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    • CommentAuthormarsaday
    • CommentTimeSep 2nd 2017
     
    At what level do you start the cavity wall insulation ?

    You can see i have placed a joist in its finished position temporarily for today. This will be the floor level. The breeze block course with the cavity air vents is the bottom of the cavity and i have formed a ridge of mortar in this channel so any water will hopefully push outwards.

    So would i set my full fill insulation down into the bottom of the cavity, or do i start it a little higher up, at the top of the first line of breeze blocks, which will be floor level ?

    Also does it matter if the cavity is a little narrower than the 100mm insulation. The facing bricks are wider and so the cavity is going to be 90mm wide i think.
      IMG_0739.jpg
    • CommentAuthorDarylP
    • CommentTimeSep 2nd 2017
     
    See ACDs for a starting point:
    http://webarchive.nationalarchives.gov.uk/20141202161419/http://www.planningportal.gov.uk/uploads/br/masonry_cavity_wall_insulation_illustrations.pdf
    • CommentAuthortony
    • CommentTimeSep 2nd 2017
     
    I take it down to ground level usually, on my house it goes down underground because of the basement. If worried use eps low down.
    • CommentAuthormarsaday
    • CommentTimeSep 2nd 2017
     
    Ok, thanks. What is EPS ?

    Also what is the situation with full fill 100mm, but the cavity is 90mm. I have set everything out, but my brick is a little wider. So the insulation will be compressed a little more. Does this matter ?
    • CommentAuthortony
    • CommentTimeSep 2nd 2017
     
    EPS = Expanded polystyrene
    • CommentAuthorMarkyP
    • CommentTimeSep 3rd 2017
     
    check the datasheet on your insulation, some mineral wool is rated for use below DPC. I used knauf dri-therm for my full fill, the highest density stuff with the best r-value. This is rated for use below DPC but I still had some reservations about using it there so we used EPS like Tony suggests. We formed a cavity tray right across (you can get really wide rolls of DPC, or use 1200 gauge), tight over the EPS and then used the wool from there up.

    regarding 90mm cavity for 100mm wool- we oversized the cavity slightly and the wool expanded to tightly fill it. others here more experienced with brickwork might be able to give you some hints on best method here. Tony?
    • CommentAuthormarsaday
    • CommentTimeSep 3rd 2017
     
    Thanks for info. I have spoken to someone and my full fill will cause problems apparently. So it looks like i will have to go for the rigid celotex stuff at 50mm.

    Can anyone comment on what i need to do to really make a good job of this. I am doing it myself and after reading on here i decided to go for full fill as some seemed to think it was the best solution. So it looks like this won't be possible as my gap is going to be 90mm. So do i need to silicone up the cut joints etc. Is it better to use the pre cut 450mm size pieces rather than the full sheets ?
    • CommentAuthormarsaday
    • CommentTimeSep 3rd 2017
     
    Been doing a bit more reading and rigid insulation is harder to fit.

    I will call Knauf tomorrow, as i am hoping their 85mm width product could be ok for my job. Will this pass the regs i wonder ?
    • CommentAuthorDarylP
    • CommentTimeSep 3rd 2017 edited
     
    .. who says rigid insulation is harder to fit?:bigsmile: harder to fit than mineral wool? perhaps.... from the POV of a lazy brickie, who doesn't care about the job in hand, just finishing asap and moving on to the next job / pub / footie match.... :wink:
    full fill should not be a problem, unless you are subject to extreme exposure / wind driven rain?
    sheets are cut at 450mm wide to accommodate std spacing wall ties. However your BCB may insist on 50mm clear cavity so you will be restricted to 40mm rigid boards? Probably not going to meet AD L1b minmum stds, unless you are using ins. p/b as well? ?
    Can you oversail the brickwork slightly to widen the cavity?
    Good luck... :smile:
    • CommentAuthormarsaday
    • CommentTimeSep 3rd 2017
     
    Darylp thanks for info. We are not in an exposed site and the far left wall is protected by the big garden wall. Do you mean full fill rigid is not a problem or the soft stuff ?

