External wall - PIR or full fill batts

[Moonshine]

Following on from this thread

 

 

I am have a dilemma and keep going round in circles to which one to build.

 

Build a masonry cavity wall (rendered) with PIR and a residual cavity (125mm total cavity), or fully filled 150mm cavity.

 

Both have the same U value, and I am in a severe wind driven rain area.

 

Which one would choose and why?

[joe90]

As per your last post, I have 200mm full fill with batts, BBA certified for full fill,  I know it does not wick moisture, easy to fit lt can be stuffed in awkward corners, does not need accurate fitting/glued/foamed, and yours is rendered mine is brick. No brainier . (IMO).

[joe90]

5 minutes ago, Moonshine said:

Both have the same U value, and I am in a severe wind driven rain area.

so am I!?

[Moonshine]

47 minutes ago, joe90 said:

so am I!?

 

Aren't you in the very severe exposure zone?

 

[joe90]

56 minutes ago, Moonshine said:

 

Aren't you in the very severe exposure zone?

 

YES!,!,,!,,,,,!,

[SteamyTea]

2 hours ago, joe90 said:

YES!,!,,!,,,,,!,

and you are about 150 m high.

[joe90]

3 minutes ago, SteamyTea said:

and you are about 150 m high.

well I didn’t know that, I just know it’s very flat!

[Moggaman]

Joe90, there are special wall ties for cavities over 150mm.... are they expensive compared to normal ones.... also the thermal conductivity of the batts is probably around 0.037 as compared to 0.021 for PIR so I am just wondering was it ease of construction you did it this way because Im sure a thinner layer of PIR would have achieved the same u value.

Just interested to know your thoughts

Thanks

 

[joe90]

@Moggaman my builder sourced the wall ties so I do not know their cost, I went with stainless as the total area deemed  a cold bridge with stainless was very small and IMO fairly insignificant  and basalt are very expensive. PIR is only any good if no gaps are left, this usually means foaming it in place which would be difficult. Rockwall is a more natural material and not a petro chemical product which I try to avoid. Rockwall can be stuffed into odd voids during the build making it easier to use. As my build is very “cottage”, thick walls are “in character”.

[Seadog]

I have just built with a full fill 150mm cavity, used 0.32wmk Supawool.

 

I found the cheapest place for 275mm Type 2 stainless steel cavity wall ties was Metro Fixings, my local builders merchant was a lot dearer.

 

I am in a relatively sheltered area so for me it was a no brainer given that its harder for Brickies to cockup wool than it is PIR board

 

 

[SteamyTea]

9 minutes ago, Seadog said:

used 0.32wmk Supawool

W/m.K

Or

W.m^-1.K^-1

or even

W/(m.K)

[Seadog]

Indeed it seems to change with every manufacturer !

 

For the avoidance of doubt;

 

https://www.superglass.co.uk/products/superwall-32-cavity-wall-batt/

 

 

[Oz07]

Are blown in beads a better option when it comes to moisture.

Must admit I've built a fair few places with full fill will never had a problem. The stuff just does not soak up water. I've had it blown in and in batts. Used to be cheaper to get blown in than to fit loose. That's changed now. Pir is so reliant on good workmanship. 

[Oz07]

4 hours ago, SteamyTea said:

W/m.K

Or

W.m^-1.K^-1

or even

W/(m.K)

No builder has a clue about the calculations we just know

32 is the dear stuff

34 is the stuff you can pass on a 6" cab

37 is the cheap stuff people use and just have one pack of 32 on the job for when bco walks round. 

 

I use 34

[Oz07]

6"cav 

[PeterW]

Next one I’ve got on the cards is 225mm blown bead and currently talking to the installer about using them to fill a sloping roof structure that is boxed both sides with OSB... idea is that it’s a continuous bead “shell” but not quite sure if it will fly yet. 

[Moonshine]

On 22/11/2020 at 22:01, Moggaman said:

Joe90, there are special wall ties for cavities over 150mm.... are they expensive compared to normal ones.... also the thermal conductivity of the batts is probably around 0.037 as compared to 0.021 for PIR so I am just wondering was it ease of construction you did it this way because Im sure a thinner layer of PIR would have achieved the same u value.

Just interested to know your thoughts

Thanks

 

 

Also bear in mind increase cost of lintels, though I did the costings and in terms of materials full fill with 150mm was the cheapest for the same U value

[Moggaman]

18 hours ago, Moonshine said:

 

Also bear in mind increase cost of lintels, though I did the costings and in terms of materials full fill with 150mm was the cheapest for the same U value

What u value was that please ?(assuming u did PIR at 0.021)