Browse Forums Building A New House 1 Jul 11, 2021 7:57 pm Hi Everyone I'm seeking the Advise of the experts on this form, building a double story house in Sydney and decided on a sloped roof to the back of the house similar to the photo below: Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ parapet walls on the roof will run from the front of the house to the sides exposing only the back of the house, from the roof to the first floor 3 downpipes will run from the back, from the first floor to the ground will have eaves gutters on the side of the house to the ground. the question is will this be sufficient enough and cause any issue in the future, ground floor living is Ground Floor living is 162,42m First Floor living area is 135,71m Thanks in advance. Re: Custom Double Story Home Downpipe 2Jul 11, 2021 8:22 pm Is it one roof area? Your description is vague and contrary to the posted photo. The calculations depend on the roof catchment area (roof space x roof slope multiplier), your region's 1:20 Average Recurrence Interval, your gutter's cross sectional area and the downpipe size. You haven't provided any of that information. The thread needs to be moved to the Building Standards; Getting It Right forum. 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: Custom Double Story Home Downpipe 3Jul 11, 2021 8:54 pm SaveH2O I think what they are describing is something similar to the picture above but the lower floor is larger than the second floor. The upper floor 135m² will drain via 3 downpipes on to the lower floor that is only about 30m². The whole roof slopes one way like a large skillion like in the picture. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: Custom Double Story Home Downpipe 4Jul 11, 2021 9:15 pm chippy @SaveH2O I think what they are describing is something similar to the picture above but the lower floor is larger than the second floor. The upper floor 135m² will drain via 3 downpipes on to the lower floor that is only about 30m². The whole roof slopes one way like a large skillion like in the picture. Thanks Chippy you got it right, and sorry for not proving more info im in early drawing stage and i dont have the info requested by SaveH2O, the roof is one roof area not like the photo Re: Custom Double Story Home Downpipe 5Jul 11, 2021 9:21 pm chippy, you are better at deciphering than I. I was lost on this one. 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: Custom Double Story Home Downpipe 6Jul 11, 2021 10:20 pm I take it that the lower gutter will have one downpipe in the middle and the others at the ends. Having the straight gutter run gives the best efficiency. If you are close to Sydney metro, your 1:20 ARI will be about 200 mm/hr which is based on a 5 minute rain intensity average of 3.33 mm/min but the more regional Intensity Frequency Duration (IFD) is becoming more regularly used now. Without knowing the method used and the figure, I can still give you a ball park guesstimated answer provided I know the gutter's cross sectional area and the downpipe size because I would doubt that your regional 1:20 rain intensity would exceed 3.33 mm/min.. The gutter's cross sectional area is the critical one as I am sure that the downpipes would be least 90mm round which are sufficient. You can download the National Construction Code for free. The Building Code of Australia comprises Parts 1 & 2 of the NCC and the Part 2 roof stormwater drainage regulations are found at 3.5. The tables are easy to understand, you just cross reference the design rainfall intensity to the roof catchment area applicable (the factored roof slope allows for wind driven rain and is larger than the roof space area) and then cross reference against the gutter and downpipe size. Your roof slope should slot your factored roof area into the 60 sq m column serving each downpipe but this would still require a rectangular gutter cross sectional area a minimum of 7,900 sq mm or a 150 mm D gutter with a minimum 9,000 sq mm. Knowing your ARI/IFD intensities, the roof slope and the gutter size are critical to being able to give a proper answer. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. 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