100-150 wide cavities - that's unusual, maybe unheard-of, in an old building. At first sight that makes CWI an unusually effective strategy - adequate insulation value for once. However .... it would make the outer skin unusually cold in winter, for the first time in its history, where it's been kept fairly warm hitherto by internal heat loss. So it'll spend long periods below freezing, as well as being a site of interstitial condensation. How well it'll stand up to that depends what it's made of - if high quality engineering bricks, prob frostproof, otherwise it'll suffer from freeze-thaw. And the interstitial condensation may never dry out properly in summer, but accumulate year on year. It may be OK - a WUFI study is called for, always assuming you can get true physical characteristic data to input for the outer leaf.

There will be parts of the wall that have not been heated recently (eg gable walls above the ceiling level, porches, outbuildings, disused chimney stacks) - if these have done ok unheated then the rest might well be too.

Most older buildings were not designed to be heated (in the way we understand it), that idea of heating all the rooms all the time didn't come in until relatively recently.

Wufi is great but you do need to know a) how much horizontal rain hits the wall and b) how much soaks in, vs running straight off. If you use the software default values
for these you can scare yourself unnecessarily, many walls have been inadequately IWI'd because of one such exercise from which 'safe' (IE poor) insulation values were plucked.

What are your thoughts about thermal bridges along the wall-floor and gable-ceiling junctions where the inner leaf sticks through the insulation envelope? IME these have been the difficult problem with EWI/CWI of massive old walls.

Posted By: WillInAberdeengable walls above the ceiling level, porches, outbuildings, disused chimney stacks

Freestanding walls (exposed to more or less same air both sides) are pretty much tolerant of freeze/thaw, than walls sheltered/inhabited on one face which even if not historically central heated were, by definition almost, kept well above freezing, one way or another.

It's not so much input of interior moisture that causes problematic interstitial condensation (incl damage by freeze-thaw of same) in stone-cold walls newly insulated from (but vapour-open to) the interior, but the lack of re-evaporation synchronised from both faces (exterior atmospheric moisture vastly exceeds interior as the prime source of water in a wall), which can get well out of synch, leading to moisture flows in either direction. A freestanding wall doesn't mind being cold as long as it's in balance with the exterior air i.e. with maximum re-evaporation potential equally from both faces.

That's why garden walls don't deteriorate like over-IWI'd house walls of same material, and why it's a good plan to build almost an insulated house within a historic shell, with copious ventilation to outside, between. The old wall then thinks it's a freestanding wall.

l

Posted By: djh

Posted By: RobinBI need to learn about ibuttons or similar.

Now there's a blast from the past!http:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" alt="" title="" >

I don't think they're likely to be what you want because you probably want to be able to read the sensors while they're in situ? iButtons need to be put into a reader, IIRC. I have a humidity monitoring system in my walls and roof, but TBH it has rarely worked properly. (the computer part of it is very poorly engineered). I'm not sure what the state of the art is these days, or what's a reasonable price. What I think you should be looking for has:
* wired sensors, so they can be read in place
* mains-powered recording system that a
For sensors, you could use 1-wire compnents. Homechip sells some 1-wire humidity sensors at around £50 each.

I know there are some Wi-Fi , Temperature and Humidity sensors powered by CR2354 button batteries. The ones I looked at were Solar/ambient light powered with the battery back up. In a wall cavity of course they'd be purely battery and I don't know how long that would last.

Thank you all for your views, interesting as ever. For a minute I thought I was the "blast from the past" but I think perhaps we're talking about the ibuttons? As Simon mentions wire stuff sounds more sensible.
Definitely a project to be Wufi-ed. I was musing that stone barns around here are all unheated and they still stand, but thanks to Fostertom I see it's not quite the same thing.

Posted By: fostertomSeems to me, a traditional masonry wall survives best when it's an uninsulated house wall i.e. kept more or less above freezing by some heat (albeit not constant powerful central heating) from the interior; second best when basically the same wall is a freestanding garden wall or unheated barn wall; worst when (unprecedented in history) it gets IWI'd and central heated on one face.
And the greatest enemy of masonry is when its diurnal and/or seasonal re-evaporation (aka re-drying) potential is reduced, typically by altering the conditions of its interior face, by internal vapour barriers especially - all round better if configured to 'fail-safe' without relying on those, for multiple reasons.

I'm missing what you're actually proposing/suggesting here. There's a clear (aesthetic/historic) desire to retain old buildings but also to turn them into modern, warm, buildings. If internally insulating old stone walls does not work what is the answer?