I am renovating my house and am completely redoing my flat roof: ceilings, insulation and roof covering (I am planning to use EPDM rubber). In case it is relevant, I am living in the Netherlands.
My plan was to use rockwool on the inside as insulation, but now my builder is suggesting insulation on the outside. He wants to use 50mm (2 inches) PIR insulation.
Does anyone have ideas on the following:
- Is there a good argument to go with insulation on the outside of the roof instead of on the inside?
- Is PIR insulation better than rockwool?
- Or … should I insulate both the inside and the outside?
Best Answer
Dow (manufacturer of XPS panels) recommends their panels OVER the flat roof waterproofing. You do have to cover with an aggregate or a green roof. The practice is called "inverted roof"
PIR panels are similarly rated for inverted roof use.
PIR is "better" than rockwool in U-value vs thickness :