Insulation between ground and first floor?

[Cobber]

Hi,

Does anyone know if you should insulate between the ground and first floor?

Is there any advantages or disadvantages? Someone told me its not done for new homes but i have no idea?

Cheers

Cobber

[Greg Q]

If you are planning a first-rate job, then yes. There should be some kind of moisture barrier over the soil, and ideally a membrane between the floor boards and the insulation. (with good sub-floor cross ventilation this may be overkill.)

Installing fiberglass bats under a floor is a huge pain-There might be some kind of spray applied foam that would be better.

There are many aspects to good insulation...the floor is probably down the list after attic/walls/glazing/spray foam in gaps.

Greg

[Greg Q]

On second thought, the moisture barrier under the sub floor isn't nescessary in a climate like this...it IS important though where freezing temperatures are typical because of condensation saturating the fiberglass and ruining it.

Greg

[Cobber]

Thanks Greg. The sub floor is currently being built and the builder reckons they dont normally use insulation between the first and ground floor. I have left overs from when they ripped up the roof and am thinking about using them.

[Greg Q]

Builders don't normally do that because its hidden, and buyers don't know enough to ask for it. Most locally built houses are little better than tents when it comes to energy efficiency.

[Barry_White]

For your information insulating timber floors is now compulsory under the new invironmental requirements on all new homes and is in force for home additions over $100,000.00 and after June 2007 for additions over $50,000.00 and after June 2008 will be compulsory on all home additions.

Each home will have to earn 100 points under these new invironmental laws. More red tape.

[Greg Q]

Hi Barry...

What R value do the regs call for?

Greg
(who watched weatherboard being nailed to ripped and flopping tinfoil "insulation" just today.)

[Cobber]

Barry - I was referring to the upstairs addition which will have chipboard as I will carpet it but you raise an interesting point. My extension is over 100k and they are not going to insulate the ground foor under the tongue and groove timber floorboards. What do you insulate it with? Im interested because the builder has said they dont usually do it. He said the timber will sweat if you put sisalation paper underneath for example?

cheers

Cobber

[Barry_White]

Hi Barry...

What R value do the regs call for?

Greg
(who watched weatherboard being nailed to ripped and flopping tinfoil "insulation" just today.)

Not to sure on that but have heard R3.0 being bandied about.

Cobber

In answer to your question just using foil wouldn't suffice as it wouldn't come up to the R factor.

The proper way to insulate any way is to have a vapour barrier between the inside cladding of the house and the insulation and to use a perforated foil on the outside of the insulation and the external wall cladding.

[Greg Q]

Cobber, I'm not Barry, but you can do a Google search on this stuff. "Fine Homebuilding" magazine, often covers this topic. Your builder claims the timber will sweat? Normally a well-sealed house has a higher relative humidity that the outside air. This water vapour will make its way through the membrane of the house to the outside air. In very cold climates, this water vapour is problematic with traditional fiberglass batting insulation, as it causes clumping, reduces the "R' value, and promotes mold growth.

The current method of coping with that is to line the joist cavities with heavy plastic, then install the batts. Chicken wire can be stapled to the bottom of the joists to hold the insulation in place, unless you can find paper-backed batts which can be stapled directly.

What spacing did the builder use on the joists? If its greater than 400mm you may have trouble with standard batts.

Greg

[Cobber]

Barry/Greg - you guys have lost me there. There is no room to put thick insulation under the ground subfloor because I wont get the ducted heated in? I guess the issue is the timbe floorboards will have cracks in them later on and air will get through.

Barry - do you know where is says that its required by todays regulations? Do you have a link as it would be useful to show the builder.

cheers

Cobber

[Barry_White]

Barry - I was referring to the upstairs addition which will have chipboard as I will carpet it but you raise an interesting point. My extension is over 100k and they are not going to insulate the ground foor under the tongue and groove timber floorboards. What do you insulate it with? Im interested because the builder has said they dont usually do it. He said the timber will sweat if you put sisalation paper underneath for example?

cheers

Cobber

Cobber

If the extension was approved by council before the 1/7/06 it doesn't have to meet the requirements for extensions.

[Cobber]

Bazza - I reckon the extension was approved before then....doh.

Do you recommend putting foil underneath the joists maybe after the wiring? I saw in another post it was recommended. Cheers

[Greg Q]

Cobber, what's the distance from the bottom of the joists to the ground? I'm only talking about insulating the bays between the joists-you'd still be able to run the ducts between the bottom of the joists and the ground given 300 or so clearance.

I don't know how much you'd need for the installation...600 mm?

As a matter of personal opinion, I think foil is not worth the trouble-it has a very low R value, and even that is dependant on rip-free installation.

[thebuildingsurv]

foil will help a bit especially with drafts. Foam board to the underside of the flooring can also help.