This is a real risk
Foil backed plaster board - fine. Old lath-and-plaster - not fine.
That would be the appropriate solution if there isn't a vapour barrier yet.
Personally I would stick with the vapour barrier in the loft.
The house will be much too dry if you keep the vapour content down to outside levels.
AIUI this (one of the reasons) why we have eaves ventilation. Water vapour penetrates the ceiling, but is continuously swept away by the cross flow of air between the eaves (and any originating from rain that has been blown under the tiles on unfelted roofs).
Probably, yes. But since the attic is well ventilated, it should evaporate fairly well. If in the other hand you boarded over that insulation, you would get pretty serious condensation on the board underside.
No, thats why foil backed plasterbaord is available.
All good solutions.
Bit foil backed board is usually simpler.
Yes (well 1 W/m.K, since k is not dimensionless) ...
... no, that's way too pessimistic, you've forgotten to include the surface boundary layer resistances again. The U value for 9 in. solid brickwork is usually in the range 2 - 2.5 W/m^2.K, depending on exposure, brick density, moisture content, etc. etc. Still an order of magnitude worse than a good modern wall of course.
[Snip description of internal insulation.]At least.
There are many advantages to insulating old solid wall properties externally:
- it doesn't make your rooms smaller;
- reduces cold bridging (between floors, etc., hard to insulate internally);
- far less internal disruption;
- gives a high thermal mass, and long thermal time constant;
- avoids the 'summer condensation problem' which can occur with internal insulation.
And some disadvantages:
- much more expensive, external appearance affected, detailing critical around doors, windows and eaves.
As the owner of detached solid-wall house I find the idea of insulating externally quite attractive, if it could be done well. Various proprietary external insulation 'systems' have come and gone over the period since the 70s 'oil crisis'. Does anyone here have any relevant experience to report, good or bad?
And you have forgotten that the outer boundary layer is nonexistent in any wind.
;-)
Its certainly worth thinking about.
You include the both surface resistances when calculating wall U-values. A lower figure (0.04 v. 0.13) is used for the outside surface to take account of wind etc.
BR443
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