Browse Forums Renovation + Home Improvement 1 Jun 06, 2014 5:03 pm Hi, I am planning to add an extra floor to a house, to make a dual occupancy. The existing house is double brick so should support a concrete slab floor. There seem to be various systems for building this floor: Bond Deck (metal deck with poured concrete) Formcraft Formdeck (pre-made lightweight concrete blocks with a poured layer ontop) Smart Slab (steel frame with a metal deck and pour concrete on top of that) - similar to Bond Deck I think. Does anyone have any experience of any of these. What are the advantages / disadvantages of each? What are the pitfalls to avoid? thanks! Mike Re: Another floor - Suspended Concrete Slab 2Jun 07, 2014 12:27 pm Quote: The existing house is double brick so should support a concrete slab floor. First off you need to get a structural engineer to come and assess whether your existing house can support an additional level over a suspended concrete slab. Stewie Re: Another floor - Suspended Concrete Slab 3Jun 10, 2014 12:50 pm I'm looking at a similar thing. Bondek looks good, looks like we should be able to do an 8.4m unsupported span on 1mm bonded & 110mm concrete (if I'm reading the span table right), with two temporary supports during cure. Need to get the engineers report but I'm not expecting issues with that on this site. Re: Another floor - Suspended Concrete Slab 4Jun 10, 2014 1:46 pm Thanks Bryn. That's really useful. Similarly, I don't expect any issues from the engineer's report. We have approx 8.8m span, so (if i am also reading the table right), I need the same as you. 110mm is much shallower than I expected, which is great, but raises 2 questions: 1) Will this be load bearing - i.e. can I build the internal upstairs walls where I like or do they need to be above the existing walls? 2) Have you seen any data on the sound insulation properties of the bondek & concrete combination? I'm guessing it wouldn't be great and would need soundproofing above and / or below? Re: Another floor - Suspended Concrete Slab 5Jun 10, 2014 1:51 pm I don't have specific's on that yet- re: load bearing, check with your engineer. If its lightweight stud frame it might be ok. I need to clarify this as well. As for noise, slabs are pretty reasonable. I don't think we'll need anymore then a good underlay above (acoustic underlay under timber floor) & decent ceiling below. I'll likely size-up the gyprock below to block more sound. Soundchek isn't really worth it as extra sheets of standard gyprock can get the same performance ranting for less money... Re: Another floor - Suspended Concrete Slab 7Jun 10, 2014 9:16 pm Bondek is similar to Kliplok roofing except it is just for pouring concrete over and gets left in place after the pour rather than using frames and formwork ply which gets removed after. Stewie Re: Another floor - Suspended Concrete Slab 8Jun 10, 2014 9:38 pm Be wary when looking at Bondek (or Kingform etc) span tables. Check the actual deflection with wet concrete on top (i.e during the pour). The allowable span tables are based on the ultimate load bearing capacity. Typically these deflections are ok for a carpark put not acceptable for residential construction. The solution is to put additional props and bearers in place during the pour (i.e. use more props and bearers than that which is in the span tables). This will reduce the sagging of the bondek during the pour. The other issue to look out for is dynamic deflections. Bondek slabs are very thin compared to traditional reinforced concrete slabs. This means that there is more spring in them. This is not a problem for single occupancy dwellings but can be an issue for multiple occupancy buildings. On the multi-storey apartment buildings I have worked on, the ceilings had to be supported on resilient mounts to prevent vibrations from the apartment above being transmitted to the apartment below. Professional acoustic advice is recommended for multiple occupancy buildings to prevent structure borne noise transmission between dwellings. The other issue to consider or get advice on is fire separation between 2 dwellings. The ceiling of the ground floor house may need to be fire rated. Re: Another floor - Suspended Concrete Slab 9Jun 11, 2014 11:00 am An industry bible to download and read for anything regarding acoustic and fire design is Gyprock - The Red Book. http://www.gyprock.com.au/Pages/resources/red-book.aspx It is a relatively hefty pdf at 44mb though. You will have to wade through a lot of info but everything you need to find out is in there. Sticking some Bondek down is all fine but the slab really should be designed by a structural engineer. I don't know which state you are in but in NSW it would be compulsory as part of the DA for a dual Occ. Have you had plans drawn up ? Stewie Re: Another floor - Suspended Concrete Slab 10Jun 11, 2014 11:15 am Thanks Beetaloo. I did wonder if the thinness of the slab might create issues with sound. Stewie, Of course I need a structural engineer to design the slab - but as with anything - I think it's worth understanding the issues and the options first. The gyprock red book looks useful - thanks for that. Does anyone have any experience with any of the other slab systems - Formdeck, Smartslab, etc.? Fair Trading can issue orders to rectify and complete but once the matter goes to NCAT these orders are automatically vacated. You will have to terminate contract and sue… 21 29631 How are you doing Ben? Extremely interested in hearing what you are doing or plan to do! 12 15088 The concreter will take and reuse. In my case I bought structural LVLs and scraped them back and used them as joists. 1 5118 |