Browse Forums Owner Builder Forum 1 Apr 09, 2017 3:17 pm Hi Everyone, Just after some advise on what the going rate is in the Melbourne Metro area for a conventional suspended slab. After initially completing our structural engineering with a Steel/Posi-truss/StructaFloor solution for both floors (3 story home), however given we plan to live in the home for quite a while, we have now decided to conduct a feasibility study into what it would potentially cost to specify a suspended slab for the first floor (basement / ground floor). Our engineer has completed a preliminary design for costing purposes and I'd now like to conduct a sanity check as to the potential cost. In summary the design comprises of: - 230sqm suspended slab (1.0mm Condek sheet / SL102 top mesh / N12 Bars @ 300ctrs between ribs / 40MPa concrete) - 450 x 2000 x 9000mm band beam (qty: 2) [16 x N20 Bars Top / 16 x N20 Bars Bottom / 40MPa concrete] - 450 x 1200 x 9000mm band beam (qty: 2) [8 x N20 Bars Top / 8 x N20 Bars Bottom / 40MPa concrete] - 500 x 1600 x 5500mm band beam (qty: 1) [10 x N20 Bars Top / 10 x N20 Bars Bottom / 40MPa concrete] - 450 x 1800 x 6000mm band beam (qty: 1) [6 x N20 Bars Top / 6 x N20 Bars Bottom / 40MPa concrete] - 4 x concrete columns [Note: These are currently shown as blockwork columns but will be changed in the detailed design phase] Any thoughts as to what the rough price would be for the above? Both builder & retail pricing would be appreciated. Additionally, we need to install approximately 16 solider piers along the boundary to support excavation. Given we are on a slope pier depths will vary from 5.4m on the high side to 2.5m on the shallower side. I'm told there is a significant price difference between buying the cages assembled vs unassembled. Is there any value in purchasing the steel components loose and assembling them onsite? I understand this would be a tedious and time consuming exercise however I have enough time at my disposal should there be an opportunity to save significant coin! Thanks in advance. Re: Cost of Suspended Slab - Melbourne 2Apr 09, 2017 3:46 pm Chops_47 it depends on what you are trying to achieve with the slab span distance,1-way/2-way,band beams,service runs, dropped ceiling, etc. Cast in situ concrete on reusable formwork would be the cheapest by far. There are many options.. you will need to optimise Span/Depth/weight,so more info required If you were to place the rebar you would save approx $800-$1000 /Tonne Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Cost of Suspended Slab - Melbourne 3Apr 09, 2017 4:25 pm The main issue we have is head height in the garage therefore we are limited to keeping the beam depth to a maximum of 500mm. We're also trying to keep the garage as open-span as possible however we also have various point and distributed loads to consider from the 1st and 2nd floors above, hence the need to include columns. In regards to service runs I'm happy to have exposed duct/pipework as we are going for an industrial theme in the garage in either case. Trying to avoid beam penetration as much as possible and none are specified at this stage. I also questioned the need to use Condek as opposed to reusable formwork but wasn't really given an answer.. prelims turned up with Condek so I'm working with this for the moment.. Would I be correct in assuming Condek is the stronger of the two solutions? What price delta can be expected between a Condek vs reusable formwork? Re: Cost of Suspended Slab - Melbourne 4Apr 09, 2017 7:31 pm Chops_47 The ribs provide minimal one-way sagging reinforcement you still require additional bottom reinforcement depending on your design? The formwork may require a day to put up and an extra day to strip, so you save time on stripping but require more ,joist,stringers,props to hire.... formwork costs $20/m2 Last time I looked.... Bondek cost $100/m2 OB hire labour at $35/hr I do suggest you breakdown the 2 options and compare in a spreadsheet, then get 3 quotes and reverse/compare the alternate approaches for comparison should converge to an accurate price BTW more design info is required Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Cost of Suspended Slab - Melbourne 5Apr 30, 2017 11:47 am After giving the matter additional consideration we have made the decision to proceed with a suspended slab. We are currently in the process of finalising the preliminary design to then allow the engineer to complete the detailed design. The direction will be to use timber/ply formwork as opposed to Condek as the later is more expensive and does not offer the industrial aesthetic we are after in either case. I'm also investigating whether it is possible to use steel columns as opposed to cast concrete but can't seem to find any examples showing how the steel would connect to the slab reo. Also, I'm not entirely sure if thermal brakes can be added into the suspended slab to assist with thermal management? We have three areas that will be exposed to the elements so I'd like to ensure we don't have a situation in winter where heat is being transferred outside when we are trying to maintain a steady indoor temp.. In regards to cost I believe the slab configuration will be approx. 