Budget Airtight Membrane

[Rich]

has anyone used a normal VCL such as https://www.screwfix.com/p/capital-valley-plastics-ltd-vapour-barrier-green-300ga-2-5-x-20m/12869?_requestid=575880

and taped the joins to form a airtight membrane? 

 

Im trying to sense check this idea as it would seem to me these plastic membranes would be airtight if applied correctly. Would anyone have any advice to the contrary?

 

thanks in advance. 

[PeterW]

Yep. 

[Onoff]

Yep. Though I only paid lip service to the taping. Used more as a draughtproofing thing.

 

 

 

[Rich]

1 hour ago, PeterW said:

Yep. 

 

Was this on a full build? If so was it successful when the air test was carried out? 

 

1 hour ago, Onoff said:

Yep. Though I only paid lip service to the taping. Used more as a draughtproofing thing.

 

 

 

 

The pics help a lot thanks ??

[PeterW]

Air test not needed but given that you can open a door in a howling gale and nothing moves, it would suggest that  it’s working. Only issue has been where there was some wind washing in a small enclosed attic space and it moved a little and tends to rustle a bit. Sorted when the insulation settled down. 

[vivienz]

I'm waiting for a reply from an Irish (ROI) supplier of airtight tape. The price advertised on their website is very competitive, so I will report back once I get a response.

[bissoejosh]

I'm also looking for membranes / tapes  as Passive house system no longer sell via their website unfortunately.

 

Anyone found any alternative suppliers?

[Nickfromwales]

Prices etc can be followed here ?

[Pete]

https://passivehousesystems.co.uk/ and use the code 15%aocx 

[bissoejosh]

7 hours ago, Pete said:

https://passivehousesystems.co.uk/ and use the code 15%aocx 

They no longer sell via the website.

[Pete]

37 minutes ago, bissoejosh said:

They no longer sell via the website.

Ok thanks. I only bought some about 4 weeks ago.

[bissoejosh]

1 hour ago, Pete said:

Ok thanks. I only bought some about 4 weeks ago.

 

Ah you were lucky, I must have just missed the switch. Annoying as I'm having difficult sourcing the order elsewhere. 

[Onoff]

Before I knew better I tried and failed to use double sided DPM tape to join the ceiling vcl in the picture above. Far too thick! So much so that it bowed the ceiling boards at the joint. I ditched it and just used foil tape as elsewhere.

 

Tbh if "air" gets through the foil tape, Sika EBT around where the insulated pb meets the window frame, silicon at the floor and ceiling junctions with the tiles, tile adhesive, CT1 and Wiska gel etc then good luck to it. 

[Miek]

If you are relying on that VCL as your air tightness I would question its long term durability. Imagine repeatedly pressurising and depressurising a house  ( think decades here) with that thin budget plastic taking the strain. I've used the screwfix green VCL and the quality is quite poor IMO. Good as a VCL but not as an Air tightness layer. 

[Rich]

15 hours ago, Nickfromwales said:

Prices etc can be followed here ?

 

Thanks nick, very helpful.

4 hours ago, Miek said:

If you are relying on that VCL as your air tightness I would question its long term durability. Imagine repeatedly pressurising and depressurising a house  ( think decades here) with that thin budget plastic taking the strain. I've used the screwfix green VCL and the quality is quite poor IMO. Good as a VCL but not as an Air tightness layer. 

 

I can see your point of view, however is this the only benefit the dedicated membranes have over this cheaper option? If so surely this can be mitigated depending on the wall buildup. 

[Onoff]

5 hours ago, Rich said:

 

Thanks nick, very helpful.

 

I can see your point of view, however is this the only benefit the dedicated membranes have over this cheaper option? If so surely this can be mitigated depending on the wall buildup. 

 

+1. Can't see how my wall vcl will ever really "flex". It's sandwiched between fully filled joists and mrpb / Aquapanel screwed over the top.

 

 

The only cold spot in the walls is through not around the 2G window where it's noticeably colder.

 

My ceiling vcl integrity is somewhat compromised by the multiple penetrations of 4 spots, 2 speakers and a bfo body dryer plus various 20 & 25mm conduits, the wc extract pipe, rainfall head etc. Add to that an occupancy switch etc. All area I've plans to mitigate / improve. With hindsight! 

[Miek]

7 hours ago, Rich said:

 

Thanks nick, very helpful.

 

I can see your point of view, however is this the only benefit the dedicated membranes have over this cheaper option? If so surely this can be mitigated depending on the wall buildup. 

 

I don't know if this is the 'only' benefit, this would depend on what you are comparing it to exactly. yes this could well be mitigated if the wall build up immobilised the membrane sufficiently, as in a sandwich between rigid components. But I wouldn't use it for example if you intended to have a service void on one side of the membrane, which a lot of people want for ease of wiring etc... 

[Jeremy Harris]

18 hours ago, Miek said:

If you are relying on that VCL as your air tightness I would question its long term durability. Imagine repeatedly pressurising and depressurising a house  ( think decades here) with that thin budget plastic taking the strain. I've used the screwfix green VCL and the quality is quite poor IMO. Good as a VCL but not as an Air tightness layer. 

 

 

So would I, very much so!

 

I have no doubt about the membrane, the real issue, and one that has taken a fair bit of R&D to solve, I believe, is the long term adhesion of any tape to it, even the very best stuff.  Airtight membranes have been developed so that they have a surface coating, or sometimes a laminated layer, to increase the surface energy and better allow adhesive bonding to work in the long term.  Some types of plastics are particularly poor, including polyethylenes and vinyls, and without some form of surface treatment any adhesive will fail within a year or two.

 

If opting to use a budget VCL, bearing in mind that the VCL is a critical component with regard to the longevity of the underlying structure, then I would ensure that it is mechanically sealed at every joint.  One way to do this is to wrap the edges over, tape them and then secure the joint with a batten.  Fair bit of extra work, though, and given the highly critical function of the VCL I'm not sure this is an area that I'd want to save a few pounds on.

[Square Feet]

I bought some cheap Cromar 3 off ebay for a loft renovation I did recently.  From memory it was £27 or £28 for a 50m roll.  I think that is about half price.  It was seconds, but out of the 50m roll, only about 2m had to be ditched, the rest was fine.  

As JSHarris says, tape adhesion was a bit of an issue as I tried to use duct tape without success - it worked ok for a couple of weeks, then started to come away so you need the proper stuff.