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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthoradam_w
    • CommentTimeJan 29th 2018
     
    Morning all!

    I met with Building Control Friday for some pre-application advice (that word advice should really be used very loosely) where I proposed my following build up;

    Cladding,
    Batten 38mm,
    PIR Board 60mm,
    Breather Membrane,
    Stud 70mm,
    Interstud PIR Board 60mm
    Racking Board 11mm
    Plaster Board 12.5mm

    Cumulative U Value - 0.20W/m.K

    To which he suggested that, that's not the traditional way of doing things, most use the following build up;

    Cladding,
    Batten 38mm,
    Breather Membrane,
    Racking Board 11mm,
    Stud 89mm,
    Interstud PIR Board 70mm,
    Plaster Board 12.5mm

    Cumulative U Value - 0.28W/m.K

    His justification for this was that the remaining and also majority of the house is brick and block with an estimated U value of 1.1-1.2W/m.K so would the extra expense and complications of my suggested build-up be worth the hassle and expense.

    As part of my extension I do plan to add 100mm of external wall insulation to the existing house to bring the U value down to a much more acceptable 0.26W/m.K but I guess the argument still stands, it is worth having continuous external wall insulation on a timber frame or should I just thicken the frame and do it all inter-stud?

    As always, your opinions and experiences would be greatly appreciated!

    Many thanks,

    Adam
    •  
      CommentAuthorfostertom
    • CommentTimeJan 29th 2018 edited
     
    Without question I'd do:

    Cladding
    Batten 38mm (why so fat?)
    Cheaper sidewall-type breather membrane
    EPS board (breathable, unlike PIR)
    Racking Board 9 or 11mm OSB3 glued and screwed, nogged all joints
    Stud 70mm (flimsy), pref 89mm
    Interstud blown-in cellulose, or something else that's breatheable
    Plaster Board 12.5mm

    Advantages:

    Breathable right through
    Much more reliable insulation value in use (fulfilling full theoretical performance) from:
    ....continuous outer insulation layer killing thermal bridging, and
    ....complete full-fill without convection paths by using blown-in cellulose
    Continuous outer insulation keeps all structure free of even transitory condensation
    Super-easy robust airtightness by putting the OSB external to studwork and the blown-in cellulose also contributes
    Humidity buffering by the organic-source cellulose
    Electrician free to puncture the plasterboard, run cables behind (subj to cable rating)
    EPS and cellulose much more eco-virtuous than PIR
    Note - see video (I can dig it out) on the importance of installing cellulose behind 'scrim' (like on the underneasth of your sofa) before fitting plasterboard
    • CommentAuthorTimSmall
    • CommentTimeJan 29th 2018
     
    I'd go for insulation over stud. I used non-foil PIR (because I had a load cheap), but I'd consider foil PIR OK too. I used 45 x 95 mm stud at 600 centres. Particularly if you are going to go with rigid insulation between the studs, then 600 centres will cut down on work and thermal bridging vs. 400s.

    I used 18mm T+G (glued) OSB3 racking board as the air tightness layer. The T+G OSB is quite a bit more pricey, but saves a lot of labour on separate airtightness detailing work.

    I like blown/sprayed cellulose but getting it at decent cost is often tricky sadly. Make sure it's well packed in studwork, or you'll end up with voids at the top of the stud bays a year later...
    • CommentAuthorTimSmall
    • CommentTimeJan 29th 2018
     
    "EPS and cellulose much more eco-virtuous than PIR"

    Hmm. Embodied energy per unit insulation is similar I think?

    Non-foil-faced PIR has similar vapour openness to EPS.

    EPS performs worse in fires (despite typically including a fire retardant). The fire retardant historically used in EPS isn't particularly nice (HBCD?), but not sure if it's been banned yet, but if I remember correctly, most of the proposed alternatives aren't that nice either.

    EPS does better in wet conditions (and is cheaper for the same insulation value).
  1.  
    I think FosterTom is probably referring to the blowing agents used which, traditionally at least, have always been more harmful in terms of global warming potential and ozone depletion for PIR.

    Carbon/EE is only part of the picture.
    • CommentAuthorTimSmall
    • CommentTimeJan 29th 2018
     
    As far as I know, pentane is used as a blowing agent for nearly all EPS and PIR.

    Pentane has an ODP of zero, and a GWP circa 5 (some sources 1, some say 11).

