saveasteading

If it doesn't show any signs of decay then all is well....for the moment. Better left out in the air so it can dry intermittently than encased in any screen, so the best thing you can do is progress.

No. the concentrated load needs to be spread efficiently. An ordinary block is likely to crack and then concentrate the load directly below. Why would you want to not have a padstone? Tell us please. If the geometry has gone wrong then you can make it on site perfectly well, but ask the Engineer to give you new dimensions. needs high quality concrete, I would put some reinforcement in it because, why not? You can also buy all sizes of padstone bricks and blocks, and build to suit. Basically it is made from structural concrete without the usual fillers that keep costs down. Assuming someone has designed this for you, ask them for a revised detail if you have to.

Today I will mostly be doing the same again, trying frametherm in the U value calcs, adding in the effect of heat loss through the rafters and studs, and finding a way to get better numbers. 1. pass all the tests to prove it to the BCO 2. actually get what is best for the building and bills in the long term. Perhaps these are in reverse order. Question. Please excuse the avoidance of jargon and scientific precision, and I am thinking here only of keeping heat inside. We 'know' that a shiny layer helps insulation, by reflecting the radiation, but only when it faces an air gap. Theoretical U value for the gap jumps from .18 to .44 if I remember correctly. BUT does that not depend on the aspect? Heat (radiation) from inside travels through plasterboard, hits metallic layer on inside face and it is reabsorbed back into the plasterboard and the membrane itself No help and no hindrance OR hits the shiny stuff on the other side of the gap and bounces back into the gap. Warms the air and helps the insulation level. Then the reverse occurs at the outside...let's say PIR is left 50 short of the sarking. to provide a ventilated space. Then the reflection is again inwards, to no advantage. and anyway the air gap is ventilated so the effect of the gap is low or nil.. Which could bring us onto multifoil, which is not in our recipe, so I won't go there. Red pens out as necessary.

Yes primitive isn't it? Sarking is standard in Scotland. 150 or 225mm boards still available in quantity at merchants, £20/m2, pressure treated.. But mostly used for maintenance. Osb is normally cheaper, and is certainly quicker. Contrary to the understanding of some, not all Scotland has any more severe weather than the rest of the UK, but it is simply a sensible thing to do for UK weather generally. I don't think our steading would still be standing after 120 years if it didn't have it. Did the people who wrote the BS consider the differences? Nuff said. The slates are impermeable until they break, but at least have double cover unlike modern tiles. The gaps are very permeable.

Do you have a dpm under the concrete? If so the PIR boards will trap the water in the concrete for ever. That would be a bad thing. I will have to think why, but it just is.

2 layers of metal cladding. firstly lay metal cladding as if it was the weather layer, supported on rails. Then there is a steel spacer system to provide a raised support. lay fibreglass to completely fill the space another layer of steel cladding, screwd through a thermal break layer. all ends must be completely closed off to keep birds etc out. the height of the spacer system dictates the amount of insulation you put in. anywhere between 100mm and 400( if you are in Iceland.) The advantage is the low bulk for delivery, and steel/insulation direct from specialists. Also it is all manageable by hand whereas composite panels are very heavy. This works but whether I advise you to try or not depends on your ambition and skill-set.

Yes that is correct. The wind whips through the slate to the sarking. Currently it then whips through the 2mm gaps and the whole building, and that is where the detailing comes in. We are now proposing a partial rebuild of about 20% and will use metal to differentiate old and new, but to the same geometry. Metal cladding I know nearly all about. Would normally seal every single joint of panels and flashings with very special mastic tape and fillers, but the whole industry doesn't necessarily do the same. For the steading we will do what others do, and set it on double battens with the air through it and any dribbles running down and away. NOT secret fix but screws proudly on show. Metal cladding that is permanently wet will rot in a short time, regardless of coating and galvanising, unless it is utterly undamaged, cut properly and has hole-sealing screws. The next worst thing is bird mess, just as it is for cars. Hence double thickness plastisol if near the coast..

For something that will work better and satisfy the rules Civil Engineer. For an attractive approach to the house: Architect. All with capitals.

Short answer. Could look good, certainly characterful, but will be a very cold surface.

