Solid Shed build,vapor barrier question

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Hornbeam":1ca5c94u said:
I have generally found that people on this forum offer clear constructive advice. I think this is true for virtually everything written so far on this thread. However when given advice rather than take it you seem to question the advice and ask why your method wont work. There are plenty of ways of skinning a cat but my general advice is stick to what has been proven to work well and be aware that not following standard approaches can lead to a lot of potential problems (look at how much problems there were with rot/mould timber framed housing when the detailing wasnt right

Thanks for your reply, i find you to be the most plesant of people on here, your posts are informative and you give reason without the need to belittle or insult.
People ask questions thats how they learn and most people on here seem to get highly offended by it and throw their dummys out the pram "fine do it yourself then see if i care"

Personally my brain will not allow me to believe there is only one way to build a shed or even that that example can not be added to in anyway. So unless somebody can explain why what i have suggested above with my rudimentary drawing would not work i will continue to think it.
 
Good morning all
Instead of this bickering, wouldn't it be more constructive for someone to suggest a
decent youtube video series on the correct way to do it for the UK environment?

It probably would clear things up for a lot of folks.

Tom
 
yuzi87":1wauozt7 said:
.......... So unless somebody can explain why what i have suggested above with my rudimentary drawing would not work i will continue to think it.

It won't work from a number of different aspects. Firstly, the outer cladding is a rainscreen only, and you can assume that wind-driven water will not only penetrate it, but will blow onto the inner face of the void. This has been proven numerous times with arthroscopic videos. So, you have to consider both sides of the void to be wet. Now, imagine your novel arrangement but with the cladding removed. What would happen if you turned a hose on it?

Secondly, you've been told pages back that putting a vapour barrier outside insulation provides a site for interstitial condensation, which will run down the inner face and pool at the bottom, eventually rotting your sole plate and the bottom ends of your studs, but long before that, providing an ideal breeding ground for moulds. You've also been told that the inside of a wall should provide at least 5 times the vapour resistance of the outside. Given that you are proposing putting the same material on the inside and the outside of the wall (18mm OSB), then logically you should have a maximum of one fifth of the amount of OSB on the outside as you do on the inside. In other words, instead of you proposed slots at the top and bottom, you need to remove 80% of the OSB from the outside. This of course leaves 80% of your insulation exposed to the wind driven water ingress that we talked about in the previous paragraph. As insulation performance drops to virtually nil when soaked, you will need to protect it by the installation of a breather membrane. Breather membranes only work if they have a void outside them, so you would need to counterbatten the OSB off the face of studs & membrane, before counterbattening your external cladding. Your walls just got 25mm thicker.

Slots at the top and bottom with insulation pushed up hard behind them will not be interlinked. In other words, they don't provide ventilation for the rest of the wall which is covered by OSB. Yes, they allow moisutre out at those locations, but they do nothing about the vapour that arrives at the back of the board a foot away.

Now, with 80 percent of your external OSB removed, can you tell us again what purpose it serves.

All this you have been told. It's all there in the previous pages, and in the threads you have been linked to. Please do not come back again with "this is what I am doing, now tell me why it's wrong" (in terms). Work with the principles you've been given repeatedly.
 
Ttrees":2yoy560u said:
Good morning all
Instead of this bickering, wouldn't it be more constructive for someone to suggest a
decent youtube video series on the correct way to do it for the UK environment?

It probably would clear things up for a lot of folks.

Tom

There isn't one, as far as I know. You could look here and see one being built properly. Or here.
 
MikeG.":3vla0556 said:
yuzi87":3vla0556 said:
.......... So unless somebody can explain why what i have suggested above with my rudimentary drawing would not work i will continue to think it.

It won't work from a number of different aspects. Firstly, the outer cladding is a rainscreen only, and you can assume that wind-driven water will not only penetrate it, but will blow onto the inner face of the void. This has been proven numerous times with arthroscopic videos. So, you have to consider both sides of the void to be wet. Now, imagine your novel arrangement but with the cladding removed. What would happen if you turned a hose on it?

