Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




  1.  
    Hi all,

    Im not finding much help with this online, or even chatting to insulation suppliers:

    My house will be single leaf 215mm blockwork with 200mm EWI. About half of the build will be clad with timber, my problem is that 200mm is to far to mechanically fix the battens for the cladding, there might be significant sagging.

    Possible solution: fix a 100mm thick stud externally to block wall (within EWI layer), this way the fixing would only travel trhough 100mm of insulation to meet stud.

    Anyone dealt with this kind of thing before?

    Thanks a lot, any help much appriciated :smile:



    J
  2.  
    Can you either suspend the battens for the cladding to something solid at the top or (preferable IMO) sit them on the ground (with DPC) so that the load is transferred to either the top fixing or the ground and the fixings through the EWI just locate rather than carry weight
    •  
      CommentAuthordjh
    • CommentTimeJun 7th 2020
     
    If the EWI is in two 100 mm layers then it is possible to recess battens in the first layer so the screws don't need to be as long. Other possibilities include supporting the battens to support the cladding (assuming there are such!) either from the ground or from the top (eaves or gable). How heavy is the cladding?

    Having said all that, 100 mm studs in a 200 mm insulation layer don't sound that disastrous!
    • CommentAuthorteach_glas
    • CommentTimeJun 7th 2020 edited
     
    Thanks for the input guys, will have to calculate weight of cladding...

    I foolishly didnt use the search funtion before posting, but found an interesting thread here:

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13358

    Your suggestions are covered, but also the possibility of using an I-Beam instead of a stud.. that would yeild less of a cold bridge im assuming?
  3.  
    Posted By: djhIf the EWI is in two 100 mm layers then it is possible to recess battens in the first layer so the screws don't need to be as long. Other possibilities include supporting the battens to support the cladding (assuming there are such!) either from the ground or from the top (eaves or gable). How heavy is the cladding?

    Having said all that, 100 mm studs in a 200 mm insulation layer don't sound that disastrous!



    Its actually a flat roof with parapet wall (single story). Might be tricky to hang from top with a flying joist or similar?

    I like the two 100mm layers idea with recessed battens.. any examples of this being done?


    Thanks for the input!
    • CommentAuthorbarney
    • CommentTimeJun 8th 2020
     
    Have a look for a product by "nvelope" - you want to look at the NV 6 range

    Regards

    Barney
  4.  
    In another thread last month I had written:

    ''After the Grenfell Tower lesson I would now think twice about battening straight over 'naked' EWI. If it were me I would do the 2 x base-coats as a bit of a fire-retarder, and as the result is apparently not to be seen, we are back to 2 x base-coats and paint (or not, even - check with suppliers. Certainly one supplier does a lime-based base-coat which can be left as the top coat).''

    Of course when I wrote that I was thinking graphite EPS. Also I should have suggested running that past the system provider's tech dept. and BC first. If you are using (completely non-flammable) Rockwool it's less of an issue, though more expensive IIRC, and much heavier in itself.

    djh comments above: '' 100 mm studs in a 200 mm insulation layer don't sound that disastrous!''. Surely you could do it with only 50 depth and, if your datum points and measuring ability are better than mine, maybe 50 width?
    • CommentAuthorteach_glas
    • CommentTimeJun 8th 2020 edited
     
    Posted By: barneyHave a look for a product by "nvelope" - you want to look at the NV 6 range

    Regards

    Barney


    Thanks for this, any idea how they get round the cold bridging effect of all that aluminium?
    • CommentAuthorteach_glas
    • CommentTimeJun 8th 2020 edited
     
    Thanks Nick, what you posted is definitely food for thought...


    Posted By: Nick Parsonsdjh comments above: '' 100 mm studs in a 200 mm insulation layer don't sound that disastrous!''. Surely you could do it with only 50 depth and, if your datum points and measuring ability are better than mine, maybe 50 width?



