On 16 Dec, 08:52, "Bob Mannix" wrote:
"stuart noble" wrote in message

...



The Natural Philosopher wrote:
stuart noble wrote:

So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft
insulation has been done and where interstitial condensation is present
and a breathable (Tyvek) sarking felt has not been used under the roof
covering.

I'll take your word for it.

he's right. I have more hole in *my soffiits and ridge than there are in
Gordon Browns economic policy. Totally wrecked the insulation
effectiveness till I boarded over it.

But that's what they said was the regulations.

Dry as a bone too!

My point is that freezing air with 100% relative humidity, such as we have
now, can't, by definition, dry anything. I wouldn't go looking for a
solution to a problem that may exist only on odd days in the year.

Well, your first point was actually referring to 90% humidity which will dry
slowly. You have now switched to the safer 100% which, of course, won't dry
anything.

Ventilation is always the key as it will stay dryer in the lead up to days
like we have now and will dry quicker afterwards so the incidence and
persistence of such conditions in the loft will be much improved. If there
are freezing, wet conditions with no wind for an extended period AND you
introduce warm damp air into the loft, you will have a problem whatever,
granted, but, over a year, a well ventilated loft will have fewer problems.

--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

It suddently occured to me that there is a toilet vent going into the
roof space from the upstairs toilet which comes on automatically with
the light, and children being children it tends to get left on. If I
turn this off and cap the vent pipe while it is turned off this will
reduce the amount of warm air getting into the loft, as when it is off
the fan is a clear straight route into the roof...

A job for tonight.

Thanks all for the help - and as always the additional "discussion"

Cheers

Steve