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    • CommentAuthorWoo
    • CommentTimeNov 15th 2014
     
    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 :bigsmile:) 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...
    • CommentAuthorWoo
    • CommentTimeNov 15th 2014 edited
     
    Front (SW facing), rear (NE facing), typical window, planned floor-plan (but with current window layout - we want to make at least W8 a lot bigger).
    •  
      CommentAuthorfostertom
    • CommentTimeNov 15th 2014
     
    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.
    • CommentAuthorWoo
    • CommentTimeNov 15th 2014
     
    We do actually have two wind turbines installed - I think 'artisanal' would be a polite way of describing the setup - which are providing all the electricity at the moment. Defining the electricity needs/system is a priority so as to be able to do the wiring setup once the walls are decided.

    With the lovely damp climate, breathability does seem to be the way to go. Have been looking at the various hemp-lime renders that can be direcly applied, but not reached any conclusion yet. Part of the interior is already insulated, though I'm not sure if it's with rigid boards or some kind of stud wall - however, since that part of the interior is the one that's going to change because of the removal of interior walls, I daresay we'll soon find out :smile: - plus we can see if there were any problems building up behind it.

    There's definitely no point even trying to go for PH standard of insulation; I don't think we'd make it, not with the problems of thick stone walls in a driving-rain environment. There is/was a project to look at different SWI methods on a neighbouring island and we plan to go and visit some of the properties to see how they worked out.
    For heating and hot water, we're looking at a combination pellet boiler with solar and underfloor heating, but no decisions made yet. Available cash will probably play a role in the final choice...
    •  
      CommentAuthorfostertom
    • CommentTimeNov 15th 2014
     
    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.
    • CommentAuthorEd Davies
    • CommentTimeNov 15th 2014
     
    What's the floor, currently? Do you have plans to insulate it? I'd put that at the top of my list of things to think about as it's the hardest to do retrospectively and the most likely to introduce serious damp problems so worth getting right first.
    • CommentAuthorringi
    • CommentTimeNov 15th 2014
     
    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)
    • CommentAuthorWoo
    • CommentTimeNov 15th 2014
     
    Hm, knowledge of the floors is my weak point. I know that the whole LH part is stone slab, and the extension is concrete. No idea what the rest of it is underneath, but it's covered with some kind of board. Orkney didn't build much with timber joists, for obvious reasons, and it would be weird if half of the same building had joists and the other half was solid-floored, but I suppose it's not impossible. Zero evidence of damp anywhere, though.

    There are plans to have underfloor heating where possible, but I doubt we'd seriously think about taking up the slab floor, so it would be limited to wherever there's cement. But maybe if we're feeling particularly masochistic, we might.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 15th 2014
     
    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.
    • CommentAuthorEd Davies
    • CommentTimeNov 15th 2014 edited
     
    My experience is limited to renting a 1.5 storey house in Tongue (so not drastically different climate from Orkney but a bit less unsheltered from wind) for 20 months including two winters. It had a small amount of IWI (boarded out with, I guess, 50 mm of mineral wool or something behind). Upstairs, in the roof, had a bit more insulation and was OK but downstairs the solid floor just sucked the heat out making it impossible to get the temperature much above 14 °C in the worst bit of the winter and economically unfeasible to do so much of the time for a large hunk of the year.

    What the floor actually is in different parts of yours is probably very much a matter of history since it was built. The other house up the road which was similar to the one I was in had a major fire in the 1930s and was rebuilt with a suspended timber floor.

    I had the opportunity to buy the one I was in but the floor put me off. I've sometimes wished I had but not since I heard that it flooded last winter.

    As FT says, there's the option to put insulation down outside. I don't think that was sensible on the house I had because the groundwater level was so high - water basically flowed directly under the slab as far as I could see, despite the owners putting in serious drainage between it and the hillside above.

    If your ground water is lower (are you basically on sand? - I did look at a couple of houses on West Mainland which seemed to be so) then FosterTom's suggestion might make sense. However, I don't think that fits with the suggestion of IWI too well. Basically, 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.

    I suppose the other question is how much head room you have? I.e., can you lay a useful amount of insulation on top of the existing floor and still have room to walk around? Doors would need thinking about, of course, particularly if there are big lintels across where the holes have been knocked through.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 15th 2014
     
    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
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 15th 2014
     
    Can you make the walls air/water tight from the outside? Then that may make some of the airtightness issues easier to deal with.
    If you can get the place airtight/watertight, you can fit MVHR and then not have to worry about condensation too much.

    May also be easier just see what it the best insulation you can get on the floor for your money, and forget UFH.

    May be time to start looking at Aerogel backed boards too. See if anyone else is renovating and get a truck load delivered,
    •  
      CommentAuthorfostertom
    • CommentTimeNov 15th 2014
     
    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.
    • CommentAuthoratomicbisf
    • CommentTimeNov 15th 2014
     
    Posted By: fostertomMHRV 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.


    I see your point, but that does assume that the alternative to MHRV is some other adequate ventilation such as opening windows, use of extractor fans etc even in cold weather. I don't think that's a safe assumption to make.

