Shed insulation

[Con Owen]

Hi
I wish to insulate my shed (14 x 11), floor is already insulated, wall framework is 75 x 35mm, roof is 45 x 45mm. In the winter months I will probably use some form of electric heating as required (although no power installed yet, that will be the next project, so will have to make allowance for where wiring is to go). What would be the best method and insulation material? My intention was to use 25mm polystyrene (with 50mm air gap) on the roof with 50mm in the walls, both then covered with 12mm plasterboard. However, I saw a post regarding the dangers of this material and it has put me off using it. Also I am not clear what to use as a vapour barrier and where it should be placed. Any advice would be much appreciated.
This is the first time I have posted, hope that I have placed in the correct forum.

 

[dellboy]

hi
saw your post and intended to do similar using barrier on the inside of the outside walls followed by 3 inch polystyrene finished up with a plywood inner lining
what did you go for in the end ?

 

[Colin C]

Are you both going to put you power in the wallor on the walls because if what I have been told is right.
Polystyrene will rot the plastic on the out side of the cables if it is inside with it,I would check if you are putting your cables in the walls

 

[mailee]

I used rockwool in my walls and then used thick builders polyethene as the damp membrane. i also left a gap between the outside cladding and the rockwool and then placed cladding on the inside. Like this:

 

[Colin C]

I used rockwool too and the difference was shocking as I now have just one heater in the workshop to keep it warm
Plus it is never on as high as both a of my heaters before :wink:

 

[RogerS]

Recommended sequence of layers is (from inside to outside)

You > inner lining (eg plasterboard/fibreboard)

> vapour barrier (250/500guage polythene)

> insulation (must be permeable type such as rockwool)

> breather membrane (building paper ...keeps timber framed shell watertight but allows vapour from inside to escape )

> ventilated cavity

> external cladding

(taken from Carpentry and Joinery 3...damn good book)

 

[woodbloke]

In my shop I used 50mm rockwool with a vapour barrier (Screwfix) next to the external skin (6mm marine ply), internal skin is exterior hardboard, 100mm standard fibre glass from B&Q in the roof space - Rob

 

[Con Owen]

Hi
Dellboy
I have not insulated shed yet. My intention was to use polystyrene. However, having read a post by SF in one of the forums (he is a Firefighter I believe) it put me off using it - certainly in the roof anyway. I would strongly recommend that you look at it.

Colin
No I was not aware that polystyrene may rot cables ( if used I was going to place the cable in the walls with the polystyrene--a thought, what if I placed the cable in conduit, would it rot it too do you think?). I will check this out. It seems that polystyrene is not the way to go. I was going this route as it was probably the most cost effective.

Mailee
I like the way you have done your insulation. I have a problem with your method for my roof, in that I understand I have to retain a 45mm airgap in the roof for ventilation, then I would have to put the Rockwool followed by the dpm and plasterboard making a total of of approx 160mm (assuming 100mm Rockwool) that I would lose in the roof space, My walls are approx 2.150 mtrs high and from the walls to the ridge only approx 620mm so I would lose an awful lot of roof space, that was why in the first instance it was my intention to use only 25mm thick insulation. Incidentally How did you retain the Rockwool in the roof prior to cladding etc?

Roger
Your explanation of the layer sequence for insulation is great, before this I was confused, not now. Incidentally when the shed was made I had waterproof paper (it is a type of tar paper) placed between the cladding and framework. I don't know if this will cause a problem. As my framework is 75mm I guess that I would only be able to use 50mm Rockwool. Do you know if they do it in this size?

At the moment I am leaning towards Rockwool for the walls, the roof is something I will have to consider in greater depth.

Thanks guys for all the helpful advice

Cono

 

[Con Owen]

Rob
Thanks for the info. Why did you go for 100mm standard insulation in the roof, but use 50mm Rockwool in the walls? Incidentally what is the length and width of 50mm Rockwool?
Cono

 

[mailee]

Hi Cono, My insulation in the roof is only 25mm as I had the same problem with space. I added battens and a chicken wire affair to keep the air gap. I hald the rockwool in place with strings until the cladding was on. Hope this helps. I have not found any problem with having less insulation in the roof so far and it has done a winter and summer now.

 

[Con Owen]

Hi Mailee
Thanks for the explanation, it is very helpful to me. I will do my shed insulation the same way.
Cono

 

[dellboy]

Hi
slightly concerned about the fire risk mentioned when using this but notice that Wickes sell it for roof insulation any thoughts

As the material will be covered with plywood (or can anyone suggest anything better /cheaper)on the inside and a polythene liner will the fire risk be a major problem considering the workshop will have its fair share of combustionables in it already ?

