lining shed roof to stop heat coming through

[matz]

I have a large shed with cement fibre roof sheet. The sun heats the roof sheet up so its hot underneath (inside the shed) and heats the shed up like a furnace. To fix this, I want to line the underside of the roof sheet with celotex. Does anyone know what thickness I need to stop ANY heat getting through? I've tried 50mm and it still gets warm underneath. I dont want to put up really think stuff unless I have to due to cost.

thanks

 

[Blagard]

If it is cement fibre roof, consider cleaning the top and painting it white.
Unless you are venting the air, the shed will always heat up in warm weather. The sun Radiates heat energy and you need to be reflecting that back. Insulation is only any good if you have active cooling inside the shed. Any dark surfaces you have will absorb heat energy and eventually radiate it back. So take the walls into consideration as well.

If you line the underside of the roof with celotex make sure the foil is on the outer side to help reflect radiated energy, Ideally create a vented void between roof and celotex

 

[matz]

ok thanks for the info. The building is sectional concrete and the walls are insulated and lined inside so the walls are always cool plus where the building is situated the sun only gets on the roof,,,