    It's possible that some of the pentane is scrubbed and/or recycled during EPS manufacture, but I'm not sure. I didn't think the pentane made much of difference to the life-cycle emissions for either EPS or PIR, BICBW.
    • CommentAuthordelprado
    • CommentTimeJan 29th 2018
     
    isnt the real problem with PIR and PUR is that it degrades over time?
    • CommentAuthortony
    • CommentTimeJan 29th 2018
     
    I would go for even better U-value :bigsmile:
    • CommentAuthorTimSmall
    • CommentTimeJan 29th 2018
     
    Posted By: delpradoisnt the real problem with PIR and PUR is that it degrades over time?


    Both EPS and PIR degrade under UV light (EPS more-so).

    The K value of PIR drops as the pentane diffuses out - it starts at a λ of about 0.019 W/m·K, and reaches a steady state of about 0.026 W/m·K for commonly used insulation densities.

    The values quoted by the manufacturers are the 30 year average for a full uncut 2.4 m x 1.2 m sheet with the foil intact.

    With EPS the pentane diffuses out much quicker (within a week of manufacture?), so you get a quoted the a straight λ of 0.038 W/m·K (white) or 0.031 (grey / graphite enhanced).

    Both have their limitations, but I don't think I'd say that EPS is "much more eco-virtuous" than PIR. Particularly if the EPS has fire retardants added ("FRA" EPS).

    I believe there is an effect where the pentane in PIR insulation cells condenses and starts to transport heat across the cells at low temperatures, but this effect disappears once the pentane has diffused out (nearly all of the PIR I used in my project is non-foil faced, so it shouldn't suffer from this effect, or at least not for long).

    Under very wet conditions with really hostile vapour drives, both can moisture saturate under very unfavourable conditions.

    Apart from that I'm not aware of any degradation for either?


    I think you can say that cellulose is "more eco-virtuous" than both...
    •  
      CommentAuthorfostertom
    • CommentTimeJan 29th 2018 edited
     
    Tim, looks like I need to re-research, before next specifying time, but I reserve my position!

    Posted By: TimSmallI used 45 x 95 mm stud at 600 centres. Particularly if you are going to go with rigid insulation between the studs, then 600 centres will cut down on work and thermal bridging vs. 400s.
    Totally agree - get organised, order sawn regularised in more generous section at wider spacing, not that abominable CLS where half the timber's been planed away.

    Posted By: TimSmallT+G OSB is quite a bit more pricey, but saves a lot of labour on separate airtightness detailing work
    T&G only helps in the middle of an area of boarding but you still have the edges and angles to deal with and usually lots of need for odd butt joints. As you say, 9 or 11 square edged is way cheaper as well as dead easy to handle, cut and fit.

    Instead of timber noggings to back every joint, get organised with 0.7mm dryliner's galv flatstrap and angle simply tacked across the studs/rafters. Can be hard to source, so make up a cutting list and order what you need (incl bending to exact angles) cut from galv sheet by local sheet metal co e.g. cladding supplier like Cladco here in the SW.
      2011-07-26 040reduced.jpg
    • CommentAuthorTimSmall
    • CommentTimeJan 29th 2018 edited
     
    Ref PIR performance loss at low temperature (for new / pentane-rich PIR).

    Figure 8 - https://www.researchgate.net/profile/John_Straube/publication/312054592_THE_EFFECT_OF_TEMPERATURE_ON_INSULATION_PERFORMANCE_CONSIDERATIONS_FOR_OPTIMIZING_WALL_AND_ROOF_DESIGNS/links/586d125208aebf17d3a70a37/THE-EFFECT-OF-TEMPERATURE-ON-INSULATION-PERFORMANCE-CONSIDERATIONS-FOR-OPTIMIZING-WALL-AND-ROOF-DESIGNS.pdf

    Also a number of samples (not sure of age):

    http://www.greenbuildingadvisor.com/sites/default/files/Schumacher%20-%20Graph%201%20copy.jpg

    This only effects the portion of the insulation at that temperature tho', and the effect disappears once the pentane has diffused out I believe.
    •  
      CommentAuthordjh
    • CommentTimeJan 29th 2018
     
    Posted By: TimSmallRef PIR performance loss at low temperature (for new / pentane-rich PIR).

