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Green Building Bible, Fourth Edition
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    • CommentAuthorajdunlop
    • CommentTimeJan 22nd 2020
     
    I am about to IWIing another room in our house with insulated plasterboard on a metal frame.
    I'm thinking about what to to between the joists.

    In the back of the house I dealt with this by cutting away a section of ceiling in the ground floor room and inserted mineral wool and used an airtightness membrane and tapes. This worked fine but was a bit fiddly and meant the ceiling had to be put right after.

    This time at the front of the house I am doing the first floor room 1st so was trying to think of ways to deal with between the joists from above.

    Our house is an end terrace so I have to deal with two walls in each room and with that two directions of joists. I am trying to work out how to extend the insulation down between the joists and specifically what to do with the floorboards (these are exposed).

    This is easy for the wall where the joists are at 90 degrees to the wall, cut slots for each joist in the insulation then reduce the width of the floorboard along the wall as required.

    The problem is the wall where the joists are parallel to it. No slots required in the insulation so that's simpler but what do I do about the edge of the floorboards? They will be unsupported if I have to cut them back to allow the insulation to go bellow floor level.

    If it is too difficult I will leave it and do the same as the back of the house when I tackle the front ground floor room.
    • CommentAuthortony
    • CommentTimeJan 23rd 2020
     
    Have a look at this, https://readinguk.org/draughtbusters/going-further/first-floor-void/

    Air tightness is at least as important as insulation. I am concerned that you will be getting draughts in between your metal battens, these could reduce or even eliminate the insulating properties of the external walls, I would stick the boards to the walls with dry wall adhesive or foam using ribbons to eliminate this problem then use six insulation fixings per board to mechanically fix them.

    At Denby Dale they fully foam filled between their joist ends about 100mm thick.

    Re unsupported edges the long strips are unsupported now, short ones will be ok if real wood floor boards, if chipboard, I would add a noggin screwed through the edge of the floorboard with four screws equally spaced

    Well done and please post some pics for us to look at
    • CommentAuthorGreenPaddy
    • CommentTimeJan 23rd 2020
     
    If I've understood you correctly, you have the following..

    - first floor joist running parallel to the wall, fixed to the wall
    - floor boards (approx 150mm wide) perp to the joist, with the end of the floor board landing on the wall fixed joist
    - you want to cut the floor boards ends off, all along that wall, so there is a gap between the edge of the cut boards and the inside of the joist
    - you will then pass insulation vertically down between the cut board ends, flush with the joist face, until it meets the ceiling below.

    If that's what you're planning, then I would say those cut floor board tails deff need supporting.

    I don't immediately see a better way of getting access to that ceiling/floor void. One question would be...is the floor joist tight against the external wall, or is there a gap once you take pack any plaster etc above. If that's the case I might settle for foaming into that joint, with a flexi tube, to make sure it gets all the way behind the joist (air tightness as Tony mentioned).

    If you really want to trim all the boards, and I'm imaging say 50mm gap between board edge and joist inside face, then poss a steel angle (75x75) tucked under the cut tails, with the vert edge of the angle pointing upwards That would then be fixed back to a new timber (or at least blocks at intervals) immed above the joist, and back into the wall.

    I assume what you then add as IWI, will land ontop of that, and cover out to the cut board edges?
  1.  
    where the joists run parallel to the wall - what is the distance (gap) between the wall and the first joist. Is the first joist as GreenPaddy suggests fixed to the wall or is there a gap between joist and wall. The size of the gap will determine what if any additional support needed by the floor boards.
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    I would have to cut the floorboards back so there was about a 200mm overhang unsupported.
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    Tony: when you say about being worried about draughts between the metal battens do you mean draughts moving around behind the insulation or through the insulation into the room?
    The insulation is phenolic foam based so air movement through the insulation and wicking shouldn't be a problem (at least as far as I understand).

    My reasons for choosing metal battens on the 1st rooms I did in the house were not wanting to have to worry about moisture issues (although we have no signs of moisture problems) and to be able to straighten up the walls. If I was to start again I might modify my approach now that I know more but I want to try if possible to keep my strategy for the whole envelope of the house as consistent as possible.

    When you say they foamed between the joists at Denby Dale (I assume you mean the GBS PassivHaus?) do you have any details on this? I have seen an article talking about how with an earlier building they added noggins between the joists and foamed behind, is that what you are referring to?

    My floorboards are the original 1920s tongue and groove ones.
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    GreenPaddy:
    Answered to your assumptions:
    - first floor joist running parallel to the wall, fixed to the wall - Yes, fixed as in joist ends go into the inner brick leaf
    - floor boards (approx 150mm wide) perp to the joist, with the end of the floor board landing on the wall fixed joist - Yes
    - you want to cut the floor boards ends off, all along that wall, so there is a gap between the edge of the cut boards and the inside of the joist - Yes
    - you will then pass insulation vertically down between the cut board ends, flush with the joist face, until it meets the ceiling below. - Yes

    There will be a gap between the 1st joist and the wall of probably 10-30mm, if the same as the rest of the house, that I could foam. I could then push some mineral wool under the floorboards in front of the joist and not worry about wicking as the foam and joist should stop that.

