Browse Forums Owner Builder Forum 1 Apr 07, 2013 11:30 am Hi. I'm just beginning my first (and hopefully last!) OB venture. Bought the land yesterday (Melbourne inner-ish city suburb) with an old house on it that will be demolished. Great spot. Probably paid 20K more than I wanted but hey ho, the kids are gonna love it here. The site I purchased has a flood SBO on it and the depth is 200-300mm, so the base of our house needs to start at 600mm or so. I'm hoping to be able to do reverse brick veneer built on a raised concrete slab (raised because of the SBO) with insulation outside the thermal mass. Still open to possibly doing double brick cavity instead of RBV but I think this will be more expensive. The main problem I see with RBV is that its not widely used therefore the literature is rather limited. And of course it will be more unfamiliar territory for most tradies which won't help. Anyway, I guess my question is does anyone have experience with domestic raised concrete slabs? Should I build them on piers scattered around the entire base, or is it feasible just to span the full house width without support underneath except at the edges? With the SBO the water doesn't need to be able to flow under the house, the house just needs to be protected from damage, so therefore I can get a supporting perimeter of brick built for the concrete - I think? Flood water flow will be down the side of the house for which I need to allow 3m or so. Obviously when we get to the drawings stage the engineer/architect will offer professional advice but I'm trying to educate myself as much as possible before then. Am I mad? Re: Raised concrete slab questions 2Apr 07, 2013 4:00 pm The foundations of your slab must be on solid ground not the topsoil. If the entire slab is to be raised 600mm it means you will have a minimum footing depth of 600mm for your foundations whether it be a waffle pod slab or a raft slab. Alternately if you require 600mm of fill over the block then the slab I would think that you will have piers placed at appropriate places under the entire slab. The height and depth of your footings will depend on your soil test and the rating that comes back with. Then up to the engineer to specify what is needed. Settlement 1/2/12 New Shed 23/3/12 Slab poured 27/3/12 Frame complete 4/5/12 Roof complete 1/6/12 LOCKUP 29/6/12 Our new build blog http://kareenhillsownerbuild.blogspot.com/ Re: Raised concrete slab questions 3Apr 07, 2013 5:41 pm Hi Smitho, You have a couple of options for your slab 1) you can do strip footings , build the subfloor block work up to required height then do an infill slab. This means filling with compact able fill then concrete on top. 2) my preference would be for a suspended concrete slab using precast prestressed concrete beams and then thin slab on top. Why I like this is because OBs can easily do it themselves and save heaps in labour costs. At this stage you can easily put in your hydronic heating and also maintain access under the home if you need to get under there. I think you will be very happy with the reverse brick. All my clients claim it is very cosy. It is madness paying large builders margins when you consider they only engage tradesmen and manage the process. Ok you don't get the materials for the cost they pay but at least you have control of your project. You would be wise to speak to a Project manager before you get too far into your process. Re: Raised concrete slab questions 4Apr 27, 2013 8:20 pm Hi. Thanks for your responses. I'm curious about the precast prestressed concrete beams. Why do you think that this structure lends itself to OB? I would have thought that you still need specialist lifting equipment and also the top level concrete screed to be done by pros. I do like the idea of keeping a crawl space underneath though. I'm considering another option of using engineered bearers on strip footings instead of concrete. I would then insulate down to the ground inside the strip footings keeping the whole crawl space inside the thermal envelope, with the natural ground level being the bottom. Does this sound sensible? And do you think I would be able to build the internal brick wall on top of the bearers? The bearers will have to span all the way to the frame on the outside and hence through the internal brickwork. Is it wise to build a brick wall with gaping holes in it? Sorry about the daft questions! Re: Raised concrete slab questions 5Apr 27, 2013 9:12 pm Hi Smitho The precast beams do need a small crane or franna but because they are already cut to size and numbered it is a very quick operation.200m 2 of floor in 4 hours. There is no propping so it is almost idiot proof. I would suggest a concreter to lay the slab but you can get it done for around $25/m. If you are tiling then it can be done cheaper. You only need 75mmm slab. You get the benefit of thermal mass with minimal concrete. You can lay internal brick on this but I would imagine not on timber bearers. I can send you some photos of this system or you can check out the photos on my website called energy efficient home. The concreter will take and reuse. In my case I bought structural LVLs and scraped them back and used them as joists. 1 3526 yep, clearly mark where the infloor heating pipes are before drilling or nailing 1 5463 Building Standards; Getting It Right! is this for a residential dwelling or a shed? If its for a dwelling, its out of tolerance and a "mistakes happen" isnt a good enough excuse to just move on. 1 1376 |