Insulating walls

Hi all,

I am hoping someone here is an insulation guru:)....my problem is that I am embarking on a major renovation here in coburg melbourne and with all the talk today regarding the future cost of energy I really want to get thebest possible insulation. Now I am putting on a weathboard extension and I had a mind to use aircell as the vapor wrap and then use something like bradford gold batts r2 ? My question is this possible as the aircell requiress a 25mm air gap with the batt and I don't know or am not sure whether there is room enough?
Someone, anyone got an idea...clearly I am pretty shaky on this but then I am a nurse...not my normal area of expertise at all...thankyou...particularly if you can help with this.

To reduce heat transfer inwards the aircell [and any other reflective type] needs a gap between itself & the weatherboards which requires battening out the wall to provide at least a 20mm spacing.
R2.0 batts are about the most you can fit to a stud wall. If you're looking at a 25mm gap between the aircell & R2.0 to reflect heat in, then no.
You may need to take into account in your calc's that the aircell figures are total R values for the wall not the product itself when working out comparisons

Thankyou for your response...since writing the above entry I have done some more research and my conclusion is that I have made a big mistake in not building or making allowance for reverse brick veneer....I had never heard of thermal responsivity and how important or superior reverse brick veneer is..if anybody is interested and if anybody hates/dreads the heat like me or extremes of temperature...then brick is the way to go it seems. Oh well I guess next time....

Good that you're doing research and all, but in reality you will find that having simple batts in your weatherboards will do a very decent job.

What you will find is that the weak link will be your windows, floors and roof. Roof heat problems are easily fixed by batts above the ceiling, then it's your window seals (gaps), then type of window panes and screens/blinds, then your floor (for older houses, gaps a plenty in the skirtings and even floorboards, then the floorboard thickness themselves).

If you have basic batts in the walls, that is the least of your worries.

Research...no I would unfortunately describe it more as an obsession!!!:C Ok I have decided to put r6 silver batts in the ceiling directly on top of the old insulation, all external doors and windows (double glazed and wood) to have seals, the floor will have hardboard underneath it and all north and west walls will have external shading (boston creeper on trellis). I will have airconditioning and hydronic heating in the house hence the emphasis on airseals...I almost forgot draughtstoppers will be placed on all vents etc.

No it is the walls I am having a great deal of trouble with...the rfl is great as a radiant barrier but I want something that will also have a reasonable acoustic barrier qualities. It really is a pity we have such small house frames cause then you could have a radiant barrier together with the required 25mm air gap and then have a polyester batt. Anyway I think I will just settle for a bradford polyester r2 batt.

I was also in same quandry but came up with simple and novel solution.

I installed as external wall cladding normal roof grade zincalume.
Behind that normal sarking
Behind that a concertina foil bat
behind that another concertina foil bat.
Wall insulation I guess is close to R5 with all windows draft sealed and low e glass.

That particular wall gets all the hot afternoon sun from approx 1pm till dusk and yesterday the room was at a balmy 21 degrees...with no airconditioning! Funny when my wife opened the windows at 8.30pm the temp rocketed to 27 degrees very quickly.

I forgot to mention I also have the R6 foil tophat bats installed in the roof space. with roof blanket and then more zincalume.

An earlier room we reno'ed, we installed r2.5 in walls with sarking and r3.5 plus old pink bats on top in roof space and that room was approx 27 degrees yesterday.

And the temp yesterday was 39 with previous 3 days mid 30's with the next 5 also expected to be over 30.

That is awesome!!

No doubt in the future more people will place a second skin on their house and eventually the government will integrate it into their building standards. The present stud walls are just too thin for the amount of insulation required for today's environment...look at Adelaide.

Um, so you would subscribe to more is better...I was wondering have you ever experienced the 'hot box' effect?
I guess you don' have airconditioning..but if you do have you found that it works more effectively...you need only have it operate for a short period and then the room holds the lowered temperature?

yes more is better when it comes to insulation within reason. Remember foil works best to insulate radiant heat and bulk insulation works best for insulate convective heat. Usually summer = radiant and winter = radiant/convective.

Yes we do have split fitted and it is does not work all that hard, even on the hottest of days.

I would suggest install the best insulation possible, including around window reveals, draft proof your windows, and shade all of your external windows as well as possible.