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Green Building Bible, Fourth Edition
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Housing - Renovation: spray foam insulation & finance

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      CommentAuthordjh
    • CommentTimeJan 18th 2023
     
    Just to note that this week's Sunday Times had an article about mortgage problems after somebody had their roof insulated with spray foam (specifically Icynene, but the problem seems more generic). Apparently it can be difficult to get a mortgage, and practically impossible to arrange an equity release mortgage in particular. Paywall so no link sorry.
    • CommentAuthorLF
    • CommentTimeJan 18th 2023
     
    Earlier this year someone was trying to sell this to my elderly parents.
    Main issue is house surveyors cannot see the timbers in the roof.
    No ventilation on timbers, so if they do get wet it is trapped and they could rot ?? No 2 inch air gap to felt.

    I will look up its fire rating too.
    I am very anti the plastic silver foil "bubble wrap" type insulation as it is burns very easily.
    • CommentAuthortony
    • CommentTimeJan 18th 2023
     
    I am very anti insulation at rafter level, 40% more heat loss assuming the loft is airtight, significantly more if it isn’t

    Insulation at ceiling level for me
    • CommentAuthorJeff B
    • CommentTimeJan 18th 2023
     
    What a timely post! Only last week I was able to advise an elderly couple on this very subject. They had succumbed to one of those “we are in the area, so we can do you a special deal” spray foam insulation chappies. Unfortunately unbeknown to me they had already put down a £1K deposit using their credit card with a further £2.6K to pay on completion.

    When I talked to them in detail it seems that the promise of an IR survey of the house never materialised and the guy did not give them any idea of how much the foam would reduce the heat loss from the roof in terms of U value or Ă‚ÂŁ's per annum, except that it would be useful to have, if ever they wanted to do an attic conversion (which they have no intention of doing)! Apparently he made a big thing about closed cell versus open cell foam in that the latter is breathable and hence no worries about water being trapped against the rafters.

    I went up into their attic and found they already have approx 250mm of fibreglass up there which has been noted on the EPC. Some of this has been squashed with boarding and I advised that this really needs to be sorted. They don't store anything up there so not a major job.

    Finally, a classic comment from the guy: “it is very cold in your attic”. Er – isn't that how it should be mate, with all that insulation up there!

    Thankfully it was well within the 14 day cooling off period and it seems they got the deposit refunded quickly, which I was pleasantly surprised to hear to be honest.
    • CommentAuthorborpin
    • CommentTimeJan 18th 2023
     
    I'm a fan of Icynene but not on rafters in an already cold loft space!

    I used it on the frame internally and it helped enormously with airtightness. If done right minimal waste and I'd argue about the chemical impact v using miles of tape to seal things.
    • CommentAuthortony
    • CommentTimeJan 18th 2023
     
    Well done Jeff!
    • CommentAuthorkristeva
    • CommentTimeJan 19th 2023
     
    Posted By: LFEarlier this year someone was trying to sell this to my elderly parents.
    Main issue is house surveyors cannot see the timbers in the roof.


    Its interesting to note that plenty of old houses have no access to loft space and / or the timbers are covered with lath and plaster, so I've often wondered if being able to view the timbers was the full reason. I have two lofts and both are covered with lath and plaster, then again I was the first to cut access into the spaces.
    • CommentAuthorLF
    • CommentTimeJan 19th 2023
     
    <blockquote><cite>Posted By: tony</cite>I am very anti insulation at rafter level, 40% more heat loss assuming the loft is airtight, significantly more if it isn’t

    Insulation at ceiling level for me</blockquote>

    Presumably because the area is so much larger on a pitched roof so you need more m2 of heat loss area.
    • CommentAuthorrevor
    • CommentTimeJan 19th 2023
     
    More convenient to have insulation at rafter level as that is so useful to keep services from freezing (water tank) or causing condensation in MVHR ducting. I have insulation at ceiling level as well but this is part of soundproofing for upstairs bedrooms.
  10.  
    Warm pitched roof keeps the rafters warm as well.
  11.  
    Getting 25 - 30 cm of loft insulation at joists level is easy, more difficult at rafter level.
    Less insulation needed at joists
    At joist level there is less of an issue with air permeation through the attic.

    However

    At rafter level you have a much more useable loft

    Horses and courses.
  12.  
    Posted By: Dominic CooneyWarm pitched roof


    Obviously can only do this if re-roofing anyway (or new build)
  13.  
    Posted By: Dominic CooneyWarm pitched roof keeps the rafters warm as well.

    only if the insulation is over the rafters which is only possible at roof referb. time and may have ridge height problems. (not to mention expense).

    I had the impression that this was talking about retro-fit insulation - so between and below the rafters, but I may be wrong on this.
  14.  
    True. My bad, I guess I was just sticking up for "insulation at rafter level" but only because warm roof makes a lot of sense to me (and the last 2 places done had room-in-roof type first floors, so really benfitted from it)
    • CommentAuthorJeff B
    • CommentTimeJan 19th 2023
     
    Posted By: Peter_in_HungaryGetting 25 - 30 cm of loft insulation at joists level is easy, more difficult at rafter level.
    Less insulation needed at joists
    At joist level there is less of an issue with air permeation through the attic.

    However

    At rafter level you have a much more useable loft

    Horses and courses.


    Insulation at rafter level - yes certainly a more useable loft, especially if you intend to do a room-in-the-roof job. However I would opt for rigid insulation rather than a spray foam between the rafters (leaving the critical 25 or 50mm air gap above) and the whole overlaid with further rigid insulation boards.
    •  
      CommentAuthordjh
    • CommentTimeJan 19th 2023
     
    We have insulation at the top of our house (barrel vault so no 'rafters' as such) and having a vaulted ceiling upstairs is so much better than it would have been if we'd put a ceiling in (and insulated that).

    And yes the original story was all about retrofit. FWIW I considered Icynene myself but eventually went with Warmcel cellulose.

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