Browse Forums Renovation + Home Improvement 1 Aug 26, 2013 9:05 pm Hi ... noob here I am considering a home extension out the back which would consist of a couple of bedrooms and living area, laundry and maybe a bathroom. The back extension I am considering will have a high raked ceiling sloping from the existing house to the backyard. This will create a low point between the house and the extension. Is this and absolute no no in terms of design ? Or is it rather common with and easy drainage solution? Please see photo I have uploaded below for a better explanation. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Thanks in advance Re: House extension - Drainage Gutter question 2Aug 26, 2013 9:12 pm This style of roof we call a sawtooth roof. Sadly It is a absolute given that it will leak at some time or other. @builderforlife Building inspector and passionate about construction When you need an expert to take a look. Re: House extension - Drainage Gutter question 3Aug 26, 2013 9:23 pm Yeah, not the best. The abutting wall also needs to be factored in the drainage calculations to allow for wind driven rain. The gutter's highpoint would also need to be mid point. The regs will require it to be designed for a 1:100 ARI but I wouldn't be accepting the minimum. 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: House extension - Drainage Gutter question 4Aug 26, 2013 9:24 pm I think the drainage solution is a box gutter that can often cause problems, particularly if done poorly, but wouldn't let that in itself put you off. Hopefully someone can post up some other suggestions or maybe make friends with an architect. http://camdenbuild.blogspot.com.au/ by invite only please pm me Re: House extension - Drainage Gutter question 5Aug 26, 2013 9:40 pm Architects do not design roof drainage systems. Most don't even know the basics. 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: House extension - Drainage Gutter question 6Aug 27, 2013 6:17 am I have built many of these on my school and industrial projects and there is no reason why it should not function well providing it is well designed, well built and properly maintained. Attention to detail is essential and I agree with SaveH2O, there is no need to stick to the minimum requirements. The box gutter must be properly sized, have proper falls and adequate overflow and you must allow for a contingency such as ball or dead cat/bird blocking the outlet. My experience with Architects is that yes they do know how to do it but Architectural draftsperson? Perhaps, maybe not. As in all matters that are really important, get it designed and then get a peer review for a second opinion, then when you build proper supervision is essential. And No it's not rocket science,it's just a gutter, good luck. 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: House extension - Drainage Gutter question 7Aug 27, 2013 8:13 am Thankyou everyone for your reply. Your responses have both put doubt in my mind and hope that this can be achieved. In other words - I don't know what to do now .... building-expert ... the contingency if the gutter is blocked ... would that be a second lined channel under the box gutter to allow water to flow ... or a low point in the middle with a pipe that runs down the wall then under the house and back to the drainage pipe at the side of the house ? I'm starting to find out nothing is easy when doing a house extension. Re: House extension - Drainage Gutter question 8Aug 27, 2013 10:26 am Yes there is a lot to know and that's why people like architects and me go to university to get education and when blended with experience can and will get it right. Overflow is a contingency to allow water escape if outlet is blocked or to allow escape in especially heavy downpour. If you get competent people to design and build for you you should be right. Lot of people think building is easy, just get the tradies and she'l be right. Big mistake for many of them. 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: House extension - Drainage Gutter question 9Aug 27, 2013 11:51 am I definitely don't think its easy ... thats why I am going to make sure I get the design right before even thinking about starting. I am actually doing some structural design subjects at the moment at UOW so I am aware of what is required, just don't have the experience with being on site to know how to overcome issues. I know what you meant by a contingency, but in your experience how would you go about this? Thanks again Re: House extension - Drainage Gutter question 10Aug 27, 2013 2:04 pm pump up the jam I am actually doing some structural design subjects at the moment at UOW so I am aware of what is required, just don't have the experience with being on site to know how to overcome issues. Box gutters are covered in AS/NZS 3500.3:2003, sections 3 & 4 as well as in appendix 1. As you are studying, you should be able to access the standards online or elsewhere if you haven't already done so. Box gutters must have an overflow provision that is not less than the gutter outlet's design flow. Just be aware that the overflow provision as per AS/NZS 3500.3:2003.3.7.5.1 must discharge to atmosphere. Box gutters must be designed to drain during a 1:100 ARI without overflowing but rainfall will exceed this every few years. You must also consider where the overflow provision will impact at ground level to prevent nuisance issues. Melbourne had a 1:500 ARI about 2 & a 1/2 years ago but it won't be 500 years til the next. I know of many instances where poorly designed box gutters have overflowed into the house during rainfall that was much less than a 1:100 ARI. The last one was about a month ago on an associate's extension. In that instance, the plumber had installed the box gutter without an overflow provision and had left rubbish in the gutter to make sure of a bad job. I don't know who designed the gutter. To cap it off, he also installed eaves gutters with the back wall level with the top of the fascia as well as installing a toilet off centre. He said that it was to make room for the toilet roll holder! It is extremely important that whoever designs the box gutter does it properly and that it is inspected by a suitably qualified expert EXPERIENCED WITH BOX GUTTERS. You must never assume that the designer and installer are competent. You only need to look at the massive non compliance of eaves gutters on new homes to have a sobering realisation. A couple of years ago, the NSW Dept of Fair Trading instructed some of their inspectors to randomly examine new display homes for eaves roof/stormwater drainage compliance. Of the 35 display homes examined, only one was found to be compliant with the standards yet eaves gutter drainage is simple to design compared with box gutters. I can PM a link to the parliamentary report if interested. Box gutters are generally believed to be required to have a 1:100 slope but they can range from 1:40 to 1:200. I have however seen some that were installed with no slope. Slope is important for several reasons including the fact that when organic material collects in the gutter and breaks down, the resultant sludge is negatively charged whereas metals are positively charged. I would schedule an annual inspection as a minimum. 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: House extension - Drainage Gutter question 11Aug 28, 2013 7:43 am We've installed quite a few over the years that were designed by either an architect or someone with hydraulics knowledge in the structural engineers group. We've never had a callback but then again we installed them or the roofing company did with our supervision. One thing we always insisted on was an overflow opening at the end of the gutter that was lower than the lowest point of the upstand part of the gutter. If there was a blockage the roof water would escape through the overflow before it would backup under the roof even in torrential downpours. Stewie I would say both styles you have pictured are steel. The lower chord of the first pic would be a massive lump if made using timber considering the size of the rafters. If… 1 6153 Hi HomeOne, I'm in the midst of landscaping a cat run down the side of my house, and the recent rains have me wondering if I need to install some sort of drainage. 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