do things.

Just to add to that - the porch is about 4m x 2.5m, is heated with a radiator, and has a door either end on the building.

Anyone?

 

[noseall]

is the 'porch' closed off from the main dwelling?

 

[PerryOne]

I am puzzled, why heat a porch?
When you open the door all the heat blows away.
A porch is usually merely a buffer against the outside weather and noise, helping to stop all the warm air from indoors disappearing.
There is no set way to decorate a porch, factors to take into account are, does the porch have a damp proof membrane under the slab and in the walls?
Does the dpm/dpc match/join the home dpc?
Do the windows and doors fit? Do they leak?
Is it damp? It reads like it is?

 

[noseall]

I am puzzled, why heat a porch?
When you open the door all the heat blows away.
A porch is usually merely a buffer against the outside weather and noise, helping to stop all the warm air from indoors disappearing.
There is no set way to decorate a porch, factors to take into account are, does the porch have a damp proof membrane under the slab and in the walls?
Does the dpm/dpc match/join the home dpc?
Do the windows and doors fit? Do they leak?
Is it damp? It reads like it is?

i was getting round to this, hence my Q.

 

[Keith9534]

The porch is heated because we have two dogs that sleep in there at night.

The outer walls are built on proper foundations and a warm floor was created ( poly insulation, 1000 gauge DPC and floor screed )

The floor slab is BONE dry.

The walls have a DPC at the same height as the house and its tied in front and back

The doors are UPVC double glazed

The porch is/was damp and thats what we are trying to sort out

A dehumidifier has been running for a while but since the roof was redone and the plasterboard removed it is scarcly finding any moisture.

I am really wondering if the damp/mould was due to institual moisture ( is that correct? ) because it was just an air gap behind the old non-foil backed plasterboard

Another more complicated way would be to put an internal wall in place with insulation between them , but don`t really want to go that route.

Incidently, since the plasterboard was removed the walls seem less cold to the touch????????

 

[Keith9534]

Sorry....the porch is closed off from the house as the original front door is still in place.

 

[jeds]

There are many ways you could do this. My personal favourite is thermal laminate plasterboard. (plasterboard with foam insulation bonded to the rear) I have specified this many, many times and it works extremely well and is easy to install. 50mm board can be fixed with long austinitic screws direct to the masonry.

A 2400x1200 sheet of 50mm board costs about £35.00

 

[Keith9534]

There are many ways you could do this. My personal favourite is thermal laminate plasterboard. (plasterboard with foam insulation bonded to the rear) I have specified this many, many times and it works extremely well and is easy to install. 50mm board can be fixed with long austinitic screws direct to the masonry.

A 2400x1200 sheet of 50mm board costs about £35.00

This sounds ideal

....and no plastic vapour barrier is needed?

 

[noseall]

if the boards are plain backed as opposed to foil they can be dot & dabbed too.

 

[PerryOne]

As you are no doubt aware, mould will grow on any damp surface where there is something it can eat, and plasterboard is an ideal food source.
I would guess, from what you write that, the walls are very cold, no insulation and they are damp from the water vapour breathed out by the dogs.
You probably have a situation where the dogs breath, being hot and 100% humid was attracted direct to the nearest cold surface, the plasterboard beside them.
As mentioned elsewhere, two inches of polystyrene or similar stuck to the wall will solve the problem.
However, this will merely transfer the water vapour onto the next coldest surface in the porch, probably the walls that will be even colder, once the insulation is fixed to them.
Foam insulation needs to be both dense and more than three inches thick before it becomes a vapour barrier, it is always best to stick foam boards direct to the wall covering the whole surface with plasterboard adhesive and pressing tight to avoid interstitual condensation.

 

[jeds]

This sounds ideal

....and no plastic vapour barrier is needed?[/quote]

Vapour barrier is a slightly tricky one. PUR foam is a closed cell material so acts as a barrier in itself. But vapour will permeate the joints between the boards so you are likely to get some moisture build up beneath. However, you're talking about a single skin brick wall, which is going to be damp anyway, so I don't think this will be a significant problem.

 

[Keith9534]

I would guess, from what you write that, the walls are very cold, no insulation and they are damp from the water vapour breathed out by the dogs.
You probably have a situation where the dogs breath, being hot and 100% humid was attracted direct to the nearest cold surface, the plasterboard beside them..

Spot on!

As mentioned elsewhere, two inches of polystyrene or similar stuck to the wall will solve the problem. However, this will merely transfer the water vapour onto the next coldest surface in the porch, probably the walls that will be even colder, once the insulation is fixed to them.

Are you saying that the water vapour will move into the room more or go out to the walls?

I`m trying to eliminate the mould growth by the best possible means.

During the winter its heated and for the last few months has had a de-humidifier working to keep it down.

I`m still slightly confused about the need for a plastic ( visqueen ) membrane directly next to the wall underneath the celotex or does it go between the celotex and the plasterboard.

Would this stop the condenastion?

The walls can get as cold as they like....lol...as long as it doesn`t encourage mould to grow.

 

[Keith9534]

Vapour barrier is a slightly tricky one. PUR foam is a closed cell material so acts as a barrier in itself. But vapour will permeate the joints between the boards so you are likely to get some moisture build up beneath. However, you're talking about a single skin brick wall, which is going to be damp anyway, so I don't think this will be a significant problem.

The wall is cold but not damp.

Are you saying that the vapour will permeate from the wall side into the back of the insualtion...or the other way around?

I intend to foil tape all the room sided joints, but I think you are saying that the mould will grow behind these taped joins????

 

[noseall]

you have only a single skin wall complete with occupants inside - bad combo'.

you have damp both sides!

single brick wall.

polythene membrane.

battens.

foil backed insulation (taped).

board and skim.

 

[PerryOne]

Mould spores are in the air where ever you are, indoors or out, here or North Pole.
They just move about in the convected air currents looking for some where to land and grow.
Growing requires both food and water.
Remove the water mould growth stops dead.
With a single skin wall, you will always have damp, during the winter more noticeable than during the summer - a matter of degree.
A single skin wall provides the same insulation as a double glazed window, is there any point in adding insulation to a small part of the structure, that will achieve little?
You can of course waterproof the outside of the walls, silicone paint will cause the walls to shed the rain and they will dry out, eventually.
However, the dogs will continue to add water vapour from the inside, this will enter the wall and transfer to the outside as water vapour is always attracted to cold, it will then disappear into the air.
Having sheets of polystyrene stuck to the wall (provided they are not dense or more than three inches thick ie waterproof) will allow the water vapour to pass through the polystyrene and the wall.
Wet plaster or plasterboard on the inside are also transparent to water vapour - and that's it.
Let the water vapour move through the wall in either direction and disappear.