The conductivity and diffusivity data in that paper is v useful, comparing different soils in one table.

This paper is about the subsoil state under open ground surface under diurnal and annual variation cycles. That changes usefully when under
a) an insulated ground cover, and
b) a more or less constant temperature applied to the surface i.e. year-round indoor comfort temp.

Under a), around the edge of the area covered, subsoil will be thermally coupled laterally with the surrounding uncovered subsoil and so will behave as described in the paper (though I'm v surprised to read that the depth at which annual temp variation dies out is as great as 10-15m - I understood more like 3m).

But toward the middle of the covered area, the amplitude of the temp variation that gets through the surface insulated cover, is much smaller; therefore the depth at which annual temp stabilises is shallower. Under a very large covered area e.g. an unheated but insulated warehouse (if such exists), near its centre subsoil temp stability will happen at zero subsoil depth; approaching the perimeter that depth will increase.

That is, under a) the temp at stabilised depth will still be same (annual average surface temp) as under open ground, but the depth at which stabilisation happens gets closer to the surface.

Under b), same as last para, but the temp at that stabilised depth is also higher: under that same insulated warehouse, except in case b) it's heated, near its centre not only will subsoil temp stability happen at zero subsoil depth, but also its temp at that stabilised-temp depth will be near to the year-round maintained indoor air temp; approaching the perimeter that depth will increase and the temp at that stabilised-temp depth will converge with that under the surrounding uncovered ground.

Subsoil at stabilised, or nearly stabilised temp, is what is useful as an annualised heat store (or look at it another way, as a massive stabiliser which holds floor temp steady whatever the weather or season). The question is, how deep into the subsoil do you have to go to access that stability, especially as it's only 'passively' useful if it's at zero depth i.e. right in contact with the floor slab.

That in turn depends on a) the size and within that b) the 'path length to perimeter' of the building in question - what proportion of the slab displays 'centre' behaviour (stabilised subsoil temp at zero subsoil depth and high temp), and what proportion displays 'perimeter' behaviour (stabilised subsoil temp at increasing subsoil depth and lowering temp).

The building's effective a) size and within that b) 'path length to perimeter' can be improved by downstand and/or 'wing' insulation; the smaller and/or narrower the building the greater the improvement for given downstand depth and/or 'wing' width.

Don't dismiss what's possible even for this small, narrow Shetland example - model it.

Posted By: ringiI expect it would all come down to how much heating of the floor is done in summer. Assuming that the floor is heated all winter.

You can assume the interior will be 'heated' in summer - we all have ways and means to 'naturally' maintain summer interior temp at much same comfort level as we do artificially in winter.

fostertom,

I mean the floor in summer will be heated to a higher average temperature then the outside air. (I am assuming off grid wind power that has no other useful usage.

But heating the walls just behind the IWI may be a better usage of the power to help drying out.

fostertom 6 hours ago edited quote
"How would you go about simulating it mike?"

I'll open another thread to answer. Poor Woo could probably do with more sound advice and less theorising here!

Had not heard of Matilda's Blanket, but apart from it doing nothing to separate floors and ceilings from potential air leakage from outside, it seems a good idea. Does take up over 3 inches on each wall installed though, and not actually sure if those electrical socket extensions are permitted under Part P, and after a quick look through the FAQ, I cannot see a U-Value, bit remiss of them that is.

Posted By: mike7I'll open another thread to answer

Good Idea

I would wonder how many they had actually installed.
May be worth given them a call though.

Found the U-Value, it is 0.28

So. Orkney is lovely, and things are happening (in the periods where we are back from abroad).

It has been interesting to live in it and find out what it's like through the winter. What I'd like to talk about today is damp :)

When we bought the place, there were obviously patches of very limited damp around (small areas with some points of mildew ; blown interior cement render on the chimney breast and under the window in the kitchen). Notably in the window recesses, which was hardly surprising because the window frames are so rotten and the external cills mostly absent, but also a little bit in a couple of ceiling corners and on walls. Despite having had the wettest winter in 20 years, and having lost a fair few joints from between the roof tiles, damp inside the house hasn't got noticeably worse. Hurrah.

We have started by completely repointing the roof. The external chimney breasts still need doing but the tops have them have been capped off : the amount of water on the internal chimney breasts has reduced to almost nothing. We have stripped the existing internal wall insulation and have found very little evidence of damp on the wall behind - what there is seems to be connected to cracks in the external pointing or from water ingress via the roof.
We have a whole variety of floors, ranging from flagstones laid directly onto sand/earth, through concrete poured on top of similar flags, to concrete slab floors with a plastic sheet on top and then chipboard-type boards on top of that, some with a bit of insulation board on top of that. Where we've taken the boards and the plastic off, the concrete surface has been slightly damp or moist, but not pooling with water and without any visible sign of the moisture moving out towards the walls particularly. The kind of moisture that was dried out after one evening of the gas heater being in the room. Where we have taken the floors back to soil already, the soil was... like soil. Not bone dry dust, but not damp enough to cling to your hand either : it is pretty free-draining with a lot of sand in it. The only wetter spots have been near the base of the external wall at one point where the outside path slopes towards the house instead of away from it (that's being sorted too).

We plan to put in wet UFH throughout, in a concrete slab floor. We don't have the foundation depth to dig out for a limecrete solution and brutally speaking, we don't have the cash for the newer systems (Ty-Mawr's Sublime, e.g.) that don't require quite so much depth. The floor would therefore be of a classic construction : DPM, insulation, pipes and screed, concrete.

The plan for the walls is some kind of breathable internal insulation : haven't decided which, yet. What could you all advise in terms of ways to help make sure that we don't have a problem with damp displaced to the base of the walls? Air "bricks" (the walls are solid/rubble construction) or vents at the base of walls?

That's reassuring, Triassic. We are definitely going to lime-plaster inside - outside is still under discussion - and we had the same feeling about the effects of the UFH keeping the damp out. It's important for us because we'll probably be absent for regular periods of time.
Getting quite excited now...