Concrete Slab Insulation

[dallas]

g'day all,

i'm looking for any advice / experiences with insulation and/or heating of concrete slabs... as part of my upcoming underhouse renovations (due to start in around a month - pier removal, excavation and concrete slab).... as this will eventually become a living space, i'm thinking of the future heating / cooling requirements...

what can i use to insulate the slab, from preventing the ground from chilling the slab during winter? i'm also looking at slab heating (elec. heating cable laid within slab at time of pouring), so slab insulation is critical... does anyone have any material suggestions / links for slab insulation, or any experiences??

cheers


D

[silentC]

We put Cableheat cables in a slab in Sydney. Takes a few hours for temperature changes to take affect, so you really only use them in winter or when there's a reasonable cold spell, so you need something else for those odd cold days in spring or autumn.

Best to run them on off peak because they chew the juice, depending on what you put in. Get the kilowatt rating and you can work out roughly how much it will cost per hour by looking at the charges on your electricity bill.

They really just take the edge off. We found on really cold nights you still needed to run a space heater of some sort (gas in our case).

They work best with tile floors but you will get cracks in grout and possibly tiles due to expansion and contraction. Floating floor might be better for that reason.

[Pulpo]

Not sure how cold Shell Harbour gets.

I would recommend looking at US web sites on slab insulation very common.

http://www.hunterpodsupplies.com.au/

Try the above link, they were certainly knowledgable and helpful.

Polystyrene under the slab would help but spending on wall and roof insulation would be more cost effective.

As for heating the slab the rolls royce is hydronics; water tubing through the slab.

Good luck

Pulpo

[Fat Pat]

You'll spend shed-loads of money putting floor heating in.

You need to ask the question "Is it worth the money in Australia?"

I spent some time in Europe, and the average person with central heating or the fancy floor stuff can spend $ 1000's a year. We don't get that cold over here, unless you live in the real high country, and even then.....

Better spend you money on a suitable floor covering (timber/carpet/cork/etc) and put on some trackie daks when you get particularly nippy.

They'll sell you the stuff, but it costs and arm and a leg to run. Anything that requires an electric element ultimately does.

Sorry to be the bringer of bad news.

[simon c]

It's not so uncommon in Victoria

But I see that you, are in NSW, so it may not be so important

[mrsxtro]

Just out of interest (as we are considering doing a similar project)....

Have you costed the whole job? Ie. excavation, restumping, retaining walls, drainage, concrete slab, building etc. A round figure estimate would be very helpful! We are trying to decide whether it is worth the money or whether we should sell and buy a bigger house.

Thanks in advance.
-mrsxtro

[dallas]

Just out of interest (as we are considering doing a similar project)....

Have you costed the whole job? Ie. excavation, restumping, retaining walls, drainage, concrete slab, building etc. A round figure estimate would be very helpful! We are trying to decide whether it is worth the money or whether we should sell and buy a bigger house.

Thanks in advance.
-mrsxtro
Mrsxtro,

i've been to a number of builders for quotes, and in a quick reply, most come in around the $20K for the following work: removal of piers, excavation, RHS beams, concrete slab, drainage and small retaining wall (400mm high) along 2 sides of house where it cuts into existing ground level. My room is approx 4.5 x 7.5-8m, and has 12 existing piers to be removed and about 8m3 dirt to remove...

what i have noticed tho, is that each builder has suggested a different way of supporting the 2 sides of hte house that will be excavated to form the new level...obviously there is more than 1 way to skin a cat, and each will come with engineers signoff, but they do vary... from a retaining wall to pick up existing footings (sounds fine once done, but will be a period of 'non support' ~ not too sure about that transition period tho!, with the other option of 5 underpinns (to around 2.5m deep) to hold the walls up, allowing me to excavate at my leisure....

approx price to remove piers and put beams in is between $7-9K, with a slab / retaining wall / draining / footing work forming the rest of the $$$... big thing to consider is how the extensions will effect the existing footings... shallow, then no probs, but as soon as you start exposing footings, then your into underpinning / retaining walls etc, and that raises the difficulty level, and of course the $$$$....

the other idea i'm now toying around with is not putting in a slab, rather a floor supported by typical bearers and joists (say duragal) just above the ground level, and finishing it off with recycled timber floorboards to match up with existing garage level.... will mean deeper excavation, but that's the beauty of underpinning I guess... again still considering all options at the moment...

if you need anymore help, then feel free to ask away...

Oh, and big thanks to all the reply's so far... much appreciated... as you've probably picked up, i'm thinking of replacing the slab with a timber flooring system... but again, work in progress... any options / comments welcome...

D

[journeyman Mick]

.............the other idea i'm now toying around with is not putting in a slab, rather a floor supported by typical bearers and joists (say duragal) just above the ground level, and finishing it off with recycled timber floorboards to match up with existing garage level.......

D

Dallas,
you will need at least 600mm clearance from the ground to any timber to prevent fungal problems. You'll also need subfloor ventilation, these requirements might make things a bit more difficult/expensive.

Mick

[dallas]

thanks for that mick... i sat down last night adn went through the details and the clearance issue was looking to be the showstopper. Not too sure about whicn floor covering to go with, as i will want to be able to roll a car on it if needed... so the options i see I have are:

- concrete slab (painted etc?) wife isn't a fan of painted concrete
- concrete slab with floating floor / recycled floorboards over top
- 100mm thick paving (no slab)
- slab w carpet / lino over it: as it's adjacent to garage / workshop, feel this isn't the best idea...

will see what the final $$$ fall out from each builder, and will give it some thought over the weekend... i've got some snaps of the existing area if anyones interested... just gotta work out how to post piccies...

here are some links to the piccies if interested:

the existing entrance from garage to sub floor space:
http://www.myfishingpictures.com/img/023940.JPG

shots standing in doorway viewing sub floor space:
http://www.myfishingpictures.com/img/023941.JPG
http://www.myfishingpictures.com/img/023942.JPG

once beams / flooring is done, i'll knock in some windows / glass bricks up the far end to allow some more light in... eventual use will be for extended workspace, with an old lounge / bar up far end to have a few brews with mates...


D

[Al Pal]

Dear Dallas
what you need is FOAMULAR METRIC 250 Extruded Polystyrene.
it comes in sheet sizes .600mmX1.2mm.
Thicknesses available :
25mm
30mm
50mm
75mm
100mm
For underslab applications you will need 30mm or 50mm .
Foamular has a higher R rating than the Esky type foam .

Available in aal states

Go to www.foamular.com.au (http://www.foamular.com.au) for all the teck' specs' you need.

Al pal

[Barry_White]

I live on the New England Tablelands where the winter temperatures go down to minus 9 degrees C. We have a concrete slab with carpet in the lounge, dining, bedrooms and main hall. In the kitchen, family room and entry hall we have 6mm thick cork and in the morning I walk around on the floors in my bare feet.

I think cork is an ideal floor covering on concrete

For heating we have a wood fuel stove in the kitchen and a slow combustion heater in the lounge.

My personal opinion I think insulating under a slab is a waste of money where you are located.