# Shed Build - Vapour Barrier and Insulation Help



## Brdy (20 Oct 2022)

Hi Guys,

Struggling to understand from all the different guides online and even Mikes guide in this forum which is brilliant, but I’d like to confirm with everyone how my new shed should be insulated.

I’m looking to build a 2.4 x 4.8m pent roof shed.

If I use 50mm rock wool insulation in the walls should it be laid out like this from outside in…

Cladding | Batten | Vapour Barrier? | Insulation | 11mm OSB 3



Also the roof, using kingspan or celotex 50mm with a 50mm air gap, from top to bottom…

Felt/Onduline | Vapour Barrier? | Batten | OSB 18mm | 50mm air gap | 50mm Insulation | 11mm plywood


I’m just slightly unsure about the vapour barrier locations really if anyone could help that would be brilliant.

Many thanks.


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## Fitzroy (20 Oct 2022)

Cladding - batten - breathable membrane - insulation - vapour barrier - osb. However OSB is so glue filled you can exclude the internal vapour barrier. 

Roof
Onduline (no idea how you would use felt without a solid substrate) battens - roofing breather membrane - osb - air gap - insulation - plywood. With the cavity between insulation and osb vented at the ends. 

However you are going to a lot of effort to put 50mm of insulation in place. 50mm of kinspan may be worth it, but 50mm of rockwool won’t do much for you.


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## Fitzroy (20 Oct 2022)

The cladding or roof covering is a rain screen. Any thing that gets past is is kept off the building structure by the breathable membrane. 

The internal OSB or vapour barrier keeps the warm moist air from penetrating into the walls where at some point the temperature is low enough for condensation to occur. If this does happen then the breathable membrane lets this moisture evaporate overtime, the roof cavity behind the insulation needs to breath for the same reason.


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## Brdy (20 Oct 2022)

Fitzroy said:


> Cladding - batten - breathable membrane - insulation - vapour barrier - osb. However OSB is so glue filled you can exclude the internal vapour barrier.
> 
> Roof
> Onduline (no idea how you would use felt without a solid substrate) battens - roofing breather membrane - osb - air gap - insulation - plywood. With the cavity between insulation and osb vented at the ends.
> ...





Fitzroy said:


> The cladding or roof covering is a rain screen. Any thing that gets past is is kept off the building structure by the breathable membrane.
> 
> The internal OSB or vapour barrier keeps the warm moist air from penetrating into the walls where at some point the temperature is low enough for condensation to occur. If this does happen then the breathable membrane lets this moisture evaporate overtime, the roof cavity behind the insulation needs to breath for the same reason.


Thank you for this, what would you suggest for wall insulation? I’d like to try and keep the sound down as the neighbours are fairly close by to me, so don’t want to run loud machines all day


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## Molynoox (21 Oct 2022)

Sounds insulation is achieved mainly though density, adding more or denser materials to the walls. You can add extra layers of plasterboard for example, and can get special acoustic versions. But also watch out for air gaps, they kill your sound insulation.

So your vented roof (if you follow Fitzroy advice above, which I agree with 100%) is not going to be doing you any favours in that respect.

I have a vented roof in mine and 100mm PIR all round - it does insulate the sound pretty well, but I think sound escapes a little through the _*tiny*_ gaps in the light fittings, into the roof, and out of the air vents. So it's not optimised for sound, although like I say it is pretty good, and easily good enough for what I need (workshop machines and blasting loud movies)

But I wouldn't change it because I like having a vented roof (I've optimised it for condensation basically, not for sound)

Martin


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## HOJ (21 Oct 2022)

If you are proposing to use the space all day everyday with machines running, presuming you won't run into the issue of disturbance to neighbours, I'd suggest you build it bigger, put a pitched roof on and work towards sound reduction over vapour control, however I doubt you will keep the door shut on a nice day, so its going to be a case of finding the balance of purpose and function over the limited issue in an environment such as this with vapour control, sometimes the focus goes towards this more than is really necessary, your not going to be living in it, sleeping, cooking, bathing etc which is how the potential vapour/moisture problem propagates itself.


