Where should I put a vapour membrane on IWI

[Iceverge]

13 minutes ago, thetdog666 said:

apart that's why I was going for PIR to get the u value up

 

Do some maths on it. Gut feeling on these things is almost useless as it's been swayed by years of advertising. 

 

14 minutes ago, thetdog666 said:

I currently have netting and 100mm under the suspended floor. I'm going to take the floors up to. Do you recommend I keep with rock wool for the floor aswell?

 

 

This method is good for suspended floors. Otherwise dig them out and use 2-300mm of rigid insulation. 

[thetdog666]

10 minutes ago, Iceverge said:

 

Do some maths on it. Gut feeling on these things is almost useless as it's been swayed by years of advertising. 

 

 

 

This method is good for suspended floors. Otherwise dig them out and use 2-300mm of rigid insulation. 

That's the method I was going for but again using 75mm pir instead.

 

My joists are 90mm thick so thought 100mm mineral wool would help much

Edited January 8 by thetdog666

[Iceverge]

25 minutes ago, thetdog666 said:

That's the method I was going for but again using 75mm pir instead.

 

My joists are 90mm thick so thought 100mm mineral wool would help much

 

Get out the calculator and do some sums is my advice. 

 

 

[thetdog666]

11 minutes ago, Iceverge said:

 

Get out the calculator and do some sums is my advice. 

 

 

I will have a look over the next couple of days. 

 

Say I was to go the 80mm pir then 20mm ontop would any vapour barrier be required then?

Edited January 8 by thetdog666

[Iceverge]

1 hour ago, thetdog666 said:

I will have a look over the next couple of days. 

 

Say I was to go the 80mm pir then 20mm ontop would any vapour barrier be required then?

 

That leaves a 10mm gap. Gaps are bad. Air will move in there. Moving air = thermal looping. AKA, convective cooling inside your wall

 

I would tape the face of the PIR in this scenario as your airtighess layer. Like I said earlier vapour isn't a real issue. It's airtighess you need to worry about. 

 

Why in would you opt for 20mm PIR and not 25mm?. It's harder to source and dearer to boot. 

 

 

[thetdog666]

46 minutes ago, Iceverge said:

 

That leaves a 10mm gap. Gaps are bad. Air will move in there. Moving air = thermal looping. AKA, convective cooling inside your wall

 

I would tape the face of the PIR in this scenario as your airtighess layer. Like I said earlier vapour isn't a real issue. It's airtighess you need to worry about. 

 

Why in would you opt for 20mm PIR and not 25mm?. It's harder to source and dearer to boot. 

 

 

I'm stripping everything out start of next month. Il see if 90mm will fit ok. Would pushing the 80mm PIR right back and leaving an air gap at the front be better?

 

New kitchen is really tight so literally ever mm counts. I will get away using 25mm most places but one wall will need 20mm

[Iceverge]

7 minutes ago, thetdog666 said:

Would pushing the 80mm PIR right back and leaving an air gap at the front be better

 

Any internal insulation won't be doing much then. 

 

If you're ready that caught for space is it worth doing the insulation job at all? 

[thetdog666]

1 hour ago, Iceverge said:

 

Any internal insulation won't be doing much then. 

 

If you're ready that caught for space is it worth doing the insulation job at all? 

ok il double check 90mm is good. 

 

Im sure it will make a big difference if I do it and this is the time while I'm getting a new kitchen

[thetdog666]

there is also 2 exterior walls i can go with 50mm pir on top which will make a big difference. I will be double checking that when i get home in a  few weeks

 

Edited January 8 by thetdog666