I am building a house in Brisbane (But have not ever lived there permanently). In my research about what insulation to use, I came across an argument based on research done in Townsville, that, in hot climates, foil insulation is preferable in ceiling insulation because it reflects heat and particularly because it has the unique property of doing this better one way than the other (ie stops heat from getting in from the roof cavity but allows any heat in the rooms below to escape at night when the weather cools off). It seemed to suggest that no insulation in the walls was better too - in the cause of allowing heat to quickly escape in the cooler night. Of course there were other necessities like shading the walls and managing window opening as well as good orientation.
Insulation in Hot Climates
(35 posts) (10 voices)-
dymonite69
MemberAussieSue,
You are on the right track. Brisbane has a predominantly cooling requirement. The main reason for overheating is due to direct solar radiation. Good radiant protection with shading of windows and walls and foil insulation will help. This components are mandatory.
Batts are useful if you need to prevent heat loss from cold winters or if you are often using refrigerative air conditioning. However the downside is that they inhibits heat loss at night during summer.
Window placement to allow prevailing cooling night breezes to flush heat can help mitigate this effect.
It is not recommended to go over R 2.5 batts (in addition to your foil).
The final decision is related to whether you can tolerate the winters in Brisbane without bulk insulation or if you intending to use AC a lot in summer.
Posted Wednesday 4 Aug 2010 @ 1:14:49 am from IP # -
termite
MemberCan't speak from experience re the insulation, but can offer other climate-relevant suggestions and observations:
Don't forget ceiling fans and through ventilation. The biggest enemy is the humidity, which doesn't let up at night. I manage mostly with the fans, though I use air conditioning when guests demand it. It's a hassle to shut the place up, and it's not well insulated anyway, so it warms up again as soon as the air conditioning is turned off.
I moved to BrisVegas three years ago, renting. The house has bars on the windows, probably the result of unnecessarily frightened tenants. Normally I would consider this ugly, but have come to appreciate the freedom of being able to leave windows open when I go out - so the house is much cooler than the glasshouse-effect of other places. Shade is vital - not just the windows, but as much of the surrounding area as possible. If you can, avoid paving and grassed areas in favour of tall shady trees. Where I am staying has deep verandahs north and south and awnings over the other windows - big benefit, though it is quite dark inside. Retractable awnings are even better, to let winter sun penetrate deeply. Also, if you can, try for an elevated (high-set) design on a concrete slab. Not only does it offer protection from flood (Brisbane has a large flood zone, check council maps on their website), it means any termite attack is more visible and you get the chance to funnel cool air near the concrete slab into your living areas. The old Queenslander design has a lot going for it, except for the maintenance cost of all that timber in a hot, humid climate. A highset design is also good if you're on the side of a hill, as it keeps your 'feet' clear of temporary waterways caused by heavy downpours (common problem).
Definitely consider a white roof. I can't for the life of me understand why there aren't more. The house opposite me has one and looks fabulous.Posted Wednesday 4 Aug 2010 @ 1:29:37 am from IP # -
aussiesue
MemberThanks for this feedback. My house is raised, white roof and will have variable shade pergolas on the north side, where the living and biggest windows are; fans in bedrooms and living areas. I hope to use completely natural ventilation and would love it if I needed no heating in winter. But I live most of the year in the tropics (outside Australia) so feel the cold even in Brisbane.
I am assuming I will therefore need to use some form of heating for a couple of hours at night (I have stayed at my sister's house in Brisbane in winter which receives no northerly sun and it is OK during the day but needs a little heating at night).
My questions are: 1.should I insulate the ceiling with bulk insulation in addition to foil and if so, on top of or below the foil? (I already have foil/bulk "blanket" immediately under the colorbond roof);and
2. Should I insulate the walls with bulk insulation (they are foil wrapped but immediately under the cladding with no sir space)?
Posted Wednesday 4 Aug 2010 @ 1:44:00 am from IP # -
termite
MemberThis has been a mild winter, I use a couple of ceramic heaters and switch off bars as required. Little of Brisbane has access to natural gas; lots of houses have gas tanks (expensive to refill etc).
Whichever insulation you select, make sure you can close off unused room space with doors or other thermal barriers, so that any heating is of a small volume, and can easily minimise draughts. Consider under-floor insulation.I keep thinking that we should be able to design houses whose insulation profiles change with the seasons - to be able to remove and add layers, rather than find something that will work perfectly for both heating and cooling. The trouble is in making such layers and their mechanisms weatherproof and durable.
Posted Wednesday 4 Aug 2010 @ 1:57:50 am from IP # -
dymonite69
MemberThe best configuration is foil under the roof, batts on the ceiling.