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## Brdy (21 Oct 2022)

Thanks for helping me understand. It will just be lighter hobby use as apposed to all day everyday, so probably a few hours on a sat and sun. I’ll opt for a moisture control but fill with some insulation on the walls as intended to help warmth.


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## charles79130 (21 Oct 2022)

Brdy said:


> Thank you for this, what would you suggest for wall insulation? I’d like to try and keep the sound down as the neighbours are fairly close by to me, so don’t want to run loud machines all day


Because I was considering noise and not upsetting my neibours I built my shed 5x3 meters from 4x2” including double doors and insulated withe 4” wool for sound and heat loss


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## Brdy (21 Oct 2022)

charles79130 said:


> Because I was considering noise and not upsetting my neibours I built my shed 5x3 meters from 4x2” including double doors and insulated withe 4” wool for sound and heat loss


Did it do the job?


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## charles79130 (21 Oct 2022)

Yes no complaints from neighbours also I put 50 mm Kingspan in the roof and under the floor so cooler in summer and not freezing in winter I also used the latest rubber material for the roof guaranteed for 25 years but it is exspensive approx £400 available on EBay but it will see me out 
hope this helps
Chas


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## Jones (21 Oct 2022)

I think you have breather membrane and vapour barrier mixed up. Vapour barrier is thin plastic sheet that is used on the warm side of the insulation to keep moisture from moving into the insulation. In your case the OSB can be considered a vapour barrier so you won't need an additional one. A breather membrane goes on the outside of the insulation and behind the roof or wall cladding. It prevents any water coming through the cladding entering the building and allows any moisture that has penetrated to evaporate through. There should be a clear air space to allow air circulation to the outside of the membrane this may need battens and counter battens depending on their orientation. On the insulation front solid insulation will need an air gap between it and the membrane, rockwool etc will not and can be full fill.


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## Brdy (21 Oct 2022)

Thanks for this, just in regards to the roof, would I put it over the rafters, then batten, then roofing sheets?

And should I use Osb under the roofing sheets? Or just on the inside of the building

EDIT: Actually this question is covered in Fitzroys first post.

Thanks!


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## charles79130 (21 Oct 2022)

Brdy said:


> Thanks for this, just in regards to the roof, would I put it over the rafters, then batten, then roofing sheets?
> 
> And should I use Osb under the roofing sheets? Or just on the inside of the building
> 
> ...


Osb kingspan osb then roof membrain


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## Jones (21 Oct 2022)

If you're using sheet roofing there's no need for OSB on the roof, you can drape the membrane between rafters to form gutters then batten across and nail sheets to that. If you pull the membrane tight you will need to counter batten as well. I would use a 3 or 4 X1 batten, it's stronger and you can't miss it. I have had mixed success with coroline and onduline, if they are in shade and subject to leaf litter collecting then moss can grow which degrades the sheets quickly, less than 10 years life. In the open it lasts much better


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## Lard (21 Oct 2022)

Not wishing to repeat anything already said but a vapour barrier (VP) does exactly that, ie it stops vapour from being able to pass through it. What it doesn't do is stop the passing of air molecules and so a VP stops moisture but allows ventilation. ......EDIT - sorry, thats wrong...my error!

Jones (above) hit the nail by saying that what you don't want is moisture getting into any insulation as some (moreso a lot) lose/reduce their insulationary properties when wet.....therefore always main VP on the warmer side of insulation. If you want to add a second (elsewhere for other reasons) then that's your choice


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## Brdy (21 Oct 2022)

Lard said:


> Not wishing to repeat anything already said but a vapour barrier (VP) does exactly that, ie it stops vapour from being able to pass through it. What it doesn't do is stop the passing of air molecules and so a VP stops moisture but allows ventilation.
> 
> Jones (above) hit the nail by saying that what you don't want is moisture getting into any insulation as some (moreso a lot) lose/reduce their insulationary properties when wet.....therefore always main VP on the warmer side of insulation. If you want to add a second (elsewhere for other reasons) then that's your choice



Is the ‘warmer side’ the outside of the insulation?

Also, should I use different types of VP for roof and siding?

Is there a particular product or brand that is best or just the first VP I can find?