ProDave, I came across this about an energy survey. which is perhaps relevant to your annoyance at your energy rating The SBEM prediction for post-improvement emissions (8,135 kgCO2) is extremely high in comparison with all other modelling programmes. The reason for this is almost certainly that SBEM assumes a greater use of electricity (mainly for the proposed heat recovery ventilation system) than the other programmes. This is covered in more detail in section 7.4, but the result is that it skews the post-improvement average (an 88% improvement at 2,589 kgCO2); removing SBEM from the equation would change this substantially, giving a 93% improvement to 1,480 kgCO2 and more on p23 here if still annoyed and interested https://www.changeworks.org.uk/sites/default/files/Historic_Scotland_Technical_Paper_8.pdf

yes but. There is quite a variation on it so a 25mm gap is handy for lots of reasons. Also some areas of loose render that will have to come off. Lime plaster....never again, having been ripped off once. I have been looking at fibre board today...maybe on some of the roof, although the eaves have zero over-sail so is a tricky detail. Is it an alternative to plasterboard on the ceiling? The 600 granite walls will have a U value of 1.8 according to the documentation IF dry and IF not severely ventilated. But the good news is that the ground is superbly free draining so rising damp should not be a problem, and I am proposing to close the voids off to allow local ventilation but no draughts. More curveballs please. The analogy fails though if I say I may come back to that one.

Correct and won't be doing that. Metal cladding will be ventilated . Also would not happen if every joint was sealed but that is usually not done in domestic. If presented as a holistic design then yes , or I should hope so, as the traditional sarking is 200 wide then 2mm gap, so lots of ventilation. Under osb with 2mm gap per 1200 then no, and that is what the 50 gap is for. But my question is about the logic of zero gap when the material is full-fill cavity batt. BCO's like proven details, fair enough, but things only change when questioned. There is a view on this forum that the gap is only there over PIR to boost the U value with a shiny face onto an air gap. As if they would do that to us. Also, sarking has always (?) been standard in Scotland and so there are far fewer accidental leaks. I couldn't believe that in a modern English house there was just the felt, and in an older one there were only tiles, and the snow could blow in. On our project the sarking is about 50 years old we think. It is rotten only where water pours in due to a complete hole in the roof. Where there are tiles they are sound, (and they were not treated)

Which I do appreciate will be good in the traditional hot week in August, especially where we plan to have metal cladding instead of slates. If I was to mention decrement do you think the BCO will understand? We have bought samples of PIR and Knauf batt and tried them for practicality. both ok, and will maybe get a bit of Frametherm to try too. I'm a bit confused as I think I have seen some of your photos showing PIR. What is the construction here? frametherm tight up to osb? You will have a VB above the osb, which we won't., as the rafters, sarking and slates are already there.

Ok, so it didn't take much persuasion to get me to reconsider mineral wool instead of PIR. My original plan was to use cavity wall batts, especially as they are waterproof, would completely fill the gaps between rafters and would be easy to cut and fit. Against it? not such a good U value, although it doesn't shrink. wastage will be bad with cutting to fit 390-410mm gaps. Also a lot of batts have developed form dense to rather loose, and almost like loft insulation, and I somewhat doubt the performance. (No names but I have found that the cheapest fibreglass needs a lot of puffing to get to theoretical thickness, and just doesn't look 'right'. Considering filling between rafters in the existing roof, with sarking boards 200 wide and penny gaps, slates above but no vapour barrier.........does this really need an air gap? My logic is that any drips getting in the gap will as easily evaporate again, whether running down a 25mm space or sitting on the tightly placed surface.

Good point. No they will have to stay politely outside, which is selfish I know. but we can put boxes up either on walls or on trees. Bat nests are just made of ends of scaffold plank and some batten. Cost nil if from offcuts, and half an hour to make?

I'm good on rodents! Had buildings approved 'as built' by Mars , M and S, Waitrose among others. It was interesting observing their inspections as they headed straight for where they expected to find gaps....and were surprised to find it was dealt with. 6mm for a mouse I think, but insects can be much smaller of course. Once in mice, rats and wasps will chew away PIR if necessary to make a nest. On site so far we have also seen a slow worm, so we will create piles of recovered stones and timber for refuges. There is already a midge dormitory, so we need to encourage swallows and bats, and will.

ouch. can we even fit it without 1mm gaps?

Dry is good. I have a philosophy that nobody wants a building: they just want to keep the weather out. That doesn't apply to bankers, dictators and trillionaires who want us to notice their building, using OPM. If I was you I would be showing off your project at any opportunity. Beautiful re the ventilation. Some people say that the walls are porous and no further ventilation is necessary or desirable. Yet it seems that BCO's ask for vents at 1m cc near the base. I don't think we have a issue as there will be no rising damp and the wall is either porous (both ways) or not. I see a strategy statement coming on. Cpd, did you apply an impervious membrane to the inside, bottom of the walls? I think this is sensible but it does not seem to be standard.

