Hi all and Happy New Year,

I'm trying to find the best solution to a condensation problem in a loft in a 1980's new built block of flats (top floor flat with loft access).

The condensation forms on the inside of the roofing felt then drips down onto stuff stored up there. The loft is well insulated just above the ceiling. I don't want to increase ventilation due to water pipes being up there (as I don't want frost damage).

Maybe some sort of screen fitted over the rafters or some kind of insulation between the rafters? What would people suggest as a cheap and easy to fit solution? It does not have to look good.

Thanks

S

On 01/01/2021 11:18, wrote:
Hi all and Happy New Year,

I'm trying to find the best solution to a condensation problem in a
loft in a 1980's new built block of flats (top floor flat with loft
access).

The condensation forms on the inside of the roofing felt then drips
down onto stuff stored up there. The loft is well insulated just
above the ceiling. I don't want to increase ventilation due to water
pipes being up there (as I don't want frost damage).

The simplest solution would be to improve the ventilation of the loft
space and/or the impermeability of the vapour barrier between the
occupied space underneath and the loft.

You can't really prevent the roofing felt from being cold so you have to
get the humidity lower somehow.

Prevent moisture getting in or allow more fresh air to displace it.

Maybe some sort of screen fitted over the rafters or some kind of
insulation between the rafters? What would people suggest as a cheap
and easy to fit solution? It does not have to look good.

The condensation you describe is capable of allowing serious rot to
develop in roof timbers as well as cosmetic damage to stuff it drips on.
Advice on Usenet may be worth less than you have paid for it...

--
Regards,
Martin Brown

On Fri, 1 Jan 2021 11:24:52 +0000, Martin Brown wrote:

You can't really prevent the roofing felt from being cold so you have to
get the humidity lower somehow.

Prevent moisture getting in or allow more fresh air to displace it.

+1

or combination of both.

Are the holes where cables penetrate the ceiling for light fittings
vapour proof or just a roughly cut hole with loads of space around
the cable? Particulary for fittings in rooms with high humidty,
kitchen, bath/shower rooms. Are any ceiling down lighters open at the
back? They ought to be fire proof anyway to slow the spread of fire
from the room to loft space.

--
Cheers
Dave.

Are the holes where cables penetrate the ceiling for light fittings
vapour proof or just a roughly cut hole with loads of space around
the cable? Particularly for fittings in rooms with high humidity,
kitchen, bath/shower rooms. Are any ceiling down lighters open at the
back? They ought to be fire proof anyway to slow the spread of fire
from the room to loft space.

Yes, non-fireproof downlighters in kitchen and bathroom (as was at purchase last year) but now fitted with LEDs. Didn't realise these may be contributing to moisture ingress. I'll also have a look at sealing wire holes in ceiling for normal light fittings (non-downlighter type).

Thanks

I still think though that in order to get condensation, there has to be a
temp difference somewhere. So maybe beefing up the loft insulation over the
pipes also might keep it down.
Anyone tried stretching that substance called papronet across the void. It
seems to stop drips in greenhouses quite well while stopping the drips its
porous enough though allow air through.I will age though. Goes brittle.

Brian

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...
Are the holes where cables penetrate the ceiling for light fittings
vapour proof or just a roughly cut hole with loads of space around
the cable? Particularly for fittings in rooms with high humidity,
kitchen, bath/shower rooms. Are any ceiling down lighters open at the
back? They ought to be fire proof anyway to slow the spread of fire
from the room to loft space.

Yes, non-fireproof downlighters in kitchen and bathroom (as was at purchase
last year) but now fitted with LEDs. Didn't realise these may be
contributing to moisture ingress. I'll also have a look at sealing wire
holes in ceiling for normal light fittings (non-downlighter type).

Thanks

On 01/01/2021 11:18, wrote:
Hi all and Happy New Year,

I'm trying to find the best solution to a condensation problem in a loft in a 1980's new built block of flats (top floor flat with loft access).

The condensation forms on the inside of the roofing felt then drips down onto stuff stored up there. The loft is well insulated just above the ceiling. I don't want to increase ventilation due to water pipes being up there (as I don't want frost damage).

