Jeff-C Posted January 5, 2014 Author Share Posted January 5, 2014 So this is how I have planned to construct the insulation for the internal walls. Outer wall is the actual cabin wall, then the foil bubble wrap to create the vapour barrier. There is an air gap made by batons that will (unfortunately) have to be secured with screws through the foil barrier to the wooden cabin wall. On top of these batons will be fitted the celotex, and then butted on to the celotex will be the ply wood (possible MDF) new internal wall. This will be secured by screws through the board and celotex into the the batons. Question is, it the air gap and baton positioning correct? I can't seem to get a proper answer from anyone. Quote Link to comment Share on other sites More sharing options...
cymaz Posted January 5, 2014 Share Posted January 5, 2014 Any help ? Here Here Thought the thickness guide would help not the fact there is hemp in the wall. Edited By cymaz on 05/01/2014 09:21:21 Edited By cymaz on 05/01/2014 09:24:00 Quote Link to comment Share on other sites More sharing options...
Jeff-C Posted January 5, 2014 Author Share Posted January 5, 2014 Hi cynaz thanks for the post. The thickness guide is a little useful as it shows batons and air gaps, but the problem is I am very limited to internal size that can be taken up. It's a maximum of 50mm, and everything as detailed comes in just at that. The only thing I am really worried about is the position of the foil vapour barrier. The manufacturer and a builder says it can be installed touching the external wall, with the air gap on the internal side of it. Yet when I see pictures and videos of people installing cavity walls, the put the insulation board in first touching the external wall, then the air gap and then celotex. Quote Link to comment Share on other sites More sharing options...
roger graves Posted January 5, 2014 Share Posted January 5, 2014 After working for insulation manufacturers for some 15 years the golden rule is vapour barrier always on the warm side of the insulation. Quote Link to comment Share on other sites More sharing options...
Jeff-C Posted January 5, 2014 Author Share Posted January 5, 2014 Hi Roger so on my diagram, if I do a straight swap for the foil (blue) and the celotex (grey), this will be correct. Basically meaning external wall touching celotex - air gap crated by batons - foil bubble wrap (foil facing in) and then the internal ply wall touching foil. Would this be correct? Edited By Jeff-C on 05/01/2014 12:24:50 Quote Link to comment Share on other sites More sharing options...
roger graves Posted January 5, 2014 Share Posted January 5, 2014 Yes the first thing that the moisture laden air meets must be the VB. Incidently air gaps are only used where ventilation is needed, I assume you don't plan to have air circulating behind the insulation? Quote Link to comment Share on other sites More sharing options...
Jeff-C Posted January 5, 2014 Author Share Posted January 5, 2014 Roger, The cabin is a tongue and grove style (link on the first page). So there is going to be draughts and on corner joints.That is why i thought that the foil barrier would be best placed on the wooden cabin wall (internal side). But then I thought about the foil touching the wood might cause condensation between the foil and wooden surface and eventually lead to mould growing inside the wall. That is why I am now not sure if the barrier should be before the insulation or after it. I have always been told that I need an air gap otherwise the conductive cold will come through the wood, through the foil, through the celotex, straight on to the ply internal wall - effectively making the insulation pointless. The air gap acts as a 'warm' cushion to stop the conductive cold from the external wall. The foil reflects the infrared heat back in to the shed, and celotex insulation keeps the warmth in. A bit of a simplistic view I know, but I want the internal of the cabin to be as airtight as possible, and as warm as possible whilst operating within my very tight space constraints. I don't need it to be a bedroom, but I do need it to stop going below freezing with an efficient small heater on in there during the winter. Edited By Jeff-C on 05/01/2014 13:21:39 Quote Link to comment Share on other sites More sharing options...
roger graves Posted January 5, 2014 Share Posted January 5, 2014 First thing I did with my similar cabin was to go round internal corners and seal any gaps with mastic........result no draughts. No air gap between insulation and cold surface in a fridge. Quote Link to comment Share on other sites More sharing options...
Jeff-C Posted January 5, 2014 Author Share Posted January 5, 2014 So your suggestion is to do away with the air gap? I have lined one wall already in the bubble foil fixed to the external wall. Should I pull that off, install the batons to the external wall to the same depth as the celotex (25mm). Push fit the solid insulation up to the external wall between the batons, cover all of that with the foil wrap, and then attach the boarding to the batons over the foil. This means I would effectively gain an extra 18-20mm of space inside (makes fitting my already bought shelving units a lot easier), and every surface is in contact with each other. Don't fridges have gas that pass between the internal and external walls? Plus fridges are almost always running, I want my heating in my cabin to only really be on at night and when it is under 5 degrees. Quote Link to comment Share on other sites More sharing options...
roger graves Posted January 5, 2014 Share Posted January 5, 2014 A very simple solution and time tested..................wall............screw battens............fill gap with insulation (your choice).........1000g vapour barrier stapled to batten with taped joints.............finished surface (plasterboard, chipboard etc. job done. On Monday call any Ins Mfr and speak to their tech dept to confirm. Quote Link to comment Share on other sites More sharing options...
Ernie Posted January 5, 2014 Share Posted January 5, 2014 Hi, It's a long time since I did this, but the point of a vapour barrier is to prevent interstitial condensation ( inside the structure of your wall) The warm air inside your shed will condense when it touches a cool surface inside the wall, and so wet the structure. The best place for your vapour barrier is therefore close to the inner finish ernie Quote Link to comment Share on other sites More sharing options...
Jeff-C Posted January 6, 2014 Author Share Posted January 6, 2014 Roger - I believe you!! When put in terms like that, I get it Sorry it has taken so long to get there. I feel rather naffed off with the company that sold me the insulation, and the builder who told me I needed the foil to be on the external wall with an air gap inward of it Ernie - That all makes sense. Next weeks job then is to remove the already in place barrier, purchase some more appropriate sized timber batons, and start all over again! Quote Link to comment Share on other sites More sharing options...
kc Posted January 6, 2014 Share Posted January 6, 2014 I suggest you consider using plasterboard to line the walls instead of ply.It's a very easy material to use and cheap. Best installed with special plasterboard screws which self countersink and are very cheap. Quote Link to comment Share on other sites More sharing options...
Ernie Posted January 6, 2014 Share Posted January 6, 2014 Hi, There are plasterboards available with a foil lined inside, so that it forms a vapour barrier. You'd need to look at how to fix it, so that you don't damage the barrier ernie Quote Link to comment Share on other sites More sharing options...
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