Below is a thread from the Free.uk.trade.roofing Newsgroup where you can find
independent advice on all roofing matters.
Spray on Foam in the Roof space.
Can anyone tell me if this is a good idea, for the cost? I have been quoted
£3800 for a 3 bed-semi size house. Will I make this back in reduced heating
costs? Will the foam prevent condensation? Are there any potential problems
or worries? I am thinking it is a good product, but want impartial advice
before going ahead.
Thanks in advance.
David Macdonald
Is this sprayed under or over the slates / tiles David ?
--
Keith
under the slates from within the roof void, to form a white foam appearance
David Macdonald
I don't recommend spraying the foam inside the roof, it makes repairs later
almost impossible and stops the roof breathing.
Steve..
Spot on Steve. You ever stripped one of these roofs ?
Keith.
1. It will limit the cross flow ventilation into the loft, especially if
the foam carries down to the eaves. This can cause major condensation.
2. If you /whoever decides to have the roof stripped at a later date,
the costs will be hefty. No slate salvage, additional labour costs,
clear all the crap from the loft (been there !)
3. No remedial works can be carried out to the battens, rafters and
other timber works. (renailing, treating etc).
Don't know what area you are in, but surely £3800 isn't far short of a
strip and reslate ? Especially beneficial if the existing slates are
Welsh or good condition foriegners. An underfelt (BS747 1F) could be
introduced at this time, as an insulation, in conjunction with over
fascia vents.
Keith.
I have discovered that a total stip and re roof would be less. BUT the
product I'm looking at comes with an underwritten 25 yr guarantee for the
whole roof, and I will also be saving on heating costs. I have been
previously advised to double up the insulation between the joists, but with
loft boards and compressing of fibreglass will remove the air, and hence the
insulation qualities. This means that with a new roof, with breathable
qualities, I will still be loosing a lot of heat through the roof.
David Macdonald
Sounds like the salesman has really done his bit on you.
I agree with previous posters and would not have this product fitted. It
is the house you need to insulate not the roof.
Your money would be better spent re-roofing and investing in thicker
loft insulation. I would lay 100mm between the joists and another 150mm
crossways across the joists and either fit breathable felt or put vents
in the soffit to let the roof breathe.
Danny Burns
www.buildsure.co.uk
[snip]
> I have discovered that a total stip and re roof would be less. BUT the
> product I'm looking at comes with an underwritten 25 yr guarantee for
the
> whole roof,
Does it guarantee the cement mortar and lead details ?
You haven't stated the age of your property, but guess it's a 1930's
style. Typically this would have at least one valley, and probably
cement mortar hips,ridges, and/or verges (gables). If the valley(s)
still have the original lead, it might be 70 years old. Replacement of
this lead would be totally impossible.
Suggest the guarantee would only be for the foam falling off, and the
slates slipping ? Is there any indication of the additional weight ?
>and I will also be saving on heating costs.
What would you expect ? At £50/quarter (optomistic) it would take <get
calculator> 19 years to recoup !
I have been
> previously advised to double up the insulation between the joists, but
with
> loft boards and compressing of fibreglass will remove the air, and
hence the
> insulation qualities. This means that with a new roof, with breathable
> qualities, I will still be loosing a lot of heat through the roof.
Some confusion here;
The warm air in the roofspace is no longer of any use to you.
(unless it's for a 'warm roof' ie loft room) you need to get rid of it.
For a 'cold roof' the answer must lie in the insulation at upstairs
ceiling level. Even loft boards have an insulation value.
BTW, I believe the work only takes 2 days ?
I have no idea on the cost of the foam, but am seriously considering
changing my company name from Hampshire Roofing Services to Hampshire
Foam Services ;-)
Keith.