Dormer Roof Insulation (Retro-fit)

Fracasmac

Hi all,

would really appreciate some advice. Our house was near-completion when we purchased and we unfortunately did not pay enough attention to the builder's lackluster attempt at insulation.
The first floor has two bedrooms and a small WC/Shower opening out onto a double-height hallway. The roof of this hall is clad in wood. We have access to the apex of the roof from above the small landing and there is access to the back eaves from an opening in a press in a bedroom.
The existing insulation consists of a single sheet of glass wool and is not fit for purpose, particularly given our windy coastal location.
Using the access points available we could only do a patchy upgrade of the insulation. Importantly, the sloping roof sections (which make up the majority of the area) are inaccessible so it seems we will have to insulate from the inside.
At the moment we are considering insulated plasterboard, but we have concerns re. how much headroom might be lost and also regarding potential build up of moisture between layers. Multifoil insulation underneath plasterboard is another possibility where the headroom would be less impacted but again the concern remains re. moisture build up and layering.
The wood-clad double height hall ceiling is a feature that will unfortunately have to be covered over. The little WC/Shower is also in the eaves, the walls are half tiled and the entire shower cubicle is tiled. This will be an especially problematic area, as its very tight and layering of materials is a potential minefield.
Advice please!

BryanF

Research air-tightness

There was a thread here a few years ago where the guys dealt with air-tightness & insulation upgrade from the outside. Taking of sectiona of the lower roof slates. This your best bet.