jen and mark Posted February 21, 2022 Share Posted February 21, 2022 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 Link to comment Share on other sites More sharing options...
Mr Punter Posted February 21, 2022 Share Posted February 21, 2022 An extra layer of polythene is cheap and won't hurt but if you have taped carefully you should be fine but you are relying in the longevity of the tape. Link to comment Share on other sites More sharing options...
Iceverge Posted February 21, 2022 Share Posted February 21, 2022 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. 1 Link to comment Share on other sites More sharing options...
Mr Punter Posted February 21, 2022 Share Posted February 21, 2022 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. Link to comment Share on other sites More sharing options...
saveasteading Posted February 21, 2022 Share Posted February 21, 2022 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. Link to comment Share on other sites More sharing options...
jen and mark Posted February 21, 2022 Author Share Posted February 21, 2022 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? Link to comment Share on other sites More sharing options...
PeterW Posted February 21, 2022 Share Posted February 21, 2022 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 1 Link to comment Share on other sites More sharing options...
jen and mark Posted February 21, 2022 Author Share Posted February 21, 2022 Cheers @PeterW we are using Ultratape and it is sticking really well! Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 21, 2022 Share Posted February 21, 2022 Have you thought of doing an air test before you go any further to try and find any poor areas. you can rig up your own if you are a bit handy. 2 Link to comment Share on other sites More sharing options...
jen and mark Posted February 24, 2022 Author Share Posted February 24, 2022 Great idea - any tips on rigging your own air test? Link to comment Share on other sites More sharing options...
Iceverge Posted February 25, 2022 Share Posted February 25, 2022 Used radiator fan inserted in OSB cut to size of a window sash . About £30 of material. Cable and croc clips to your car battery. Much more puff that the official blower door. 1 Link to comment Share on other sites More sharing options...
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