3 October 2007 at 8:16 pm #30837Peter BayerParticipant
How much insulation can one get away with putting internally on a solid masonry wall?
In this instance the wall in question is 55cm thick and rubble filled ,but as is the nature of old buildings numerous structural timbers pass from the heated space into the wall
and are embedded within the wall as load spreaders,as a result a good vapor seal is
unlikely and any interstitial condensation would be a disaster.The other factor is the
winter weather ,driving rain followed by frost, will this lead to damaged stonework if the
outside surface temp of the wall drops too low?
4 October 2007 at 1:29 pm #34830Anonymous
Both faces of the wall need to be able to breathe so that the rubble core can dry quickly. Using impervious renders/tanking or vapour barriers is not a good idea, particularly where there are timber elements embedded in the wall – it's a sure-fire way to turn your joist ends and lintels to mush!
My own preference would be to retain the breathability of both faces of the rubble-stone wall by using a lime/hemp render on the inside to a depth of about two inches. This can be finished off with a smooth coat of lime plaster or left with the rough texture if desired.
On the outside, you need to repoint with lime and then limewash; this will help prevent penetrating damp and will protect the stonework from spalling if you get frost.
And check both drainage and guttering – taking particular care to ensure that soil levels outside are below internal floor levels, and a french drain can be a major benefit.
4 October 2007 at 8:59 pm #34831Mark SiddallParticipant
On of the benefits of Peter W's preference for 2 coat plaster rather than pb'd is that you can achieve a greater level of airtightness (when applied appropriately). This would reduce the water vapour leaking into the cavity and causing any problems. (This is not to say that an air-vapour barrier, rather than a simple vapour barrier, would not also achieve a workable solution.)
9 October 2007 at 6:23 pm #34832David OlivierParticipant
They were retrofitting old (150-250 yr old) homes in Canada up to 30 years ago with thick insulation and internal airtightness membranes and details designed to seal around the first floor joists.
Very severe climates compared to the UK. Building envelopes would be more likely to fail from interstitial condensation (not rain penetration – that's another matter) at design temperatures around -30 degC than around -5 degC. The subjects included Georgian stone farmhouses, solid brick Victorian houses and timber-framed Victorian and Edwardian houses.
See, e.g. THe Superinsulated Retrofit Book (1981).
I keep in close touch with practitioners there – we can learn a lot from the North Atlantic timewarp – and I've never heard of any problems.
2 December 2007 at 1:04 pm #34833Mark SiddallParticipant
4 December 2007 at 8:25 pm #34834SimmondsMillsParticipant
Thanks Mark for that interesting Canadian link!
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