    Interesting. PIR/PIC has a crazy temperature dependence! The numbers shown in fig 8 don't match my remembrance of PIR conductivities I've seen in the past though. I don't know the difference between the US and EU standards for determining k though. But those curves are quite worrying for PIR/PIC in particular at typical UK temperatures.

    I'm no expert on PIR. I decided early on by looking at their fire combustion products that I could live with EPS or phenolic in my house but not PIR/PUR. In the event I didn't use any phenolic either; just EPS in the foundations.

    John Straube is one of my heroes - he's done a lot of excellent work (especially on straw :bigsmile: )
    • CommentAuthorRick_M
    • CommentTimeJan 29th 2018
     
    Posted By: TimSmallNon-foil-faced PIR has similar vapour openness to EPS.


    Is EPS sheet insulation sold in different grades? When I tested one type it allowed air to pass through easily (so it must be vapour open).
    •  
      CommentAuthordjh
    • CommentTimeJan 30th 2018
     
    Posted By: Rick_MIs EPS sheet insulation sold in different grades?

    Very much so - EPS70, EPS100, EPS250 even EPS 500 I think. The numbers refer to the compressive strength (in kPa) and are accompanied by an increasing density. Thermal conductivity also varies somewhat with the density.
    • CommentAuthoradam_w
    • CommentTimeJan 30th 2018
     
    Good morning all!

    Wow that is a lot of information to wake up to, I've tried to digest as much as possible, its great to have so much input!

    Starting with FosterTom's points, I concede that 89mm will be better for my framing and I tend to agree that the 9 or 11mm OSB3 square edge would be fine for the racking and air tightness providing I seal all joints and faces. Would regular silicone be suitable for this application?

    Also Tom, is that dryliners strap, purely for air tightness where the boards meet? Looks like a good idea!

    I think I'm tending towards the EPS as far as the external wall insulation goes, it seems affordable, efficient, easy to work with, breathable but also availability over the non-foil back PIR, am I missing something as I cant see it anywhere?

    I think I'd feel more comfortable using an external wall insulation system over the BC minimum recommended technique but how much is enough? 50,60,80,100mm?

    As i'll be cladding over the EPS with the 38x50 battens, (30mm being the minimum manufacturers requirements and 38mm be the nearest timber size as far as I'm aware?) what would you all recommend for the density variant? Having never dealt with EPS before, Its hard to gauge so your experiences would be appreciated!

    With regards to the inter-stud insulation, I did receive a price for icynene spray insulation at £18/m2 @90mm, this works out over twice the price when compared to EPS. Would it be almost as effective to fit the EPS to the best of my abilities and then use a low-expansion foam around any cavities or complicated areas?

    Again, I'd like to thank you all for your input, its greatly appreciated and all contributing towards what I hope will be a very special family home!

    Adam
    • CommentAuthorTimSmall
    • CommentTimeJan 30th 2018
     
    I think 9 or 11 mm OSB can have poorer airtightness, so 18mm might still be better? You can also get coated 12mm OSB (Smartply Propassiv), but 18mm looked like a better deal last time I priced up.

    For sealing edges, I used polyurethane wood glue all round, with backing where necessary (mainly sheet material offcuts) because it expands to fill any voids. You can often pick up boxes of 12 bottles on eBay which are remnants from large T+G flooring jobs. Good search terms are:

    caberfix D4 12
    egger d4

    I used small offcuts of metal stud sheet steel (Gypframe etc.) where plasterboard sheets were butt-jointed (on joins at right-angles with the studs, i.e. no extra noggins).

    The "Smartply" brand OSBs are formaldehyde free, but often a little more expensive. Airtightness is good (at least for 18mm) tho, so might be worth seeking out.
    • CommentAuthorTimSmall
    • CommentTimeJan 30th 2018
     
    Not sure what the state of play is with fire retardants in EPS, looks like it must be labelled now, so might be worth checking?

    https://www.gov.uk/guidance/using-persistent-organic-pollutants-pops#hbcd-additional-exceptions-to-the-ban
    • CommentAuthorTimSmall
    • CommentTimeJan 30th 2018
     
    Seconds and Co often have cheap non-foil PIR (and non-foil phenolic), but PIR/Phenolic prices seem to have remained quite high since the BASF factory fire about a year ago, so this also favours EPS at the moment.

