Richard Greenland

Last week I discussed eaves soffits and fascia boards, this week it’s another type of soffits, i.e. ceilings.

Slightly saggy ceilings aren’t necessarily a problem, most older buildings have upstairs ceiling joists which are way undersized by today’s standards. These bow downwards especially if heavy objects are stored in the loft. Ceilings on downstairs rooms shouldn’t sag as they’re attached to the much thicker floor joists above. If they’re sagging, they need replacement – see below.

Laths seen from the back with plaster visible between them

Ceilings and timber-frame screen walls come with two main types of covering. Lath-and-plaster is an old system of tacking rows of thin wooden strips between the joists then covering with lime and horsehair plaster. It sets soft and gritty with a thin pale top layer and softer darker underlayers. These are the ones which tend to fall down!

Modern timber ceilings are made of plasterboard – a sheet of plaster sandwiched between layers of thick paper. This is then screwed into place and plaster-skimmed. The top layer looks quite different to lime plaster, and should be smooth and even with a pink or grey colour.

Plasterboard ceilings probably won’t present problems unless they have insufficient screws/ clout nails. There should be fixings every 150mm to joists at the sheet’s edges and every 300mm to joists in the middle.

Old lath-and-plaster ceilings showing signs of irregular cracking or bowing can collapse suddenly on the occupants and are dangerous. Unstable ceilings need complete removal and replacement. If merely a bit suspect, and reasonably flat, I usually screw new plasterboard sheets underneath to hold everything in place and provide a better surface for my plasterer to finish. It saves masses of work and mess taking the old ceilings down, then putting it all back. You must be sure to put plenty of screws into the joists to secure the boards really safely. Your carpenter should be able to do two good sized bedrooms in 1 – 2 days, and your plasterer to skim both in a day. With materials it might cost £400 – £600 for two rooms. Artex can be steamed off or covered the same way – see my blog on this.

If the ceiling is very saggy in places your plasterer may not be able to skim, even if it’s covered with new boards. To check, place a straight board or spirit level about a metre long over any obvious bulges. If there’s more than about 25mm space at either end of the stick, it probably all needs to come down and have new joists and boards, and put all the insulation back too. This could easily cost twice as much or more than a simple board-over, and fibreglass dust is dangerous to lungs. Another less messy alternative is to build a separate ceiling underneath – good for reducing mess if the house is occupied, but it lowers the ceiling.

Some houses and tenament blocks have concrete ceilings (often beam-and-block), which should have few problems so long as the roof doesn’t leak. Uninsulated concrete is VERY cold and not good for tenant retention. It can be insulated with 2 x 2 battens or deeper, and sheets of closed-cell phenolic foam such as Celotex. Fibreglass is a relatively poor insulator at these thicknesses. If there are upstairs neighbours concrete can be surprisingly bad for noise transmission

Next week I’ll talk about internal walls.

Rich