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    • CommentAuthorPikey
    • CommentTimeOct 19th 2009 edited
     
    Im having enormous difficulty finding/specifying fixings to hold down my Celotex 'EL3150' boards to the plywood deck they will be laid on.

    The two 'solutions' I've come up with so far are roofing bolts with washers (although this doesnt seem like a great idea - puncturing the insulation multiple times with metal bolts), and cold applied bitumen adhesive (which would take ages and some of the boards are warped a bit and would not stick down properly.

    Any ideas? There must be fixings available that are designed for this. I've seen 'insulation clips' but they only go up to 100mm long and my insulation is 150mm thick!

    Jeff :smile:
  1.  
    You could use cementitious glue (like the styrofix used for External Insulation) or fixing foam and weigh the Celotex down with Concrete blocks until the glue/foam goes off. Have a read of some of the other threads here, you may not be getting the U-value you think you are getting with Cellotex!
    • CommentAuthordwas
    • CommentTimeOct 19th 2009
     
    Always follow the manufacturers written instructions: http://www.celotex.co.uk/downloads.asp?i=9 (link downloads PDF). Otherwise, if it fails, you don't have a leg to stand on!

    To quote (read the full doc.):
    "Hot-applied systems
    The felt vapour control layer (VCL) in accordance with BS 6229 should be fully sealed at all laps prior to applying the insulation. At perimeters and abutments the VCL should be turned up around the insulation board edges and a flap of approximately 300mm should be bonded to the top surface of the insulation board. The VCL should be....partially bonded to timber decks.
    On timber decks the VCL may be nailed to the deck, but laps should be sealed with the appropriate adhesive.

    Mechanical fastening
    The boards should be laid with all joints tightly butted together over the VCL and then mechanically secured through to the deck. When used on metal decks, these roof boards should be laid with the long sides at right angles to the corrugations. When mechanical fasteners are utilised, they should be selected to suit the type of deck used. A plate washer with a surface area of not less than 45cm2 must be used with each fastener. Fasteners should be installed between 50mm-150mm from the edges and corners of the board.

    Celotex recommends the use of BS 6399:2 Code of Practice for Wind Loads when determining the
    number of fixings required for insulation boards in flat roof applications.

    Use of adhesives (Pay heed Viking House!)
    When using adhesives, the installer should take care not to use products that contain chemicals likely to attack the insulating foam such as ketonic solvents. Celotex EL3000 contains no chemicals or solvents likely to damage the PVC membrane. When using adhesives, the installer should check the compatibility of the adhesive with the adhesive manufacturer."

    Return the warped boards!

    Sorry to ruin your day!
    • CommentAuthorJulian
    • CommentTimeOct 19th 2009
     
    Pikey
    What membrabe are you using on top? I used 150 KS boards under roofkrete4 and used 180mm screws - the absolute minimum per board with a ply "washer". Once the roofkrete goes on the whole thing is fairly bombproof. But if the warping is bad (how bad is it?) you could speak to the supplier and especially if these are 1st quality boards and not seconds get them to replace as DWAS says. There is a spray foam adhesive that is designed for fixing internally - nasty stuff as well.
    • CommentAuthorPikey
    • CommentTimeOct 19th 2009 edited
     
    The three top boards got damaged by a little bit of rain - because the supplier was late delivering them and I was there on my own and couldnt get them into the dry by myself!

    dwas - the instructions you have so helpfully copied and pasted say the insulation should be 'mechanically secured through to the deck' - the whole point of this thread is to discuss how exactly to do that.

    I never thought of using roofing felt as the VCL, might actually by a nifty way of doing it - then I can clout nail the felt down and bitumen-sticky-gloopy-black-glue the insulation boards to it, with concrete blocks to weigh the centres down to sort out the warping. Possibly a couple of long screws and big washers aswell.

    Fischer do a very handy-looking fixing, with a plastic washer and a screw inside - but, as I say at the top, they only do them up to 100mm long :angry:
  2.  
    Hi, Ive not done this on the roof, but when sorting out the warping (they are all a little bannanered) fix one end first and weight it down, then push the sticking up end down. A slight bow over 2.4 m still raises it up quite a bit. Dont fix at the ends and try to push the middle down becuase it quite a nice strong arch which will resist (the ends have no where to go).
    Internally ply worked quite well 45sq cm is 3inch dia so any sort of thin off cuts (ive used thinnest 6mm ply)
    The very long screws or specialist fixings get expensive. if going into a batten for example you'd need at leat a 180-190 screw (check something cheap like screwfix) and it does get expensive.
    Cheers
    Mike up North
    • CommentAuthordwas
    • CommentTimeOct 19th 2009
     
    Pikey
    Perhaps I was too subtle, referring to the manufacturers written instruction, I should have highlighted the para referring to BS 6399:2 Code of Practice for Wind Loads. But who wants to splash out £100 for that? Next best thing is ask Celotex or if you've an engineer, ask them.

