ventilating/insulating a shed roof

[Bigbob]

Hi peeps,
My first post here so here goes.
Im currently insulating my recently purchased shed,for general woodwork and the like.Shed is 12x8,3/4" t & g with a mineral felt roof on top of OSB.

Now I've spoken to a couple of people about this and some are telling me to insulate the roof and leave an air gap others are telling me because my shed roof has no ventilation there is no point in leaving an air gap as all I'll do is create a vacumn of hot air.(suppose if there is no gap ,theres no room for a build up of hot air)

I've also been told to put insulation in and leave NO gap but just put an air inlet low on oneside of my walls and another outlet high on an opposite wall to create air flow(sounds reasonable enough)

I do plan on using a heater in the winter and would prefer it not to be like a sauna in the summer so which method would you guys think would be the best.

 

[bob_c]

From my understanding of insulation,just because its well insulated doesnt mean it will be overly hot in summer,it could be cooler.(unless there are a lot of South facing windows,glass has little insulation value which is why conservatories get so hot during the day and cold at night)Remember,insulation keeps heat in.It should also keep heat out!
There is also no such thing as a vacuum of hot air.

 

[Adam]

Could you cut a hole and put some mesh across to allow some ventilation into the top space?

Adam

 

[chippy1970]

BIG BOB,

Welcome, just use celotex or kingspan cut in between the rafters dent worry about an air gap just push it tight to the under side of the OSB.

You only need an air gap if its a ventilated roof ie it has vents in the soffit. I have celotex all over my workshop in the roof, walls and Jablite in the floor. Its warm in the winter and cool in the Summer, I used 50mm thats all you really need for a workshop.