Tyvek, can it be used either way round, advice please

[happyhero]

Hi I built a fancy shed a while back and used some Dupont Tyvek breather membrane on the walls - I took some advice from a builder friend at the time, anyway I have some left and I am about to insulate my floor suspended wooden lounge floor with some Kingspan sheets (kids and wife always complain how cold our house is in winter so got to do something).

I have the Kingspan but a lot of the sites that give advice on insulation recommend laying a breather membrane over the top of the insulation before laying the floorboards, so my questions are as follows:-

Can I use this Tyvek that I have on the floor, ie is a breather membrane a breather membrane or do I need a different one?

Which way round do I lay it on my floor (ie cold side is under the floor) as for example on a roof or on the walls of my shed the printed side faces the cold?

Or is it uni-directional ie does it make any difference which way round you use it?

I have put it on the roofing section as I thought the roofing guys may know more about this stuff, apologies if that was not the right thing to do, I was wondering about putting it under the building section.

Any help or advice appreciated

 

[freddiemercurystwin]

The idea of a breathable membrane is three-fold, to keep water (rain) out of the structure during construction, provide a backup water proof barrier behind/under the wall cladding or roof tiles and allow air to escape from the inside to the outside. There is no need to use one in a floor. Anything you have read on the web that says otherwise is unfounded for example the Kingspan guidance makes no such recommendation http://www.insulation.kingspan.com/ireland/pdf/tf73.pdf

 

[happyhero]

I was just trying to seal the kingspan a little further from letting any drafts through, ie you can cut it fairly well but not 100% so there may be some small gaps here and there.

I did originally think of getting 100mm foil tape to bridge the joists and stick the Kingspan together, they do a tape for this, it would almost create one skin across the floor but they recommend not to totally seal. One reason not to seal is that if there were any spillages it would stay wet a long time under the floor whereas with a breathable membrane it could slowly dry out.

Here is one of the sites I use, http://www.greenbuildingforum.co.uk...ywords=SUSPENDED&Type=Topics&btnSubmit=Search

not sure if it is ok to post this here but please somebody remove it if I have done the wrong thing here. They have experts and DIY guys on there.

I am wondering now too if I should have put this post on the building section, don't know if it can be moved at this point.

 

[freddiemercurystwin]

You seal any gaps with expanding foam. No need for tape either. Where in the Kingspan techy guidance did you notice it mentioning a breathable membrane? You can stick the thread where you like, those in the know on this forum will give the same advice.