Insulation - Flatroof

johnnyjb

Hi i was wondering could some one help me with my query?

I have a ground floor single story extension with a flat felt roof and want to insulate the inside ceiling.

I was thinking of installing insulated slabs and plastering , but friends have told me that it is easier to put rolls of insulation in between the joists and cover with standard plasterboard slab.

Is there must of a difference in insulation values in the 2 methods.

This is a diy job with a budget but would stretch budget if really need to

Also, if i was to use insulated slabs would it be recommended to remove the existing plastered ceiling slabs- or could i secure the insul slabs to existing plastered ceiling

Thanks

wayoutwest

Johnny-What is presently behind the existing plasterboard?

johnnyjb

sorry for the late reply

I havent taken down the old ceiling yet but i dont think ther is any above the ceiling.

I cut a little notch out and didnt find insulation , i poked a measuring tape up to meet the plywood roof and got a depth of 8 inches.

gman2k

if you have 8 inches, make sure you use max 6" of insulation to leave min 2" of ventilation space.
You have what's known as a cold roof.
Modern flat roofs are constructed as warm roofs - with the insulation on the outside of the roof, and no ventilation.
I would advise you to install 6" Rockwool insulation, just come up with a method to leave your vent space above.