Good morning Arnold. The day job is designing and testing metal cladding systems for Tata Steel albeit on slightly larger sheds.
There are a number if issues around using a single skin material. Steel is a very good conductor of heat and any moisture in teh air humidity is likely to condense out onto the back of the steel if the steel surface temperature falls below the dew point (which it will do).
To combat this you can take a number of approaches.
- Reduce the humidity in the building by ventilation or a dehumidifier
- Using a fleece backing does not stop condensation but it holds it in the fleece stopping it dripping. Once the temperature warms up again the moisture in the fleece evaporates. Personally I dont like this approach as you are treating the effect not the cause
- Insulate and minimise contact of air within the shed with the metal sheeting including any cold bridges.
I would do both 1 and 3 (dehumidify).
Before speccing your insulation you need to define the construction method. Are you making a structural frame to fit cladding to with columns and rafters at each end with purlins between. For steel sheds, purlins are usually exposed on the inside but could be included into the insulation cavity.
Key issue is generating an internal air tightness later which well fitted OSB will do
Polystyrene is a cheap good insulation but it is very poor in fire. Much better to use a PIR insulation. Alternatively use glass wool but you will need about twice the thickness for the same level of insulation
External skin, trapezoidal sheeting can be laid vertically or horizontally. Horizontally looks less industrial.. Maintain an air gap between the insulation and the sheet but only has to be small, there is a lot of extra air flow in the deeper part of the profiles. Also for walls try and pec a wall profile (this has wider crowns and narrower troughs so looks better)
Foam composite panels use a PIR foam core sandwiched between 2 thin layers of steel. They are available in roof and wall profiles and although relatively expensive will make an extremely well insulated shed. One caution is that they are not great at sound insulation.
Make sure you fit a drip flashing to deflect water away from the base and the water can drain away from the base of the shed
Using fibre cement for the roof means that you will have a structure which behave similarly to steel with the fleece backing. Also note that most fibre cements are quite brittle so easy to crack during installation and the roof would be fragile so shouldnt be walked on.
The roof can be made with steel profile in exactly the same way as the walls.
A cautionary note on painted steels. It can be quite difficult to tell the differences in quality of sheets just by looking at then. The cheapest polyester coating have very thin zinc coatings under the paint and you will be lucky to get a 10 year guarantee . At the other end the best sheeting will have a thicker (8 to 10 times as thick) plastisol coating and will use a zinc/aluminium alloy as the protection for the steel. This coating almost totally eliminates corrosion at exposed cut edges. The other big advantage of plastisol is it is much more robust and scratch resistant.
If you have any questions drop me a pm
Ian