 

[mailee]

I agree with you Dellboy about the combustables in a workshop. It is always going to be a tradeoff in materials used. You must choose the materials which are within your budget when it all comes down to it. I have a fire extinguisher in the shop but who is to say it will be enough to put out a fire if one develops? I have the hose pipe close at hand just in case.

 

[paulm]

Cono,

Try googling for celotex or kingspan for your roof space.

This is what the builders used when we had a loft conversion a while back. It's a dense but very light foam centre, fire retardent I assume as it's designed for this type of application, and has foil facings back and front.

I think you would need only a thinner thickness of this stuff for an equivalent insulation value from the rockwool, but don't know the technical details.

It's not cheap, the kingspan is a lot more reasonable than the celotex if I recall, but would be a good option for the roof space and perhaps more cost effective rockwool in the walls ?

Cheers, Paul.

 

[woodbloke]

Con Owen wrote:

Why did you go for 100mm standard insulation in the roof, but use 50mm Rockwool in the walls? Incidentally what is the length and width of 50mm Rockwool?

I wanted to keep the walls as thin as possible so as not to loose extra space in the 'shop - 50mm per side don't sound allot but it all counts. :lol: I wasn't too worried in the roof space as the roof bearers were 100mm so I used 100mm fg to fill in the space. Rockwool is good stuff and is not sold on a roll, you buy it from your local building suppliers in large slabs approx 1500x500mm, about 10 slabs or so to the pack. Its then very easy to cut to size with a large kitchen knife and fit snugly into a recess - make sure you wear a mask though - Rob

 

[Con Owen]

Hi Paul
I Googled Kingspan, their roofing insulation boards have been accredited with two fire safety awards so as you say they are OK for the roof and I can use Rockwool for the walls. Thanks for the info.
Cono

Hi Rob
Thanks for the info. I most certainly will use a mask plus suitable protective clothes and gloves. Some years back I insulated the loft in our previous house, wore a mask initally but my glasses kept steaming up so I could not see to cut the fibre glass to size. I took the mask off to overcome this, it did, but caused me some resperatory problems for a day or two.
Cono

 

[woodbloke]

Con Owen wrote:

wore a mask initally but my glasses kept steaming up so I could not see to cut the fibre glass to size

I had this problem with the gogs - solved it by using an Airshield now, expensive, I know but in my view, money very well spent. Wearing it the 'shop to do normal woody stuff presents no problems at all, whereas before, the bins got steamed up, you take a couple or four breaths to clean them, inhale a load of fine dust in the process and wonder why at the end of the day you've got a breathing problem, or at least you can feel the dust catching in the back of throat and then on your chest - Rob

 

[Woody Alan]

Hi

I have just recieved an order of 20 8x4 sheets from these people
http://www.secondsandco.co.uk/
50/60mm fire retardant at about £10 a sheet some single foil side some double ring them and have a chat they deliver all over UK for £30 an order and even sell on ebay, I saw some one inch sheets go for two pounds each was tempted to buy and sell on. You could double those up for thicker use.

Cheers Alan

 

[Con Owen]

Hi Rob
I did try the Trend Airshield a couple of years ago at the D & M show. Found it to be uncomfortable, perhaps I did not put it on right. The price seemed to be over the top too. It does get good reviews both here and in the trade mags-maybe I will try it again.
Cono

Hi Alan
Thanks for the info. I will check Seconds and Co out. Their price is certainly attractive, a couple of weeks ago I was quoted between £10-14 for 8 x 4 sheet of 50mm ordinary polystyrene. The fire risk put it out of consideration. Would I be right that the foil backing would form a vapour barrier in itself making a dpm between it and the plasterboard I intend to use unnecessary or do you think the framework between which the insulation will be placed will make a dpm necessary?
Cono

 

[Woody Alan]

Cono

I am using the foil as the vapourshield, I am not a hundred percent sure it's the right way but to be honest as long as I don't make any vapour pockets these things can be a little over the top. For inbstance my workshop has been up for about 10 years it's felted on OSB and rockwool directed under with plastice under that and then plasterboard, in theory not reall right because of the felt over and poly under so no air movement but I haven't had a problem ( apart from rubbish felt that is :-( I am making sure that the insulation doesn't touch the cladding though.

Check your P.M's

Alan