Reasonable Insulation Requirements KDRB

Howser · Jan 07, 2019 9:35 am

Hi All,

We are looking at doing a KDRB, approx 45sq house double storey in Melbourne.

We have had an energy report back and the values seem crazy - R6 in ceiling, thermally broken windows with U Values of 2.90

The is quite a bit of north facing glazing (but shaded), minimal west facing. Does this seem extreme?

alexp79 · Jan 08, 2019 4:12 pm

Well, U=2.9 is not that crazy for standard double glazed set ups.

R6 in ceiling is well above minimum recommended values for your climate zone (which is 4.1), but probably has something to do with the size of the house and its orientation.

But Melbourne is quite chilly in winters, so I wouldn't be bothering too much about having this extra insulation in place.

IMHO double glazing should a must rather than "good to have" for Melbourne, too.

Howser · Jan 09, 2019 7:13 am

From what I can see 2.9 means having low-e on one side at the very least, with tints and wooden frames - that starts to get expensive.

Im going to speak to the energy assessor and see what he says.

Either way - how does performance of the glass get examined; does the building surveyor look at the documents from the window company?

alexp79 · Jan 09, 2019 1:31 pm

Howser

From what I can see 2.9 means having low-e on one side at the very least, with tints and wooden frames - that starts to get expensive.

Im going to speak to the energy assessor and see what he says.

Either way - how does performance of the glass get examined; does the building surveyor look at the documents from the window company?

Well, from my point of view, it is better to invest in better things when you build the house.

Double glazed windows will increase thermal comfort in the house, acoustics and will also reduce your energy bills.

There are many options available including importing from China. I know that ECOECO on forum here can offer good quality double glazed windows at reasonable prices. I believe you should be looking into roughly between $300 and 400 sqm for thermally broken aluminium frames with Loe E glass, it is definitely a bit higher than single glazed, but to compare, the best performing windows you can get in Australia with U values under 1.0 cost over $1,200 per sqm.

I am not sure if wooden frame is the way to go, though. Timber being timber has its own problems. You can always go for power coated aluminium which will look like timber if you are caring about the looks.

Yes, if it is in your KDRB, they would have to check windows specs/WERS data with your window company/installer.

JB1 · Jan 17, 2019 4:30 pm

Even if you only need R4.

It makes sense to go R6 as the cost isn't much more.

Note R2.7 is much more expensive than R2.5 in the walls.

You don't have to go thermally broken windows to get U Values of 2.90.

As mentioned, ECOECO offers good value windows. Their Awning windows with Low-E glass has a U value of 2.8.

Also add decent wall wrap and sarking, that may reduce your insulation and window requirement however as an owner builder why not use the money you save upfront to upgrade your insulation/windows. You'll save money in the long run and also be more comfortable.

JB1 · Jan 17, 2019 4:33 pm

I must say, I'm super impressed with Low E glass.. make a big difference to the Summer heat with West Facing windows.

Howser · Jan 18, 2019 7:55 am

Thanks for all the feedback!