    Do you mean a 50x50mm stud? This would mean the fixing would have to travel 150mm unsupported through EWI.

    Is this acceptable?



    I'm looking more and more towards 200mm I-Beam studs (at 800 centres?) with OSB sheathing on top to further break thermal bridge.
    Similar to this:
      Timber I-beam.JPG
    • CommentAuthordickster
    • CommentTimeJun 8th 2020
     
    Or do vertical cladding, no sagging?
  5.  
    Posted By: dicksterOr do vertical cladding, no sagging?


    Surely the weight will be distributed on the horizontal batten.. which could sag?
    • CommentAuthorMike1
    • CommentTimeJun 8th 2020 edited
     
    Vertical battens fixed to rafter / flat roof joist projections at the top to prevent sagging, with fischer Thermax fixings at intervals vertically - they can fix up to 240mm of material.
  6.  
    ''Do you mean a 50x50mm stud? This would mean the fixing would have to travel 150mm unsupported through EWI.

    Is this acceptable?''

    Yes, I did mean a 50x50 stud, but I envisaged it on top of the first layer of 100mm, fixed with sufficiently stout fixings to keep it all tight. The stud thus has 50mm EPS over it, and the cladding screws are only going through 50mm of EPS before they hit a stud.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 8th 2020
     
    Posted By: Nick Parsonsfixed with sufficiently stout fixings to keep it all tight
    To be clear, the fixings' task is not to 'keep it all tight' as in clamping the batten to the inner EPS so that friction prevents it from sliding down, which it won't reliably - the fixings have to be 'stout' and numerous enough so the act as cantilevers.

    Unless following the suggestion of ... who was it recently - djh? ... who suggested 'angling the fixings upward' - gd idea that cd change this whole discourse.
    •  
      CommentAuthordjh
    • CommentTimeJun 8th 2020
     
    Posted By: teach_glasI'm looking more and more towards 200mm I-Beam studs (at 800 centres?) with OSB sheathing on top to further break thermal bridge.

    I'm not sure how the OSB helps? I would just put the membrane over the EPS and screw through that into the I-beam flanges for the cladding.

    Posted By: barneyHave a look for a product by "nvelope" - you want to look at the NV 6 range

    That looks like Rolls-Royce solution. Any idea of the cost?
    • CommentAuthorbarney
    • CommentTimeJun 8th 2020
     
    Not sure DJH - I was going to use them on my barn build out in France, but I haven't got to detailed costs yet (CV-19 got in the way), based on it being circa 300mm clay block, circa 250mm insulation with horizontal cladding to most areas and some brickwork panels (akin to a UK cavity wall) in others - that being enough to get initial costs from a French builder.

    To answer the question on thermal bridges, you don't use that many, and there is a thermal break between the base and the flange and of course, it's supporting a timber stud not a metallic element if you were using aluminium rainscreen instead.

    I'll see if I can get a UK cost, but for me, they gave certainty of a solution without faffing around either hanging stuff from rafters or standing it on timber, etc in a bit of a suck it and see approach. That way, I can deal with walls as one aspect and roof as another (from a very big social distance)

    Regards

    Barney
    • CommentAuthorbogal2
    • CommentTimeJun 9th 2020
     
    Wouldn't it be easier to just fix I-beams to the wall. then a sheathing boards and fill the cavity with warmcel? You could get a similar U-value with perhaps 250-300mm of warmcel and reduced fire risk also presumably.
    • CommentAuthorbarney
    • CommentTimeJun 9th 2020
     
    In my case, I don't want any timber elements in the wall build up that are unseen due to potential termite problems.

    I'm happy that the oak cladding can be observed, everything else is clay block, rockwool, cementitious board and aluminium (or possibly steel) brackets which won't be subject to any insect etc attack.

    Basically, I wanted a system that reflects current commercial practice, has certification, and is reasonably fire resistant.

