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VCL or PIR and foil tape?


jen and mark
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I know this may have been asked a thousand times but could someone suggest the best way forward for us?

 

We are completing a steel barn conversion and are unsure whether we need a VCL on the warm side of our build.

 

Our construction is from outside in:

Mix of larch and steel cladding

Cross batten

Tyvek Housewrap

Some block (4ft high) from ground

Timber studs above filled with insulation

Continuous layer of PIR all joints filled with spray and taped with foil tape.

Service void

plasterboard and scrim.

 

All steels have been sprayed and boxed in with XPS insulation to mitigate thermal bridging as best we can (The main steels are in the ground so know thermal bridging will always be an issue)

 

My question is, do we need a VCL (plastic sheeting or intelligent) before we install the timber service void (50mm) or will the taped, foiled backed PIR suffice? (Careful 'self build' detail to the tapping!)

 

Many thanks in advance

 

 

 

 

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I would advocate a seperate airtight layer with a good membrne and proper airtightnes tape. 

 

It will only amount to hundreds of pounds but will have the most dramatic effect on the comfort if you get it right. You will save a few £ on the tape with less joints too if you use a membrane. IIRC you're on a tightish budget so you may be able to use seconds PIR with imperfect facing then too to save a few quid. 

 

By the way are you planning to insulate the service void? It would seem a waste not to, espically as mineral wool is about the best bank for your buck when insulating.

 

 

 

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21 minutes ago, Iceverge said:

By the way are you planning to insulate the service void? It would seem a waste not to, espically as mineral wool is about the best bank for your buck when insulating.

 

But a right pain if you want to run another cable for instance.

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17 minutes ago, Iceverge said:

I would advocate a seperate airtight layer with a good membrne and proper airtightnes tape. 

Agreed .

There are gaps at all PIR joints and the panels are likely to joggle a bit in windy conditions.

Sticky tape will likely lose its stick over years, 

Plastic sheet can harden and crack...I know it shouldn't in the dark, warm conditions but I've seen enough inappropriate plastic failure to doubt quality..

 

We are doing much the same and I am planning on investing in a reinforced aluminised membrane. 

that will need tape over joints too, but at some stage we have to say 'enough'

the scrim will keep the membrane intact, and is also easier to handle. Under £1/m2 I recall with some shopping around.

 

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Thanks for all the replies.

 

We did consider a VCL so we  purchased Gerband SD control airtight membrane for the ceilings in the en-suites (but was too expensive to buy for all round). We will go for green plastic (cheapest option) over the PIR any recommendations for gauge?

 

On another note,  we used Visqueen ecomembrane for our DPM. We used the 'official' visqueen tape to tape all joints and carried the DPM up our block work. The visqueen tape is rubbish and has stated to peel away! Any suggestions for a good DPM tape?

 

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I don’t think you need the visqueen and just buy decent aluminum tape to cover the joints. As it won’t be subject to movement or light/heat variations then it will not degrade. 
 

Ultratape Rhino is good and not expensive for what it is - available in 50/75/100mm widths on 50m reels. 
 

https://www.sealantsandtoolsdirect.co.uk/tapes-and-trims/aluminium-foil-and-heat-tape/ultratape-rhino-aluminium-silver-grey-foil-tape-75mm-x-46m

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