Costs v's Benefit of Upgraded Insulation/Sarking to New Home

I'm in the process of building of new home (30sq, concrete tile roof, brick veneer, Western Sydney so gets hot and cold). What's the general concensus on :

1. Sarking - not provided as standard by builder. Need to pay extra.
2. R2.5 batts standard. $600 to upgrade to R3.5.
3. Extra to cover double garage with batts.

Any opinions on whether it's noticable to upgrade batts, cover garage and include sarking?

My gut feeling is that is will, but that's just it - only a gut feeling. I currently have cellulous fibre in my old house but not the garage, and the roof cavity gets really hot in summer - don't know if the fibre is ordinary or it's the fact that the garage isn't covered. It does a reasonable job, but only if you remember to "shut the house down" before you leave for the day - otherwise it's freezing or cooking when you get back.

Sydney is a mixed temperate climate. You need to both address heat gain in summer and heat loss in winter. Both sarking AND batts will be beneficial respectively.

Nominal recommendations for Sydney climate - R 3.5 ceiling R 2.0 walls

Insulation

Don't use the R value for sarking. It is a radiant barrier not a conductive barrier.

Insulation is a law of diminishing returns. A moderate amount makes a big improvement but adding more has a much smaller incremental value.

Going from no insulation to R 3 is a six fold improvement. But from R 3 to R 6 is only double that again.

Definately go sarking and insulation. It is extra but the cost you will save in your heating and cooling bills will pay for themselves in no time. You wont regret it if you go the full but you will regret down the track if you dont. I find it funny that the sarking isnt supplied - unless your building a project home? Sarking has other benefits also, not just insulating properties. Definately go the sarking. Definately go insulation. As for the garage, see what the extra is. If only a few hundred dollars I'd suggest do it.

Without knowing the configuration of the home & therefore to generalise - I would go for the RFL definitely. (I assume you're referring to the roof) R3.5 ceiling insulation to a max. of R4.0. No insulation to the garage ceiling but R2.0 wall insulation to the garage dividing wall(s)

Going by the insulation levels you've quoted as 'standard' I would assume that possibly the builder has allowed for R1.5 insulation to the walls. If this is the case upgrading this area to R2.0 would be my choice initially - you can upgrade the ceiling at a later date as you will have access.

Agree,

We've asked our builder to add RFL to our specs in addition to batts. All my research indicates that it will help with heat incursion in summer.

Another benefit for a tile roof is that it also keeps out a lot of the dust. Our 12 yo home in Perth has a tile roof and the ceiling cavity is coated in fine grey dust from sand blowing around during summer when it gets dry and windy.

PS forgot to add that RFL may have a bad name due to the problems of badly installed material. It can be fatal if not installed correctly - the foil layer is a good electrical conductor, so if it comes in contact with live wires you can have a fatality waiting to happen (eg stapled on top of electrical cables). A capable builder should ensure that it is installed properly.

Sorry SouthFreo I think we doubled up while I was editing my post.

Definitely showing my girly side here - what does RFL stand for? I know it's the silver/blue stuff I call sarking, but what does RFL actually stand for?

reflective foil laminate