Hello fellow Scottish builders

[saveasteading]

Moving along with the subjects raised.....assuming you are interested......if not, please jump to question at the end.

Is PIR better, hence used in cold stores?

 

The steel buildings I worked with for 30 years were of superior quality with very low air leakage, even before it became a rule. Comparing to other buildings  I have been involved with the difference was very clear. Steel buildings built without proper spec, by various suppliers and poor understanding  or supervision , had thermal bridges, air leaks, squashed or missing insulation and more. Build quality and attention to detail  is vital.

It didn't especially matter what material was used as long as it was done well.  Hence composite metal/PIR/metal as roof or wall cladding is not better but it is more difficult to do badly.

 

Next matter: cold stores. They are insulated boxes within boxes. I have been on the ceilings (ie in the roof space, which can be spacious, and it can get quite hot up there. Also in the gap between cold-store walls and building walls: as this is a narrow space it can get unpleasantly hot. So the structure reflects a lot of the heat, and keeps the air and wind out, then the voids take a lot  of the heat that gets through. The cold-store itself then has an advantageous start with no direct light, and moderated air temperature.

The very big advantage of PIR for cold stores though is that it is used as a ready-made structure, with slabs standing full height from the floor, and then roof slabs sitting on the walls and also suspended from the structure. Any other insulating  material would require additional structure. The PIR box could not work outdoors as has to hang from the ceiling, could not stand wind or snow, and would not be weathertight.

 

Tinfoil on PIR or plasterboard. I have looked into this seriously, as it seemed too good to be true. It used to be said that the foil on plasterboard helped the insulation, but they don't  seem to say that now. 

On PIR cladding sheets, the metal is 0.8mm thick, but is a strength, weather and abrasion skin, not for thermal reasons. 

If I remember correctly, a tinfoil skin, even sitting in the dark, will theoretically catch some heat, but then simply transfers it to the material it is touching. If hanging, and subdividing a void it works to some extent, but by creating smaller pockets of air.

 

 

Now a question for you please.  Back to self-build domestic. I see it written (here and in sales literature) that there must be  a gap between the outer masonry skin and  PIR. However one of the advantage of cavity rock wool is that it is full-fill. I am wondering why does PIR need the gap but batts don't? And is it written in regs or just acknowledged practice?

 

 

[Adsibob]

On 24/04/2021 at 18:43, A_L said:

Spreadsheet decrement delay calculator - https://www.concretecentre.com/Publications-Software/Design-tools-and-software/Dynamic-Thermal-Properties-Calculator-(1).aspx

I find it 'buggy' but it might just be my ancient Excel,

Anybody aware of any other free decrement delay calculators?

[scottishjohn]

On 25/04/2021 at 19:07, saveasteading said:

Next matter: cold stores. They are insulated boxes within boxes. I have been on the ceilings (ie in the roof space, which can be spacious, and it can get quite hot up there. Also in the gap between cold-store walls and building walls: as this is a narrow space it can get unpleasantly hot. So the structure reflects a lot of the heat, and keeps the air and wind out, then the voids take a lot  of the heat that gets through. The cold-store itself then has an advantageous start with no direct light, and moderated air temperature.

The very big advantage of PIR for cold stores though is that it is used as a ready-made structure, with slabs standing full height from the floor, and then roof slabs sitting on the walls and also suspended from the structure. Any other insulating  material would require additional structure. The PIR box could not work outdoors as has to hang from the ceiling, could not stand wind or snow, and would not be weathertight.

the one built next to me is made purely from slot together sheets and is held upright by an exposed  exo skeleton steel frame work no side sheeting of any kind  with a tin roof on the top for snow loads  with about a 30cm gap from the pir roof panels  and bird guard mesh -so they no not get a nesting problem  up there 

you could break into it with an electric carving knife or chain saw  and steal  all the frozen seafood  etc 

 it is dark silver outside and white plastic interior skin 

 so it is not a box within a box -just pir foam 

 if other types of insulation were cheaper to do same job --then they could fill the slot together panels with  any material 

Edited July 6, 2021 by scottishjohn

[saveasteading]

13 hours ago, scottishjohn said:

it is dark silver outside and white plastic interior skin 

 Interesting.

