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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.

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    • CommentAuthorCharli
    • CommentTimeJun 13th 2019
     
    My 1905 year old slate roof needs some work doing.. quite a lot of work. More slates are held on with bits of wire than are actually nailed on! Ridiculously complex roof with plenty of valleys and ridges (though on the image- only the front half of the house is mine!)

    The top floor of the house protrudes into the roof by 1.2m with sloped surfaces. These are insulated internally with 50mm of PIR. There is also 250mm of mineral insulation in the loft on the flat portions of ceiling. There are cold bridges where the wooden joists block the mineral insulation but aren't sloped to be covered by the PIR. I should have put PIR on the flat ceilings too.. but hindsight...

    So given I'm going to get the roof redone anyway- what can/should I do to further insulation? Currently it's just slate- no felt. Joists seem sound, cross battens (I'm not very good on roof terminology, sorry!) really all want replacing I'd say. Lead valleys seem watertight, some of the chimney flashing needs redoing (there's 3 chimneys). Most roofers will strip slate off, replace wood, put felt and slates back on. But then I might be missing a chance to insulate further and I'm of the opinion that you probably can't have too much insulation.
      roof.PNG
  1.  
    This link (https://www.oadby-wigston.gov.uk/pages/recovering_of_existing_roofs_and_the_building_regulations) gives a good indication of what you *have* to achieve. If you don't (unless practicalities warrant a waiver), you won't be complying with Building Regs Part L1B.
    • CommentAuthortony
    • CommentTimeJun 14th 2019
     
    Redo all leadwork

    Re use the slates they look like good ones ally or copper nails

    New battens,
  2.  
    When we stripped our roof, we fitted TLX Gold multifoil insulation on top of the rafters (this is a breather membrane and mutifoil in one product, with a 75mm air gap and 25mm celotex between rafters and 100mm celotex beneath the rafters.

    If you use TLX Gold (and I would have a look at it if I were you) then make absolutely sure that your roofers follow the instructions and seal all of the edges or you'll lose the benefit of air tightness.

    http://www.tlxinsulation.co.uk/tlx-gold/tlx-gold.aspx

    Once the insulation was fitted, we plastered the underside to make it a little more airtight and to prevent damage to the insulation by moving boxes and whatnot up in the loft.

    I'd agree with Tony and redo all of the leadwork - it's false economy to keep the old stuff. You don't want to have to do the roof again.
  3.  
    Posted By: Pile-o-StoneWhen we stripped our roof, we fitted TLX Gold multifoil insulation on top of the rafters (this is a breather membrane and mutifoil in one product, with a 75mm air gap and 25mm celotex between rafters and 100mm celotex beneath the rafters.


    Woohoo! Multifoil is still alive! How I miss that thread ;)

    Paul in Montreal.
  4.  
    I think it won the page-count award hands-down, Paul!
    • CommentAuthorCharli
    • CommentTimeJun 17th 2019
     
    I think I'm asking the wrong tradesmen- they've all looked at me like I've got a second head when I ask about insulation. They're more than happy to just 'redo the roof' as in replace battens/leadwork/etc but don't want anything more complicated.

    Something along the lines of TLX gold, some PIR between rafters (I've no idea what size the rafters are actually, will have to go up and measure) and if necessary some underneath (there's already 50mm on the room sloped surfaces) would be ideal (can't change the roofline- conservation area!).

    Oh, and to find a roofer willing to fit this stuff properly! I draw the line at dancing around on the roof for DIY.
    •  
      CommentAuthordjh
    • CommentTimeJun 17th 2019
     
    Posted By: CharliOh, and to find a roofer willing to fit this stuff properly!

    Where are you? Somebody may have a suggestion.

    A quick search indicates the NFRC https://www.nfrc.co.uk/ might be a place to look to find 'reputable' contractors, but I've no personal experience to back that up.

    I wasn't clear from your original post exactly what your situation is and where the insulation is in regards to ventilation? It seems like your roof is 'cold' and the insulation is at ceiling level, so is a completely separate job?

    There's no point in putting insulation above a ventilated space, so we need to be clear what the situation is and is intended to be.
    • CommentAuthorCharli
    • CommentTimeJun 18th 2019
     
    I'm in Derbyshire, if anyone has any suggestions :)

    Currently the loft is cold- in that the insulation is in the flat ceiling. However the upper floor of the house extends up into the roofspace- these sloped bits of roof in the upstairs rooms are internally insulated (with 50mm PIR). And there are cold bridges where timber exists between the two types of insulation.

    I can have external-access to the roof, and internal access to the loft- however the actual loft is only 1.4m tall so you can't really work in there. Thinking about it I can't see how I could attach sheets of PIR in there- you wouldn't be able to maneuver anything! And it is a really complex shape.

