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Suspended slab options/prices

(9 posts) (7 voices)

Started 1 year ago by sib
Latest reply from mle

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sib
Member

Hi there. This may well have been answered/addressed in other posts, so apologies if so.
We are designing an addition to our Melbourne home. Approx 70m2. Due to flood overlay, new build has to be approx 800-900mm above ground level. Soil is reactive clay.

Initial thoughts was to use a suspended concrete slab to enhance passive thermal properties and obtain greater thermal mass. Current design sees winter sun hitting the floor during the central part of day via high northern windows in a skillion, while summer sun is minimised due to orientation and eaves. Otherwise, structure was planned to be insulated timber.

We've been told that cost of a suspended concrete slab is significantly more than usual timber floor structure, owing to height of slab and soil type, and flood overlay issue. Can anyone comment on the cost differential? What is the thermal delta between the suspended slab and insulated timber flooring? If a slab is cost prohibitive, what options do we have to maximise our winter heat retention in timber floor?
Many thanks

Posted Monday 16 Apr 2012 @ 11:57:43 am from IP #
pulpo
Member

A suspended slab is not cheap.

900mm off the ground could be more difficult than 2m.

Not sure if the soil type adds too much more as the slab is suspended.

Piers or supports in the ground either way will need to be significant.

At a guess cost difference hmm, start at 4 times excluding finishing.

You might be able use preformed concrete floors (no idea of costs).

Have good insulation under the floor boards.

Thermal mass if just an open room will be difficult.

A trombe wall.

A thin slurry with tiles?

Some water thermal mass, how to place or store, who knows.

Good Luck

Pulpo

Posted Monday 16 Apr 2012 @ 11:00:54 pm from IP #
TonyT
Member

For a new suspended floor, my present plan is to use a sandwich of "conform" (the steel that is used for a suspended concrete floor) to carry 100mm of insulation beneath pipes for hydronic floor heating then a floating wood/bamboo floor.

The insulation will be 80mm of fibreglass wool plus 20mm of (? extruded) polystyrene foam.

An alternative is to build the floor from Structural Insulated Panels (SIPs) with pipes then bamboo on top.

The goal is to use naximum insulation with MINIMUM thermal mass and to control a flow of hot water to deliver ACTIVE (rather than passive) under-floor heating.

The area of the windows on the North wall will be 25% of the area of the floor.
The windows will be fully exposed to the winter sun.
During those few hours when the sun is shining in winter, the captured solar heat will be sufficient to keep the room warm without the cost of additional heating.

When the sun is shining, a larger area of glass would capture more heat than is needed, even in winter.

Because a well-insulated solid wall is a MUCH better insulator than glass (even triple glazing), more glass causes larger heat losses during the large number of winter hours when the sun is not shining.

With less glass, additional heat would be needed even when the sun is shining.

Posted Tuesday 17 Apr 2012 @ 4:05:53 am from IP #
dave lawrence
Member

have you considered using precast hebel floor panels.
i have seen that done ,and it has many of the benefits you are looking for .
need a crane to efficiently place all the panels .
you can then pour a screed over the top and tile where required or lay floating floor .
excellent insulation , low thermal mass, relatively quick to install.

Posted Tuesday 17 Apr 2012 @ 4:14:59 am from IP #
TonyT
Member

Great idea !
I need to compare the costs of the different methods of construction.

Posted Tuesday 17 Apr 2012 @ 4:20:03 am from IP #
dave lawrence
Member

proximity to crane and manufacturing factory will be of critical importance to determining costs .
I have seen hebel panels used for flooring and roofing making redundant most of the framing timbers normally used. very underrated product,i believe.
If not wanting to use massive custom built panels can also buy smaller panels 1800x600 which sit on bearers @1800 crs .
also ensure local expertise exists to install .. this is more important than most people think

Posted Tuesday 17 Apr 2012 @ 4:52:15 am from IP #
Farmer
Member

Hi sib,
Could you use perimeter footings, retaining block work, and fill the complete foundation and pour on top. Some internal piers may be required.
farmer

Posted Tuesday 17 Apr 2012 @ 8:28:14 am from IP #
Littlehouse18
Member

We are using a product called Deltacore in our new build in Fremantle. See http://www.deltacorporation.com.au . We are putting a 100mm topping onto it because Hydronic tubes are also being installed. Though its normally suggested a 50mm topping coat is well sufficient. The Deltacore planks are pre-cast concrete slabs with hollow cores running along the length of the "plank". Strong and light. They can span up to 8 meters unsupported are about 1100mm wide and come in a variety of thickness's. We are using 150mm thick planks and it works out to roughly $100 per m2 delivered. From people we have spoken too, this system is about one third the price of a suspended slab poured on temporary from work. We would also be interested in hearing from anyone else who has used Deltacore.

Posted Friday 11 May 2012 @ 5:09:55 am from IP #
mle
Member

Hi there Littlehouse18,
Did you go ahead with the Deltecore system? If so, how did it work out for you in terms of cost, installation, routing of plumbing/electrical services etc? Appreciate any feedback.

Kind regards

Mal

Posted Monday 1 Apr 2013 @ 1:22:38 am from IP #

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