I thought that the cold-store panels only came in white and with a food-friendly plastic coating that is not good in weather.

But you say there is a dark silver (anthracite?) outer sheet. Do you think this is integrated (ie a special) or a separate sheet outside. Presumably it is profiled for any chance of strength against the wind.

it would be feasible to fix the weather sheet to the insulated panels using stand-off brackets, combining strength, saving structure.

 

PIR is very much cheaper for these panels than mineral wool, and the differential increases with thickness.

 

If you notice any more quirks I'd be interested to hear.  The cold-store installers have never been interested in new ideas, hence always a box in a box and some structural redundancy. But perhaps here is a new idea...but is it a good one...?

 

The gap at eaves may work in uk summers, as the occasional build up of heat under the roof will be ventilated away. No birds, but  insects may be an issue, and the food retailers are rightly  paranoid about vermin. I have been there during inspections of my finished buildings, by Mars, Nestle, M and S, Waitrose. It was encouraging that they took it so seriously, and they checked all the 'right' areas where most buildings are vulnerable.

 

I wonder how the base is done. Traditionally there is a 300mm pit in the concrete slab, in which they fit polystyrene and then a steel floor. That needs to extend to, or beyond, the wall panels, which will be a special detail in 'your' case or it will clash with the 'skeleton'.

 

 

 

[Hastings]

@saveasteading

I am saving a Scottish stone farmhouse too. Deep retrofit rather than demolition, for sustainable reasons as well as heritage/feelgood reasons.

Hardly changing the original layout at all. Airtight, breathable, MVHR design.

 

Having added 100mm to the inside walls with the new internal timber frame I now have entirely got used to the reduced rooms size. To the extent that I am now adding an additional 50mm service void and insulation layer. In retrospect I wished the original TF design had been for even more insulation thickness.

 

The building has been derelict for more than 10 years so qualifies as a new build for VAT reclaim purposes. A mixed blessing because newbuild status brings almost full building regulations with it, regs which often clash badly with old parts of the structure. In this case the only remaining parts are the old stone walls (everything wooden - stud walls, lath&plaster, windows, roof, floors, lintels - was removed) and their openings but they almost entirely dictate the design layout. If the property HAD been lived in less than 10 years ago I would have had many more options and a much easier ride.

 

The main issues I wish I had known right at the outset:

