Browse Forums Building Standards; Getting It Right! 1 Jan 22, 2014 5:42 pm As a result of some recent posts on Homeone, I've formed the impression (maybe erroneously) that your building plans give you your slab height from ground level by means of the RLs (reduced levels). So if we have a reference point on the northeast corner of our house plans which says RL:40:66 and an RL in our entry of 41m, does that mean that the slab will be .34m high? Or is it more complicated than that? Re: Calculating slab height using RLs 2Jan 22, 2014 6:35 pm Hi Liliana You have it right Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Calculating slab height using RLs 3Jan 22, 2014 6:59 pm Hi Building Expert, Thanks for that! Next question..... if your land is on a fall estimated to be 300mm from N to S and 500mm from W to E, which part of the slab is .34m high? Only the entry where the RL of 41m is notated? Or all of the slab, which would mean your slab would be on a slope!! Re: Calculating slab height using RLs 4Jan 22, 2014 9:04 pm The slab isn't 0.34 high it is 0.34 above the reference point. The builder will probably level the site by cutting the higher parts and filling the lower, so the level slab will be about 200mm above the (altered) ground level . The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Calculating slab height using RLs 5Jan 22, 2014 9:30 pm Hi Bashworth, That makes sense, except the site was not levelled and the slab is different heights. But I suppose what you are saying is that at each point the slab should be .34m above the reference level. The garage has an RL on the plans of 40.6m which should mean it is .06 below the reference level. But if the land slopes 300mm from North to South and the garage is at the lowest point, then the land the garage sits on would have to have been built up. So, in fact, your plans don't tell you the height of your slab from ground level. Re: Calculating slab height using RLs 6Jan 23, 2014 5:21 am I am glad you are asking and educating yourself so this probably doesn't apply to you but please people learn from our ongoing very harrowing experience of our builder pouring our slab too high, please understand what height it should be and if at any stage you are not sure it is being constructed at the correct height make noise until someone listens to you ( council, builder ) before the slab is poured and don't let them blow you off like I did! Get an independent survey done if you have too. Re: Calculating slab height using RLs 7Jan 23, 2014 5:58 am Hi Liliana Below is extract from NCC 2011 Volume Two Australian Building Codes Board 3.1.2.3 Surface water drainage Surface water must be diverted away from Class 1 buildings as follows: (a) Slab-on-ground — finished ground level adjacent to buildings: the external finished surface surrounding the slab must be drained to move surface water away from the building and graded to give a slope of not less than (see Figure 3.1.2.2)— (i) 25 mm over the first 1 m from the building in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving); or (ii) 50 mm over the first 1 m from the building in any other case.************* (b) Slab-on-ground — finished slab heights: the height of the slab-on-ground above external finished surfaces must be not less than (see Figure 3.1.2.2)— (i) 100 mm above the finished ground level in low rainfall intensity areas or sandy, well-drained areas; or (ii) 50 mm above impermeable (paved or concreted areas) that slope away from the building in accordance with (a); or (iii) 150 mm in any other case.************ Looking at the above, your builder has not got the surface drainage right nor the slab heights Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Calculating slab height using RLs 8Jan 23, 2014 7:15 am Hi Building Expert, Yes, you're right - according to the Building Regulations, the slab is not the required level above ground (nor is there adequate drainage). I was just wondering whether there was some absolute way to work out, from your plans, the exact height of your individual slab and I'm also trying to understand why the builder claimed the (designer-supplied) "levels" were not right. Also why we arrived at a situation where the house couldn't be built as per the surveyor-approved building plans because of height problems with the boundary wall. In addition, we need to excavate behind the house to get the ground to the right level for paving and I need to know whether it is safe to do so or whether we are going to disturb the foundations. Maybe the engineer who did the original engineering plans is the one to ask - though, as far as I can tell, the engineering plans were not followed as they specify 172mm freeboard. Re: Calculating slab height using RLs 10Jan 23, 2014 7:22 am building-expert Below is extract from NCC 2011 Volume Two Australian Building Codes Board 3.1.2.3 Surface water drainage Surface water must be diverted away from Class 1 buildings as follows: (a) Slab-on-ground — finished ground level adjacent to buildings: the external finished surface surrounding the slab must be drained to move surface water away from the building and graded to give a slope of not less than (see Figure 3.1.2.2)— (i) 25 mm over the first 1 m from the building in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving); or (ii) 50 mm over the first 1 m from the building in any other case.************* Hi BE, I have always thought that the slope must be 50 mm over the first metre for all class 1 buildings but when reading the above, this is an urban myth! What is defined as "low rainfall intensity"? The intensity would obviously also have to pertain to the region's ARI but which one, 1:10, 1:20, 1:50, 1:100 or one of the others that I haven't mentioned? 