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my ground floor single story extension which has a flat roof is freezing cold. it's totally unheatable in the winter. we've tried turning up the heating, adding an extra radiator (portable oil filled one) to no avail. the rest of the house is ok, it's a 30s semi so gets chilly in places but nothing like the flat roof bit, brrrrrrr.

anyway. i don't think i can do this job myself but before i get a man round i want to give myself an idea of the options available. i'm sure we could insulate the roof on the outside somehow but not sure how effective this would be. we could also convert the flat roof to pitched but again, not sure how effective or costly this would be. i hate the flat roof anyway and would love to get rid of it. we also have no plans to build on top of the extension.

There are about 18 million homes with badly designed and built extensions that gobble up heat, leaving the people cold and miserable.
For some reason the Government chooses to ignore the evidence and concentrate on fitting totally useless fiberglass in the roofs of already cold houses.

The thing to do is pull the ceiling down, it is probably plasterboard and will come down in fairly large pieces and will not make much mess.

Then fill the space between the joists with closed cell polystyrene, you can get it from Wicks, or Jabwall or similar from any builders merchants.

Measure the gap between the joists quite carefully and cut the polystyrene with a sharp knife. This way it doesn't make too much mess. Using a saw will leave bits of polystyrene sticking to everything.

Its important that the polystyrene is a tight fit as the wind will suck your expensive warm air out from any cracks or holes.

When the spaces between the joists are packed tight, then nail or screw another layer of two inch thick polystyrene below the joists across the whole of the room. Again tightly pack.
Taking care to mark on the walls where the ends of the joists are, so that you know where to place the screws that will hold up the next layer of plasterboard.

When done, tape the seams and have a go at plastering, or get someone in to plaster for you. Job done.

Once the polystyrene is filling the gaps between the joists you will feel a lot happier and warmer – and you will probably reduce your heating bill by about 20%

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