    I bought my non-foil PIR direct from a SIPs panel manufacturer as factory waste, and a few bits from Seconds and Co.
    • CommentAuthorTimSmall
    • CommentTimeJan 30th 2018 edited
     
    Posted By: djh
    John Straube is one of my heroes - he's done a lot of excellent work (especially on straw :bigsmile:)


    In http://www.greenbuildingadvisor.com/articles/dept/musings/cold-weather-performance-polyisocyanurate - when asked whether builders should switch to EPS, or and EPS/PIR sandwich Straub is quoted as saying:


    "... it’s very painful to try to install a torch-down roofing membrane over EPS, because the EPS melts. Solvents can also melt EPS. Asphalt can melt EPS.

    So normally, I would advise builders to just up the thickness of the polyiso."
    •  
      CommentAuthordjh
    • CommentTimeJan 30th 2018
     
    Posted By: adam_wI tend to agree that the 9 or 11mm OSB3 square edge would be fine for the racking and air tightness providing I seal all joints and faces. Would regular silicone be suitable for this application?

    Silicone is not good when used as a sealant as it tends to pull away after a short time. It is OK when applied to one side of a joint and allowed to harden and then used as a compression gasket when the other side of the joint is pressed into place afterwards. For filling gaps with adhesive/sealant it's better to use a gap-filling adhesive such as the D4 glues or some MS adhesives.

    As i'll be cladding over the EPS with the 38x50 battens, (30mm being the minimum manufacturers requirements and 38mm be the nearest timber size as far as I'm aware?) what would you all recommend for the density variant?

    The question of the gap is interesting. Which manufacturer suggests 30 mm? I found this page - https://www.thenbs.com/BuildingRegs/NBSShortcuts/ShowContents.aspx?section=026&topic=b_01_FSHCT_BR_02601&tl=no - which suggests even larger gaps.

    As regards the EPS density, you aren't really concerned about the compressive strength of wall insulation so EPS 70 or anything else will be fine. You're interested in thermal performance and have limited thickness, so graphite EPS is probably worth paying for.

    It might be worth getting a quote for cellulose as an alternative to Icynene. Blown/sprayed in products are less work than trying to fit rigid insulation between studs and then seal up, and the blown/sprayed products are likely to provide a more reliable result (assuming you avoid cowboys).
    • CommentAuthoradam_w
    • CommentTimeJan 30th 2018 edited
     
    Dave and Tim,

    Thank you both for your further details with regards to these matters, I think I'm nearly there now!

    I can see lots of positives of EPS and as far as I'm aware, no heat will be required to assemble my house, so I think that's the way I'll go, Graphite based of course Dave ;)

    Having said that, Dave, when you say that I'm not concerned with compressibility, would that still be the case for the roof as I'll have the weight of the tiles + potentially snow?

    I'll make sure to use the D4 glues where applicable, I'll try and find myself an online bargain, thank you for the tip Tim!

    Dave, I'm going with the Marley Cedral Weatherboard, their datasheet specs minimum 30mm clearance, so 38mm should be sufficient

    With regards to the use of steel sheet for joints, I have an alternative suggestion, I've just this weekend fitted a rubber roof to my newly built shed that when combined with the contact adhesive, stuck to the OSB board like the proverbial to a blanket! I've got quite a bit left over and I think this would be much more forgiving at the eves, what do you guys think?

    As for the internal insulation, is the Rockwool 'flexi' worth considering? I can't seem to find a cellulose installer down my way?

    Thanks again,

    Adam
      Cedral.jpg
    •  
      CommentAuthordjh
    • CommentTimeJan 30th 2018
     
    Posted By: adam_wHaving said that, Dave, when you say that I'm not concerned with compressibility, would that still be the case for the roof as I'll have the weight of the tiles + potentially snow?

    For a roof (or floor) you do care about compressibility so you'll need to work out the loadings to make sure you're OK. The main thing to avoid is point loads that can cause local compression and/or puncture damage. For my flat roof we laid 9 mm over the top of the EPS 70 before glueing an EPDM mebrane on top.

    FWIW, most of the EPS under my floor slab is EPS 70, with some EPS 100 for the heavily-loaded sections such as the ring beam under the external walls. So even EPS 70 is quite strong as long as the load is evenly distributed.

    With regards to the use of steel sheet for joints, I have an alternative suggestion, I've just this weekend fitted a rubber roof to my newly built shed that when combined with the contact adhesive, stuck to the OSB board like the proverbial to a blanket! I've got quite a bit left over and I think this would be much more forgiving at the eves, what do you guys think?