    Regards

    Barney
    •  
      CommentAuthordjh
    • CommentTimeJun 9th 2020
     
    Posted By: barneypotential termite problems

    Ouch! That makes quite a difference. Even with cement blocks etc, you'll still need regular termite treatment, if the situation is anything like where my wife's family live. Also think about ant-proofing cupboards etc especially food stores, as well as hard surfaces at all entrances.
    • CommentAuthorbarney
    • CommentTimeJun 9th 2020
     
    I'm not sure it's a big problem, but I am south of a line that suggests that wood problems move from being woodworm to being termites.

    From experience of the area, I'm pretty sure there isn't a real problem with termites or ants etc, but I think it's an item in the regional building code for that part of France.

    Given that the starting point was hollow concrete block with internal insulation, and sprayed lime render to the outside I'm happy that a move to clay block (keeps the brickie happy), external insulation (keeps me happy), oak cladding with some brickwork (keeps the better half happy) and sprayed lime internal plastering (keeps the plasterer happy). Using non timber commercial hangers with rockwool and fire board seems a sensible way forward

    Regards

    Barney
    • CommentAuthorteach_glas
    • CommentTimeJun 17th 2020 edited
     
    Posted By: fostertom
    Unless following the suggestion of ... who was it recently - djh? ... who suggested 'angling the fixings upward' - gd idea that cd change this whole discourse.


    This is really interesting, I wish there were some examples of this being done to show my engineer!



    Posted By: djht sure how the OSB helps? I would just put the membrane over the EPS and screw through that into the I-beam flanges for the cladding.


    Does anyone know how much thermal bridging I am introducing with the I-Joists embedded into the EWI? Can anything be done to further reduce this at masonary?

    Even if fixing a giant steel screw through the EWI was possible.. im sure this introduses it's own set of (possibly worse) thermal bridging issues?


    Thanks so much for all the replies so far, really helpful :smile:
    • CommentAuthorEd Davies
    • CommentTimeJun 18th 2020
     
    Posted By: teach_glasThis is really interesting, I wish there were some examples of this being done to show my engineer!
    Sorry, can't find any online references but I helped out years ago with a Pavatherm roof which was fixed this way. Long Spax screws at 30° to the roof normal up and down the slope through counter battens, ~200mm of Pavatherm into oak rafters. So it's not an entirely novel idea though I've not heard of it being applied specifically to a wall.
  7.  
    The structural engineer might comment that the bending force normal to each fixing would be reduced, if it is skewed, but this is exactly offset because the fixing has to be longer, so the bending moment at the root of each fixing is the same whether straight or skewed. It's equal to the weight of the cladding per fixing, times the thickness of the insulation.

    Unfortunately the deflection (sag) in each fixing is proportional to the moment x length^2 so longer fixings sag more.

    If you have the same number of fixings per m2, the weight of cladding carried by each fixing is the same, so the shearing force on each fixing is the same.

    The weight of cladding is also carried by pinching the insulation between the frame and cladding, so there's friction between the insulation and cladding. This requires the fixings to compress the cladding horizontally against the insulation. If the fixings are skewed, they need more tension force, to get the same horizontal compression.

    To sum up, skewed fixings are longer, bendier and need to be tighter than straight fixings.

    I guess this is why carpenters down the centuries have tried to drive fixings straight not skewed!

    Edit: the same goes for embedding a batten in the insulation, the two fixings (batten to wall, and cladding to batten) behave mechanically like a single long fixing, in terms of sagging, shear, tension, etc. The batten provides a thermal break in the fixings but it does reduce the insulation thickness a little.
    • CommentAuthorEd Davies
    • CommentTimeJun 18th 2020
     
    With a skew fixing, won't some of the weight be taken in tension so there'll be less bending moment?

    In the extreme case, imagine the screw was a piece of rope. Put it horizontally and it won't support the cladding at all other than maybe in tension to hold the cladding against the insulation so friction does the job.

    Put the rope at an angle downwards and it's easy to see that can support the cladding, with the reaction to the pressure against the insulation providing the counter to the horizontal component of the tension.

