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Wall insulation: R-14.2 or R-22.7?

AussieAdrian | Posted in Green Products and Materials on

I’m after some advice on whether I should shell out the extra money to bring my walls up to R22.7. My all my walls are 3 inch concrete with no insulation at the moment. I am planning on having kooltherm k5 external cladding installed. This comes in R14.2 or R22.7. I currently have R22.7 batts in the roof. My house is located in Melbourne Australia, the local sustainable building guide recommend R15.9 for walls. The R22.7 is about 25% more expensive.  So I’m looking an extra $1500-$2000 for the 22.7. So do you think it is worth putting the extra money in for the 22.7 or save that money? Maybe put it towards double glazing or underfloor insulation? Note all R values are imperial not metric. PS. When is America giving up on imperial and joining the rest of the world on metric? It’s a pain converting everything but worth it for the good advice one this forum. 🙂

Edit adding metric R-values as it seems like lots of non Americans on this forum
Imperial.      Metric
R14.2.             R2.5
R22.7.             R4.0

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  1. Expert Member
    Akos | | #1

    Looking at the temperature profile in a mostly cooling dominated area with average winter timer temps of 10C, energy loss through your walls would not be much.

    My guess bumping up your walls from R14 to R25 would save little on heating costs and have no effect on cooling costs. Underfloor insulation would probably save little energy as well.

    You are better off on spending your money on getting the house air sealed. If this means new windows then go with low E double pane units.

    If you have larger east of west facing windows getting those shaded or replacing them with low solar heat gain units is definitely worth it. A cool roof and extra roof insulation might also be worth it.

    1. AussieAdrian | | #3

      Thanks for taking the time to look into my issue Akos. As far as Melbourne being a cooling dominated climate I'd have to disagree, we would only use our AC on 30 or so days. But we have the central heating on almost every day of winter. You can feel the coolth coming from the external walls on cold days.
      We are actually replacing our aluminium single glazed windows with double glazed low E windows at the same time as we get the external wall insulation installed.

      1. Expert Member
        Akos | | #7


        A concrete building with wallboard you are starting from roughly an R2 (Yankee units) building. This is why you need heat on what we would consider "mild sunny days" in Canada (as reference, my heat barely runs once outside gets above 12C).

        Once you insulate the house, your heat will use will decrease significantly, your AC use will stay about the same.


        Just checked your RH and day/night temperatures. Since the summer humidity is low and you have decent diurnal temperature variation, insulation+thermal mass of the concrete will help with reducing your cooling loads. Again, I doubt that extra insulation will help that much though.

  2. STEPHEN SHEEHY | | #2

    When are we joining the rest of the metric world? Give me a fortnight to think about it.
    Although buying a metric tape measure sure made building kitchen cabinets easier.

    1. AussieAdrian | | #4

      Converting to metric would make everything easier. Although 60 years after we changed from imperial to metric we still measure some things in feet and inches.

  3. this_page_left_blank | | #5

    $2000 for 55% more r-value doesn't see like much. The wrong side of the minimum recommended level is not where you want to be.

    Metrification is a long, slow process in North America. The building industry will probably be the last holdout. Canada has been fully metric for almost 50 years, and we still use inches for lumber and most building plan sets.

    1. Expert Member
      Akos | | #8

      Yes, but does that 55% R value increase save you $50/year or $250/year in energy cost. In a milder climate, I doubt it is the latter.

    2. AussieAdrian | | #10

      Just found this interesting article on diminishing returns on upping the R-value. So the 55% more R-value might only give me walls that perform 5% better. I'm really leaning towards the R14.2 as it seems to hit the right mark on return on investment.

  4. Expert Member
    BILL WICHERS | | #6

    Keep in mind that extra insulation and air sealing will also provide better comfort so don’t look at it strictly as a cost/payback type of decision. If you’re noticing cold walls already, then more insulation will help.

    Canada isn’t fully metric yet. My brother in law is a builder over there, much of the building materials are still in imperial units. Sometimes you even see goofy things like the attached pic for sliced bread. Apparently the thickest slice is too big for metric measurements ;-)

    I would love to see more metric measurements in the us. I work in the telecom industry and we have to work with both systems. Fiber optic cable, for example, is manufactured mostly in metric units, but often sold in feet. I have one vendor that gives pricing in meters but sells by the foot for example. I am constantly doing conversions.

    The automotive industry is mostly converted but they’re quiet about it. The electronics industry is similar (surface mount components are almost entirely defined using metric units). The building industry is almost entirely imperial units though, still. I’ll agree they will probably be the last to change over.


    1. AussieAdrian | | #9

      I guess my main concern is that there is no noticeable difference between the R14.2 and R22.7 in my climate, with my plans to upgrade the windows at the same time I'm looking at $20,000 for windows and insulation, so a $2000 saving would be very handy.

    2. Expert Member
      MALCOLM TAYLOR | | #14

      The mixture of measurements up here is an absolute mess. You buy weed by the gram. Want more? Then it's by the quarter or half ounce. The building code is entirely metric, but try and ask a yard guy where the 38 x 235s are.

  5. 300TTto545 | | #11

    I would save the $2000.
    The only argument against that is that solar is hard to come by in the winter so saving $1 in the winter is way more important than $1 in the summer. Your electricity costs in the winter will climb faster than the summer.

  6. CollieGuy | | #12

    For some of us it would be a tough call. I live in Canada and our 270 m2 home, built in 1968, had just R7/RSI 1.2 of fiberglass insulation in the loft and walls, which was presumably deemed adequate in its day and complied with local codes. When we took possession in 2002, we bumped that up to R60/RSI 10.6 and R22/RSI 3.9 respectively. Combined with various other improvements, our space heating costs are substantially lower and our home vastly more comfortable.

    It's hard to say what energy might cost five, ten or fifty years down the road, but we have no regrets with our decision to push things a little further than what might be justified at today's prices. If nothing else, we have the peace of mind knowing that we won't be forced to sell our home if our operating costs exceed future budgets.

    To put this in hard numbers, in the year prior to taking possession, the previous owners consumed 5,700 liters of fuel oil and 11,848 kWh of electricity -- over $7,500.00 CDN at current prices. In the past twelve months, marked by a colder than normal winter, we've consumed just under 200 liters and 8,844 kWh, a savings of some $6,000.00 in this one year alone. Obviously, our climates are very different, but for us, the additional insulation and other upgrades have proven worthwhile.

    1. AussieAdrian | | #13

      My house currently has no wall insulation just the concrete wall which gives almost no insulation, R 0.7 or RSI.06 or so. We also only have single glazed aluminium windows. I'm of the opinion now that installing the R14.2 /RSI 2.5 and replacing the windows with double glazed low E will make a huge difference and that bumping the walls up to R22.7/RSI 4 would only make a marginal difference.

      1. CollieGuy | | #15

        I don't disagree; what you say makes perfect sense. In my case, I wanted to reduce our home's energy requirements beyond what might be cost justified, and so I was willing to pay more for each kWh saved at the margin (akin to German engineers who question why anyone would want to use one screw when you can use twelve).

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