DIY Doctor UK DIY Forums

Hi all, my back bedroom has a very high ceiling, and only single brick construction on 2 exterior walls. The room has damp patches on the 2 exterior walls. I want to put in a lower ceiling, using new joists and plasterboard, and I want to 'dry line' the 2 exterior walls as this room is very cold. Could someone suggest what size timbers to use for the ceiling joists ( 4x2 ? ), the room is 9'x12", and what timbers to use on the 2 walls, what insulation to use between the timbers, and what type of boarding to use on ceiling and walls. Do I need to sand and cement the other 2 interior walls prior to plastering ? I know it's a long question, but I would really appreciate some feedback on this. Thanks.

Griff.slap,
4x2 should be okay, you want make sure they are well secure when fitted, as you don't want the weight of the plasterboard to bring them down. Plan the spaces of joist and centres out, so you reduce the number of cuts you need to make in the boards making the cost less and installation less time consuming. Plus plan for your lighting!
Regards
KB

This is a job you only want to do once.
The best solution for the ceiling is to fit underneath the joists a water vapour proof lining and under that close fit (taking care to avoid any holes) one inch polystyrene and under that plasterboard. (make sure you seal round the wire to the light fitting.)
If you have access to the roof space,and there's enough room fill the spaces
between the joists with poly foam. (It will find its way into the most unlikely spaces and make a hole free filling)
If there is no access then cut four inch thick polystyrene to fit tightly. (It won't be as good a filling)
Then do the same on the walls - different type of foam.
This will give you a room that requires little or no heat.
The big issue, is leakage of air, due to rising heat and the sucking effect of the wind. Stop heat loss and save money.

Hi be careful when using polystyrene insulation, they don't like PVC cables! Makes them go brittle and the electrical insulation will fail could cause a fire!
KB

Many thanks for the help on my single brick walls. Should I also use the foil backed plasterboard on the walls, screwed to 2x2 batons with insulated foam boards between the batons ? I think this site is brill for us amateurs, and I will still need a professional plasterer to skim over, so we won't be taking work off the pro's. Once again many thanks.

Hi Griff.slap,
I'd be looking to resolve the damp problem first, is it rising, pointing or roof that is causing this? otherwise all you will be doing is hiding the problem and it will cause other problem if it is not sorted out!
Once that problem is sorted out you could put up a stud frame to board to or dot'n'dab the wall if you think it is needed. Moisture boards are good but no need if no moisture ingress!
KB

Hi KBrownie, I think I have solved damp problem, there were 3 ridge tiles which weren't secure, and rainwater was running down the loft wall and making the top of the interior bedroom wall damp. But the wall was an exterior wall and only single brick, so was very cold. My father had a massive radiator fitted, which heated the room, but caused condensation when the heat hit the cold wall. I think that I can solve this problem, using your and others suggestions. Once again, many thanks to all.

Hi,
If it's a single skin wall i'd put up a stud (timber) wall. Using moisture boards (foil back) I'd also consider polyethene sheets to cover plaster wall pre stud, so between exsisting wall and timber. So you can then insulate between stud work before boarding
good luck
KB

Hi Kbrownie, you have answered all my questions at one go ! I will do as you suggested and place polythene lining on walls before studding them, then put insulation between timbers under foil backed board. Just a couple of questions, what sort of insulation would you recommend, and what would you do with the other 2 interior walls ? Dab on boards, or browning ? Thanks.

Hi again,
Insulation Kingspan best and easy to install, May cost a little more than rock wool? Don't use polystyrene if you ever install electric cables with it they don't get on!
Other walls, choice is yours really, wouldn't put anybody of either.
Good Luck with your project
KB

Many thanks to you Kbrownie, your help has been much appreciated, I will start the project in the Spring, and will let you know how I get on. Cheers.