Advice on outbuilding wall insulation

filipe

filipe

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Cambridgeshire
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Hi,

I have an outbuilding (garage/shed) which was there when I bought the house and I'm planning to insulate it so I can enjoy my DIY longer throughout the year.

This is how it looks from outside:
185865-af1d1cdf63dd164e7e5376f54763f0be.jpg


This 3D model shows the frame construction in more details:
185863-5d3c91e69cf77b26913c372223ff8628.jpg


Basically the frame is just laid on top of a single-wall brick base. There is no DPC and the feather edge boards are nailed directly to the wooden studs.

Before the insulation, my understanding is that a DPC sheet should laid on the current concrete floor which then goes up against the brick wall. This internal floor DPC sheet should continue up the brick wall and then out under the wooden frame (bottom plate) which means the brick may get wet/humid with rain but then evaporates out. A breathable barrier should also be placed between the feather edge boards and wooden frame.

None of this is practical to do now as I would need to rebuild the whole thing. Would it make sense to install a breathable barrier from the inside of the shed leaving a gap between the feather edge boards and the barrier? In this case, the wooden frame would be on the "outside". My rationale is that any humidity on the brick and studs would end up evaporating out via the gaps on the feather boards (or via some vents) as the air would still be circulating behind the feather edge boards.

I wonder if having this breathable barrier right against the stud would make it prone to rot. Any other ideas?

Thanks!
 

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Coat the walls on the outside surface with a quality clear water repellent (silane based not silicone).

Only worry about the floor if it's getting damp. If so, use a floor paint. Otherwise, bitumen and a floor covering of vinyl tiles or lino.
 
I bought a 14x8 shed once which had been used as a room for a nursery School in the playground, had been heated etc. It had polystyrene for insulation wedged inside the sheds framework and been boarded over with chipboard T&G flooring but what they had done first was line the inside of the shed with plastic sheeting, effectively tanking it. You can buy liquid DPC for the floor if it's a big damp issue but if the brickwork doesn't have a DPC then the shed could taking on moisture through the bricks
 
The floor is going to be simple. I'll level it, then I will lay a plastic sheeting to act as DPC before insulating it with Kingspan/Celotex style boards.
@mrgobby What you described is what I was trying to explain in my post. Simply tank the frame from the inside. I suppose what they have done didn't damage the shed then!?

@^woody^ I thought about improving the water protection of the cladding. I will have a look into your suggestion.

Thanks!
 
There was no damage, basically the lining contains moisture in the room and not in the wall of the structure which could over time damage it. I bought and removed it then reinstalled it in our garden but chucked the plastic sheeting away as it was a faff to refit and tbh it was just for use as a big garden shed although since then kids have come along so if I were to turn it into a kids den/hideaway I'd re-line with plastic sheeting and heat it so it served a purpose again. Floor ideas fine.
 
I finished it a long time ago, but never posted a picture of it. This is the inside back in 2022. It can be snowing outside but with a standard electric heater it is nice and cosy inside.

I built both the desk and the cupboard above it.

outbuilding.jpg
 
Looks good ! The OSB boarding is the look these days in some modern builds I am seriously considering it instead of plasterboarding my new addition of block and concrete tiled workshop only because I can’t plaster so it’s a cheaper finished option but still can look great
 
For a workshop, the OSB is perfect. It is cheap, easy to install, stronger for when you hit stuff on the walls and great for the occasional screws. I diluted the paint quite a bit to ensure I would see the wooden chips texture which I think looks great.

...Perhaps more flammable though.
 
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