    Apparently block work needs to be much more accurate if using rigid because if the wall is not flat the boards will kick out. This is a worry for me as all this is new, but i am determined to really try get all this brick work done. i can afford to pay someone, but the enjoyment is in doing it all myself and i want to learn. One day i would like to do a new build and all this experience is good prep.

    Ok i have been out and measured my cavities accurately. I have a 90mm cavity on the right hand wall and 85mm on the left side. The frontage is 80mm on the right side and finishes up at 70mm on the far left side.

    The stone henge foundations which were left in place from the conservatory have really cocked me up while doing all this work. They were 500mm deep and taking them out was harder than bolting into them and building new foundations around them. I have got my lines wrong when laying the foundation blocks as i got near to this foundation.

    Rectifying this mistake is easy however. The line of external brick is actually just below patio level so will be hidden. I really need to remove this and build a new line of base brick the full length of the building. I have the foundation space to lay a new breeze block and build up from there. I can then set the external skin in the correct position. I will make this a 105mm cavity so i can use the 100mm insulation. There is a big patio door in the wall as well so, not so much building work needed.
    • CommentAuthorDarylP
    • CommentTimeSep 3rd 2017
     
    full fill mineral / glass wool is flexible and can accommodate the vagaries of a cavity easily.
    rigid (Celotex, Kingspan etc etc ) needs a flat level plumb inner leaf to be pressed hard up against, via the retaining discs on the cavity wall ties.
    there is a Xtratherm (& Celotex too?) product that is rigid, but allows a 5mm clear cavity, but it is expensive and slightly more difficult to use than 'normal' rigid boards.
    If you are building up the inner leaf, and can keep the outer-face of the blocks clear of mortar snots, the rigid may be best?
    Is this subject to Building Regs approval, Building Control sign off? :confused:
    • CommentAuthormarsaday
    • CommentTimeSep 3rd 2017
     
    Yes i have building regs on it.

    Reading up it seems the minimum full fill insulation is 100mm. So it seems i will have to go for rigid insulation.

    Building will be slow and steady. I have plenty of time so will be very careful.

    With my cavity sizes though i can use 50mm rigid, but is it ok to have a 35-40mm cavity gap ?

    I am kicking myself because i forgot about the external bricks being a bigger size.
    • CommentAuthormarsaday
    • CommentTimeSep 3rd 2017
     
    Bit more research and i am sure i can do 85mm soft fill cavity plus an insulated plasterboard internally. There are products by Knauf, clotted, kingpan so plenty to go for.
    • CommentAuthortony
    • CommentTimeSep 3rd 2017
     
    I would not try to compress batts i.e. Don't try 100mm batts in a 90 cavirty, I used 300mm in a 305mm cavity if the cavirt is narrow it tends to pus the masonry out of the way when laying it.
    • CommentAuthormarsaday
    • CommentTimeSep 3rd 2017
     
    Yes this is what i understand.

    I think the solution is to use an 85mm bat and top up with insulated plasterboard inside. Knauf do a board as do kingspan etc. I will speak to knauf tomorrow.
    • CommentAuthorMarkyP
    • CommentTimeSep 3rd 2017
     
    if you do start again with the outer skin, give yourself a bit more wriggle room and go with a 110mm cavity for 100mm insulation. If you are using dri-therm, it expands a good deal beyond it's nominal size so will soak up the extra space. At least mine did.
    • CommentAuthortony
    • CommentTimeSep 3rd 2017
     
    It. Is possible to corbel brickwork out and blockwork in to widen the cavity that you have to accommodate 100mm batts.
    • CommentAuthormarsaday
    • CommentTimeSep 4th 2017
     
    Spoke to knauf this AM and i need to use the correct size for the cavity made. So i can make the front wall bigger, but the sides will have to stay at 85mm. I will upgrade the internal insulation with 25 or 30mm rigid insulation between batons.
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