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new build one and half storey: roof insulation

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  • 09-01-2010 9:22pm
    #1
    bb12
    Registered Users Posts: 881 ✭✭✭


    i've been reading loads about attic insulation, roof insulation etc but i still can't find the definitive answers to my question re: roof insulation in a one and half storey house.

    what would be the standard spec for this in a new build? ie one that would satisfy current building standards?

    my builder so far has offered me the choice of:

    rafters: 150mm moy metac insulation plus 50mm thermawall slabs (38mm insulation + 12mm plasterboard)
    or the option of using 100mm Kingspan Thermapitch TP10 as an alternative to the moy insulation

    flat ceiling above rooms:150mm fibreglass between joists + 250mm laid over joists: total = 400mm

    would this be enough for current building standards do you think?

    also how is the insulation usually installed in one + half storeys? ie
    is the norm to insulate the rafters from the eaves to the ceiling level of the upstairs rooms and then go across the ceiling joists? therefore the floor hatch area between the rafters and the rooms would also be insulated.

    or is the square of the rooms just insulated ie. the outside of the room walls and the ceiling joists therefore having no insulation in the rafters and therefore the attic space in the hatches would not be insulated...

    hopefully you can understand what i mean..or if anyone has any useful links which would explain this type of roof construction and insulation clearly that would be great. i find the homebond manual pretty useless for this.


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    #2
    Poor Uncle Tom
    Registered Users Posts: 14,547 ✭✭✭✭Poor Uncle Tom


    bb12 wrote: »
    i've been reading loads about attic insulation, roof insulation etc but i still can't find the definitive answers to my question re: roof insulation in a one and half storey house.
    That's because there is no one definitive answer, every house and spec are different and dependant on the specifier/designer.
    bb12 wrote: »
    what would be the standard spec for this in a new build? ie one that would satisfy current building standards?
    There are many more then one combination that would satisfy the Building Regulations.
    bb12 wrote: »
    my builder so far has offered me the choice of:

    rafters: 150mm moy metac insulation plus 50mm thermawall slabs (38mm insulation + 12mm plasterboard)
    or the option of using 100mm Kingspan Thermapitch TP10 as an alternative to the moy insulation
    Both of these alternatives work well. Personally, I prefer the first, but that's just me. The 50mm breath space between the insulation and the felt is very important, this means the rafters in the first example would have to be a minimum of 200mm deep and 150mm minimum in the second.
    bb12 wrote: »
    flat ceiling above rooms:150mm fibreglass between joists + 250mm laid over joists: total = 400mm

    would this be enough for current building standards do you think?
    This is acceptable. Remember, when you are layering quilt insulations run alternate layers at right angles.
    bb12 wrote: »
    also how is the insulation usually installed in one + half storeys? ie
    is the norm to insulate the rafters from the eaves to the ceiling level of the upstairs rooms and then go across the ceiling joists? therefore the floor hatch area between the rafters and the rooms would also be insulated.
    This is how I always specify it.
    bb12 wrote: »
    or is the square of the rooms just insulated ie. the outside of the room walls and the ceiling joists therefore having no insulation in the rafters and therefore the attic space in the hatches would not be insulated...
    Not how I specify it.
    bb12 wrote: »
    hopefully you can understand what i mean..or if anyone has any useful links which would explain this type of roof construction and insulation clearly that would be great. i find the homebond manual pretty useless for this.

    http://oee.nrcan.gc.ca/residential/personal/new-home-improvement/choosing/insulation-sealing/roofs-attics/khi-halfstorey-attics.cfm?attr=4
    Read this link for information only, as it is Canadian it has no direct bearing on our Building Regulations.


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