    I am trying to get my head around your other suggestion if I cut the floorboards. Am I correct in understanding you suggest the metal angle will take the weight of the board ends and this could then be supported between the joists at their ends? When you say the IWI could sit on top of that, what is the that?
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    It is looking like the simplest thing might be to foam behind the parallel joist on that wall and add noggins between the joists along the other wall and foam behind these. Then add some mineral wool in front of the parallel joists and in front of the noggins to bring up to similar U-value to the insulated plasterboard.

    If I do this no floorboards need cutting (apart from trimming a small bit to be able to get my foam behind the parallel joist) just a few that have already been lifted before along the wall with 90-degree joists.

    Would I just use regular expanding foam or something else? I have a foam gun with a flexible extension, just need to make sure it isn't clogged up.

    Any better suggestions or things to look out for?

    I will need to make sure under the joist is airtight when I do the room below but that shouldn't require interfering too much with the ceiling, maybe cutting away a small bit from the wall to get access.
    •  
      CommentAuthordjh
    • CommentTimeJan 23rd 2020
     
    Is this really any less work than cutting the ceiling and doing the job from below?
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    djh: The room below is the living room and has a fireplace and huge awkward sash windows to deal with so I just thought if I could deal with it now it might be one less thing. Also it us unlikely I will get to doing the living room for a couple of years so that could be a couple of years without the draughts.
    However if I can do it better from below or with lots less effort then I will leave it for now, still undecided.
    • CommentAuthorgyrogear
    • CommentTimeJan 23rd 2020 edited
     
    In my humble opinion, doing IWI is extremely invasive in any case, and I suspect the OP is right to be wanting to try and compartmentalise the upset. Whence the interest of researching a feasible methodology to suit the site and conditions.

    One of the main renovation criteria being to avoid "killing the green advantage" by avoiding quick-fix works which might bring a short-term gain at the expense of impeding or interdicting potentially higher-value future operations.

    (In French this is referred to as "tuer le gisement vert").

    gg
    • CommentAuthorGreenPaddy
    • CommentTimeJan 23rd 2020
     
    So here's what I'd do, now I understand a bit better;

    1. foam as deeply as possible down behind the joist parallel to the gable wall. 10 to 30mm is pretty good, and will plug all the drafts.

    2. do not cut any floor board ends. You'll end up with a complicated dogs dinner.

    3. take a floor board up at each side of the room, exposing the ceiling void & rafter tails

    4. Blow in a load of polystyrene beads, to fill the first joist to joist void. Vacuum cleaner in reverse, or some such method that people on here will attest to.

    5. at each of the rafter tail gaps along each wall, tightly wedge in a piece of insulation board so that it runs between adjacent joints, and full depth ceiling to joist top, leaving 20mm gap to the wall. 100mm polystyrene board would be good for that. Even put 2 layers in if you want to go crazy, first one, then push it back under the floor boards, then second one.

    6. Then foam fill that 20mm gap to wall, making sure foam gets to the bottom/ceiling first, before withdrawing the nozzle.

    7. do a final to-up of the poly beads at that first joist to joist void.

    Air tight ceiling void, with a great insulation value, and no chopping of ceilings or floor boards, not much tuer 'ing of the green gisement, si tu me comprends.
    •  
      CommentAuthordjh
    • CommentTimeJan 23rd 2020
     
    Posted By: GreenPaddy1. foam as deeply as possible down behind the joist parallel to the gable wall. 10 to 30mm is pretty good, and will plug all the drafts.

    How do you get access to do this without chopping the ends off floor boards?
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    Posted By: djh
    Posted By: GreenPaddy1. foam as deeply as possible down behind the joist parallel to the gable wall. 10 to 30mm is pretty good, and will plug all the drafts.

    How do you get access to do this without chopping the ends off floor boards?


    I suspect many of the floorboards will stop short of the wall anyway (we have skirting and quadrant mouldings to hide these gaps) and can trim a little off some is necessary.
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    Sounds good except I am not getting these bits:

    Posted By: GreenPaddySo here's what I'd do, now I understand a bit better;

    4. Blow in a load of polystyrene beads, to fill the first joist to joist void. Vacuum cleaner in reverse, or some such method that people on here will attest to.

    7. do a final to-up of the poly beads at that first joist to joist void.

    Air tight ceiling void, with a great insulation value, and no chopping of ceilings or floor boards, not much tuer 'ing of the green gisement, si tu me comprends.


    Where are the beads for? I am not sure what you mean by joist to joist void.
  2.  
    Posted By: ajdunlopI would have to cut the floorboards back so there was about a 200mm overhang unsupported.

