On 24/05/2021 10:58, Tricky Dicky wrote:
I am about to start dividing off my extended garage to create a man
cave. This involves a studded dividing wall which along with the
other three outer walls need insulating. Incidentally the garage is a
timber framed structure with CLS roughly 4x2 frames with 18mm shiplap
over a breathable membrane and lined behind with plywood. The plan is
to fill up the spaces in the framework with either Celotex or
Kingspan foam panels.

So the question is, can the foil coating do as a vapour barrier using
sealing tape across the framework as I did when insulating the
kitchen floor or do I need to add a polythene sheet over before
boarding the inner wall?

The foil will act as a vapour barrier if any joints are taped up with
foil tape.


I have been watching some YouTube of people doing similar things and
have been left confused. The following video is a compilation of a
number of videos of a professional build of a garden room.

https://youtu.be/S92rEaAj188

The guy insulates the bays between frames with foil coated foam
panels before adding a rock wool bat sound deadening layer and then a
vapour barrier before plaster boarding but then cuts holes in the PB
for sockets destroying the vapour barrier behind?

Got to admit some of the work looks rough and some to my mind over
engineered. See what you think the relative insulation is towards the
end of the video or you can look at the daily video record of 15
daily videos.

ok not had a chance to look at the videos.

However, the general rule for vapour barriers is that they need to be in
a position where they can prevent warm moist air reaching a cold
surfaces - especially if those are in voided off parts of a building
(aka interstitial spaces).

So in the case of the rigid Kingspan et al boards (aka Polyisocyanurate
foam (PIR)) with a foil cover, there is a barrier on the warm side of
the insulation. With something like rockwool there is no "built in"
barrier, and the insulation itself is also air permeable - so there is
some logic in preventing the warm wet air reaching the warm side of the
insulation since that (and its moisture) can permeate the insulation and
migrate toward the cold surface.

Where you have rockwool over PIR boards, its probably less critical
since the warm side of the PIR boards will likely be above the dew point
anyway.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/