Stone built internal wall insulation advice please

[JamesP]

As @Beau mentions above, we used 25mm X 50mm batten fixed to the wall using similar fixings, very solid with the woodfibre board.

[sb1202]

7 minutes ago, saveasteading said:

The vapour barrier goes on the back of the stud and holds it all in place

By the back do you mean facing the exterior wall? 

[sb1202]

10 minutes ago, Beau said:

I've battened out over old wobbly stone walls a few times. I use 25mmx50mm battens fixed back to the wall with adjustable screws like this. Even though the battens are thin I've had no problems with movement. https://www.efixings.com/adjustable-screws-tx-flat-countersunk-zinc/ You can quickly create a fair wall without any complicated packing out. I will leave advise on insulation and vapour barriers to others

Yeah, used these in a lot of other work.

[scottishjohn]

1 hour ago, Ferdinand said:

I've seen videos using a foil edging tape. Apparently this works better than foam.

and not sure tape will stay adherred for next 50 years 

[saveasteading]

33 minutes ago, sb1202 said:

46 minutes ago, saveasteading said:

The vapour barrier goes on the back of the stud and holds it all in place

By the back do you mean facing the exterior wall

Yes. So you have the damp masonry, then an air gap, then the membrane protecting the stud and holding the insulation.

[sb1202]

51 minutes ago, saveasteading said:

Yes. So you have the damp masonry, then an air gap, then the membrane protecting the stud and holding the insulation.

Sorry, I'm more confused now than when I started. The walls aren't damp. In other parts of the house that are insulated albeit different walls, there is plasterboard, plastic sheet, wool insulation and air gap. There's no vapour barrier and no damp anywhere. There's no damp anywhere in the stone cottage.

 

I've seen and read that there's no vapour barrier needed if the PIR is backed. 

Is this a breathable vapour barrier or a plastic sheet?  A plastic sheet on the cold side would trap moisture coming from the warm side and would be wicked into the timbers would it not?  

 

[scottishjohn]

51 minutes ago, sb1202 said:

A plastic sheet on the cold side would trap moisture coming from the warm side and would be wicked into the timbers would it not?  

conversly putting it on the warm side between insulation and inhabited ppart would lessen the chance

and as said before most moisture in the house comes from occupation and breathing asuming outer walls are dry as you said and with the air gap there which will be vented to eaves it should stay dry  if cold  as cold air holds less moisture 

[saveasteading]

The walls are damp. Not very and the tendency is outwards but they are not dry.

 

The pir is non continuous at  the studs and the studs are exposed unless you put this vapour barrier backing on. 

The polythene is on the inside.

 

53 minutes ago, sb1202 said:

There's no damp anywhere in the stone cottage.

Thats great. We are trying to keep it that way.  

When you start insulating the place you will decrease the heat needed, and the current costly drying of the walls.

[scottishjohn]

normal way to build modern houses is TF  and sheeted on the back and vapour barrier on inside of insulation  and a breathable barrier on outside of TF

 not really possible unless you going to build stud walls as panels and breathable membrane attached before panels are raised into place

 so you could do it that way  if making new stud walls is  your chioce

Edited Friday at 16:13 by scottishjohn

[sb1202]

3 minutes ago, saveasteading said:

the studs and the studs are exposed unless you put this vapour barrier backing on. 

The polythene is on the inside

Yeah, I get that but the confusion is the type of vapour barrier. Should this be breathable or non-breathable on the cold side? If I go to toolstation of screwfix for example,  and search for vapour barrier, they sell plastic sheet under this and there are lots of different types. 

 

Also, does the vapour barrier on the cold side need to be completeley sealed or can it be overlapped? It would be etxrtremely difficult to seal large sheets with a 50mm gap for example.  

[scottishjohn]

4 minutes ago, saveasteading said:

The walls are damp. Not very and the tendency is outwards but they are not dry.

If it was pointed both inside and out with cement mortar --not lime then there will be no  or littlem ovement of moisture through a granite wall

 

 great if outside was lime pointed as it can go out that way , othherwise it can only move downwards through the wall to foundations 

 and there will be no DPC in the walls 

 

thats the reason fro having ground level at outside lower than floor level  - especially  ona ahouse with no DPC

[scottishjohn]

1 minute ago, sb1202 said:

Also, does the vapour barrier on the cold side need to be completeley sealed or can it be overlapped? It would be etxrtremely difficult to seal large sheets with a 50mm gap for example.  

If you make new stud walls just wrap the membrane around edges of panels before you fit them -then you have a complete seal  ,by the time they are screwed together

[saveasteading]

31 minutes ago, sb1202 said:

completeley sealed or can it be overlapped? 

Breathable. Overlapped. Stapled to the timber. No tape. 

[sb1202]

2 hours ago, saveasteading said:

Breathable. Overlapped. Stapled to the timber. No tape. 

Done! 

[Redbeard]

4 hours ago, sb1202 said:

Sorry, I'm more confused now than when I started. The walls aren't damp. In other parts of the house that are insulated albeit different walls, there is plasterboard, plastic sheet, wool insulation and air gap. There's no vapour barrier

The plastic sheet IS the vapour control layer. It sits on the warm side of the insulation, immediately behind the plasterboard (or wood-wool or wood-fibre - choose your weapon!). These days I prefer intelligent membranes, which are reckoned to be completely vapour-closed in cold weather. (well, so is plastic...) and somewhat vapour open in warm weather (plastic isn't) so in my view it is a 'pessimist's membrane- (i.e. It should be 100% vapour-tight, and no let any vapour thro, but if you take the view that few things are guaranteed to be 100%, if any w.v. has got thro it can 'breathe' back out in summer.