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Calculating slab height using RLs 11Jan 23, 2014 7:32 am Your thread got me thinking about this too. My answer would be yes and no. Yes.. a plan can tell you the exact information only if your builder provides you with the cross section information on it. No.. the cross section information is not a must for the plan and things can get messy when you start working with the actual ground as your block and other folks can always give you surprises. Re: Calculating slab height using RLs 14Jan 23, 2014 7:53 am Sometimes there are tiny cross-section "mini plans" indicating the degree of slope and the slab height etc information. On my plan, there are 4 of these for indication of cross-section slopes for driveway. And in the first draft of construction plan, there are much more. Not sure if it is due to the complex and steep slope that I have. Re: Calculating slab height using RLs 15Jan 23, 2014 7:57 am Liliana The Nullarbor???? hahaha The ARI (intensity) doesn't relate to annual rainfall. I'm guessing 1:100 as per AS/NZS3500.3:2003 5.2.3 (surface drainage systems) The intensity figure will be interesting. The plumbing and building codes are not always harmonious. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Calculating slab height using RLs 16Jan 23, 2014 8:11 am snowing Sometimes there are tiny cross-section "mini plans" indicating the degree of slope and the slab height etc information. Do you mean something like this from our engineering plans? I've had a look at your thread and your house plans Snowing. (Very nice, by the way.) You have a FFL (finished floor level) inside the house and not an RL. Are they different? Re: Calculating slab height using RLs 17Jan 23, 2014 10:27 am Hi Liliana The whole point of hiring a building designer is to come up with plan and documentation that will satisfy not only owner's requirements but also all legal constraints overcome all natural site limitations and adversities and make it all fit. That is a recipe for construction. Builder is the cook and he has to follow a recipe and there is no excuse (that is what he promised to do in the warranties). If there is a problem with design levels then fine, that should be brought up in writing with the owner and the designer with a request for direction and or variation to the contract. Then review takes place and decision is given, and probably variation approved. It is just not good enough to say levels are not right and builder doing it his own way. You will end up with a dish you don't like. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Calculating slab height using RLs 18Jan 23, 2014 10:51 am Oh dear, I am so sorry to read you have issues too, what is wrong with them??? I agree we pay licensed 'professionals/experts' whatever you want to call them and really they can turn out to be complete duds. With so much regulation in Australia how the heck does this happen? That is exactly what happened with ours, the builder blamed the drafty and me for hurrying him into council (it took months) and then did exactly what he wanted with no regard to what was approved. As you say Building Expert there is always the chance and time for variations before the ground is cut. In our case there was a few months where the plans and engineering could have been amended in council with a section 96 - so absolutely no excuse. So anyone who has not yet had the ground cut/slab laid, please look at your levels and understand what they mean. Ask questions and get expert advice if you doubt what they are telling you or if you think the slab will be too high or too low. Obviously not all builders (if you can call them that) understand what they are doing or don't care. Re: Calculating slab height using RLs 19Jan 23, 2014 11:12 am Hi Lenny171,
Our house is built and finished. It is because of ongoing problems with pipes and paving that I am revisiting this issue. The first time we knew there was a problem was at the first site meeting. The ground had already been cut and the crew were on site to do the concreting but couldn't proceed while the builder and building designer had an argument. We never got to the bottom of the issue because we had varying explanations from both the builder and building designer and felt under pressure to resolve the situation by taking our house off boundary. At no stage were we approached by either of them prior to this to say that there was an issue and what the issue was. Subsequently the builder claimed the site levels were wrong but, in writing, would only state that the plans, as drawn up, would have taken us over the 3.6m boundary limit. The building designer, when pressed at the time, stated that she had instructed the builder to lower the whole house and raise the slab in the garage if he wanted to but that he had ignored that and he had just dropped the garage floor a bit thinking the roof would follow. Whichever explanation you believe, it seems slab heights are not fixed by plans and they are a moveable feast! And you can get building permits for houses that can't be built! PS And taking the house off boundary doesn't seem to have resolved all the issues anyway if the problems with our slab height are anything to go by. Re: Calculating slab height using RLs 20Jan 23, 2014 11:16 am You've got me paranoid now I think ours is all fine... bit of a retaining wall job at the front and left hand side. Minimal on right hand side. Turf should level up nicely everywhere else. https://www.dropbox.com/s/l22csud0yq6y1vq/Driveway.jpg Broker here - legislation says that every true broker must put the clients best interests before theirs so in theory they must offer you the best options for you on their… 2 46313 0 2222 ok thanks - yes was wondering if that should have been listed as Option Three! 2 7995 |