    Sounds like a reasonable idea to me, although I expect it will perish before steel rusts through.

    As for the internal insulation, is the Rockwool 'flexi' worth considering? I can't seem to find a cellulose installer down my way?

    Rockwool slabs are certainly a lot easier to install without gaps than rigid sheets. I think you can find cellulose installers via http://www.warmcel.co.uk/warmcel/installers/
    •  
      CommentAuthorfostertom
    • CommentTimeJan 30th 2018 edited
     
    Posted By: adam_wI concede that 89mm will be better for my framing and I tend to agree that the 9 or 11mm OSB3 square edge would be fine for the racking and air tightness providing I seal all joints and face
    The racking OSB, glued and screwed to monolithically cover the entire stud frame, makes it into an extremely strong monocoque, unlike conventional studwork and half hearted sheathing which can move around, work at the joints, as it ages. So the well restrained studwork can be cut to the minimum - see the photo above - eliminating as far as poss all the doubled-up members (unless demanded for point load etc) and noggings which are only there to make sheathing and plasterboarding easier but which as thermal bridges make a big hit on the overall insulation performance. 9 or 11 OSB is fine for this purpose, structurally, as long as seriously glued and screwed leaving no unrestrained (buckleable) edges. Check with your Structural Engineer if in doubt.

    Posted By: adam_wis that dryliners strap, purely for air tightness where the boards meet?
    Also for structural restraint of all edges, as above. You'll be using gapfilling polyurethane glue - see pic below of the outside - which seems to bond fine to the galv steel - has to clean of oil, grease, mud, dust, cement splashes etc of course. Sometimes (pic above) the galv stuff cockles and needs lots of screws locally to pull it flat enough for the glue joint - no prob with a power driver. Mind, you'll be on your own with this method - completely strange to the entire building industry and not really adopted even here on GBF - but it works v well. Note the steel, so tiny in the direction of heat flow, does nothing to degrade insulation, unlike timber noggings. Same can be used internally as well, to support plasterboard edges where necessary.

    Posted By: TimSmall9 or 11 mm OSB can have poorer airtightness, so 18mm might still be better?
    True - and considerably variable batch to batch. So team it up with blown-in cellulose or Icynene, which have significant airtightness of their own, unlike, unfortunately, EPS boards even if carefully fitted and foamed in. If not cellulose or Icynene (and discounting vapour-impermeable PIR, PUR, XPS etc) then 18 OSB prob safer - but figure in the considerable extra cost of buying (esp if T&G) and fitting same.

    Posted By: djhIt might be worth getting a quote for cellulose as an alternative to Icynene. Blown/sprayed in products are less work than trying to fit rigid insulation between studs and then seal up, and the blown/sprayed products are likely to provide a more reliable result (assuming you avoid cowboys).
    The last is key, and here's the video
    http://www.greenbuildingadvisor.com/green-basics/video-dense-packed-cellulose-1 .

    Posted By: TimSmallYou can also get coated 12mm OSB
    That's airtight but also vapour tight, which requires a completely different approach, if not going for breatheability.
    Posted By: TimSmallThe "Smartply" brand OSBs are formaldehyde free, but often a little more expensive. Airtightness is good (at least for 18mm) tho, so might be worth seeking out.
    I've never heard that, about Smartply airtightness - gd news if true. Smartply isn't formaldehyde free, just 'no added formaldehyde' which prob just means that their Irish trees already have enough natural formadehyde, compared to Sterling's Scottish ones!

    Posted By: TimSmallFor sealing edges, I used polyurethane wood glue all round, with backing where necessary (mainly sheet material offcuts) because it expands to fill any voids. You can often pick up boxes of 12 bottles on eBay which are remnants from large T+G flooring jobs. Good search terms are:

    caberfix D4 12
    egger d4

    I used small offcuts of metal stud sheet steel (Gypframe etc.) where plasterboard sheets were butt-jointed (on joins at right-angles with the studs, i.e. no extra noggins).
    All good - except that offcuts as backing need holding in place, unlike flatstrap.