    I was hoping I could increase the insulation of where the rooms protrude into the roofspace from the external of the roof.

    I'm in a conservation area so I can't change the roofline- but may get away with less insulation than the regs mention if it is impossible to fit it.

    The council outsource all building regs work to an external company, who won't talk to me until I give them money. But given they haven't said they can help with what I am asking, I don't feel inclined to give them money quite yet.
    •  
      CommentAuthordjh
    • CommentTimeJun 18th 2019
     
    Posted By: CharliCurrently the loft is cold

    And presumably ventilated?
    • CommentAuthorCharli
    • CommentTimeJun 19th 2019
     
    Posted By: djh
    Posted By: CharliCurrently the loft is cold

    And presumably ventilated?


    By the massive gaps between the slates, yes!
    • CommentAuthortony
    • CommentTimeJun 20th 2019
     
    Reroofing triggers part L1b of the building regulations and though never enforced the require the insulation to be upgraded as part of the works.
  5.  
    Yep!

    Charli, are you only prepared to do insulation on the 'cold side' - in the voids where it won't have to disturb ceilings etc.? Are you going for 'best you can', or have you got an overall Plan? How about drawing it out, estimating U values (or calculating - it's easy) for each area, and looking for 'weak spots'? Don't forget to calculate (and discount for) the timber fraction (the amount of the 'insulation' that's wood).

    I would not use multifoil, by choice. I don't claim it's the makers' fault, but I have seen it used wrongly, and where I have seen it used in conjunction with PIR the much-discussed space-gains (or reductions in losses) have seemed minimal. If I were using PIR ( or Pu) anyway, I'd probably just use more.

    Watch out for potential thermal by-pass between layers of insulation where the ventilation enters at the eaves. Consider a 'deflector' of breathable membrane.
  6.  
    We got more interest from joiners than from roofers about insulation.

    You could get the roofer to strip the slates, the joiner to fit PIR between the rafters in the sloping-ceiling area, working from outside and leaving ventilation gap, then the roofer back to replace the membrane and slates.

    Best select one trade eg roofer, then get them to recommend a joiner they frequently work with, as they'll need to coordinate timings and keep each other's work dry. Roofer has to organise scaffolding (ours was keener to work from a ladder!)

    For the small triangle attic area, just add lots more mineral wool on top of the ceiling, joiner does this later, or DIY. Maybe need to add ventilation slates to compensate for loss of gaps between slates. (Edit: this would often be done with vents in the soffits, but you hardly have any soffit between the windows! Do you need any work on the timber, repairs to fascias bargeboards etc? Joiner does this while scaffolding is up. Take opportunity to paint?)
    • CommentAuthorCharli
    • CommentTimeJun 21st 2019
     
    Posted By: tonyReroofing triggers part L1b of the building regulations and though never enforced the require the insulation to be upgraded as part of the works.
    I'm in a conservation area, so if I can't physically fit enough insulation in I can apply to not have to meet the building regs. No idea if the council would accept this or not.

    Posted By: Nick Parsons
    Charli, are you only prepared to do insulation on the 'cold side' - in the voids where it won't have to disturb ceilings etc.? Are you going for 'best you can', or have you got an overall Plan? How about drawing it out, estimating U values (or calculating - it's easy) for each area, and looking for 'weak spots'? Don't forget to calculate (and discount for) the timber fraction (the amount of the 'insulation' that's wood).

    Only prepared to do the cold side at this point- the inside was 'done' 6ish years ago. I have no plan, other than I wanted some ideas to propose to roofers to make sure 'something' was done. So far they seem happy to do nothing- which I don't want!

    Posted By: WillInAberdeenWe got more interest from joiners than from roofers about insulation.

    For the small triangle attic area, just add lots more mineral wool on top of the ceiling, joiner does this later, or DIY. Maybe need to add ventilation slates to compensate for loss of gaps between slates. (Edit: this would often be done with vents in the soffits, but you hardly have any soffit between the windows! Do you need any work on the timber, repairs to fascias bargeboards etc? Joiner does this while scaffolding is up. Take opportunity to paint?)


    I'll try asking some other trades- good idea.
    There's mountains of mineral wool on the horizontal ceiling already (over 300mm)- but if I PIR the sloped ceilings then it might make sense to do the whole roof up to the peak (or it might not, I don't know!). There's big bits of timber at this junction that currently are a cold bridge (not at the eaves, but where the flat ceiling becomes a sloped ceiling- the mineral wool has to be clear of the wood for ventilation and the PIR doesn't start until under the timber).

    If there's a scaffold up I could potentially do the insulation myself. I wouldn't mind that.
    • CommentAuthortony
    • CommentTimeJun 21st 2019
     
    Best plan would be to DIY it and to do it well, you only need to do the sloping ceilings
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