Hello
Long-time lurker, now got a reason to post something.

Just bought a not-quite-sure-how-old-probably-19thC stone cottage in Orkney, lovely exposed coastal location, nice thick walls, weird layout. The plan is to knock some walls down and 'ecovate' it as much as possible.

While all advice is welcome (it's a bit late for "Buy a sensible building somewhere else", mind ) for the renovation/retrofit of various elements, we'd be very interested to hear any specifics about the windows.

It's currently got 2 over 2 sash windows nearly everywhere, and uPVC casements in a modern extension on the back. There's also a couple of unused doors on the front, SW face which we want to turn into windows. We've had some advice to suppress the windows on the rear, NE face, but that's not going to happen - on the contrary I want to make bigger ones...

Given the deep recesses, the climate and exposure (mmm, wind-driven rain off the North Sea), what would the collective wisdom be?

- Concentrate on insulation and draught-proofing first, rehab all the sashes and keep them, u-values be damned?
- Secondary glazing?
- Replacement - of which? With what? I keep seeing references to alu-clad timber frames in places like coastal Maine, and then reading that alu-clad timber is useless for anywhere damp/salty... Is triple-glazing worth it anywhere?

I've had a bit of a browse on here and I know there are a couple of hardy souls in Shetland and N Scotland - any tips?

So many questions...

Lovely.

I understand that Orkney has a particularly constant and reliable renewable energy resource - wind - which is easily harnessed. Given that 'going free' in glut, serious case for relying more on space heating than on super insulation - tho airtightness would be worth maximising! With that very high external surface to useful floor are/volume ratio, that's a big help and cost saver - to super insulate all that e.g. to PH standard would be really prohibitive.

Just for once, I'd say a good case for modest IWI, which, while modest (e.g 60mm insulation), is generally trouble free because the inner face of the existing masonry is kept somewhat warm and above dew point.

I would tend to expect super-breathability to be best, rather than internal VCL, but I would certainly evaluate alternatives in WUFI, based on actual local weather data rather than advice from elsewhere.

Really, do somehow do or get some WUFI simulation done - could give expensive news, to achieve safety, or alternatively make it surprisingly straightforward. Anyway, in that climate, don't think of trusting the old Glaser assessment method, still enshrined in Bldg Regs etc.

Can you get firewood on Orkney for a reasonable cost?

Does anyone know how much enough wind turbines to provide heating will cost?

Has any research been done with using low temp solar to heat walls OUTSIDE of internal wall insulation? So the walls get warm enough to dry out for at least some of the year. (Not that there is much space of IWI)

To avoid disturbing floors, downstand perimeter insulation down to base of found, encloses the block of underfloor subsoil within an insulation 'coffer dam'. The trench can also function as a french drain, to guarantee no rising damp never. Leca or expanded glass as semi-insulative aggregate in addition to the EPS. If on solid rock, as you may be, then the 'downstand' can instead be a shallow horizontal skirt or wing, with topsoil back on top of it.

Posted By: Ed DaviesBasically, the thick wall would be too much of a path down under the internal wall insulation then up over the external ground insulation.

The other thing is that there's probably no foundations and if the ground's a bit soft you'd have to be very careful not to undermine things.

Prob all true, but still worth looking at

MHRV will neither help nor hinder any possible danger of interstitial condensation.

Specifically, unless comparing with living completely airtight and unventilated (unlikely) it won't reduce internal RH.

Given adequate ventilation by any means, internal RH depends only on current external RH as modified by raised internal air temp. It's wrong to think of MHRV 'removing water vapour' any better than any rudimentary kind of ventilation - think of any ventilation as making internal water content identical (small time lag) with external water content.

If you experience internal RH being lower than external, that's solely because you've raised the temp of the outside air, as it comes in and becomes internal. That's true for any ventilation - leakiness, open windows, MHRV, regardless of MHRV's heat-exchange facility.

So MHRV can't make any difference with risk of intersitial condensation, if that's based on expectation of lower internal RH.

ST mentioned MHRV in connection with condensation and I was just making the point that MHRV won't help at all with risk of interstitial condensation i.e. doesn't remove need to get the wall buildup/insulation etc right.

Love the windows, keep them, refurbish them and then fit insulated internal shutters. I wouldn't even consider upvc or even alloy faced ones, you can diy or get a decent joiner to make the insulated shutters that will keep the heat in when it is most needed at night. Don't just hack out and try and make wider windows, if you really, really need more window area put in more the same size. It will change the fenestration massively for the worst.

Lot of chimneys that will need something doing with them. I think they will be a bit of a challenge.

Posted By: SteamyTeasomething I mentioned, and modelled years ago (internal RH following external RH)

So that's something we agree on? - just checking.

Posted By: SteamyTeaThe point I was making is that if you can stop any water from the outside making its way though the walls, then you are in a better place to start with

If you mean liquid water, can't disagree with that - just a matter of best-practice pointing prob i.e. def not with strong cement mix. And a fair degree of airtightness will follow from that.

Why def not cement mix? because it's imperative that the whole wall face is as unresistant to water vapour as possible, while being well resistant to liquid water. It's so important to get that distinction right.

So far so good but then I want to clarify what you mean by

Posted By: SteamyTeaIf you can get the place airtight/watertight, you can fit MVHR and then not have to worry about condensation too much.