Thanks again.

EDIT: I think I misunderstood again, so what you are implying is I am better off with a breathable membrane as apposed to the Vapour Barrier


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## HOJ (21 Oct 2022)

Lard said:


> What it doesn't do is stop the passing of air molecules and so a VP stops moisture but allows ventilation.


For clarity, a vapour barrier or vapour control layer (VCL) is basically plastic sheeting, it stops moisture from getting in to the timber frame, and is used to create an airtight seal on the inside (warm side) of a building as @Jones has clarified



Jones said:


> I think you have breather membrane and vapour barrier mixed up. Vapour barrier is thin plastic sheet that is used on the warm side of the insulation to keep moisture from moving into the insulation. In your case the OSB can be considered a vapour barrier so you won't need an additional one. A breather membrane goes on the outside of the insulation and behind the roof or wall cladding. It prevents any water coming through the cladding entering the building and allows any moisture that has penetrated to evaporate through. There should be a clear air space to allow air circulation to the outside of the membrane this may need battens and counter battens depending on their orientation. On the insulation front solid insulation will need an air gap between it and the membrane, rockwool etc will not and can be full fill.


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## Brdy (21 Oct 2022)

HOJ said:


> For clarity, a vapour barrier or vapour control layer (VCL) is basically plastic sheeting, it stops moisture from getting in to the timber frame, and is used to create an airtight seal on the inside (warm side) of a building as @Jones has clarified


Oops! When Lard mentioned about Jones’ above post, I read his post directly above and not further up which you have quoted! Haha thanks for clearing the confusion up.


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## Molynoox (22 Oct 2022)

The information provided at the very start from Fitzroy is already spot on so maybe go back to that for reference.
Or maybe a diagram will help. I have one somewhere hang on...

Found them.... the attached diagrams show good and bad design examples plus the reasons. Note that OSB on outside is debatable as an optimised design but it's what 99% of people do (without issues) so I wouldn't get too hung up on that personally 

Martin


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## Brdy (22 Oct 2022)

Molynoox said:


> The information provided at the very start from Fitzroy is already spot on so maybe go back to that for reference.
> Or maybe a diagram will help. I have one somewhere hang on...
> 
> Found them.... the attached diagrams show good and bad design examples plus the reasons. Note that OSB on outside is debatable as an optimised design but it's what 99% of people do (without issues) so I wouldn't get too hung up on that personally
> ...


That’s perfect thanks!

It’s interesting as some have said that there should be no gap between inside Osb and insulation, although your diagram shows a gap.


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## Molynoox (22 Oct 2022)

You will need a gap (service void) for electrics and the best place to put it is on the warm side such that moist air will not condense on cold surfaces.

Note: if you put your OSB on the *inside*, as opposed to just plasterboard like on my diagram, then it does change the wall design principles, it can actually reverse the logic somewhat, provided your outside wall is fully breathable (i.e. no OSB). In those cases it could make sense to have the PIR tight against the inside wall. Then you would put electrics either surface mounted in conduits on inside wall (industrial look) or you would have them on the outside surface in the cavity created by the battens (that method is not preferred by most electricians)

Martin


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## Brdy (22 Oct 2022)

Molynoox said:


> You will need a gap (service void) for electrics and the best place to put it is on the warm side such that moist air will not condense on cold surfaces.
> 
> Note: if you put your OSB on the *inside*, as opposed to just plasterboard like on my diagram, then it does change the wall design principles, it can actually reverse the logic somewhat, provided your outside wall is fully breathable (i.e. no OSB). In those cases it could make sense to have the PIR tight against the inside wall. Then you would put electrics either surface mounted in conduits on inside wall (industrial look) or you would have them on the outside surface in the cavity created by the battens (that method is not preferred by most electricians)
> 
> Martin


Ah that’s it then I was going to go with conduit electric incase I want to add stuff in the future, plus it’s easier to hang stuff on the walls if I can see where the wires are.