10% more expensive than the steel/posi/structafloor solution which is mostly due to the number and size of steels required (approx 6 tonne) for the latter configuration. I've tried to obtain accurate costs from trades but unfortunately the industry is at the stage where work is plentiful for them so motivation to quote for new and somewhat difficult business is low. Instead, I've costed the solutions up using the Rawlinson's Guide to at least give me some surety that we're on the right track. Re: Cost of Suspended Slab - Melbourne 6Apr 30, 2017 3:52 pm Funny how these things work. A few hours after I posted the comments above I received a call from one of the concreters. Long story short he's provided an indicative cost of around $350 per SQM for the suspended slab with timber/ply formwork. Based on what I've seen in Rawlinsons however this should be around $350 per cubic metre. Can anyone shed some light on what it should actually be? Re: Cost of Suspended Slab - Melbourne 7Apr 30, 2017 8:47 pm With respect to your query about thermal breaks, I'm not sure about Class 1 buildings, but in a Class 2-9 building, the underside of slab is required to be insulated to achieve DtS provisions of the BCA. I'd suggest in Melbourne insulating the slab would be very beneficial. Either you'll have a cold floor or an inefficient heating system... Building Services Engineer Renovating our 1960's modernist home in Brisbane https://forum.homeone.com.au/viewtopic.php?f=53&t=82091 Re: Cost of Suspended Slab - Melbourne 8May 01, 2017 9:01 am Chops_47 Unfortunately that's what you deal with in not knowing and being able to compare apples with apples Tradies love confusing clients with differing quotes and units LOL... There is a price difference of 5 Times (Ouch!) Rawlinsons? $350m3/200mm= $70/m2 (assume 5m2 per m3 concrete) A guesstimate should be between $70-$100m2 BTW, If you want accurate costs you must provide accurate Engineering/construction details, info and data, sizes,spans, site access, etc,etc You need to account for all the variables and analyze all the alternative costs.. remember to be realistic with your costs, labour rates, variables & Constants Thanks for the update.. Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Cost of Suspended Slab - Melbourne 9May 01, 2017 12:11 pm quote "We have three areas that will be exposed to the elements so I'd like to ensure we don't have a situation in winter where heat is being transferred outside when we are trying to maintain a steady indoor temp". The BCA (now NCC- National Construction Code) requires suspended floors in Melbourne for Class 1 buildings (houses) to have a total R value of 2.25. Note the NCC is now a free download. Volume 2 covers Class 1 buildings Re: Cost of Suspended Slab - Melbourne 10May 01, 2017 1:45 pm 1960sModernistHome With respect to your query about thermal breaks, I'm not sure about Class 1 buildings, but in a Class 2-9 building, the underside of slab is required to be insulated to achieve DtS provisions of the BCA. I'd suggest in Melbourne insulating the slab would be very beneficial. Either you'll have a cold floor or an inefficient heating system... Just spoke to our energy rater and he's confirmed we would need to run insulation under the slab. Suggested it would most likely be 50mm foam to the entire underside of the slab.. Re: Cost of Suspended Slab - Melbourne 11May 01, 2017 1:47 pm Beetaloo The BCA (now NCC- National Construction Code) requires suspended floors in Melbourne for Class 1 buildings (houses) to have a total R value of 2.25. Note the NCC is now a free download. Volume 2 covers Class 1 buildings Thanks for the tip! I took the easy way out and just called our energy rater Re: Cost of Suspended Slab - Melbourne 12May 01, 2017 2:04 pm StructuralBIMGuy @Chops_47 Unfortunately that's what you deal with in not knowing and being able to compare apples with apples. Tradies love confusing clients with differing quotes and units LOL... There is a price difference of 5 Times (Ouch!) Rawlinsons? $350m3/200mm= $70/m2 (assume 5m2 per m3 concrete) A guesstimate should be between $70-$100m2 BTW, If you want accurate costs you must provide accurate Engineering/construction details, info and data, sizes,spans, site access, etc,etc You need to account for all the variables and analyze all the alternative costs.. remember to be realistic with your costs, labour rates, variables & Constants Thanks for the update.. Exactly! Unfortunately I'm in the position where I know too many professionals and not enough trades who would be able to help out in this case.. I assume your guestimate of $70-$100m2 doesn't include labour, reo, etc? Rawlinsons Construction Cost Guide: https://www.rawlhouse.com/construction-cost-guide.php In regards to costs I fully agree with your comments but it's almost impossible to make a comparison when the trades themselves won't provide information. Case in point is the steel work where I've received quotes with variations of 50% for exactly the same technical spec. In the case of windows I've had quotes vary from $40K to $160K but in this case technical specifications does vary due to the manufacturers raw components. Re: Cost of Suspended Slab - Melbourne 13May 01, 2017 3:16 pm $100m2 is all inclusive simple slab (2 way span) , I pay guys that with a truck, basic formwork, with bugger all overheads. In regards to working out what's a fair price you just need their final quote and you can extrapolate all the other info quite easily On owner builders trades quotes, trades generally try to peg some of the builders Profits & Margins for themselves, +50% difference in quotes is not that uncommon across all trades. so Take some time off and pour the concrete yourself Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Cost of Suspended Slab - Melbourne 14May 01, 2017 8:24 pm What about Hebel Powerfloor with steel structure? You get the benefits of concrete (no noise or bounce) and may not require additional insulation. Supposedly lower cost than in-situ suspended reinforced concrete. Curious too about Bondek being more expensive - On quite a few projects I've worked on the builders have used Bondek as it worked out lower cost than formwork suspended slab. That may be because form workers on unionised sites are expensive and unreliable, and could also be because Bondek slabs allow fitout works to commence on the floor below much quicker. On a domestic project these are probably irrelevant Building Services Engineer Renovating our 1960's modernist home in Brisbane https://forum.homeone.com.au/viewtopic.php?f=53&t=82091 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 30295 How are you doing Ben? Extremely interested in hearing what you are doing or plan to do! 12 15420 custom probably not. Volume, most defiantly, but spec would vary. If youre doing a knock down, there additional costs associated with that that will eat into your budget… 1 10534 |