Batts under the roof means you will lose heat into the roof space (unless you plan living there then there is no point).
Foil on the ceiling will get dusty and lose its effectiveness.
Foil under the roof also acts as a vapour barrier to allow condensation to run to the gutters.
It seems your winter heating requirement is low. It makes sense to insulate the walls and ceiling equally rather than having good insulation in one part and none in another. e.g. R 1.5 to everything is better than R 2.5 to only the ceiling.
Posted Wednesday 4 Aug 2010 @ 2:01:36 am from IP # -
aussiesue
MemberThanks for the help. I think I have confirmed that it is the foil that does the job keeping heat out in summer and the bulk insulation is just for keeping heat in in winter. So basically it comes down to personal preference for either excess heat in summer due to slowness of cooling down at night because of bulk insulation; or slightly excess chill in winter due to warmth escaping through foil insulated ceiling and uninsulated walls.
Do I need oil insulation in the ceiling as well as the foil blanket under the roof?
Posted Wednesday 4 Aug 2010 @ 2:09:57 am from IP # -
Frateco
Memberaussiesue, having lived in brissy for 20 years, I can speak from experience that our winters are short - only talking about a maximum of 4 weeks in total (and that's not consecutively). You might get 2 weeks where the temp gets down to 5 deg min at night. My wife who hates the cold gets by with blankets and trakky daks when watching TV.
My advice is to focus on reducing heat and humidity. The humidity is a real issue in summer so plenty of window placement for breeze catching, ceiling fans and shading. Any western walls, shade as much as possible to stop heat transfer in with verandahs, plants, awnings. We live in an old 2 storey house with beds on western face and even tho we had ceiling fans, we had to put AC in to combat the heat and humidity at nights. The bedrooms catch no breeze so make sure your bedrooms are well shaded and can catch breezes.
personally, if you are not putting in AC, I would keep to a low R value on all walls and concentrate on getting the heat out quickly. Batts have a short time lag which means if they get heated up, the heat will transfer through it quickly into the room. So if your western wall is heated up in the arvo, expect your western room to get hot in the night hence our problem. You then need to get the heat out of that room.
have a look at website http://www.subtropicaldesign.org.au/. Here's a paper from the website that is a good initial read:
http://www.subtropicaldesign.org.au/images/stories/pdf/reference/TheNewQueenslander.pdf
Hope this will help you move into a great part of Australia.
Posted Wednesday 4 Aug 2010 @ 6:13:12 am from IP # -
aussiesue
MemberThanks Frateco. I will look at that website. Great advice from someone who actually lives in Brissie to favour heat mitigation over warmth retention. I'm wondering now though whether one bedroom (a western corner of the house = therefore with one NW and one SW wall) will be too hot and require A/C and if I should therefore insulate on that basis. I plan to try to create a microclimate in that corner using shade and shade plants, but maybe that won't be enough. The room is a "spare" so not used as a bedroom except for occasional guests.
Posted Wednesday 4 Aug 2010 @ 7:28:55 am from IP # -
aussiesue
MemberWell, I just re-looked at my BERS certificate and rang the certifier and found that I have to have foil under the roof, foil in the walls, R2.5 batts in the ceiling and R1.5 in the walls, unless I can think of some other way to get my 5 star energy rating under the model. So looks like I may not have a choice.
Posted Wednesday 4 Aug 2010 @ 7:58:33 am from IP # -
dymonite69
MemberI think these offer a very flexible solution:
http://www.shadecraftsman.com.au/retractable_shade_systems.htm
One could probably cobble together a system DIY.
Posted Wednesday 4 Aug 2010 @ 10:28:39 am from IP # -
aussiesue
MemberI was going with the cobbled together DIYs using pergola plus (maybe?) Naturereed or similar to roll up in winter along with deciduous vines. Once the vines grow I wouldn' expect to need the naturereed. (But I may use a roll up blind or second hand sail rolled up horizontally.
Posted Wednesday 4 Aug 2010 @ 10:38:45 am from IP # -
aussiesue
MemberMy BERS certifier informed me that it would be possible to get my five star rating with just foil insulation in the ceiling by using a special type of folded aluminium "batt" which has an R value of 4.5. It looks like I can do this (ceiling only) for approximately twice the price of doing the ceiling and walls with batts. But it looks like it might be a better option.
Posted Wednesday 4 Aug 2010 @ 10:47:16 am from IP # -
Frateco
MemberMake sure your retractible material is UV resistant or it will degrade rapidly. Have a look at the canvas with polymer coatings, the same they use on canvas awnings. I can tell you that there won't be many occasions in summer you will want it retracted - winter will be the best time.
