Walls

Dry lining a wall from the inside is the cheapest way to make a cold room warm, and it is also the fastest way to make a damp problem worse, so the order of operations matters. If a wall is wet we find out why first. Water coming in from outside, a blocked gutter soaking a gable, a bridged cavity, a high ground level outside, a failed damp proof course, all of those have to be dealt with before anything is fixed to the inside of that wall. Cover a wet wall with insulation and board and you have simply hidden it while giving the moisture a warm cavity and timber to work on. Once the wall is sound, the build up is the whole job. Insulated plasterboard can be bonded to a flat, dry wall with adhesive, which is quick and loses the least room, or fixed to battens where the wall is uneven, wavy or in an old house where you want a small ventilated gap. Mechanical fixings go in either way, because adhesive alone is not what holds a heavy board up over twenty years. Then comes the part that decides whether the wall performs or rots: the vapour control layer on the warm side, taped at every joint, carried around reveals and sealed at the floor, the ceiling and every socket box. A gap in it is a route for warm moist air to reach the cold masonry behind, and that is where the interstitial condensation happens that nobody sees for five years. The junctions are the other weak point. Where the lined wall meets an unlined internal wall, a floor or a window reveal you get a thermal bridge unless the insulation is returned a few hundred millimetres into the junction, and those corners are exactly where mould shows up first.

What you give up, and what you get back

You lose some floor area: about sixty millimetres for a modest lining, up to a hundred where the insulation is thicker or the wall needs battening. Radiators, sockets, switches and skirting all have to come off and go back out further, and a window reveal gets narrower unless it is handled carefully. What you get is a wall surface that is no longer cold to the touch, a room that heats in a fraction of the time, and an end to the black corners. On a solid walled house with no cavity to fill, it is usually the only practical way to get there.