# Insulating attic with spray foam: good or bad?



## elenina (22 Sep 2011)

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


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## onq (22 Sep 2011)

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

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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.
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## IVORMAP (4 Oct 2011)

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


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## onq (5 Oct 2011)

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

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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.


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## elenina (13 Oct 2011)

*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


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## onq (13 Oct 2011)

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


[broken link removed]

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.


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## elenina (14 Oct 2011)

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


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## elenina (14 Oct 2011)

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


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## bluemac (14 Oct 2011)

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..


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