Thanks again really appreciate it


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## Fergie 307 (22 Oct 2022)

Fitzroy said:


> Cladding - batten - breathable membrane - insulation - vapour barrier - osb. However OSB is so glue filled you can exclude the internal vapour barrier.
> 
> Roof
> Onduline (no idea how you would use felt without a solid substrate) battens - roofing breather membrane - osb - air gap - insulation - plywood. With the cavity between insulation and osb vented at the ends.
> ...


is there any need to have a solid sheet roof under onduline, just seems like a waste of material. I can see it might help with noise in that it would enable you to pack the space more densely, but can't see the point otherwise. I have never done this I just put the breathable membrane over the joists, then battens and onduline. Insulation on top of the inner ceiling, and was always told that ideally the insulation should not be in contact with the underside of the membrane. And for cladding interior walls I have never understood people's liking for osb, nasty stuff and no longer even particularly cheap. I always use 18mm water resistant t&g 8x2 chipboard flooring sheets. Nice surface, neat joints and cheap. Have numerous buildings over the years built this way without any issues. If you have not used onduline before then my advice would be to make sure your horizontal battens are no more than 18 inches/450mm between centres. It has a nasty habit of sagging over time if not adequately supported, particularly if it is at a shallow pitch or in a location where it gets the full force of the sun.


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## Fergie 307 (22 Oct 2022)

Brdy said:


> Ah that’s it then I was going to go with conduit electric incase I want to add stuff in the future, plus it’s easier to hang stuff on the walls if I can see where the wires are.
> 
> Thanks again really appreciate it


Great tip I was shown for getting a pull cord through a long run of conduit with a number of bends. Find a piece of soft foam about an inch square and tie a brick line, or similar strong cord to it. Shove the foam into one end of the conduit, and use a shop vac on the other end, pulls it through in seconds.


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## Brdy (22 Oct 2022)

Fergie 307 said:


> Great tip I was shown for getting a pull cord through a long run of conduit with a number of bends. Find a piece of soft foam about an inch square and tie a brick line, or similar strong cord to it. Shove the foam into one end of the conduit, and use a shop vac on the other end, pulls it through in seconds.





Fergie 307 said:


> is there any need to have a solid sheet roof under onduline, just seems like a waste of material. I can see it might help with noise in that it would enable you to pack the space more densely, but can't see the point otherwise. I have never done this I just put the breathable membrane over the joists, then battens and onduline. Insulation on top of the inner ceiling, and was always told that ideally the insulation should not be in contact with the underside of the membrane. And for cladding interior walls I have never understood people's liking for osb, nasty stuff and no longer even particularly cheap. I always use 18mm water resistant t&g 8x2 chipboard flooring sheets. Nice surface, neat joints and cheap. Have numerous buildings over the years built this way without any issues. If you have not used onduline before then my advice would be to make sure your horizontal battens are no more than 18 inches/450mm between centres. It has a nasty habit of sagging over time if not adequately supported, particularly if it is at a shallow pitch or in a location where it gets the full force of the sun.



Thanks guys, regarding the Onduline, it will be south facing and shallow pitch so will be sure to go max 450mm centres thanks, I’ll also look into the chipboard flooring, I’m assuming hanging vertical not horizontal.

Thanks for the shop Vac tip!


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## Lard (22 Oct 2022)

Lard said:


> Not wishing to repeat anything already said but a vapour barrier (VP) does exactly that, ie it stops vapour from being able to pass through it. What it doesn't do is stop the passing of air molecules and so a VP stops moisture but allows ventilation.


Apologies for my previous posting with incorrect info (the crossed out bit) and also VP instead of VB. 
Was trying to write 2 things at the same time and should have reread before posting. I think I had heat transfer on my mind and not air transfer.

Its all about interstitial condensation and dew points.


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## Goesbysteve (23 Oct 2022)

Molynoox said:


> The information provided at the very start from Fitzroy is already spot on so maybe go back to that for reference.
> Or maybe a diagram will help. I have one somewhere hang on...
> 
> Found them.... the attached diagrams show good and bad design examples plus the reasons. Note that OSB on outside is debatable as an optimised design but it's what 99% of people do (without issues) so I wouldn't get too hung up on that personally
> ...


Does that recommended air gap design change when dealing with solid concrete block walls?

Could you share the link to that original source if the images please?