Maybe some sort of screen fitted over the rafters or some kind of insulation between the rafters? What would people suggest as a cheap and easy to fit solution? It does not have to look good.

Thanks

S

Do the top floor flat(s) have downlighters ?. These,
especially if fitted in bathrooms where an electric
shower is in use will allow moisture vapour into the
loft. Properties built in the 1980's may not have
had enough (or any) loft ventilation and if the top
floor flat owners have added more insulation in there
they have made the loft colder so increasing the
chance of condensation.

Where in the country is this building ?. Does it
stay in shadow a lot at this time of year (so the
solar gain does not warm up the loft) ?.

Have any other flat owners done something silly like
fit a new kitchen and terminate the cooker hood inside
the cavity wall ?.

You imply that the water tanks are in the loft. Do they have
tightly fitting lids ?. If not, get them retrofitted.
A slab of 4 inch celotex is better than nothing. If they are
well insulated make sure there no insulation under the tanks
and 'building regs' pipe insulation (with 19mm walls) should
protect the pipes. Pay attention to bends.

Apart from that, just make sure any stuff you store up there
is inside sealed plastic bags for protection.

On 01/01/2021 11:18, wrote:
Hi all and Happy New Year,

I'm trying to find the best solution to a condensation problem in a
loft in a 1980's new built block of flats (top floor flat with loft
access).

The condensation forms on the inside of the roofing felt then drips
down onto stuff stored up there. The loft is well insulated just
above the ceiling.

But not it would seem, equipped with a vapour barrier.

What you probably would find easiest is to board over the joists with
something impermeable, Foil backed plasterboard - extra celotex
insulation - or even just tack a plastic sheet over the insulation.

HOWEVER that does run a risk of transferring the problem to that vapour
barrier - the real fix is to have the impermeable layer INSIDE the
insulation. In short replace your ceilings with foil backed
plasterboard...or if the attic is rockwool between joists, lift that and
paste foil down (or lay a thick plastic sheet) on the plasterboard and
replace the insulation


I don't want to increase ventilation due to water
pipes being up there (as I don't want frost damage).


Insulated pipes with any water movement through them should be OK

Maybe some sort of screen fitted over the rafters or some kind of
insulation between the rafters? What would people suggest as a cheap
and easy to fit solution? It does not have to look good.

You are tackling the symptoms, not the cause. The cause is a combination
of too little ventilation and too little vapour barrier.

On reflection the simplest cure is to lift the insulation, lay down a
plastic sheet over the joists, and replace the insulation.

Make sure that any hatches are airtight and have a vapour barrier as well




--
Of what good are dead warriors? €¦ Warriors are those who desire battle
more than peace. Those who seek battle despite peace. Those who thump
their spears on the ground and talk of honor. Those who leap high the
battle dance and dream of glory €¦ The good of dead warriors, Mother, is
that they are dead.
Sheri S Tepper: The Awakeners.

I'm now looking at these easy-fit devices to modestly increase natural ventilation on the back of the roofing felt, has anyone used these?
https://www.amazon.co.uk/dp/B00M97O5...v_ov_lig_dp_it
Thanks
S

On 01/01/2021 19:35, wrote:
I'm now looking at these easy-fit devices to modestly increase natural ventilation on the back of the roofing felt, has anyone used these?
https://www.amazon.co.uk/dp/B00M97O5...v_ov_lig_dp_it
Thanks
S

You can achieve the same with chunks of expanded polystyrene
pushed into the overlap midway betwen joists. Much cheaper,
but doesn't solve the underlying problem of reducing the
amount of moisture vapour getting into the loft.

Fire hoods on downlighters are a start, but even they are not
a vapour barrier so you might want to make up your own downlighter
covers out of something fermacell or other class O board material
and cover them with turkey foil too.

Final report: The damp loft is now dry thanks to those Amazon spacers (to push out a gap in the roofing felt). Amazing how such a passive device added with a bit of wind works so well. Anyway I would recommend them or equivalent without hesitation. Now on to the next problem...