# Insulating a concrete shed for a workshop. Advice needed!



## Stone (11 Apr 2013)

Hi, I'm new to the forum, so thanks in advance for any help given... 

OK, I'm wanting to make a workshop from my shed, and here are the basics: 

What's there already: 
The shed is 8' x 12', made of 2' wide vertical concrete panels. 
It has a 4' wide wooden door and a window. The floor is a big flat concrete slab. 
The roof is corrugated and sloping - I think it's corrugated concrete or some fibrous hard stuff. 
The roof is watertight. The floor/wall join is fairly basic, in that the wall slabs are just sitting on the base. I've sealed it with exterior frame sealant. 
There are chunky wooden worktops and shelves along some of the longer sides. 
There's electricity, with lights and sockets, but it looks dodgy. 
In the winter when it was really cold and then warmed slightly, there was condensation in the shed with lots of drips from the roof. 

What I want to do: 
I want to make it into a workshop where I can work on my lathe, bandsaw, etc. I'll keep the worktops/shelves where they are. 
I'd like to insulate the walls/floor/roof 
I want to get the electrics taken out and re-done (will get an electrician in for this) 
I may only be living here for a few years rather than many years, so I'm not looking for a 'dream-workshop' solution. Just a 'basic but good' solution. 
Ideally I'm looking to do this myself (apart from the electrics) so simpler solutions would be better. 

Here are my questions: 
What would people suggest as insulation material for the walls, floor and roof? With the wall insulation, I need something that will cut easily, so that I can fit it around the shelving/worktop structures. 
What would you suggest about ventilation/condensation? 
Would insulating the whole shed mean that winter condensation is less likely to happen? Or do I need to put a ventilation grill of some sort in the door to get air flow? 
When I insulated it, would the door and window just let in the cold air because they're not insulated, or is this not a big deal? 
I'm guessing it's best to sort out the electrics first, then fit insulation round it - is that best, or the other way round? 

I think that's about it... 
Thanks ever so much if anyone can offer advice or suggestions  It's very much appreciated!


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## carlb40 (11 Apr 2013)

Personally i would rip every thing out and start with a bare shell. 

Roof wise, do you have rafters/beams at the moment? If so i would insulate between the joists, leaving a 1 inch gap between the insulation and roof.

Walls - i would build a 3 x 2 stud walls within the existing structure, fit wiring - plenty of sockets. Then again insulate between the timbers. 

Floor - 2 x 1 roofing lathe screwed to the concrete base, insulate between timbers. 

Board everything - floor 3/4 boards either ply or floorboards. 1/2'' ply on the walls. 1/4'' ply on the ceiling 
That way everything is sealed in.

Cheapest insulation will be fibreglass. Polystyrene for the floor - your feet will thank you in winter


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## Stone (11 Apr 2013)

Hi Carl, 

thanks for your reply, there's some good ideas there. 

Polystyrene for the winter floor sounds like a good plan. Mostly it seems a bit thorough and deluxe for my short term needs, but that could be because I've never installed stud walls and drilled into concrete! I'll have to think that one through quite a bit. One of the reasons for leaving the shelving/worktops in place is that the concrete drilling has already been done.

With the roof, there are metal bars going across the shed at the tops of the walls, with the corrugated roof attached to these bars.

Thanks for your ideas!


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## LJM (12 Apr 2013)

I think that's about as basic as it gets. You may be able to use smaller timbers for the walls, and you could even replace the ply with sheets of polythene on the walls and ceiling, but the that brings it's own disadvantages. The benches can be re-installed, screwed into the timbers.

There are cladding systems, that could be used eternally, leaving more space inside and removing the need to take out the benches, but it would then be more complicated to marry up the wall insulation with the roof insulation without and gaps. 

Good luck


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## MickCheese (12 Apr 2013)

At a previous address I had a prefab garage like you describe, I think. 

Building out the walls will leave you with a corridor. 

I found that after a while the sealant I used under the slab walls let water in. 

The roof was impossible to insulate 

So not a lot of help, sorry. 

Everything I tried failed. I got so frustrated that I decided the only satisfactory solution was to knock it down and use the slab to build a new workshop with block work. 

Good luck. 

Mick


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## Cowboy _Builder (12 Apr 2013)

I've just put the slab down for exactly the same project ,i will clad the walls with 50m/m kingspan insulation inbetween 50 m/m stud work,and for the roof i will fix 50m/m Kingspan ,then cover the entire thing with 13m/m OSB on the walls and 11m/m on the ceiling .You will need something bigger than 50x50m/m if you intend to fix shelves to it ,I will be having free standing shelves in mine 
This works well as i did one for a friend around 10 years ago , and he has since put a floating floor in it which helps keep it warm winter ...........Allan


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## Stone (12 Apr 2013)

Thanks - someone else suggested Celotex or Kingspan, and I was wondering about this as a possible solution. It's good to hear that it has worked for someone. I like the fact that it cuts easily and is self supporting.
Good also to hear that the sealant under the slab walls is a point of concern. Yes, I've put lots of layers on, inside and out, for that one, but still know that the shed could have been built with more insight in the first place.

Yes, it's tricky - I'm tending to think that lining with a stud wall is the best way, but might have to wait for my next house when I can make a workshop to see me through many years. For this one I'm thinking more about Celotex/Kingspan, and making sure the floor and roof are done well. Not sure!......

Thanks for taking the time to write, H.


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