If you mean internal condensation then yes, MHRV only works well when the place is airtight (but watertightness doesn't come into that). If you mean interstitial condensation, then I disagree - MHRV has no effect on interstitial condensation or not, compared to any other kind of ventilation - leakiness, open windows, extract ventilation etc.

Posted By: SteamyTeaThis nonsense about 'breathing' ...

Nonsense? even if we say that 'breathing' simply means good water vapour permeability right through from inside to out, and we're clear that it has nothing to do with air permeability or liquid water permeability?

Posted By: SteamyTeaIf you got a foot or so of stone and rubble, almost regardless of what you do internally, there will be points where condensation form somewhere within the wall. But that would have been the case for that wall for decades or even longer.

Maybe, maybe not, it doesn't matter - the key thing is its re-drying potential. Nothing wrong with temporary interstitial condensation, even in contact with timber etc, as long as it can promptly dry out again, seasonally or diurnally.

Trouble comes from modern ideas that misguidedly obstruct water vapour diffusion e.g. vapour barriers, strong renders and pointing. Maximum re-drying potential both outward and inward is an absolute must, especially these days as insulation levels increase. Note - maximum unobstructed drying potential to the inside as well as the outside - to inside is a hard one to accept!

The danger is that interstitial condensation can never quite dry out seasonally or diurnally and so the liquid water content accumulates steadily year by year. Modelling all this in WUFI is how to check what's happening and to change things till it's safe - and it's sensitive to the local weather data that's plugged into the WUFI model. What's safe in Orkney is completely over the top in SE England, and vice versa - so rule-of-thumb wisdom can mislead badly.

Posted By: SteamyTeaMuch easier to control the internal environment with some MVHR (or mechanical ventilation) ...

Again, MHRV (or any kind of ventilation) can't 'control the internal environment' (if that means RH), but yes, better than no ventilation at all in an airtight building. Back to the top of this post

Posted By: SteamyTea(internal RH following external RH)

RH is 'controlled' (i.e. reduced) not by the MHRV but by the warming-up if the incoming outside air.

Posted By: SteamyTea... than relying on a wall to absorb and release condensation at just the right temperature, in the right amounts, regardless of temperature differences

I don't understand that - not how it's all expected to function.

Posted By: SteamyTeaAll you need it the temperature distribution along with the likelihood of hitting the dew point at those temperatures

That sounds like a static Glaser-type check, or at best a series of static checks through the year. But Glaser is proven theoretically unsound because static - the real behaviour is crucially dynamic i.e. a continuum through time, over a year or multiple years of actual local weather. Glaser usually gives over-optimistic results but can equally prove over-onerous by failing to exploit large dynamic effects. Glaser used to work safely with low levels of insulation but is completely inadequate and misleading nowadays, even though still enshrined in BS 5205 (is it?) and bldg Regs.

Having said that, ST's scientific instincts have clearly worked for him.

Dig in and see - as long as it's not full-bedded in cement mortar (unlikely) any low-mid figure amongst wall vapour resistivities should be realistic - try varying same to see how sensitive; err on the high side.

How about the wind generation idea - uniqueish in UK in that it's reasonably constant year round, night and day - is that true? Could it therefore provide an adequately continuous input to cheap to install electric underfloor heating, with the floor mass acting as store to tide you over when the wind drops?

If there's enough electric that way, maybe not even need underfloor insulation - it's not true that heat would indefinitely be lost downward. True initially, but the subsoil would steadily warm up to an increasing depth downward, over a couple or 3 years, establishing an ever-flatter temp gradient downward, hence ever-diminishing heat flow downward (well not 'ever' - it'll equilibriate in a year or three).

That model is fine if the floor plate is very large, with little perimeter effect. But particularly in your long thin case, heat doesn't just go straight down, but curves down, out and back up to big loss at the surrounding ground surface. That's where downstand or 'wing' perimeter insulation (or a bit of both) would help - to greatly increase the path-length of the heat through the ground, which does give good thermal resistance if sufficiently 'thick' (i.e. long path length).

That is, it puts the heat input place (floor surface near the perimeter) much further away, path-length wise, from the heat loss place (ground surface beyond the 'wing' of insulation). Tho it's true what Ed says, that without EWI that insulative skirt will be somewhat short circuited by heat escaping up and out via the foundation wall thickness - but still worth considering.

The effect would be rock-solid constant floor temp, whatever you set it to, all year round, night and day. All that subsoil, coupled uninsulated to the floor slab, would form a huge lo-temp heat store having immense capacity to instantly increase its upward heat output temporarily, without depletion, when inside air temp threatens to drop - or indeed to cease heat production when inside temp threatens to rise. Inside air temp will faithfully follow slab temp +/- a degree or so, without needing thermostat regulation.

However electric input to the slab would be thermostat controlled, to maintain the desired slab temp - but that input could peak and trough, as long as it averages out over a few days.

If you have wind turbines and want an off grid life style, then this guy's blog is worth a good read http://lifeattheendoftheroad.wordpress.com/2014/11/

Perhaps an indelicate question Woo, but is your budget in the low, medium or high tens of thousands? Knowing will help the chaps on here prioritise your spending, if necessary, I'd imagine?

Posted By: fostertomHow would you go about simulating it mike?

More to the point how would you do it?

Thermal Inertia formula will tell you everything you need to know.