    Better still, use a SIPs roof panel.
    • CommentAuthorRobinB
    • CommentTimeOct 20th 2009
     
    When we costed SIPS v home-made version, (a sandwich of OSB and foam board insulation) the SIPS came out nearly double 18k v 10k. Is that normal?
  3.  
    Posted By: RobinBa sandwich of OSB and foam board insulation


    ...not a SIP... as the OSB is not bonded therefore not acting together structurally....

    J
    • CommentAuthorPikey
    • CommentTimeOct 20th 2009 edited
     
    I phoned Celotex, a very helpful man emailed me a list of fixings suppliers, from which EJOT seem to have what I need http://www.ejot.co.uk/buildingfasteners_htk.odl

    Dont know how much they are yet though...!
    • CommentAuthortony
    • CommentTimeOct 20th 2009
     
    When I used to do it I didn't fix the insulation but laid a sheet of ply on top and fixed that through to the joists. (all end sheets were joined on a joist and always staggered with the insulation joins.)

    look like nice fixings tho
    • CommentAuthorCWatters
    • CommentTimeOct 20th 2009 edited
     
    Perhaps also google "warm roof fixings"...

    http://www.google.co.uk/search?hl=en&q=warm+roof+fixings&btnG=Search&meta=cr%3DcountryUK%7CcountryGB

    Will find several sources for specialist fixings but mostly for fixing the insulation to rafters rather than ply. I guess that's the problem though?
  4.  
    For our tiled roof I used 'inscrew' helifix hammer in fixings but that was through a counterbatten, through the insulation boards and 40mm into the rafters below (not into a plywood deck). They were a bit pricey though, but I am quite pleased with them and the use of them, a bit like a cross between a nail and a screw (you have to buy a special tool to hold them straight while you hammer them in).
    •  
      CommentAuthorfostertom
    • CommentTimeOct 20th 2009 edited
     
    Like this? http://www.helicalc.co.uk/suretwist%20warm%20roof.pdf
    How did you know where the rafters were, with great accuraCY, TO BE SURE OF HITTING THEM THRO 150 of insulation? The fixings have to be exactly centred and exactly square, and you can't see the rafters. Esp if you've overlaid the rafters with OSB under the insulation and you really don't want to puncture the OSB by missed fixings, as it's supposed to be airtight.
    • CommentAuthorwookey
    • CommentTimeOct 21st 2009
     
    Re expense of British standards - these are usually available for free at your local library. Ours (cambridge) lets you log on from home and download them, which is incredibly useful - I am now able to comply with a whole pile of British Standards which used to be effectively secret.
  5.  
    I didn't have OSB over the rafters, and I only had 75mm insulation over the rafters, the other 75mm was between the rafters. Started at one end of the counterbatten and worked towards the other, like in the document linked to above, using the hand held tool on the left. I think with that other hand held squaring tool 150mm would also be easy, once you are through the counterbatten it's easy nailing. You also need to make sure you use the right quantity of fixings per square metre for the thickness of insulation you are using.
      counterbattens.jpg
    • CommentAuthorPikey
    • CommentTimeOct 21st 2009
     
    Another sheet of ply on top would cost another £400, plus we've already paid a premium for the specific insulation designed to have EPDM applied directly to the top, so its not an option. Even if the EJOT fixings cost £400 it's still a better option.

    I think I've just about accepted that the fixings are going to have to go through the ply into the joists, not just into the ply.
    • CommentAuthortony
    • CommentTimeOct 21st 2009
     
    So your membrane is going straight on top of PUR? sounds like madness to me.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 21st 2009 edited
     
    I agree PUR between rafters is madness in itself - my heart bleeds for those poor rafters, forced to carry all of the in/out traffic of water vapour, and because stone-cold (edge exposed to outside air) very liable to internal condensation hence moisture content well above rot-risk level.

    But apart from that, 'straight on top' (plus downslope battens over) is what's recommended, isn't it? Why not? Condensation on underside of breather? If so, that's bad news anyway, which a bit of airspace won't help - it'd still drip.
    • CommentAuthorCWatters
    • CommentTimeOct 21st 2009
     
    Posted By: tonySo your membrane is going straight on top of PUR? sounds like madness to me.


    I believe Kingspan make a membrane specifically for that. You have to use counter battens on top of the membrane to lift the tile battens off it. That's because with the membrane resting on the PUR it lays flat. On a normal toof the mebrane drapes between the rafters preventing water becoming trapped above tile battens.
  6.  
    More talk of interstitial condensation risk where PUR is used between rafters. Seen this on several threads. Yet to see any proof. Load of old cobblers IF installed in accordance with manufacturers spec. Been doing it this way for years. Never had a problem.