Because "Mexican" design (ie BV with small eaves overhang, 2.4 eaves height design) has dominated here with project builders, a lot of deck designs now include a "flyover" roof where the roof of the verandah "flies over" the eaves and sits about 600 above the main roof. The idea is that it gives height to the verandah roof for fans and heat has a chance to vent up and out over the roof.
To capture north light in summer, you can have some clear UV retardant light panels (Laser Lite) installed. Not too many tho or it will get uncomfortably hot underneath.
Posted Thursday 5 Aug 2010 @ 3:43:59 am from IP # -
Frateco
Memberaussiesue, don't do too much for spare room. Remember it's nice they visit but you don't want them too comfortable !!! Have a look at retractable awnings (the ones that sit out from the window at ~30 deg) for those windows as well as window tinting. That should be enough to stop most heat. You can get retractable awnings that are foil-backed.
Talk to the certifier because if you have a ventilated roof (assuming you have a trussed roof) and have reflective foil sarking under your roof, you only need to add no more than R2.0 batts. Your white roof lets you reduce the required Rvalue by 0.5 which I'm sure he allowed for.
All the energy-efficiency software is based on southern conditions being factored down for "non-Mexican" conditions. Just make sure you ventilate your roof space and if you really want to go the hog, vent your rooms with motorised vents that have thermosettings. As the room temp increases say to over 25 deg, the room is forcibly vented to get the heat out.
Posted Thursday 5 Aug 2010 @ 4:04:39 am from IP # -
Frateco
MemberPS Just be aware that those motorised vents are noisy. They're like the bathroom exhaust fans - mine is an absolute jet roarer so much so my wife doesn't turn it on when she has a shower!!!
I only use the one in the living room when I come home and want to get the heat out of the house. On for 10 minutes tops and I notice the diff.
Posted Thursday 5 Aug 2010 @ 7:27:06 am from IP # -
aussiesue
MemberI am just building a basic kit home but have gone to great lengths to orient it to the north and changed where the glass areas are to suit the orientation, added wider eaves and pergolas etc. So the BERS rating was done on the basis of the house unrelated to the site plan or the roof colour (since that wasn't specified, although maybe "light colour" was). I get the impression there is a basic formula used by certifiers (at least in cases like mine where the plan is submitted by the kit home supplier) which ends up with "R2.5 insulation to the ceiling, R1.5 to the walls and ceiling fans" (which, together, seem to be weighted most heavily in the model - at least the model I've played around with). I don't mind insulating with bulk insulation in this way, (and this is certainly the simplest, and right at the moment with lots of specials about, the cheapest) just as long as I don't make the heating in summer situation actually worse. (I am assuming that when they say R2.5, R1.5 etc in the BERS star rating report that they are referring to bulk insulation...???)
Posted Friday 6 Aug 2010 @ 5:22:45 am from IP # -
ghostgum
MemberWhen they say R2.5 it usually means bulk insulation. But the problem is that (at least previously) the energy rating program didn't handle reflective foil insulation well. Foil would be R1 up, R3 down. Bulk R3 would be R3 up, R3 down. As written above, you want a reflective foil layer under the roof and in the walls, particularly in northern states.
Posted Friday 6 Aug 2010 @ 6:13:57 am from IP # -
aussiesue
MemberGhostgum, do you know if it matters that the foil that was wrapped around the outside of the studs has no air space between it and the cladding? I'm assuming this foil is there for some insulating reason and not just as a moisture barrier. Would I find an R value for such a foil somewhere?
Posted Friday 6 Aug 2010 @ 6:24:27 am from IP # -
dymonite69
MemberKeep the issue of "r values" for foil separate. I'd wish they remove it from industry usage. Foil simply acts as a radiant barrier in summer. It's R value is trivial for preventing winter heat loss.
You should only consider the R value of the batts for winter loss.
The shiny side should not touch anything. It needs a one inch gap. But it is ok for the non-foil side to touch something.
Posted Friday 6 Aug 2010 @ 7:22:04 am from IP # -
ghostgum
MemberRFL usually has foil on both sides, with one side also covered by an anti-glare layer, so the builders don't see sun spots on their retina as they install it.
It's better if it has an air gap on each side. In my house the wall RFL will (unfortunately) have the wall batts partly or mostly pushed against it.
Posted Friday 6 Aug 2010 @ 7:50:55 am from IP # -
dymonite69
MemberHigh reflectivity/Low emissivity is a SURFACE property. Cover it up or have something in contact with it and it is lost. The anti-glare side is only about 85% reflective versus >99% on the shiny side. A mirror is no longer a mirror once it is misted up. A mirror doesn't reflect if something is touching it.
Posted Friday 6 Aug 2010 @ 9:32:43 am from IP #
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