Is a double layer of r1.5 = r3

[Shannon Nash]

Gudday,

Some r1.5 batts advertised in a local auction (house lot unused). I have been told to use r3 or 3.5 in the ceiling of a house.

Is a double layer of 1.5 = 3.

The batts are wool (aparently better) so if they are equivalent as per calc above may have a look at the auction.

Would appreciate advice.

SN

[OBBob]

Its probably not the ideal way to go about it but the document at http://www.sustainable-energy.vic.go...on%20types.pdf seems to suggest that you can add R values to get a total.

Top of page 4 says - "Each of these components has its own
inherent R value, the sum of which provides the
overall R value".

This interests me a little because I wanted to upgrade old insulation and was trying to work out if you are better just to add new stuff over the top or remove the old stuff first.

One point is that it is very important to fit the bats well, which may be harder with 2 layers? Its usually the trapped air in the bats that insulates, so you don't want the air getting around the bats too easily.

[rrich]

Shannon,
An "R" value of 3 doesn't seem to be much at all. Here I have R 30 in the ceiling and R 19 in most of the walls. R 3 doesn't seem to be worth the effort IMHO.

Our electric bill with the A/C running was $157US last month. Next door neighbor with a slightly larger house (20%) had a bill of $630. I know that he has much less insulation than we do.

[OBBob]

The US 'r' values appear to be different to Aus by a factor of about 10 just looking on other web sites.

3.5 is a fairly standard ceiling spec here.

[elphingirl]

Hi Shannon

I also reckon you can additems together to get your total R value, as long as you don't compromise the way it is assumed that they will be used.In the case of a double layer of batts, be careful you don't compact them at all - then you won't receive the full benefit.

We put the wool batts into our house, except for some sound insulation, and they were so nice to deal with, no pricklies on your hands, it rips easily for shaping into specific areas (better than leaving gaps, or folding the batts), and no worries about inhaling crap into your lungs.

Cheers

[GraemeCook]

Your right Shannon; for batt type insulation just add the R-values together. This rule does not apply for reflective insulants though.

To convert from American to metric R-values you just divide by 5.68. Thus USA R30 = Australian R5.2.

I saw some of those wool batts at a home show and they felt lovely, almost cuddly. The only downside that I have heard is an allegation that rodents also like them.

Cheers

Graeme

[rod@plasterbrok]

Wool batts and Polly are much more comfortable to use but unfortunatly much more expesive.

Once they are in the wall or ceiling there is no benefit over glass.

I have had quite a few snoozes on poly or wool batts over the years and as a sometimes installer much prefer to use polly. But a a seller we sell glass wool 10 to 1 over polly.

Cheers

[rrich]

To convert from American to metric R-values you just divide by 5.68. Thus USA R30 = Australian R5.2.

Graeme,
Thank you for that! Now that I understand the real numbers, a value of 3 or 3.5 makes so much more sense.

[Markw]

Poly batts are supposed to be rodent free. The little bug**rs get their claws caught in the fibres and don't like that at all.

Just remember to wear good respiratory protection in your roof space. A standard P1 type disposable respirator (dust mask) is sufficient. That black dust up there will normally contain lead. It comes from raindrops collecting the pollutants out of the air as it falls when cars ran on leaded petrol. The water dries out but leaves the pollutants behind on your tiles and the wind blows it under the tiles.

[b1ueshift]

That's correct the R values add together. An R of 1 means one watt of heat transfer for each square metre per degree celcius of temperature difference. An R of 3 means one third of a watt of heat transfer for each square metre of area per degree celcius of temperature difference.

Naturally it's different in the US.

[Cobber]

The Australian standard I believe is 1.5R in the walls and 2.5R in the ceiling because thats what the builder will put into the extension currently being built. I'll probably add some more in myself what do you think?

[Doughboy]

With regards to insulation

Put in what you can afford... In Canberra i put R5's in my ceiling and looked at having the walls done as well. I was told by a number of people that insulating the walls of existing houses was not recommended cos it would pose a risk with electrics and so on, also I was told if you are planning on insulating the walls make sure you have your wiring sorted cos it will make any post insulation wiring very difficult indeed.

Hope this helps

Pete

[Doughboy]

Sorry I forgot to mention yes two 1.5's are equal in performance to r3's and if you put a layer of silver insulation over the top of the bats you will be able to get a better 'seal' therefore increasing the efficiency of the bats...

Pete

[Markw]

Et All
Don't rely on someone just saying "do what you think is right" - it just doesnt work that way.:mad: :mad:

Australian Standard 2627 - Thermal Insulation of Dwellings gives varying R values for where you live in Australia and these values change with the type of heating and cooling you have in your house. Obviously someone who lives in Cooma having heating only will be different to a house in Broken Hill with heating and cooling. These values are minimums you can always go more than, but less than is not worthwhile.

As to a risk with electrics for wall insulation what a lot of trash. Modern day cabling (post 1980s) is designed to be capable of withstanding burial in insulation such as bats. Especially when you consider the following:

Most houses built post 1970 were brick veneer and the thermal insulation is retained between the studs. For electricals using the dwelling's outer walls ie power points, light switches etc, the cabling should be running down between the outer brick wall and the inner wall created by the outer face of the studs. You only need to drill top plates on internal walls.

Remember you must not have the batts touch the outer wall if its brick veneer - leave an air gap - as this may wick in moisture. This is done in pre-existing houses by using packing tape stapled the the studs to support the batts.

Current housing being built must have insulation in the walls. Councils require that all new building works comply with AS2627. Your local council should be able to advise what the required R values are for your area and may save you having to buy the Standard - they have to be good for something after all the money you pay each year.

From my own experience, we just had major extensions done. The changes in the house as far as how cold or how hot it now gets compared to previous are enormous. I only wish that more of the old section of the house had the gyprock removed as I would have installed more R1.5 batts.

[GraemeCook]

Marks spot on with his references to AS2627.

But remember that the Standards are merely the legal minimum and have not yet been updated for increases in energy costs.

The real reason that you install insulation is:

*** To increase the comfort inside the house, and
*** To reduce heating and cooling costs.

I saw some calculations a couple of years ago that concluded that the optimal cost effective ceiling insulation for Melbourne and coastal Tasmania was R = 3.5. But energy costs have risen substantially since then, and are unlikely to fall. A greater insulation than R=3.5 is probably benefit/cost justified.

What you save by under-insulating you will spend on heating and cooling, plus interest. And you will not be as comfortable.

Cheers

Graeme