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Advice on insulating an attic space in old Queenslander cottage

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  1. #1
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    Default Advice on insulating an attic space in old Queenslander cottage

    Hi there,

    We are currently turning out attic in to a liveable space. I'm getting very confused in regards to insulating it and I'm hoping for some advice.

    Our house is an old Queenslander cottage. The space is roughly 8 metres by 8 metres with a steep pitched roof (close to 45 degrees I think). It is 2.7m at the highest point.

    We've put in a yellow-tongue floor over new structural beams. Batts were installed between the ceiling downstairs and the new floor. We've put in 4 skylight windows in the roof. The roof itself is galvanised iron. There is no existing insulation of any kind. The gable ends are old weatherboards.

    Before we started this project the space used to get incredibly hot. Now we have the floor down and can get up there easily we notice how much sound comes in to the space.

    So we want to insulate for thermal purposes and acoustic purposes.

    We're doing this project bit-by-bit as our budget allows. Ultimately we plan to have a bathroom and bedroom in the space.

    In terms of insulation we're planning on putting in 88mm R2.5-rated acoustic batts (Bradford SoundScreen, Australia's most trusted acoustic insulation - Specifications). Whe would install these directly under the roof. Later, once budget allows, we plan to plaster the area using Soundcheck plasterboard (Gyprock Soundchek plasterboard - Gyprock).

    I've had lots of different advice from various different people. Some people have actually said that the insulation I'm planning is a bad idea as it may trap condensation between the roof and the plasterboard which could rot the eaves (?!) and cause moisture damage to the plasterboard. We looked at 'anti-con' but I understand that can't be installed without taking the roof off, which I don't plan to do!

    Any advice appreciated.

    Thanks,

    Barry

  2. #2
    4K Club Member OBBob's Avatar
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    Insulation is a tough area. There are people on here that know a lot about it and hopefully that can guide you. A couple of comments ...

    How deep are the rafters?
    Is there no existing blanket or foil under the tin? This could be a challenge, it can be retrofitted from below for thermal purposes but that will not help drain condensation.
    There is a lot of discussion about whether sound rated insulation and plaster is worth the extra money ... or is it like the price hike that comes with putting the word 'wedding' or 'baby' in front of a a product?

    One key thing for sound is that it will find any gaps and undermine your whole plan, so whilst it's open it'd be worth filling any holes with filler, foam, etc. to help seal it out. The way I think about it is ... sit in your car (you don't need to be moving) and it's fairly quiet, open the window just a crack and all of a sudden you have all the outside noise, open it fully and you have only a bit more noise. The point being that the tiny crack let in the majority of the noise. It's not the whole solution but it's cheap and easy whilst the roof space is open.

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    Hi OBBob,

    Thanks for your quick response. The rafters are 100mm. It's a very old house so whilst there are in pretty good shape considering the age, there is a bit of variation in them.

    In terms of blanket or foil under the tin - there is absolutely nothing. We've been in the house for ~6 years now and it gets very cold in winter and very hot in summer!

    Also given the age and type of the house - yes there are lots of gaps. E.g. in the gables there are some pretty big gaps between some of the weatherboards. I was going to use some 'no more gaps' or similar to fill them.

    Thanks,

    Barry

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    Something else that may be relevant (I'm not too handy so please forgive me if I get my terminology wrong...)

    The horizontal battens are spaced at roughly 300mm. But the iron roof is not attached to all of them. There is a 'double thickness' batten approx every 700mm which the iron roof is attached to.

    So we did consider whether we could run 'anti-con' between these battens. The gap between the iron roof and the battens is ~30mm. I don't think that is enough space to install anti-con?

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    4K Club Member Marc's Avatar
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    Without getting into too much detail I think that you need to have a barrier for the condensation right against the iron roof, insulation between the rafters and then your ceiling.
    I am not sure what is available in your corner of the woods, but I would look for someone that can spray insulation foam against the roof from the inside. That way the moisture in your attic will not have a cold surface to condense against. Then you can fill with batts and nail your ceiling. I would stay away from plasterboard and go for plywood for the ceiling.

    Have you made provisions for the stairs? Remember that if you want to do this a liveable space, you need complaint stairs and will not be able to do attic stairs. Narrow or spiral stairs are OK if you call that non liveable, even if you use it for everyday afterwards. Otherwise the stairs need to be the right size and they will take up the good part of one room below. Probably the reason most folks stay away from attic renovations.
    “In the fields of observation chance favors only the prepared mind.”
    Louis Pasteur



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    4K Club Member OBBob's Avatar
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    Quote Originally Posted by Marc View Post
    ... and they will take up the good part of one room below. ...
    And often upstairs because they need to be central to achieve the headroom requirements.


    On the thick and thin battens, is it possible the house originally had tiles, which were replaced with tin at a later time?

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    OBBob - yes, someone has said to us that it is likely we had a tile roof at some point in the past.

    Regarding stairs / headroom, etc - we're not planning on getting the attic certified as a live-able space. Because of the pitch of the roof the room would have to be very narrow to get the required ceiling height.

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    Default Advice on insulating an attic space in old Queenslander cottage

    Quote Originally Posted by grizzlyscotsman View Post
    OBBob - yes, someone has said to us that it is likely we had a tile roof at some point in the past.

    Regarding stairs / headroom, etc - we're not planning on getting the attic certified as a live-able space. Because of the pitch of the roof the room would have to be very narrow to get the required ceiling height.
    Hmm... I guess you're aware that it's not really meant to be optional to certify it as habitable if you're using it for a bedroom and bathroom? It's up to you how you progress but carefully with insurance and implications of you plan to sell in the next seven years.

    It might be worth reading up on the habitable requirements because I think you can average the ceiling height across the room, which may allow you to achieve a feasible / legal design.

    Spray foam as Marc suggested might be a good option. I think there are even DIY kits if you're keen.

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