    In cold weather, just when the risk of condensation is highest, there's a natural tendency not to open the windows enough to ventilate adequately. I know I'm as guilty of this as anyone.

    So a more realistic choice might be between MHRV and inadequate ventilation.

    Ed
    •  
      CommentAuthorfostertom
    • CommentTimeNov 15th 2014
     
    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.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 15th 2014
     
    Tom
    Let's not derail this thread about something I mentioned, and modelled years ago (internal RH following external RH).
    The 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.
    This nonsense about 'breathing' comes from a time when houses where poorly built, poorly heated, poorly ventilated and no real understanding of the dynamics.
    If 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.
    Much easier to control the internal environment with some MVHR (or mechanical ventilation) than relying on a wall to absorb and release condensation at just the right temperature, in the right amounts, regardless of temperature differences.

    By the way I have RH and Temp sensors in every room, 2 in the loft, a couple of calibration sensors, plus a weather station and access to MET office data to triple check my data, and guess what, my condensation risk analysis I did on my roof 3 or 4 years ago seems to be still holding true. All you need it the temperature distribution along with the likelihood of hitting the dew point at those temperatures. Really easy to do, though data heavy.:wink:
  1.  
    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.
  2.  
    Has it been lived in recently?
    •  
      CommentAuthorfostertom
    • CommentTimeNov 16th 2014 edited
     
    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.
    • CommentAuthorEd Davies
    • CommentTimeNov 16th 2014
     
    Don't know but I'd guess that the hard part about using WUFI or the like on a project like this is being sure of the vapour properties of the existing wall - not knowing exactly what stone and mortar has been used and how the middle is filled and so on.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 16th 2014
     
    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.
    • CommentAuthorWoo
    • CommentTimeNov 16th 2014
     
    OK, have read through the comments about four times and can safely say that I think I need to improve my knowledge about insulation :bigsmile: And MVHR - though I confess to being a big fan of opening windows. Including in the winter.

    The place has been lived in, on and off, for the past three years. The previous owners were the ones who put in some of the IWI and got the roof more or less repointed. In terms of damp in the existing building, there is no sign of any if you don't count a patch on one ceiling below where we know the roof needs some more work. The last time I was there it had been raining solidly for three days just before, and the un-insulated walls were dry - cool to the touch but not damp or cold. I don't think there are any problems with liquid water coming through from the outside. Heating is currently provided by three open fires - hence all the chimneys, but this will change. Willie, the plan is to insulate the hell out of all the chimneys that will stay, and close up the ones that won't.

    One of the reasons we were thinking about UFH is because it could provide a half-solution for the problems of insulation v. breathability : there are plenty of places up in Orkney which were redone in the seventies and eighties and had appalling problems afterwards with condensation and mould due to vapour-impermeable systems. We'd like to avoid that, obviously, and certainly there're much better products available now than then : if we could insulate as much as possible without creating problems, install a heating system which ensures a minimum ambient temperature which in turn assures a certain level of drying-out is going on all the time, make sure low-tech measures such as draught-excluders and insulated shutters are in place, then I reckon we're away...

    It seems as though the rest of the floors might be concrete, according to our neighbour, which means putting in UFH might not be as onerous as if all of it was stone slab.

    Current plan is to move up there in a couple of weeks' time - nothing like settling in at the worst time of year - and start making actual plans for actual work...
    •  
      CommentAuthorfostertom
    • CommentTimeNov 16th 2014
     
    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.
  3.  
    If you are going to install wing insulation make sure you get the detailing right.

    Some friends have been trying to solve a dampness problem in their basement and it turns out that it is as a result of the botched installation of wing insulation some years ago.

    It seems that the ground had been dug out around the house and wasn't properly compacted before installing the insulation.

    Then as the ground settled over time there was a fall in the insulation towards the house which was then directing moisture on the membrane above the insulation in towards the house rather than away from it.

    Once you are aware of the potential problem it is very easy to ensure that it won't occur.
    • CommentAuthorTriassic
    • CommentTimeNov 16th 2014 edited
     
    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/
    • CommentAuthormike7
    • CommentTimeNov 17th 2014
     
    Posted By: fostertomHow 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?
    ............
    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.


    I think any simulation would show that on a building this narrow there is no possibility of interseasonal storage/year on year build up of temperature. Might be interesting nevertheless to see what could be achieved over much shorter time periods - I guess even in Orkney the wind drops sometimes.
    • CommentAuthorGarethC
    • CommentTimeNov 17th 2014
     
    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?
    •  
      CommentAuthorfostertom
    • CommentTimeNov 17th 2014 edited
     
    Posted By: mike7on a building this narrow there is no possibility of interseasonal storage/year on year build up of temperature
    Deep enough downstand and/or wide enough wing insulation effectively broadens the building. Add 1.2m wide strip all around it and then reassess the 'narrowness' of that perimeter.

    I wouldn't say 'no possibility' - it def will have some effect, I'd say v significant.

    How would you go about simulating it mike?
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 17th 2014 edited
     
    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.
    • CommentAuthorringi
    • CommentTimeNov 17th 2014 edited
     
    I 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.
   
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