Workshop insulation

[rayjares]

My first post, apologies for a long one!

Looking through the posts on shed insulation there appears a lot on construction from scratch and includes the insulation in the build. I’m sure there’s many others like me who have a ready built building from one of the various suppliers. Mine is a 3m x 4m workshop from Waltons to which I extended with another 3m x 4m giving a 3m x 8m workshop/shed. I’ve read Mike Garnham’s post “Build a shed Mike's way” and Scandinavian methods by Krysstel from Norway. Whereas the principles are desirable in a new build I have an existing building and looking for a way to improve the insulation.

The construction is 50mm x 25mm framing with a 12mm shiplap cladding. I insulated the walls with 25mm styrene sheets, a 25mm x 25mm styrene spacer between styrene sheets and outer cladding which gives a 25mm air gap. The inner wall is hardboard.

One method I’m toying with is to de-construct the workshop and turn the panels around so that the outer cladding becomes the inner wall. This leaves the 50mm x 25mm framing exposed between which I will place 50mm styrene panels. This will then be covered with a breather membrane. At each of the framing uprights I will fix 25mm x 25mm battens onto which will be new shiplap cladding. This allows for a 25mm airgap with an insect mesh top and bottom. What’s missing from this is the internal vapour barrier.

My question is, would this be a viable option or is there other ways to achieve the desired additional insulation?

Ray

 

[Emanuel]

Why are you turning the panels around?

 

[rayjares]

Experience with an old shed tells me that if I attempt to remove the existing cladding it will end up as firewood. Reversing the panel means only shelling out for the new exterior cladding.

 

[tomatwark]

How about removing the internal hardboard, putting vapour barrier over the existing insulation, them 9mm OSB, then 60 x 40 cls on edge running at 90 degrees to the shed fame ( you can set this up as fixing points as well), insulate with 50mm celotex between the cls , then an internal vapour barrier, then 12mm MDF.

You will lose some internal size but is has to be easier then trying to rebuild the shed inside out.

Remember this is not a house so you can do it away to suit you.

 

[RobinBHM]

You could just clad the outside with 50mm insulation, ideally PIR foam like celetex, quintherm, ecotherm etc. Use foil faced stuff and tape all the joints, including door and window reveals. Fit 50 x 25 tile battens and clad with new featheredge. It isnt a perfect solution as there is some risk of condensation getting to the original shiplap and ideally you will need to fit a vapour barrier to the inside.

You wont lose any internal space that way and you will create a complete insulation layer with no timber in the way to act as thermal bridging.

Having an external cladding that is fitted with a vented cavity behind is a much better construction method than a conventional single skin shed.

The problem is you may not have enough roof overhang, but maybe you could extend the overhang into the gutters -possibly less work than turning the shed inside out and better insulated as a result

 

[rayjares]

Thanks for the suggestions.

tomatwark, your suggestion appeals to me over my de-construct. Why the 9mm OSB over the existing insulation. Wouldn't the vapour barrier be sufficient then add the 60 x 40 cls?

RobinBHM, your idea does fulfil my idea of having a vented cavity. As for the roof, the T&G panels will be replaced with OSB/Felt/Onduline (or equiv)

You both have given me food for thought and I'll now have to save up my pocket money and get planning for the summer.

Thanks
Ray

 

[tomatwark]

You don't need to put 9mm OSB on I guess, but it will stiffen the shed up.

 

[OLD]

Most of the heat will go through the roof what have you done to address this. All so if the 25mm insulation in the walls is fitted tight with no gaps or gaps are foam filled whats the problem your insulated.

 

[mindthatwhatouch]

There is enough glue in OSB/Ply to create an effective enough vapour barrier.
Rather than turn the panels around I would clad the existing with a breatheable membrane, batten and clad.
replace the 25mm Polystyrene with some well fitted 50mm celotex.
What about roof and floor?