Insulating attic with spray foam: good or bad?

Discussion in 'Home energy' started by elenina, Sep 22, 2011.

  1. elenina

    elenina Guest

    Considering insulating our converted attic with spray foam under the roof tiles, has anybody heard of negative feedback on this practice? Or indeed positive one, worth the money in the long run?
    Thank you
     
  2. onq

    onq Former user

    Posts:
    4,401
    Whats the age and construction of your house and roof and what kind of foam were you considering?

    I haven't used foam insulation or specified it but I'd be concerned in relation to -

    - access to services after the fact
    - ease of follow-on repair if required
    - off-gassing during curing and afterward
    - possible increase of fire risk in attic (downlighters)
    - possible increase of fire spread in attic
    - compromising attic ventilation
    - compromising longevity of timber construction

    These are just a few of the issue that may arise, given the many problems that AAM get asked about in relation to quilted and warmboard-style insulation.


    ONQ

    http://www.oneillquigley.eu

    All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
    Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
     
  3. IVORMAP

    IVORMAP Guest

    i looked into same recently ,first point is you need a breathable membrane beetween insulation and underside of roof,it depends on age of house newer houses have it as standard older houses dont so you will have to retreo fit which add to cost otherwise its very good in that it also renders the attic airtight
     
  4. onq

    onq Former user

    Posts:
    4,401
    Unless there is a 50mm air gap between the insulation/membrane and the underside of the roof covering, the attic space may not be compliant. TGD F 2009 refers, Diagram 11 Page 28. As a minimum you need to vent moisture away.
    If the product is properly tested it should as a minimum have an Agrement Certificate and you should consult with a competent building professional to interpret this. Many of them are not written in plain English but Technospeak and require "translation".

    The spray on foam may not be fitted with a proper vapour check - this could result in a build up of moisture within the insulation, particularly if the "outer" side of it is not vented as noted above, which raises other issues in terms of compliance with Part L and C.
    So you may end up with a simple application of insulation which needs additional work in terms of venting away and vapour checking - it would be advisable to get all this costed beforehand.
    If the supplier is suggesting the foam is its own vapour check I would have that statement independently validated - if "seals" in the roof joists this could lead to dry rot issues.


    ONQ

    http://www.oneillquigley.eu

    All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
    Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
     
  5. elenina

    elenina Guest

    roof insulation

    thanks for your replies, we have decided to go for traditional insulation, in your experience is there a difference between using the fibre glass "wool" type (double layer, 12 inches thick) vs 100 mm of kingspan-type solid board (sorry I don't know the technical terms)? the builder we have contacted says it's the same, he supplies both so we can decide. he usually uses the fibre glass wool type.
    Thanks a lot
     
  6. onq

    onq Former user

    Posts:
    4,401
    I would strongly advise you use another builder.
    There is no comparison, especially if you are following the line of the roof.
    Lazy builders "fix" the quilt in position with wire and then plasterboard over it.

    The quilt-

    (i) sags on the wire without the plasterboard, and
    (ii) crushes with it in place and leave no ventilation space

    The lazy builder does this because its a lot of hard work cutting the boards and placing them between the joists.

    Some charge for doing this, but don't in fact do this at all.
    They face the joists with 38mm warmboard
    They also may fail to install the correct eaves and ridge vent details.

    You have to watch attic "builders" like hawks and ensure the correct vent details are installed to comply with TGD F 2009, P 28. Dia 11.

    ONQ


    http://www.oneillquigley.eu

    All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
    Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
     
  7. elenina

    elenina Guest

    Thanks, yes we have agreed with him last night to have the kingspan-type insulation instead, I'm glad we did it now!
     
  8. elenina

    elenina Guest

    one more question - is a 100mm-thick board ok/standard?
    Thanks!
     
  9. bluemac

    bluemac Frequent Poster

    Posts:
    287
    look at rafter loc it is cut to size and just pushes in... prob not that easy but having done it the other way unless your good at cutting the boards you end up with lots of gaps or thinner areas of board.... as i undrstand it you need 50mm gap then 100mm board with then insulated plasterboard 52.5mm below that. I have done it with just the 100mm in another building as i didnt have the extra 40mm head hight and although its not regs its very insulating.

    If you ring Kingspan technical they will tell you all the options and explain them in terms of price and what is best and why..