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Housing - Renovation: shallow pitch roof insulation

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    • CommentAuthormitchino
    • CommentTimeJul 3rd 2007
     
    Our house was originally built as a single storey cottage with a 45 degree traditional slate roof. In the 1970s it was extended out perpendicular to the ridge to form two storeys, one side just has a dormer running the full length of the roof with a flat felt roof, the other side extends out 15ft and has a pitched roof perpendicular to the original ridge covered in felt. The pitch of this roof is very shallow - approx 10-15 degrees. The area under this section of the roof is approx 30 sqm.

    I want to insulate the roof, but I'm unsure how to tackle the shallow area. The roof extends beyond the edges of the walls about a foot, but there's only about 200mm between the tops of the walls and the roof. I can't even crawl all the way to the eaves. I don't want to compromise ventilation, but I'd like to get as much effective insulation in there as I can. At the moment there's a mess of old bits of carpet, ancient bits of rockwool and vermiculite spread here and there.

    I was thinking about using 150mm of space blanket all over the area, then adding another 200mm in the centre area farther away from the eaves. Or would I be better looking at incorporating an isofoil or aerogel layer?

    To be honest the roof really needs rebuilt, but we can't afford that for the foreseeable future, and I want the coming winter to be cosy, and to save some money on our current annual heating oil bill of nearly £2000.
    • CommentAuthortony
    • CommentTimeJul 4th 2007
     
    Some heating bill!! how much floor area are we talking about?

    I would do a careful job with fibreglass missing no bits out but only after I had tackled draft proofing first. It is very difficult to do any kind of a decent job with sheet insulation and the gel stuff definitely needs to be built in.

    What insulation is in the walls? is there a clear air path under the first floor to outside? and what is in the flat roof bit?
    • CommentAuthordave123
    • CommentTimeJul 4th 2007
     
    I had a similar problem to yours.
    Our House starts off at the front, 18th-century (even though it is very shallow pitch I had no problem insulating it).
    Behind that is an extension built at round about 1900, this one I had a problem with as there is no access to the shallow pitched roof whatsoever.
    I ended up taking out some of the plasterboard ceiling ,and using a long pole managed to push the installation into place. I cut the plasterboard in the middle of each joist (three joist worth) and was able to refit it, without being able to tell where it was cut.
    Hope this helps.

    Regards Dave
    • CommentAuthorSaint
    • CommentTimeJul 5th 2007
     
    Phew, That's some heating bill!

    Dave's solution sounds the easiest depending on whether you fancy skimming the new plasterboards. When I did a similar job years ago luckily patterned Artex was still in vogue, my plastering certainly wasn't.
    For a thin solution in that case you could buy aerogel fleece bonded to plasterboard to avoid the potentially visible thermal shunts against the ceiling joists and even stuff up some lighter insulation between the joist prior to refitting the plasterboard.
    If you don't want to remove the exeiting ceiling then Aerogel actually comes not as a gel but in a fleece form, like a heavy blanket. Brand name is Space Loft and is available in 3mm, 6mm and 9mm thicknesses. Thermal performance is genuinely (as tested and proven) 3 or 3+ times that of mineral wool so you need a third maybe a quarter of the thickness. Pricing ratio is somewhat more that that but in some applications its the only viable solution.
    Roll widths of Space Loft are 1.4m and rolls are 50mm to 100mm in length dependent on thickness so you would be able to cut convenient sizes so minimising joints and thus limit air infiltration
    • CommentAuthorSaint
    • CommentTimeJul 5th 2007
     
    That should of course read existing not exeiting and 50m and 100m not 50mm and 100mm.

    How do I edit??
    • CommentAuthormitchino
    • CommentTimeJul 8th 2007
     
    Sorry, been away a few days - thanks for all the comments. Yes, our heating bill is ridiculous, but our house is a rambling two floor detached 5 bed, and we live near Edinburgh at an elevation of 800ft. The house was built in 1930 by an amatuer, and then extended in the 1970s by a bunch of cowboys, so good thermal design is absent! Space Loft sounds great, are there any UK suppliers you can direct me to? I don't really want to take down ceilings at this stage, as we may replace the entire roof in a few years time. I may just opt for spaceblanket, so I can hopefully easily remove it at some point if we rebuild. I reckon I could get 150mm thickness at the eaves, and double that laying crossways a little further in. Regarding ventilation, I know you're supposed to leave a 25mm gap all the way round, but could I get away with installing a couple of vents higher up in the gable above the insulation? Another idea I had was to install soffit vents in the overhangs and have short lengths of plastic ducting attached which could be squished between the insulation and the roof to bring air into the loft. Is that a silly idea?
    • CommentAuthorSaint
    • CommentTimeJul 9th 2007
     
    Space Loft is stocked by Proctor Group in Blairgowrie so not too far from you. Call them on +44 (1250) 872261 and they will advise you on that product plus many other ideas for your "project" through their techical desk

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