We have a summerhouse/shed, built for us last autumn. We have had various quotes for insulating it and finishing it off, but we are confused because of conflicting advice from different builders. We need to make a decision urgently between two different companies and obviously want to get it right.
The floor has Celotex insulation underneath the chipboard; the walls are just shiplap wood cladding on a wood frame with no breathable/Tyvek membrane. The outside is painted with Sadolin breathable paint. The doors and one window are double glazed, with one trickle vent.
Should we use rockwool or Celotex to insulate the walls? Celotex=not breathable, expensive, very good insulation; rockwool=breathable, cheap, not as insulating - will it also act as a moisture bridge across from the outside wall to the inside cladding? Do we need to have a Tyvek lining put on before rockwool? Is this possible, now the building is all bolted together?
Will rockwool, tightly packed, still drop a little over time, or will it be fine?
Should we use plasterboard or MDF? Will plasterboard swell and crumble if it gets damp? Is there much of a price difference between MDF and plasterboard? Will MDF swell in the damp??
Any comments would be VERY gratefully received!!! Please help to clear up the confusion!!