Foil faced insulation underfloor

[BMcN]

Morning,  

 

With regards to PIR insulation when placed under floor, does it matter about being foil faced?

 

My floor will be concrete slab / DPM / 120-150mm PIR / UFH pipes / 75mm concrete screed.

 

If the answer above is yes, is there anything I could use on top of the PIR to replicate the foil face, like an aluminium VCL like this?

 

Thanks

 

 

[Onoff]

I've repaired damaged foil faced pir with heavy duty Bacofoil before. Bit of spray adhesive, job done.

[PeterW]

1 hour ago, BMcN said:

With regards to PIR insulation when placed under floor, does it matter about being foil faced?

 

Nope. Just put a thin plastic slip membrane between the insulation and the concrete. 

[BMcN]

1 hour ago, PeterW said:

 

Nope. Just put a thin plastic slip membrane between the insulation and the concrete. 

That's what I am hoping, I'd be able to reduce the cost of insulation quite a bit by going without foil. 

[PeterW]

DPM above and below - use 25mm of EPS below the first DPM instead of sand blinding, then pack the PIR in, second DPM and job done ... 

[BMcN]

What's the thinking behind the double dpm? Just to save on messing around with blinding? 

[A_L]

17 minutes ago, BMcN said:

What's the thinking behind the double dpm? Just to save on messing around with blinding? 

 

No, there is a danger that the insulation will undergo hydrolysis (breakdown to its constituent chemicals) in permanently damp/wet conditions.

 

http://blog.celotex.co.uk/technical/what-celotex-insulation-can-be-used-in-floor-applications/

[BMcN]

1 hour ago, A_L said:

 

No, there is a danger that the insulation will undergo hydrolysis (breakdown to its constituent chemicals) in permanently damp/wet conditions.

 

http://blog.celotex.co.uk/technical/what-celotex-insulation-can-be-used-in-floor-applications/

Sorry I got confused as I misread Peters post.  Yes dpm then PIR then another dpm to protect from screed. 

 

Why the recommendation of 25mm eps instead of blinding? 

[PeterW]

It’s just easier than sand blinding and protects the DPM from punctures. 

[BMcN]

16 minutes ago, PeterW said:

It’s just easier than sand blinding and protects the DPM from punctures. 

Thanks.  I'll see what depth I have as the hardcore is in and compacted but I can't remember what depth I have left to the FFL.