1. Digging out the ground floor in order to provide foundation for internal timber frame plus damp-proofing plus insulation is compromised by disturbing original stone walls which have no footings under them. 'Solved' by raising ground and mid floor levels a little, rounding the new slab edges a little away from the old walls and limiting insulation on top of new slab to 100mm PIR. Because the existing window openings can't practically be raised this makes all the windows a bit lower than is natural. The effect is slightly worse upstairs because the new mid floor (posi-joists) is thicker than the old one. The professionals that provided my drawings and calculations for planning and building control approval did not seem to be aware of any of these issues. Through previous experience renovating an old house I anticipated the stone walls disturbance issue and had the confidence to completely veto the first design suggestion of building the entire new roof structure onto the new internal timber frame which would have increased the loadings a lot and needed even deeper excavations for stronger footings alongside the old walls.
2. The trouble with a mixed newbuild/renovation is you never quite know what regs you need to adhere and what will be relaxed. Not everything was resolved before work began so things that changed as the work proceeded meant asking the authorities for a clear in-writing answer and they have often taken weeks or months to respond.
3. Building control insist that if an element like a mid floor is replaced in entirety then that new floor has to adhere to full regs. So that meant I couldn't re-use the existing really nice staircase (750mm clear width does not meet current regs) and the additional combined width of new stairs and wider upstair landing and corridor has added to the reduction in size of all the rooms (already reduced from the original sizes by wall insulation). The wider landings, wider door openings, extra landing space needed for future chair lift parking has made the new stairs steeper and right at the extreme limit of what is permitted and so a lot less comfortable to use.
4. As there was no functioning sanitary equipment present in the derelict building the rebuilt shower and WC room in the main entrance lean-to extension had to fully conform to regs, basically had to be bigger, making the remaining space within the lean-to extension, the house entrance hall, already pretty minimal, smaller.
5. Building warrant required putting 25mm diameter vents in the old stone walls every 1.5m. Achieved for all except the gable end walls (for which no drill long enough could be sourced) by purchasing 35x700 masonry drill, inserting 30mm (25mm internal) blue water pipe to line the holes. The drilling was difficult and potentially weakens the structure of the walls due to disturbing the loose stone fill which also falls in and jams the drill. The thicker gable end wall I put a single 4" drain pipe into located at the back of the fireplace where the wall is much thinner. This will also provide an air duct direct to the living room wood stove.
6. PIR: As a test, I kept in my garage a leftover piece (made by one of the main manufacturers) from a loft conversion we did to our first house 26 years ago. 4 years later it had bowed noticeably and the edges had become crumbly. I vowed never to use the stuff again. When the builders were fitting it I queried the gaps I saw between the roof rafters and the cut edges saying I thought they should be filled with flexible sealant but was persuaded by them that it was not needed and when the Building Inspector agreed that plenty of ventilation was important I gave in. Nowadays it seems that people tape over the joins to prevent thermal bypass and in the hope it will keep it in place if it shrinks. Gapotape looks like a better solution. Whatever you do it may look great when it's fitted but particularly when directly under a roof that harsh heating and cooling cycle is bound to affect the foam on one side differently to the other side. And then there's the waste issue - it can't be recycled after end of life and there are quite a lot of off cuts to dispose of. With woodfibre and the like you can quickly and easily use a lot of your off-cuts because there's no precise cutting to deal with.

4 years on and some way away yet from finishing, in retrospect I would have left the original building as is, keeping it as a garage/store/workshop and self-built anew alongsided. Similar approach to what people have done for 1000s of years, when I think about it!

 

 

[saveasteading]

Excellent information, thanks. I will read this another twice  at least, and save to file!

 

Immediate thoughts. PIR is horrible stuff. The manufacturers claim that they will have a way to recycle it fully, at some time in the future...if you get it to them.

I agree that it bends, but I have some in my current timber house walls (retrofit, using second hand panels, and they are staying in place nicely enough. the main issue is gaps, (which obviously are a heat loss issue) as you say, and that wasps  and mice excavate into it and live in it very cosily.

However, for avoidance of loss of headroom, I think 100mm of it is the efficient way.

Re the steading, various builders have said variously 1. the concrete floor obviously has to come out, 2. it is sensible to retain the concrete, 3. never break out the concrete floor.

you and I appear to agree with 2 and 3.

Vents in the stone, I have never heard of ad hope it isn't standard. I can't see the point. In full contrast to the theory of needing ventilation , I only yesterday read a blog where someone mentioned that they had cool spots in the house from old cross-walls, as there was so much air movement through the wall from outside.

Perhaps at the base where theoretical condensation might gather?

Perhaps more thoughts later.

Edited August 27, 2021 by saveasteading

[scottishjohn]

2 hours ago, Hastings said:

Building warrant required putting 25mm diameter vents in the old stone walls every 1.5m. Achieved for all except the gable end walls (for which no drill long enough could be sourced) by purchasing 35x700 masonry drill, inserting 30mm (25mm internal) blue water pipe to line the holes. The drilling was difficult and potentially weakens the structure of the walls due to disturbing the loose stone fill which also falls in and jams the drill. The thicker gable end wall I put a single 4" drain pipe into located at the back of the fireplace where the wall is much thinner. This will also provide an air duct direct to the living room wood stove.

and these holes in the outer wall --do they have go though total wall or just to the rubble fill in middle ?

surely air bricks at bottom into the cavity between walls and sealed TF kit would make more sense  and top of walls left open connected to  a cold roof space and vented through soffits or eves as it was when it had lathe and plaster

Edited August 27, 2021 by scottishjohn

[Hastings]

There's an official technical term for it I can't recall, so it must be true.   Something to do with build up of moisture in the space in summer.