    The assumption is that a screw is typically stronger in tension than it is in bending. Yeah, I realise that those are measured in different units so not strictly comparable but you know what I mean. Mostly down the centuries people have been screwing solid things to other solid things - not with something light but not very compressible when the pressure's spread wide enough in between.
  8.  
    Yes, some of the weight is taken in tension, but the fixing is longer, so overall the bending moment is (exactly) the same (see 1st para above).

    To reduce the compression against the insulation, you can use a rope to hang the cladding from the eaves (or preferably use a thick batten instead of a rope, which can also stand on the floor).

    If you support that batten at regular intervals with cantilevers sticking through the insulation, it will be less floppy. It the limit that you have lots of cantilevers, it behaves like the I beam solution.
    • CommentAuthorEd Davies
    • CommentTimeJun 18th 2020
     
    Posted By: WillInAberdeenYes, some of the weight is taken in tension, but the fixing is longer, so overall the bending moment is (exactly) the same (see 1st para above).
    That would be true if the reaction to the compression against the insulation wasn't providing a bending force in the opposite direction.

    (Or, for that matter, the second screw in the opposite direction in the case of my friend's Pavatherm roof.)
    •  
      CommentAuthorfostertom
    • CommentTimeJun 18th 2020
     
    Good thinking guys - keep it up!
    •  
      CommentAuthordjh
    • CommentTimeJun 18th 2020 edited
     
    Posted By: Ed DaviesThe assumption is that a screw is typically stronger in tension than it is in bending.

    Mostly screws are rated in tension but not in shear. Coach screws are an exception.

    I'm not a mechanical engineer, so I'm not straining my brain too hard trying to understand what you and Will are saying, but to me your rope argument is persuasive. I can see that I could build a wall and hold the cladding and insulation in place entirely with angled ropes as you suggest, so this bending argument must be spurious for some reason I haven't bothered to figure out.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 18th 2020
     
    Maybe the screws will be put in bending whether they like it or not, unlike the ropes.
  9.  
    Was trying to think how to describe the rope thing without maths, but failed...

    The proposal is to treat the skewed screw like a short rope tie, acting with the insulation as a strut, to make a tie-and-strut cantilever. Let's say the screw is skewed upwards at an angle of 30deg as mentioned.

    If the weight of the cladding per screw is W, the tension in the 'rope' is W/sin(30deg) = 2W. The compression in the insulation is W/tan(30deg) = 1.73W. These loads are inefficiently high, compared to W, especially as screws aren't great in tension and insulation isn't great in compression. You'd need extra-strong screws and insulation.

    But fortunately, as soon as you started to drive the screw, it would act as a little cantilever itself, and support the cladding even before you'd applied any tension at all. You'd probably drive the screw a little further and apply a little tension to keep it neat. That would clamp the cladding against the insulation and create some friction, which would transfer some of the weight of the cladding directly into the insulation, so reducing the load in the screw. The fixing would be secure, long before the tension in the screw had reached 2W, and you'd move onto the next one.

    But if you were feeling brutal and did manage to tighten the screw tension to 2W without breaking the head, the friction would be supporting the cladding weight (mu = ~0.5) and the 'rope tie' idea would become redundant, more of a 'clamp'.

    If you checked the next day, the insulation would have squashed a little, relaxing the tension in the screw, so it would be back to acting as a stiff cantilever again.

    So in summary, the 'rope tie' idea could work if the rope and insulation were strong enough to hold twice the cladding weight, but fortunately the screws are stiff enough that they can act like pegs (cantilevers) and so don't need such high loads. The 'rope tie' idea is appealing but it isn't analogous to how the screws work.

    The situation is a bit different on a roof where the weight of the insulation is mainly supported against the sarking by friction. The screws there act in shear, to stop the everything sliding off, and in tension if there's a strong wind lifting everything up.

    All this is probably unhelpful for the OP!
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press