Secondly, you've been told pages back that putting a vapour barrier outside insulation provides a site for interstitial condensation, which will run down the inner face and pool at the bottom, eventually rotting your sole plate and the bottom ends of your studs, but long before that, providing an ideal breeding ground for moulds. You've also been told that the inside of a wall should provide at least 5 times the vapour resistance of the outside. Given that you are proposing putting the same material on the inside and the outside of the wall (18mm OSB), then logically you should have a maximum of one fifth of the amount of OSB on the outside as you do on the inside. In other words, instead of you proposed slots at the top and bottom, you need to remove 80% of the OSB from the outside. This of course leaves 80% of your insulation exposed to the wind driven water ingress that we talked about in the previous paragraph. As insulation performance drops to virtually nil when soaked, you will need to protect it by the installation of a breather membrane. Breather membranes only work if they have a void outside them, so you would need to counterbatten the OSB off the face of studs & membrane, before counterbattening your external cladding. Your walls just got 25mm thicker.

Slots at the top and bottom with insulation pushed up hard behind them will not be interlinked. In other words, they don't provide ventilation for the rest of the wall which is covered by OSB. Yes, they allow moisutre out at those locations, but they do nothing about the vapour that arrives at the back of the board a foot away.

Now, with 80 percent of your external OSB removed, can you tell us again what purpose it serves.

All this you have been told. It's all there in the previous pages, and in the threads you have been linked to. Please do not come back again with "this is what I am doing, now tell me why it's wrong" (in terms). Work with the principles you've been given repeatedly.

Thank you for the informative post, the 80% rule is interesting i will research that further, regarding your other points i would have put the breather membrane over the osb not under, does breather membrane also require clearance behind? I guess not due to it normally backing onto insulation
 
TRADA and the BRE produced some of the early research on this, but you might prefer to just take a look at this Architect's Journal article referring to the 5:1 minimum ratio. The Centre for Alternative Technology publish a series of useful and informative pamphlets, and it was through them that I first learnt of the 5:1 rule of thumb 30 odd years ago. They don't have much online, but there is a reference here. Scroll down and click on "What is Breathability". You'll find I'm not making this stuff up.

-

If you put breather membrane on top of a vapour barrier such as OSB, it clearly no longer serves a "breather" function. It will do no more than keep the OSB dry from the outside.
 
Hornbeam":1l77jbj1 said:
Please do not confuse a vapour control layer and a breather membrane. They are 2 different things and go in different places
difference between breather membrane and vcl
Google it or check out the link below

https://blog.celotex.co.uk/technical/va ... l-celotex/

I understand the differences i was just wondering about behind the membrane and whether that could be solid, but as Mike stated i guess it cant and it needs a void to breathe and lose fill insulation wouldnt really affect that.
 
MikeG.":1tpu1hdt said:
There's no lintel over the door opening.

You mean reinforced double header etc above where the door will be? Yea i have not built that yet, last bit of framing to do
 
i do notice there is still some wobble with the frame, will this be rectified once the inner osb is installed which will offer more stability and strength or will i require some diagonal braces of some sort?
 



I guess your going to say that breather membrane is pointless due to it being not able to breath and butted up to osb and i should of raised osb roof?
If anything though it serves to stops water if somehow it gets through roof
 
yuzi87":2wx3xeu6 said:


I guess your going to say that breather membrane is pointless due to it being not able to breath and butted up to osb and i should of raised osb roof?
If anything though it serves to stops water if somehow it gets through roof

A breather membrane under OSB!! Oh boy. This really is head-on-brick-wall territory.
 
For your next build leave the top plates off until the walls are up and put them on overlapping the corners. A touch stronger that way.

Pete
 
yuzi87":393fy11u said:
I guess your going to say that breather membrane is pointless due to it being not able to breath and butted up to osb and i should of raised osb roof?
If anything though it serves to stops water if somehow it gets through roof

Okay but if water does come through the roof it’s just going to then pool on top of the breather membrane? And if vapour passes through the other way as the OSB is a vapour barrier surely that doesn’t sound too good ...moisture trapped and then mould?

Obviously it’s your shed and I maybe missing something but I don’t follow your logic.

On the racking question yes the OSB will make it much more rigid.

Good luck!
 
Blackswanwood":2lrlavvv said:
yuzi87":2lrlavvv said:
I guess your going to say that breather membrane is pointless due to it being not able to breath and butted up to osb and i should of raised osb roof?
If anything though it serves to stops water if somehow it gets through roof

Okay but if water does come through the roof it’s just going to then pool on top of the breather membrane? And if vapour passes through the other way as the OSB is a vapour barrier surely that doesn’t sound too good ...moisture trapped and then mould?

Obviously it’s your shed and I maybe missing something but I don’t follow your logic.

On the racking question yes the OSB will make it much more rigid.

Good luck!

Its fine i knew the answer as soon as i finshed building it lol, ill just raise the osb with some battons i guess
 

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