Adding thermal mass in the floor of timber framed house

G'day all and another question about our renovation plans and ideas.
I have been reading though the "Technical manual" and would like to have the benefits of some thermal mass in the floor in the lounge room that is exposed to the winter sun.

20 -20 hind-sight says we should have had some extra stumps put in but no big deal.
The technical site says we can add extra mass easily using poured concrete in a suspended slab supported on the bearers.
The room is only 3600 wide and the winter sun only shines on the first 500mm of the floor.

I know that the thermal mass will be smallish but any improvement will be of benefit, before we pay an engineer I want to get some idea of how this could be done so we can think about the cost/benefit ratios and whether or not we can do it ourselves; I am confident with concrete and have a decent mixer for the small quantity required ( or a mini mix batch from the mob at the end of the street )

We would of course insulate the bottom of the slab afterwards.

What is the possibility of putting in a bearer at 500mm sealing the bottom of the joists with form-ply and just filling in the holes between the floor joists??
It isn't a lot of concrete, about 200 liters, or 350/450Kg but we would tile over the top with matt black tiles

I have an idea in my head about adding an internal brick wall beside the chimney and, breaking open the plaster wall and putting in a beam at the top with jack studs and thermal mass inside adding extra bricks above the mantle, from the edge of the fireplace to the ceiling. The chimney base is really solid so should take the added mass.

We would then add an batten out the chimney ( we have some 40mm Tophat section ) and beyond the 40mm air gap we would insulate with a pack of rockwool.

Last inter I could feel the heat radiating from the external wall of the chimney; I hate to waste all of that thermal energy to the sky when firewood is so expensive.
Any and all opinions are appreciated, they will help us in the decision making process


Read the full thread at RenovateForum.com...