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## Molynoox (23 Oct 2022)

Goesbysteve said:


> Does that recommended air gap design change when dealing with solid concrete block walls?
> 
> Could you share the link to that original source if the images please?


Hi Steve

the images I supplied are 'debranded' versions of the content from my own website. I am not sure on the rules / ethos about providing links here - hence why I used generic versions when posting originally.

I will provide the link below because you have asked for it - in parallel I will investigate / ask moderators for guidance on doing this. 

LINK

with regards to the block walls I have no experience so won't even try and advise. I am sure the principles are exactly the same, but the materials and wall construction isn't. I just haven't given it any thought to be honest so you probably know more than me.

Martin


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## Jones (23 Oct 2022)

Regarding Martin's diagrams above I think they are wrong.
Vapour barrier, a thin plastic impermeable sheet goes on the warm (internal) side of the insulation. If there's a service void it goes behind the void, the void is internal and so heated and not subject to condensation risk ,also any electrical boxes will penetrate the barrier which is almost impossible to then seal effectively. A breather membrane aka vapour permeable membrane goes on the outside to prevent water ingress and allow any that has entered to evaporate through. If you want fitting and use diagrams try the manufacturer sites or the robust details site for reliable up to date information.


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## Goesbysteve (23 Oct 2022)

Molynoox said:


> I will provide the link below because you have asked for it - in parallel I will investigate / ask moderators for guidance on doing this.



I understand and I appreciate you sharing it.


Molynoox said:


> with regards to the block walls I have no experience so won't even try and advise. I am sure the principles are exactly the same, but the materials and wall construction isn't. I just haven't given it any thought to be honest so you probably know more than me.
> 
> Martin


Understood. thank you


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## Molynoox (23 Oct 2022)

Jones said:


> Regarding Martin's diagrams above I think they are wrong.
> Vapour barrier, a thin plastic impermeable sheet goes on the warm (internal) side of the insulation. If there's a service void it goes behind the void, the void is internal and so heated and not subject to condensation risk ,also any electrical boxes will penetrate the barrier which is almost impossible to then seal effectively. A breather membrane aka vapour permeable membrane goes on the outside to prevent water ingress and allow any that has entered to evaporate through. If you want fitting and use diagrams try the manufacturer sites or the robust details site for reliable up to date information.


Having the VB behind the service void and adjacent to the PIR could mean you didn't have to penetrate it with the electrical back boxes and could be something of an ultimate setup. My thoughts below:


The service void would need to be big enough to accommodate the back boxes, as opposed to only big enough for the electrical wiring
This would mean either less insulation (say 60mm instead of 100mm) or it would mean using thicker studs all round (lets say 6 x 2 instead of 4 x 2)
Having a bigger air gap than needed for the wiring alone may not be desirable
Another option would be to embed the back boxes into the PIR as per usual (excavating rectangular recesses) and then run all your VB sheeting *inside *the little rectangular recesses also
With it being an ultimate setup, you would also need to create an air tight seal around the electrical cables coming through the VB - how is that achieved?
I have had a little look into Passivhaus standards in the past, pretty interesting, and this is the sort of detail that's very important in those applications, so it's interesting for me to think about it, but in reality that attention to detail doesn't have a place in on sheds and garden rooms (or even houses) in the real world from what I've seen.
All in my humble opinion 

Martin


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## Fergie 307 (23 Oct 2022)

Brdy said:


> Thanks guys, regarding the Onduline, it will be south facing and shallow pitch so will be sure to go max 450mm centres thanks, I’ll also look into the chipboard flooring, I’m assuming hanging vertical not horizontal.
> 
> Thanks for the shop Vac tip!


