How did you fit your PIR into wall cavity...

[Carrerahill]

I have a thermalite/concrete block cavity wall going up, 50mm PIR specified for the cavity. We will be doing the insulation, bricklayer said he can build the thermalite walls first leaving the wall ties and we can fit the PIR, or he will build thermalite and block simultaneously and we can follow him and fit insulation.

 

The next minor issue is the sheet size, I just bought 4x8 sheets, I was sort of hoping to try and wrangle them in as whole sheets by poking wall ties through or something (I was not thinking it through when ordering materials) but I think I will make more penetrations and holes than just cutting them all square to 450mm and putting them in piece at a time, I can then foil tape them and foam joint any bad bits. 

 

So I was just looking for some feedback and thoughts from you guys as to what you did (or builder did for you).

 

I am angling towards getting the inner wall up first, cutting the sheets to 450mm slices, fit it all snug, tape it all up, foam it where needed and make sure the corners are nice and tight and what not, and generally create a full building "wrap" of insulation.

 

 

 

 

[jayc89]

How big's the cavity? I'm planning on going full-fill with EPS beads instead. Much easier, less risk of gaps etc. Can be done at any time before the internal wall coverings go on. Just need to ensure the builder closes all the cavities before they leave. 

 

For PIR, I wouldn't start poking holes through the bigger sheets, generally cavity batts are used which are 1200 x 450 to fit nicely between wall ties. I guess you could cut your sheets down to 5x per?

[Carrerahill]

Just now, jayc89 said:

How big's the cavity? I'm planning on going full-fill with EPS beads instead. Much easier, less risk of gaps etc. Can be done at any time before the internal wall coverings go on. Just need to ensure the builder closes all the cavities before they leave. 

 

For PIR, I wouldn't start poking holes through the bigger sheets, generally cavity batts are used which are 1200 x 450 to fit nicely between wall ties. I guess you could cut your sheets down to 5x per?

We have a 100mm cavity.

 

I think I will cut the sheets down, I will try and make use of the longer (640mm) last cut piece in the gables and things. 

 

On your own build, I wouldn't go for the EPS beads full fill, keep the cavity clear, there for a reason for it, let it breath. 

 

 

 

 

 

 

[jayc89]

8 minutes ago, Carrerahill said:

We have a 100mm cavity.

 

I think I will cut the sheets down, I will try and make use of the longer (640mm) last cut piece in the gables and things. 

 

On your own build, I wouldn't go for the EPS beads full fill, keep the cavity clear, there for a reason for it, let it breath. 

 

 

 

 

 

 

 

Cutting down makes sense if you already have the boards.

 

Plenty on here already have full-fill EPS beads, I think @Icevergemight be one of them. I'm not aware of any problems using that method (opposed to blown mineral wool, for example). 

[JohnMo]

People usually avoid PIR in blockwork walls because it's difficult to get gap free insulation.  Every gap is a heat leak, mineral wool cavity batts would be more forgiving and possibly better performing in real life.  Or as mentioned EPS beads.