Roof insulation on old property

looksee

I am looking at purchasing an old property that has been well renovated, but despite double glazing only has a BER of F. Presumably the roof has not been insulated; it has sound tiling and the interior ceilings are the wood laths that fix to the joists, again in nice condition.

Is there any practical way of insulating the small cavity? Thanks for any ideas .

BryanF

Hi external tiles will have non-breathable felt. Is this a detached house? Filling cavity is a bad idea.

Markcheese

To be honest, probably just attaching insulated plasterboard to the existing ceiling would probably be the most cost effective, cheapest and by far the easiest way to go.. Just get the right type for the job..

BryanF

Markcheese wrote: »

To be honest, probably just attaching insulated plasterboard to the existing ceiling would probably be the most cost effective, cheapest and by far the easiest way to go.. Just get the right type for the job..

Only

If you get the right Vapour barrier

And add adequate external ventilation to the rafter space

looksee

Ok, thanks for your answers. I have had a closer look at it and it appears it has a new roof, it was possible to see new (traditional) felt under the slates. There is nothing in the gap - the part where the cavity is very narrow is quite small. I think the inside timbers will have to go and get the ceiling slabbed, or whatever is appropriate, but it will be in the hands of someone who knows what they are doing so I don't have to make any decisions

antiskeptic

looksee wrote: »

I am looking at purchasing an old property that has been well renovated, but despite double glazing only has a BER of F. Presumably the roof has not been insulated; it has sound tiling and the interior ceilings are the wood laths that fix to the joists, again in nice condition.

Is there any practical way of insulating the small cavity? Thanks for any ideas .

Sound tiling = sound roof slates/tiles?

Wooden laths fixed to the joists? Do you mean the fixed to the rafters (the angled lengths of wood to which the roof slates are fixed. In other words, the ceiling is sloped rather than being raftered at an angle and joisted horizontally, giving a horizontal ceiling and an attic above it.

If a sloped ceiling, then you've only the depth of the rafter (minus necessary air gap between top of insulation and underside of slate) available to fill with insulation and you won't get anything either thick enough or easy enough to install in that space.

The wooden laths would likely be an add on - presumably nailed over the existing plaster due to it's cracking. Laths would have been an easy DIY solution to the problem.

I'd plump for insulated plasterboard screwed into the rafters, leaving the laths where they are, then skimming afterwards to finish. Get the max thickness you can (modern regs would be around 150mm of insulation (plus 12.5mm for the plasterboard, but 100mm would be a good compromise and the boards are easily available.

It'd be messy but if you cover the floors and walls in plastic sheeting then you'll minimize the damage.

If you want to maximise height retention/insulation and take on the extra work then pull the wooden laths down (and the plaster that likely sits above it), fill between the rafters with rigid insulation cut to size and the foam the inevitable gaps with expanding foam. Then finish with an insulated board on the underside of the rafter + skim as before. You can either use a thinner board and maximise height, or a thick board and maximise insulation.

Messy, dirty unpleasant work though, so simply nailing insulated plasterboard over what's there a lot easier.

-

If you've open fireplaces then this will pull the BER down a lot. You can block the unused ones (leaving a small opening to allow ventilation of the unused chimney. I've found a childs soft football to be the ideal solution here. If the flue pipe is 8" then a 10" ball will sit nicely, but not perfectly in the opening - you just shove it up from the fireplace and the updraft/suction created by the chimney holds it in place. The benefit is easy removal if you want to light a fire.

The boiler could be old too, which would pull things down a lot BER wise.



That's the trouble with buying poorly insulated houses in good state of decor. You pay for the decor but end up having to redo it cos of the need to insulate.