I put it horizontal, and stagger the vertical joints in each run like bricks. This has the advantage that your uprights dont have to be spaced in any exact relationship to the boards. If a board ends in between two uprights the T&G joint will hold it together, and the runs above and below will be spanning the same gap if that makes sense. You will inevitably have to trim some to length and a good tip is to use a cut off section to knock the joints in tight without damaging the T& G edge. So place your first sheet at the bottom of the wall and screw the bottom edge firmly to the uprights. I use the torx head flooring screws sold by screwfix and others. Put in further screws half way up but not fully tightened. Place the next board on top and use a cut off section slotted into the T&G to knock the joint tightly together if necessary. You can bash this sacrificial cut off section with a hammer or whatever and so avoid damage to the T&G edge. If you cant do this then just lay a piece of 4x2 on top of the board edge and hammer on that. You should find the joints close up really easily. Wheter you glue them as well is up to you. The advantage of leaving the centre screws only nipped up is that it allows the board to move away from the uprights a little, which makes it easier to close the joint with the next board. Once you have the second row in position tighten up the middle screws on the bottom row and add a further row of screws near the top of the board. Then repeat the process as you work up the wall.


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## HOJ (23 Oct 2022)

Molynoox said:


> The service void would need to be big enough to accommodate the back boxes, as opposed to only big enough for the electrical wiring
> This would mean either less insulation (say 60mm instead of 100mm) or it would mean using thicker studs all round (lets say 6 x 2 instead of 4 x 2)


The service void is created by counter battening, over the air tightness barrier (VB, VCL or what ever you wish to call it) typically using a *minimum* of a 25mm x 50mm batten fixed to face of stud, outlined by Timber frame industry specifications produced by the likes of Trada and the STA (Structural Timber Association)



Molynoox said:


> Having a bigger air gap than needed for the wiring alone may not be desirable


Not really an option, if its to be done properly.



Molynoox said:


> Another option would be to embed the back boxes into the PIR as per usual (excavating rectangular recesses) and then run all your VB sheeting *inside *the little rectangular recesses also
> With it being an ultimate setup, you would also need to create an air tight seal around the electrical cables coming through the VB - how is that achieved?


Really bad idea, you have to maintain the integrity of the air tightness barrier, this way you can't guarantee air tightness if you poke holes in it, too late to find out when you do an air test.



Molynoox said:


> I have had a little look into Passivhaus standards in the past, pretty interesting, and this is the sort of detail that's very important in those applications, so it's interesting for me to think about it, but in reality that attention to detail doesn't have a place in on sheds and garden rooms (or even houses) in the real world from what I've seen.



Agreed, all the above is absolutely pointless for a shed and to an extent Garden rooms, with low occupancy, however I would still be inclined to adopt the principals of best practice on Garden rooms, with regards houses, passive or not, it is critical, you wont get sign off by BC if it fails the air testing.



Molynoox said:


> All in my humble opinion


And mine, but I have built a few Stick and Sips timber frame houses, including to Passive standard.


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## Molynoox (23 Oct 2022)

HOJ said:


> The service void is created by counter battening, over the air tightness barrier (VB, VCL or what ever you wish to call it) typically using a *minimum* of a 25mm x 50mm batten fixed to face of stud, outlined by Timber frame industry specifications produced by the likes of Trada and the STA (Structural Timber Association)
> 
> 
> Not really an option, if its to be done properly.
> ...


All good info  

If going SIPS route, I would 100% be using the battens over the top of VB approach, nice and neat solution, keeps everything on the right side of the barrier, I like the idea a lot. I've honestly not seen it done that way on an insulated stud framed structure in the garden but there is absolutely nothing stopping you doing it that way if you need or just want it to be 'air tight'.

Its got me thinking actually - I used 5x2 for my walls, with 100mm PIR and 25mm service void, I could have instead done 4x2, VB on top, then battens and had a theoretically better design. But then I have basically built a home made SIPS panel  Also, there is a risk the electrician comes along and hacks big holes in everything anyway, depending on the depth of back box they are using. Having said that, you can explain things to them so they know you have a vapour barrier you are trying to preserve - I certainly had that conversation *multiple *times with mine 

Martin


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## Fergie 307 (23 Oct 2022)

If the appearance doesnt bother you then surface conduit is by far the easiest method. Also has the advantage that it makes it very simple to extend or modify the installation afterwards. If you havent done it before just make sure you plan the installation carefully, and bundle up your cables for installation in one go. It can be very difficult to get a cable through a conduit that already has other cables in it! You can use tipex, or small pieces of shrink wrap to identify individual cables of the same colour.
For a building where I didnt want surface conduit i simply made a suitable sized cut out in a piece of board. This was then screwed to the wall and used to guide a router to cut an accurate hole through the internal board wall. I used the plastic boxes designed for platerboard. They clip in place and are finally tightened by the mounting screws of the faceplate. Very easy and neat, and gives minimal projection behind the wall.