 

@scottishjohn They have to go through total wall and the old walls are 600 thick so air bricks would be difficult except the odd place like under some of the windows which are like mini bays on the inside. The vents are only at the wall base, 300 off ground level. Building control insisted on it, it was not in the original submission. Yes, top of walls left open to  a cold roof space. There are no soffits. Roof is self-ventilated through the gaps in sarking boards, the roof membrane and gaps between slates.

Edited August 27, 2021 by Hastings

[Hastings]

4 hours ago, saveasteading said:

However, for avoidance of loss of headroom, I think 100mm of it is the efficient way.

Forgot to mention in earlier long post that in my case this still left not enough height left to include UFH.

[SteamyTea]

18 hours ago, Hastings said:

There's an official technical term for it I can't recall, so it must be true

Do you mean interstitial?

[Hastings]

20 hours ago, SteamyTea said:

Do you mean interstitial?

Thanks but no, I think that refers more specifically to moisture within the actual building materials.

This is a bit different.

[Highland build]

Hello Scottish builders,

 

I'm just starting a build in Sutherland, in March! 10 years of dreaming, 18 months in the planning, now with building warrant in hand mortgage application approve, site insurance and warranty in place, kitchen bought in Jan sales, sudddenly things are moving really fast!

I'm project managing, got a groundworker (who'll call in his contacts for the raft concrete pour), 2 joiners (one man bands, but they often work together), an electrician, plumber, a renewables company doing the ASHP UFH and MVHRS, a roofer. It's only a wee house, 149m2, 3 bed 2 bath, closed pannel timber frame (Ochil timber) on an isoquick insulated raft. Nordan windows, standing seam metal roof, Russwood cladding.

Its exciting but also petrifying the monies about to flow out of the bank account like water and into a muddy hole in the ground! What a journey its going to be.

Material costs through the roof, will easily cost the same as a house double the size 2 years ago ? but the show must go on! just have to roll with the punches and get over the fact that this is probably the most expensive time to build. Have luckily managed to get all the trades I wanted to onboard so were all ready to rock and roll. Groundworks March, Kit Joiners May roofer June ???

I mean what could go wrong ha ha? 

Has anybody noticed how unseasonably mild and dry January has been up North..... Just waiting for that March April snow flurry ha ha. 

 

I'm sure I'm going to be on here alot asking for advice but thought it was time to stop lurking and introduce myself ha ha.

 

 

 

 

[ProDave]

Hi and welcome.  I wonder where abouts you are, might not be all that far from me.

 

Yes I have been enjoying the mild January and the lower than normal heating requirements.  A bit blowy and miserable today and tomorrow though.

[markharro]

Hi we are in Edinburgh and after a 2.5 yr battle finally got planning last month to demolish our existing house and build a new passive house. Now its a frantic rush to get a BW and sort out all the other 101 things to allow us to get the slab down before the Autumn frosts.

A number of factors have conspired to persuade me that I will project manage and dispense with a main contractor. I think I'd read somewhere that it was a good idea to incorporate a company if doing this and wondered if anyone could comment on this? Presumably to protect in case of a contractual fall-out with a contractor but any other reason for this? eg VAT reclaim?

 

thanks

[Kelvin]

On 01/04/2022 at 20:49, markharro said:

Hi we are in Edinburgh and after a 2.5 yr battle finally got planning last month to demolish our existing house and build a new passive house. Now its a frantic rush to get a BW and sort out all the other 101 things to allow us to get the slab down before the Autumn frosts.

A number of factors have conspired to persuade me that I will project manage and dispense with a main contractor. I think I'd read somewhere that it was a good idea to incorporate a company if doing this and wondered if anyone could comment on this? Presumably to protect in case of a contractual fall-out with a contractor but any other reason for this? eg VAT reclaim?

 

thanks

 

You don't need to incorporate a company to complete the VAT reclaim. I'm in the same situation as you and haven't read needing to incorporate a company to self-build and not planning to.