Insulating a shed/garden room etc.

[skotl]

Quick question about where the breathable membrane would be fitted...

In this diagram, the orange is the external cladding with vertical battens every 54cm or so.
I'm going to fix spacer fixings to the battens that the PIR will rest up against (and the OSB in front of the PIR, which isn't shown on the diagram).

So the question is whether it's important to have an air gap between the membrane and the PIR as well as the membrane and the external cladding?
I had planned to fit it to the back of the fixings (Point B) so that would mean around 25mm air from cladding to membrane and 12mm from membrane to PIR.

Then I thought it would be far easier to just fit the membrane directly to the back of the PIR (Point A) before fixing, if it didn't matter if it was in contact.

So Point A (membrane on PIR) would be easiest but I'm guessing that's a no-no as there will be moisture on the membrane?

 

[gaz1]

those pics are wrong

for vertical boards you need to use a double latte system

the blue or the green is your breathable membraine

first pic shows the way it used to be ( left pic ) nowadays we cross latte them like in the right pic

due to your latts rotting away faster if they was a water leak somewhere ( roof reference ) air flow always goes up due to heating of the boards shown in pic 3

best to fit verticals over the board and nailed through to the 4x2s behind

so in vertical boards it would be

cladding / 1st batterns / 2nd batterns / membrane / osb / insulation / osb board

 

[gaz1]

its also the same for insulating prefab garages

however with tech nowadays we can build from a plastic support

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off cuts of this under the wood frames will keep the frames away from the ground so wont rot and any water ingress from the prefab concrete and yes it does get in sometimes

the front can be arcitrived up using plastic again

so no wood frame touches the floor

the downside you lose 5" for 4x2s or 4" for 3x2s with an 1" gap between the walls

 

[skotl]

Jeez. Thanks Gaz but I'm starting to think this may be a bit over the top, given I've only got 45mm to play with and 25mm insulation.

By the way - I probably didn't explain so well in the diagram, but it's horizontal overlaid shiplap that's on the outside. So I think I'll go with my Point B suggestion to give it a gap between the membrane and insulation board.
Good point re the slight incline - I can probably manage that, too!

 

[gaz1]

sorry im lost now are you fitting horizontal boards or vertical boards onto your shed

does it already have horizontal boards on it already ?

as long as you follow post 10 wood cladding reference its fine for horizontal wood

up to you if you omit the osb board and just use the membraine sheet only on the 4x2s

its why ive posted each version up so people can choose which type they want to build and use

its your costs not mine

 

[frank horton]

U can always fit the profile sheet Horizonral....motor home style...
got given a load of 5m roofing sheets....to much cutting/waste for vertical fitting.......
so it's going horizontal at least at the back.....

 

[frank horton]

still a way to go but should be done by winter........

 

[Blobber]

still a way to go but should be done by winter........
View attachment 449590

Do you actually get winter?