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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthoromehegan
    • CommentTimeJul 16th 2021
    I live in Melbourne, Australia, and recently bought my first house. It's an 1880s brick Victorian with a slate roof. The house currently has no insulation at all in the ceiling/attic/loft (I'm an American living in Australia, please excuse any strange word or spelling choices!), so we're getting quotes to have some put in. The maximum R value available seems to be R6, so I had initially planned to just go with that, and some installers have recommended it. But one that I talked to asked first if we are planning any other significant renovations or insulation anywhere else. I said no, and he said that in that case the R6 insulation will likely only perform at an R4 level, so it may not be worth the extra cost vs. just putting in R4.

    As I mentioned, the house is brick, with no insulation either in the walls or floor (suspended timber with no access underneath, therefore no way to insulate there unless we pull up the old floor). I don't yet know if the walls are solid or cavity, so at best if they are cavity we could have bulk insulation blown in. The windows are all single-glazed, and I don't intend on replacing any of them in the near future, because they are in good working order and the old ones have been modified with draught-proofing so they seal tightly. After we get the insulation done, I plan to go through and seal up gaps everywhere that I can. I know there are a lot around the skirting boards and doors that need attention.

    So my question is, if the walls and floors may never have any insulation added to them, is it worth doing the R5 or R6 insulation in the ceiling? Or should we just do the R4 as this one place suggested?
    • CommentAuthorRobL
    • CommentTimeJul 16th 2021
    Hi Omehegan. Lovely place, Melbourne! Can get hot, never gets that cold really. From a physics perspective, every wall will transmit heat through it according to it’s area * U value = area / R. If you insulate the ceiling well, it will perform better, irrespectively of how well the walls are insulated. I’d also say that most of the cost of insulating is generally labour, so unless there are other factors involved I’d put in the thicker R6 stuff, which is I think probably around 250mm thick itchy stuff, assuming your R6 is metric. This is a green website after all:-)

    You can usually tell if your house has cavity walls by the brick pattern - cavity walls have brick pattern like ===, but take a look at the link it will be way clearer than my hieroglyphics.

    I expect floor insulation is less important in Melbourn, it won’t be a source of summer heat. Draughts wont help you though, so it’s worth sealing up cracks that air seeps out of, as well as into. Airtight and ventilate right - close up the house during the day, ventilate a lot whenever it’s cooler at night.

    As an aside, solar panels on your roof would likely drop the loft temperature quite a lot too, and give you free electricity. Am I right in thinking the insulation exercise is mostly about summer heat, as opposed to winter cold?
    • CommentTimeJul 16th 2021
    That last question is vital - makes a great difference. Also sub- tropical humidity, or not - excuse my ignorance
    Surely there are Australian Green Building website/forums where all this is well rehearsed for each region?
    • CommentAuthoromehegan
    • CommentTimeJul 16th 2021
    I'm actually thinking more about cold than heat. In winter it can get down to 0 at night, and with no insulation in the ceilings I feel like I'm just heating the great outdoors. In summer with brick walls and 3.6m high ceilings, the heat hasn't been as bad. Then again last summer (our first in that house) was relatively mild. I know there will be a benefit in all seasons.

    No humidity in Melbourne to speak of, we're quite far south.

    I haven't found an Australia-specific green building forum. There is a general renovation forum that I frequent, but there isn't much discussion of green building. I'm an engineer, I want to measure things rather than just guess or make assumptions. This seemed like the place to get help with that :)
    omehegan - Given that your winters are not that cold (relative term!) I would suggest insulating the loft with 200mm or a bit more with glasswool or equivalent and fixing all the draughts. Then perhaps secondary glazing. These will probably be the cost effective things to do. After that unless you can get grant support insulating walls and floors will never give a return on the investment. Even here where winter goes down to -18 C and can be below 0 for a few weeks the ROI on wall insulation makes it difficult to justify.
    Use the funds that would have insulated the walls to put PV on the roof, it will give a better ROI and reduce your carbon footprint
    • CommentTimeJul 16th 2021
    Hi Owen,

    I confess to being confused by your use of R values. Here in the UK we use only U-values, and I tend to think of R-values as something murricans use, and in really weird units at that. So it would be helpful to confirm what units you're using and ideally convert to U-values so they're easier for your readers to understand.

    I've been to Sydney and to Perth and to the Whitsundays, but never to Melbourne (other than the homonym village near Cambridge here). But it sounds like you have a somewhat warmer climate than here.

    I think the ceilings are a no-brainer. Put as much fluff in there as you can. (fluff is a technical term for glasswool, rockwool or plastic-bottle wool, or even sheeps wool). Easy to do yourself as long as you make sure any electrical cables don't overheat. I think the minimum here is 270 mm but more is better.

    Airtightness is the next priority but you need to think about ventilation at the same time. Airtightness is usually easier if you select the interior surface as the airtightness barrier (or close to the surface anyway).

    I would guess that a Victorian building is unlikely to have cavity walls but you need to check to be sure. We had cavity wall insulation in our last house but that was built in the 1970s and there was a government subsidy to get it done. There wasn't for double glazing so we didn't do that - the sums didn't add up.

    Local forums/mailing lists etc are likely to be most helpful since they better understand local conditions, regulations and suppliers etc. But I'm sure we'll do our best to help.
    • CommentAuthoromehegan
    • CommentTimeJul 17th 2021
    Thanks for all the input so far! I should have mentioned that I definitely will be doing PV in the next year or so, once other more pressing improvements are taken care of. Sounds like I should go for the R6 ceiling insulation and focus on the drafts.

    On the R values, this is the standard measure used in Australia for insulation comparison. We use the SI/metric version. I know the US uses an inch-pound/imperial measure with the same name but much higher relative values. See https://en.wikipedia.org/wiki/R-value_(insulation)

    Apparently U value measures heat transfer through a building element, such as a built wall with all materials included. Higher means more conductive, so worse insulation. R value is essentially the reciprocal, it's how well the material resists heat transfer. To convert between them, you just divide the value into 1. So my proposed R6 insulation would have a U value of .16. In Australia we seem to use U value to describe the performance of windows, but R value for all types of insulation.
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