    Posted By: TimSmall... torch-down roofing membrane over EPS ... the EPS melts ... I would advise builders to just up the thickness of the polyiso
    That's a v isolated point against EPS - and puzzling - thicken up the iso? when 'iso' must mean stuff with better lamda than EPS?
      2011-07-26 021reduced.jpg
    • CommentAuthoradam_w
    • CommentTimeFeb 1st 2018
     
    Hi Guys,

    I've taken in all that you've said over the past few posts and generated what I hope to be my final proposed build up, the only undefined detail is the cellulose insulation as I'm currently awaiting a quote via the link you provided Dave. If its too expensive then I think I may revert to the Rockwool Flexi idea but that doesn't affect anything structural so I'm happy!

    Anyway, have a look and let me know what you think;

    kind regards,

    Adam
      section-5.jpg
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 1st 2018 edited
     
    Mostly good - gratified that you've mostly adopted 'my' suggestion!

    Wall and roof insulation a bit thin - while you're at it, costs v little to incr to 250 or even 300 thick overall.

    But then, with the outer more than 50 or 60, the 'vertical' (downslope) roof battens and the vertical cladding battens can't be fixed simply by long-screwing through the outer insulation, with gravity resisted simply by the bending strength of the screws (friction, by compressing the the insulation, will v soon give way and slip). Both have to be positively suspended from above -
    the downslope ones by strongly fixing them to their mirror-image at the ridge, so both slopes 'hang' over the ridge;
    the vertical wall ones by suspending from some cantilever at the eave (that's why thin-coat render direct on the EPS wins - nothing needing to be suspended).

    Pic below shows a way to provide that cantilever, within the (min 100thk) outer insulation. These stub rafters, resting on the OSB, are spaced to 'hit and miss' with the structural rafters beneath, so no straight-through thermal bridge. Stub and structural rafters, not nec at same c/cs, have to be carefully laid out. Note the rail fixed to the stub rafters' undersides, from which the vertical battens are suspended.

    Why filling the first floor with insulation? Admittedly, without, the 60 EPS strip to joist-ends underside would be a weak point in the insulation. With that fill, you don't need the 60 EPS strip.

    You don't like the galv flatstrap and angles idea as noggings? There's a lot more odd bits of extra timber in the stud/rafterwork than I'd aim for. Stud sole and header I'd make single 75x95. Every little helps a lot, if done systematically.
      2011-07-26 044med.jpg
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 1st 2018 edited
     
    Builder was Andy Dodden an02ew of this forum.
      2011-08-19 040med.jpg
    • CommentAuthorborpin
    • CommentTimeFeb 1st 2018 edited
     
    One other item is I'd suggest Lindab Guttering. Bit more expensive but it is just so good. I used a coated variety in black and 5 years on it looks as good as the day it went on.

    the brackets in fostertoms last photo look a bit Lindabish.

    Also set the outer edge of the gutter so if you put a batten on the roof, it just touches the gutter. Most folk set gutter too high.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 1st 2018
     
    Lindab yes.

    You mean the plane of the top of the slates shd just touch the outer edge of the gutter? Gd kind of tip.
    • CommentAuthorgravelld
    • CommentTimeFeb 1st 2018
     
    Posted By: fostertomBut then, with the outer more than 50 or 60,
    50 or 60 what, sorry?
    • CommentAuthoradam_w
    • CommentTimeFeb 2nd 2018
     
    Tom, you are worth your weight in gold my friend!

    As you say, I think 60/50mm of external insulation is probably the structural limitation so although its not ideal, baring in mind that this is an extension to a poorly insulated property, I think its a compromise I'm happy to make.

    You should be able to see from the latest drawing that I've added even more of your design features, this time the stub rafters offset to the internal ones as suggested. Although I want to keep the overhang (lookout?) as low as possible, its probably a feature worth incorporating for that's added structural integrity.

    The reason for the first floor insulation and EPS joist wrap is that the ground floor is to be a garage so I'm trying to keep the rooms above it as comfortable as possible but if you think that this is excessive then i'll happily remove this detail.

    Please don't take offence to the lack of incorporation of your steel strapping idea, I think its a great solution to my issue I'm just not sure about sourcing such materials with such a specific angle for a relatively limited area (22m) so I've put in a timber brace that could be just 45mm wide and positioned under the stub rafters to provide support and my previous suggestion of rubber roofing material to flash the internal joints in-between those.

    Borpin - Thanks for the product suggestion but I already have guttering on the rest of the house that would be very expensive to replace so i'll just tie in with that I think for now however please note that I have lowered the guttering to the alignment you suggested, thanks for the tip!

    Thanks again for your tips, see version 6 below;
      section-6.jpg
   
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