    Suggest those of you who think there is a risk should try running a Condensation Risk Analysis. The ones I have done back up the real life experience - ie. no problem
    • CommentAuthortony
    • CommentTimeOct 21st 2009
     
    Posted By: PikeyAnother sheet of ply on top would cost another £400, plus we've already paid a premium for the specific insulation designed to have EPDM applied directly to the top, so its not an option. Even if the EJOT fixings cost £400 it's still a better option.

    I think I've just about accepted that the fixings are going to have to go through the ply into the joists, not just into the ply.



    I m not sure but I think that this is for a flat roof isnt it?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 22nd 2009
     
    Sorry Mike, this relates to the other thread, still haven't answered it properly. Don't think a CRA looks at one material next to another e.g. studs next to Cellotex in the same layer, in fact a Euler diagram based one actually ignores the studs?
  7.  
    Fostertom says: I agree PUR between rafters is madness in itself - my heart bleeds for those poor rafters, forced to carry all of the in/out traffic of water vapour, and because stone-cold (edge exposed to outside air) very liable to internal condensation hence moisture content well above rot-risk level.

    Viking: Then there's the Old German 50% building rule that states; "you are not allowed to cover Structural Timbers by more than 50% with non breathable materials". Its a bit like the Wine Barrel/Timber boat scenario where you have to take the boat out of the water every 2-3 years to paint it but not the Wine Barrel.

    Everytime I hit the quote button it comes through in a jumble, what am I doing wrong?
  8.  
    Posted By: fostertom Don't think a CRA looks at one material next to another e.g. studs next to Cellotex in the same layer, in fact a Euler diagram based one actually ignores the studs?


    Yes, I believe it does ignore the studs. That's because in a construction like this the dew point will be constantly beyond the insulation layer. ie on the cold side. This being the case, water cannot condense within. Don't forget PUR is not completely vapour closed.
    • CommentAuthorMike George
    • CommentTimeOct 22nd 2009 edited
     
    Viking, how can you argue one minute that PUR is vapour open and the next indicate that it will be cause water to surround timber like wine barrels in water? It's all about where the dew point will be, and in these constructions [providing they are constructed properly] it will be beyond the cold side of the insulation.

    You are also twisting the facts regarding the 50% rule. You even quote the main point ie "you are not allowed to cover Structural Timbers by more than 50% with non breathable materials". This is not being suggested here is it?

    I do like the 50% rule. But I don't think breather membranes were around when it was thought up. The reason I like it is because it allows any small roof leaks to be vented away rather than facilitating localised temperature drop which can bring the dew point within the structure.
    • CommentAuthorPeter Clark
    • CommentTimeOct 22nd 2009 edited
     
    Posted By: Mike GeorgeYes, I believe it does ignore the studs. That's because in a construction like this the dew point will be constantly beyond the insulation layer. ie on the cold side.


    Is this correct? or is it the case that BECAUSE the condensation analysis ignores the timber frame, it reports the dew point outside the insulation.
    But it ignores the timber because to take it into account would be more difficult to do?

    So, if we did take the timber into account somehow, we might find that the dew point is within the buildup?

    Peter
  9.  
    That's an interesting point Peter. I suppose the way to think about this is to consider two separate CRA's, one which recognises a temperature gradient though the insulation; and one which recognises a temperature gradient through the timber /over timber insulation. It will of course depend upon the level of insulation wholly above the timbers. When I get five minuites I will test this.
    • CommentAuthorMike George
    • CommentTimeOct 22nd 2009 edited
     
    Just done this using Tas software. Please note this is a hypothetical scenario and is not advocated in any shape or form.

    For Option 1

    Homogenous layers of

    12.5mm plasterboard
    150mm spruce
    75mm PUR
    Bituminous felt
    20mm airgap
    slate

    Result Zero risk of interstitial condensation

    Option 2

    12.5mm plasterboard
    Timber ignored
    150 mm PUR
    Bituminous felt
    20mm airgap
    slate

    Result Zero risk of interstitial condensation

    Note that these constructions contains neither vapour barrier nor breathable membrane [both of which would be used in best practice] External temperature needs to drop to around 5degC before any risk is indicated. At this point condensation occurs [as expected] on the underside of the bituminous felt. This justifies the need for either a good quality breathable membrane or sub felt ventilation; either of which will eliminate the risk of interstitial condensation.

    jpeg is for timber option
      hypothetical CRA copy.jpg
  10.  
    Posted By: Mike GeorgeFor Option 1

    Homogenous layers of

    12.5mm plasterboard
    150mm spruce
    75mm PUR
    Bituminous felt
    20mm airgap
    slate

    Result Zero risk of interstitial condensation


    How is this modelling the thermal bridging effect of an actual joist or timber? You have the insulation all on the outside so of course the dew point will not be near the timber?

    Perhaps I have misunderstood what you are doing here.
   
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