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## Fergie 307 (23 Oct 2022)

Molynoox said:


> All good info
> 
> If going SIPS route, I would 100% be using the battens over the top of VB approach, nice and neat solution, keeps everything on the right side of the barrier, I like the idea a lot. I've honestly not seen it done that way on an insulated stud framed structure in the garden but there is absolutely nothing stopping you doing it that way if you need or just want it to be 'air tight'.
> 
> ...


5x2 uprights, thats certainly not going to be going anywhere! I have always used 4x2, seems a good compromise between strength and cost, and the wall built up as you describe. I have mostly used surface conduit so have no need of a large gap. My main workshop has all the walls built that way. Its 7.2x10m with a central girder spine supported on girders either end, inside the external walls. 8x2 joists coming off plates welded to the top of the beam onto the top of the walls (keeps the sides of the girder free for running a hoist up and down, very handy)


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## Molynoox (23 Oct 2022)

Fergie 307 said:


> 5x2 uprights, thats certainly not going to be going anywhere! I have always used 4x2, seems a good compromise between strength and cost, and the wall built up as you describe. I have mostly used surface conduit so have no need of a large gap. My main workshop has all the walls built that way. Its 7.2x10m with a central girder spine supported on girders either end, inside the external walls. 8x2 joists coming off plates welded to the top of the beam onto the top of the walls (keeps the sides of the girder free for running a hoist up and down, very handy)


haha yeah, 4x2 is absolutely the sweet spot for strength / cost - I just have a habit of over engineering.
that's a huge building, hence the steels I suppose, it must have been fun building it  have you got a build thread on the forum?


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## Fergie 307 (23 Oct 2022)

Molynoox said:


> haha yeah, 4x2 is absolutely the sweet spot for strength / cost - I just have a habit of over engineering.
> that's a huge building, hence the steels I suppose, it must have been fun building it  have you got a build thread on the forum?


No, this was built about 15years ago, before I joined. Biggest fun was lifting the main beam without access for a crane. We fitted temporary side plates to the top of one upright so that one end could be placed on it with the other on the ground, then used a teleloader to lift the other end up, quite nerve wracking ! Was pretty chuffed that everything lined up perfectly and the bolts went straight in withoit any drama. Each wall frame was built on the concrete base and the internal T&G chipboard added, then lifted into place and bolted together before insulating, wrap, battens and featherboard on the outside. Base is 6" compacted MOT, heavy duty DPM and 6" reinforced concrete. Its used mainly for working on cars so good solid floor needed for jacks and so on. The bottom beams of the walls are bolted to the concrete slab using the self threading type bolts. DPM between the two and hanging over the sides so it extends below the floor DPM, and covered by the wall external membrane at the bottom of the wall. The walls have a 6x1 board at the bottom which overlaps the floor wall joint by about 2" and has its own dpm backing . Have never had any issues with damp, even on the end of the building which takes the full impact of any wind and rain.


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## Molynoox (23 Oct 2022)

sounds great... the beam lifting does sound nerve racking


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## Seascaper (23 Oct 2022)

Brdy said:


> Hi Guys,
> 
> Struggling to understand from all the different guides online and even Mikes guide in this forum which is brilliant, but I’d like to confirm with everyone how my new shed should be insulated.
> 
> ...


Hello,
As follows,
Exterior cladding
Vapour barrier - such as Tyvek Supro
Insulation between shed construction uprights - thickness will depend on available space but you want at least 50mm. Rolls of fibre are easy to cut or Celotex, all available in differ thicknesses.
Lining - you mention OSB, this is an absolute minimum but my advice would be to get some decent plywood, the thicker the better. If you use 19mm exterior shutter ply fro example you will have all the advantages of fixing anything to the walls. OSB can fall apart especially if it gets wet.
Regards


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