VCL, regs vs improved?

[Jenni]

Hello. 

 

I'm converting a barn, single storey, warm loft / vaulted ceilings. 

 

I'm not aiming for a super-efficient house, nothing near passiv. But I do want it to be suitable for MVHR. 

 

    My regs document states -

"Between each rafter 30mm cavity with 70mm Celotex FR 5000 insulation, 60mm FR 5000 under rafter with joints taped to form VCL and air leakage barrier. 25mm barrier using 25mm x47mm battens and 12.5mm Gyproc wallboard. Design to achieve 0.16w/m2k." 

 

My question is - does taping the joins of the insulation make a good enough / reliable VCL? 

 

If not, I'd welcome some recommendations for what to use instead please. 

 

 

 

 

 

[Big Jimbo]

The selt adhesive ali tape will do a good job for you.

[A_L]

1 hour ago, Jenni said:

My question is - does taping the joins of the insulation make a good enough / reliable VCL? 

 

This BBA certificate  says yes, section 7.2 page 7.

 

https://www.celotex.co.uk/assets/5405_pitched-roofing_bba-certificate_nov2018.pdf

 

The quality of the tape will be important.

[Russell griffiths]

Make sure the insulation is butted tight to each other as well

no point having a 15mm gap and covering it with tape. 

And tape it to the wall vcl as well. 

Edited November 20, 2019 by Russell griffiths

[Jenni]

So no need for rolls of VCL then?

 

I kinda had in my head that a designated layer would be better than taping joints, maybe easier to ensure good airtightness? 

 

Thank you. 

[Judy C]

You could fix a polythene VCL to the underside of the rafters - it's not hard - then the taped joints are belt and braces.  Especially in a shower room or similar.

[Jenni]

Hi, that would be pretty easy to do, but I thought the layer had to be on the warm side of the insulation? Iirc, to do with where condensation forms. 

[MikeGrahamT21]

Yes VCL on the warm side. You could certainly tape the insulation boards with foil tape, I did the same on my latest vaulted ceiling, however you have to look carefully over the whole surface of the boards and ensure any nicks or imperfections are taped over too, if your boards are a bit beaten up, may be worth just using expanding foam in any gaps and then an AVCL over the top held in place by your battens.