Loft room- freezing in winter, boiling in summer!

[Stringman_uk]

Hi all

As the title states really. We have a 4 storey house (built 1865) the loft has always been a room rather than a storage space. there is "bitumen sheet" on the tiles.
It has exposed beams with wool insulation and plasterboard between the beams.
Its bloody freezing in the winter (but you can warm it up with radiators) but in the summer its boiling. Window open and fan going and its still too hot.
FIL said in his loft he put in 3 layers of wool and its a much more stable temp.

As the beams are in bad decorative condition we were thinking of insulating and then plasterboarding over the beams. leaving the horizontal beams across the apex exposed.

Is Kingspan the best value to use? There are 26 rafter gaps (13 each side) about 2.2m x 0.4m each.

many thanks in advance

 

[foxhole]

You could replace insulation with rigid insulation then over board with insulated plasterboard to maximise efficiency .

 

[Stringman_uk]

That's kind of what i am thinking, when you say overboard do you mean between the rafters or over them?

 

[foxhole]

Over them .

 

[Tigercubrider]

A girlfriend lived in what was basically the attic of a Georgian stable - maybe started life as a hayloft or groom's accommodation. It had been pretty much just plasterboarded over the timbers and was a fridge/oven in winter/summer

After she left and I passed by I saw loads of kingspan type insulation delivered so I assume that the new owners did similar to your suggestions.

I believe you need to leave an airgap to prevent condensation

 

[Leofric]

To reduce the risk of condensation there should be a 50mm ventilated air space over the insulation and a vapour barrier on the warm side (under ) the insulation. You would need to consider how to ventilate the air space .

 

[wwwebber]

I am in a similar position and am intending on putting rigid insulation between the rafters and then overboarding with insulation backed plasterboard. I however also need to insulate the flooring as wind whistles through the eves into the flooring void and up through the floorboards. I will do this with rockwool which will act as sound insulation too.

FYI I dont have any type of membrane on my roof so that will be my ventilation and will also avoid condensation. I will however still leave a 25mm gap.

 

[Leofric]

just to clarify the situation and at the risk of sounding pedantic but , others are talking about 'over' the rafters , this is actually under the rafters as with insulated plasterboard, over would be on top of the rafters.