Airtight tape for use with EPS

[Adam2]

Any thoughts if I need a special tape that will work well with EPS - as in will stick and will not breakdown due to incompatibilities?

[joth]

Aluminium foil tape for silver foil faced EPS.

 

 

[Mr Punter]

10 minutes ago, joth said:

silver foil faced EPS

 

I have never come across this.  Is it available in large sheets and varying thicknesses?

[Adam2]

19 minutes ago, joth said:

Aluminium foil tape for silver foil faced EPS

 

Thanks but sorry I wasn't maybe clear enough - this is being considered for application direct to EPS (as in ICF walls).

 

Having read some more on the topic I may try and avoid tape on the EPS and use battens to secure a folded edge of a dpm type plastic sheet against the EPS - with tape over the screws. Am looking to make sure my wall to roof detail is as good as it can be - the walls of course are fine and I'll be all over the window fitters checking use of tapes etc but we're doing the roof now and there's a bunch of joists that will need some care to get right.

 

 

[joth]

35 minutes ago, Mr Punter said:

 

I have never come across this.  Is it available in large sheets and varying thicknesses?

Haha ignore me, I get my PIR and EPS crossed all the time. (I was thinking of our Cellotex GA4000 taping party)

 

[Conor]

We used Conzio 60 tape around windows and air tight paint along the wallplate. We're also using air tight adhesive render beads on the outside of the frames, plus exterior water proof tape for the door blocks under the door frames on the outside.

 

[Adam2]

Thanks @Conor - the triton paint on we've used in a similar way but will see where else we can make use of that - seems to go a long way so not bad value. The render beads sound interesting will take a look for those as well

[Hastings]

I think the plasticiser often used in PVC reacts with polystyrene over time. There are reports of electrical wiring in contact with it having the insulation sheathing 'melt' away after drawing out the plasticiser from the wire's PVC insulation.

 

A tape might have the same effect on polystyrene.

[jfb]

Am I missing something but EPS isn’t airtight itself so why would you want to tape it?  Or at least shouldn’t the airtight layer be somewhere else?

[Nick Laslett]

4 hours ago, jfb said:

Am I missing something but EPS isn’t airtight itself so why would you want to tape it?  Or at least shouldn’t the airtight layer be somewhere else?

I believe like a lot of things, this is quite a complicated topic. Using data from USA, EPS is semi vapour permeable, 5 perms @ 1 inch. As you increase the thickness this permeability decreases. You also have different densities of EPS which effect the permeability. Type VIII EPS has 3.5 perms @ 1 inch. According to the ASHRAE handbook concrete has a vapour permeability of 3.2 perms @ 1 inch. 
 

A material is classed as non-vapour permeable at 0.1 perms. These are the USA standards. 

Materials can be separated into four general classes based on their permeance:

Vapor impermeable          0.1 perms or less (Class I vapor retarder – considered a vapor barrier)
Vapor semi-impermeable 1.0 perms or less and greater than 0.1 perm (Class II vapor retarder)
Vapor semi-permeable     10 perms or less and greater than 1.0 perm (Class III vapor retarder)
Vapor permeable              greater than 10 perms (Not considered a vapor retarder)

 

https://www.buildingscience.com/documents/guides-and-manuals/gm-guide-insulating-sheathing/view

 

Some good commentary here around closed cell and open cell aspects of EPS. 
 

https://www.greenbuildingadvisor.com/question/is-rigid-eps-insulation-an-effective-air-barrier

 

 

Edited November 4, 2021 by Nick Laslett

[jfb]

I agree it is a complicated topic!

 

Is there not a difference between airtightness and vapour permeability? They would seem to be closely correlated - EPS (open cell) would appear to let both some air and moisture through. But a lime render can be viewed as airtight but vapour permeable. (Not quite sure how that works though!)

[A_L]

27 minutes ago, jfb said:

Is there not a difference between airtightness and vapour permeability?

 

Yes there is a difference. Air tightness relates to bulk air movement, vapour permeability relates to a physical/chemical process which allows water vapour to transfer through a material which has no bulk air permeability 

[SteamyTea]

6 hours ago, Nick Laslett said:

perms @ 1 inch

Just to make it confusing

1 ng·s−1·m−2·Pa−1

≈ 0.0174784 US perms

 

1 kg·s−1·m−2·Pa−1

≈ 1.74784x1010 US perms

[Adam2]

The specific application here is an ICF house with 200mm concrete structure and wanting to ensure the wall to roof junction is effectively dealt with from an air-tightness perspective.

 

Different details will be needed in different places - it's a flat roof - well flat + tapered insulation and one large mono-pitch area. I was just asking due to possibly taping a vcl to the walls and brining that up to the inside of the roof structure in some places - didn't want to risk the tape and EPS separating due to incompatibilities BUT if we do this we'll put a batten across the vcl holding it to the wall instead of tape as this will have a more reliable long term fixing anyway.

 

Thanks for the education on US perms, will be sure to pass that on to my wife ?

 

[Nick Laslett]

21 minutes ago, Adam2 said:

The specific application here is an ICF house with 200mm concrete structure and wanting to ensure the wall to roof junction is effectively dealt with from an air-tightness perspective.

 

Different details will be needed in different places - it's a flat roof - well flat + tapered insulation and one large mono-pitch area. I was just asking due to possibly taping a vcl to the walls and brining that up to the inside of the roof structure in some places - didn't want to risk the tape and EPS separating due to incompatibilities BUT if we do this we'll put a batten across the vcl holding it to the wall instead of tape as this will have a more reliable long term fixing anyway.

 

Thanks for the education on US perms, will be sure to pass that on to my wife ?

 

Hello Adam, sorry, I didn’t mean to hijack or derail the thread. I have now read up on the European equivalent to perms, which I believe is Sd-value. I will make a separate post on this topic.

 

I am also building an ICF house, when I researched tapes I found the Siga Wigluv tape specifically mentions EPS as a substrate. 
 

https://www.sigatapes.co.uk/Wigluv_100/p4850575_17610284.aspx