A couple of probing questions if you don't mind. I relish the challenge. 1. How do you plan to install the breather membrane while maintaining the ventilation cavity? Yes, I fell asleep thinking of a solution to this one. Easy to draw. Has to be done so there will be a solution.. Either: wrap the membrane round the back of a set of a few studs and staple on. then staple on the face of the last and continue. Theoretically a gap where the 2 faces touch, but de minimus. OR after that, warap another piece round the stud to lap both; OR , build as a cassette on the ground and do the same OR some better idea, that some genius is about to come up with. 2. How do you maintain that PIR is twice as good as mineral wool? I get a U value of 0.304 for PIR and 0.398 for full fill rockwool (lambda = 0.035w/mk) with 100x45 studs @400cc. PIR 0.022 or thereabouts , Mineral batts 0.34 or thereabouts (have not checked). OK then not twice and you are starting to sway me. 3. How do you plan to deal with the shrinkage and expansion of the studs with varying humidity and temperature? Won't the boards loosen and you'll get thermal looping? All buildings move. The studs will prob move less than the rest of the building. Character anyway. They are wrapped in membrane. My understanding of thermal looping is that it needs a route, and a sizeable gap. for example, double glazing has a small gap and it isn't an issue, but secondary glazing has a big gap and there is circulation. Legend has it that PIR off gasses and degrades in R value over time as well as shrinking like most other foams. I've been searching for over an hour to find a non biased long term study on this but can't. The below is a screen shot of one manufacturers declaration of dimensional stability. 4. Maybe someone more qualified can explain what this means. There is some anecdotal whisperings of this. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490 I have not heard of this before, and would have expected to. However I have an instinctive trust of mineral wool....unless it gets wet. I suspect any such issue will be related to atmospheric change (esp heat) . This will be in the dark behind a very thick wall. I don't trust PIR, never did even before recent disasters. Several years ago I tried some in a brazier to see what happens.....burns, but needs a lot of heat to start it. When grenfell was first on tele i said to my wife I could see what the problem was, and was correct. Also , years a ago, spoke to fire fighters and fire engineers......they said they don't like to be near to PIR filled composite, but can't say that publicly. So show me some better figures for mineral wool please.....it was always my wish but it needs too much thickness. Thankyou for the opportunity. any more questions please? By creating a clear ventilated cavity you'll completely negate any insulative benefits of the current stone+ rubble wall.

There are 3 layers. Outside is solid stone, mostly granite. ashlar at features and roughly flattened faces elsewhere. At openings it is ashlar to all faces, and usually sandstone. Inner is granite , smaller stones but still about 300 x 300 In the middle is rubble, and by all accounts it is normally 40% mortar. From what I have been pointed to and read, the mortar being in the middle contributes to the decent U values, and the outer stone keeps the wall pretty dry. this photo is not it, but was in someone's website and is a decent example and a literal cross-section. .

tis. them twice better dan mineral wool. Twice the price too and not nice to work with but we only have 4.5m between the walls, so don't want to lose another 200mm. Vapour and moisture layers encapsulating it within timber studs, effectively a cassette, so we don't expect any issues apart from, grumpy installers.

This will take some time to digest. Worthy of note everyone interested in big buildings (over about 13m width) is page 35....the insulation suppliers used to publish this but now don't....hence insulation is often over-specified. This is for any ground, so will be better on dry granular.

Hearts and trophies to be distributed later this evening. Good work so far team. This is the draft drawing, some changes to make, eg increase service void to 50mm. As a solution to ProDave point above, I think we add the closer filler at the top of each wall, and also vertical the same at about 8m cc. This can be a strip of rockwool bat compressed in the 25mm gap. Then the wall can breathe but not create a flow as such.

Traditionally these walls were rendered so that the rain ran off. Without the render they look very pretty.......of course we are going for pretty. But with good new pointing most of the rain will run away. I am not trying to fiddle any numbers, but am hoping for a bit more certainty in the future performance, tweaking of any details to improve the performance, and to submit a proposal that BCO will accept without any further justification.

file:///C:/Users/Jenny/Desktop/Lower%20Remore/hstp102011-u-values-and-traditional-buildings.pdf 2.4 W/m2 K for 70% stone / 30% mortar compared to 1.5 W/m2 K for a dry wall. sandstones: the average values are 1.9 W/mK for dry material and 3.0 W/mK for wet sandstone.