I have a bungalow with a very shallow (6 degree) felted roof and an old
sloping ceiling attached to the underneath of the roof timbers. There
is no loft access to most of it.

I am building a new, flat ceiling under the old one (gap of 2 to 20"
between them). I don't think the old ceiling is insulated so I will put
loft insulation over my new ceiling.

Do I need to use vapour-barrier plasterboard to stop condensation
forming in the space above the insulation? There is no ventilation here.
Or is it better to use ordinary board so any moisture can get out?

I am hoping to just paint the plasterboard. Do I need to tape the joins
or just use filler?

I will be putting 9W CFL spotlights in the ceiling. Can one cover a low
energy CFL spot with insulation or should this be avoided to stop it
getting too hot?

Thanks

Roger

In article ,
Roger Moss "rwm2 [at] rwmoss.gotadsl.co.uk" writes:
I have a bungalow with a very shallow (6 degree) felted roof and an old
sloping ceiling attached to the underneath of the roof timbers. There
is no loft access to most of it.

I am building a new, flat ceiling under the old one (gap of 2 to 20"
between them). I don't think the old ceiling is insulated so I will put
loft insulation over my new ceiling.

Do I need to use vapour-barrier plasterboard to stop condensation
forming in the space above the insulation? There is no ventilation here.
Or is it better to use ordinary board so any moisture can get out?

Normally vapour barrier board isn't necessary, but you've probably
identified the one case where it really is -- a small poorly ventilated
cold space. However, I would look to fix the poor ventilation whilst
you have a chance for access there (but still use vapour barrier board).
The old ceiling will almost certainly eventually get covered in
condensation otherwise. You need external ventilation above the layer
of insulation (both above and below the old ceiling, which you could
punch lost of holes though).

I am hoping to just paint the plasterboard. Do I need to tape the joins
or just use filler?

I would guess filler on bevel-edged board is going to give the best
result, if you aren't skimming the whole ceiling.

I will be putting 9W CFL spotlights in the ceiling. Can one cover a low
energy CFL spot with insulation

Generally not a good idea. Although they don't give off the same heat
as filament lamps, they'll die before they get as hot, so they still
need the same cooling.

However, first you're worrying about a vapour barrier, and now you're
talking about punching holes right through it! Are the CFL spotlights
sealed to airflow?

or should this be avoided to stop it getting too hot?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel coughed up some electrons that declared:

In article ,
Roger Moss "rwm2 [at] rwmoss.gotadsl.co.uk" writes:
I have a bungalow with a very shallow (6 degree) felted roof and an old
sloping ceiling attached to the underneath of the roof timbers. There
is no loft access to most of it.

I am building a new, flat ceiling under the old one (gap of 2 to 20"
between them). I don't think the old ceiling is insulated so I will put
loft insulation over my new ceiling.

Do I need to use vapour-barrier plasterboard to stop condensation
forming in the space above the insulation? There is no ventilation here.
Or is it better to use ordinary board so any moisture can get out?

Normally vapour barrier board isn't necessary, but you've probably
identified the one case where it really is -- a small poorly ventilated
cold space. However, I would look to fix the poor ventilation whilst
you have a chance for access there (but still use vapour barrier board).
The old ceiling will almost certainly eventually get covered in
condensation otherwise. You need external ventilation above the layer
of insulation (both above and below the old ceiling, which you could
punch lost of holes though).


The BCO recommended vapour barrier PB on my bay window ceilings. Those are
also now insulated and ventilated (more or less - technically to half the
building regs required area, but that's better than the previous zero).

Cheers

Tim

On Aug 20, 2:38*pm, Roger Moss "rwm2 [at] rwmoss.gotadsl.co.uk"
wrote:
I have a bungalow with a very shallow (6 degree) felted roof and an old
sloping ceiling attached to the underneath of the roof timbers. *There
is no loft access to most of it.

I am building a new, flat ceiling under the old one (gap of 2 to 20"
between them). *I don't think the old ceiling is insulated so I will put
loft insulation over my new ceiling.

Do I need to use vapour-barrier plasterboard to stop condensation
forming in the space above the insulation? There is no ventilation here.
* Or is it better to use ordinary board so any moisture can get out?

I am hoping to just paint the plasterboard. *Do I need to tape the joins
or just use filler?

I will be putting 9W CFL spotlights in the ceiling. *Can one cover a low
energy CFL spot with insulation or should this be avoided to stop it
getting too hot?

Thanks

Roger

Taping joins with paper tape is a quick and thus cheap method. However
the tape is visible to a degree, filling is much better.


NT