    IMO you would probably get away with a 200mm overhang next to the wall, especially as the floor boards are T&G and if they are in good nick. How much weight do you ever expect to be on this portion of the floor? max I would suggest would be the leg of a cupboard.

    How much IWI are you putting up. If it is 50mm and you get a 30mm gap between joist and wall then I would suggest that to fill between joist and wall with insulation would suffice. (you say that the joist sits on the inner brick leaf - does this imply a cavity wall? Do you have CWI?) So you only cut back sufficent to expose the gap to fill with insulation (I assume the insulated plaster board will fix directly to the wall and not be on battens)

    Otherwise cut back what you need and put in a new joist under the board overhang sufficiently smaller than the existing to allow ease of installation (in 2 parts bolted up if needed) and supported on joist hangers either end.
    •  
      CommentAuthordjh
    • CommentTimeJan 23rd 2020
     
    Posted By: ajdunlopWhere are the beads for? I am not sure what you mean by joist to joist void.

    Along the wall where the joists run parallel, and where you've foamed the gap between the wall and the first joist, then he's talking about the gap between the first and second joist.
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    Ah yes it’s obvious now.
    • CommentAuthorajdunlop
    • CommentTimeJan 23rd 2020
     
    Peter_in_Hungry:
    We don’t have CWI as the cavity is uneven and the outer leaf is Yorkshire stone so porous so needs the cavity to dry out.
    The insulated plasterboard is 90mm and will be fixed to metal battens.
    • CommentAuthortony
    • CommentTimeJan 24th 2020
     
    There is a real and present danger of wind from outside finding its way from the cavity into the void between the metal battens, this can come out through socket outlets or under the skirting and even if
  3.  
    ''There is a real and present danger of wind from outside finding its way from the cavity into the void between the metal battens,''

    Agreed. I'd suggest you do a lime parge coat first. Min 10mm-ish, and it can just follow the 'wows' of the stone.
  4.  
    Posted By: Nick ParsonsAgreed. I'd suggest you do a lime parge coat first. Min 10mm-ish, and it can just follow the 'wows' of the stone.

    Or just glue the PB to the wall with contiguous lines of adhesive or foam making compartments small enough to prevent circulation. i.e. not dot and dab
    • CommentAuthorGreenPaddy
    • CommentTimeJan 24th 2020 edited
     
    Hoping this sketch has attached and viewable. (For "Setcoin", read Section"...I sketch, don't spell)

    Would I bother with the poly beads for one short wall, maybe not as PiH mentions above, but this is a repeating feature in a few rooms, so get it right once, you can do for other rooms.

    Search for poly beads threads, or ask others how they fill voids. If it's easy, then go for it. If it's a big hassle, then reconsider.
      Floor Edge Insul.jpg
    • CommentAuthorajdunlop
    • CommentTimeJan 24th 2020
     
    Tony & Nick Parsons: Why is air movement behind the insulation a problem if it can't get through (because of foaming, skimming of plasterboard, use of tapes when required)? I would have thought wicking of heat from the insulation would be minimal with Phenolic Foam (could be wrong). The wall is still plastered so I could parge coat where the skirting has been removed to reduce airflow.

    GreenPaddy: Thanks for the diagram. I am thinking instead of poly beads I might be able to get some mineral wool in between the 1st joists as that wall has a chimney and so it is broken into small sections that I should be able to reach to pull the insulation through. I would also need to foam between the chimney breast and the trimmers but I think I can work out how to do that.
    • CommentAuthorgyrogear
    • CommentTimeJan 24th 2020
     
    Posted By: ajdunlopTony & Nick Parsons: Why is air movement behind the insulation a problem if it can't get through (because of foaming, skimming of plasterboard, use of tapes when required)


    This might help:

    https://basc.pnnl.gov/resource-guides/wind-washing#quicktabs-guides=1

    gg
  5.  
    ''Tony & Nick Parsons: Why is air movement behind the insulation a problem if it can't get through ''

    It's a question of whether you want the insulation value of the phenolic only, or of the whole wall-and-insulation sandwich*. And it's also not always as easy to get the joints and perimeters of the boards as 'tight' as you'd wish. If I use 'synthetics' for IWI I always use separate PIR, tape all joints and perimeters, battens on the warm side, then board. It's all very well composite boards having a VCL, but where's the VCL at the joints?

    * On the other hand if you intentionally form a ventilated cavity you can use a lower U value with significantly reduced risk of interstitial condensation.
    • CommentAuthorajdunlop
    • CommentTimeJan 24th 2020
     
    I am using 90mm (of which PB 9.5mm ) with an R-Value of 4.06.
    How much advantage would sandwiching it with the red brick inner leaf of the wall give?

    The original reasons for using battens on the cold side was to over engineer a bit so I could avoid worrying about interstitial condensation as well as straightening out the walls.
  6.  
    I am not sure you can avoid worrying about I C unless the cavity is intentionally and effectively ventilated.
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