Browse Forums Building A New House 1 Sep 17, 2013 12:42 pm I'm in the process of having a house designed by an architect, who seems to have a big preference for flat roofs and and wants to design a parapet wall, box gutter, colourbond flat roof-type of a roof. No arguments from me from an aesthetic point of view (and it would nicely conceal any solar systems from view), but I'm more than a little concerned with drainage. Is it even theoretically possible to have a good drainage system for flat roofs & box gutters? What happens if the downpipes get clogged, can the gutter be flashed so that water would not enter the building envelope/go under the roof? Re: Is good drainage possible with a flat(ish) roof? 2Sep 17, 2013 1:17 pm mesophyte I'm in the process of having a house designed by an architect, who seems to have a big preference for flat roofs and and wants to design a parapet wall, box gutter, colourbond flat roof-type of a roof. Is it even theoretically possible to have a good drainage system for flat roofs & box gutters? What happens if the downpipes get clogged, can the gutter be flashed so that water would not enter the building envelope/go under the roof? If the architect has a preference for flat rooves and box gutters, one would assume that he is experienced in good design. Box gutters must be designed for a 1:100 ARI and overflow measures must be included to prevent ingress to the building. Best practice would design a box gutter and overflow for an ARI well in excess of a 1:100. Having said that and given that I deal with persons with bad roof drainage on a daily basis, I have to say that I would never recommend box gutters as I have a personal loathing for them. mesophyte No arguments from me from an aesthetic point of view (and it would nicely conceal any solar systems from view)... PV panels need to be tilted and this can be ugly on a flat roof. 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: Is good drainage possible with a flat(ish) roof? 3Sep 17, 2013 1:48 pm SaveH2O If the architect has a preference for flat rooves and box gutters, one would assume that he is experienced in good design. Box gutters must be designed for a 1:100 ARI and overflow measures must be included to prevent ingress to the building. Best practice would design a box gutter and overflow for an ARI well in excess of a 1:100. Yes, one would assume so. Will have to check on the ARI targets that are being used for the design, thanks. I agree that with what is likely an increasingly unstable climate, ARI of 1:100 would be insufficient. SaveH2O Having said that and given that I deal with persons with bad roof drainage on a daily basis, I have to say that I would never recommend box gutters as I have a personal loathing for them. So what would you recommend, from a drainage point of view? SaveH2O PV panels need to be tilted and this can be ugly on a flat roof. True, but with a relatively high-sitting building and with parapet walls I'm thinking they would be all but invisible from ground level. Re: Is good drainage possible with a flat(ish) roof? 4Sep 17, 2013 2:49 pm mesophyte I'm in the process of having a house designed by an architect, who seems to have a big preference for flat roofs and and wants to design a parapet wall, box gutter, colourbond flat roof-type of a roof. No arguments from me from an aesthetic point of view (and it would nicely conceal any solar systems from view), but I'm more than a little concerned with drainage. Is it even theoretically possible to have a good drainage system for flat roofs & box gutters? What happens if the downpipes get clogged, can the gutter be flashed so that water would not enter the building envelope/go under the roof? Get a guarantee from the architect that if it leaks in the next 7 years they (not the builder) will accept full responsibility and all associated costs in fixing the leak - see how keen they are then to design in box gutters. I just don't understand architects who go out of their way to design in potential problems, I just don't get it. Ok, it is possible to over design/size the system but as you've mention "what happens when or if it somehow gets blocked" - either design in a couple of redundant drainage points as backup, but if they get blocked, eventually you'll get flooded. I've seen it happen. A few years ago I was working in a building on Coronation Dr, Milton when a hail storm came over. It dumped that much hail that it blocked the drains on the box gutters on the roof and flooded the top floor and damaged a floor below. Solar panels can be fitted flat to a very shallow sloping roof. We have a flat array on a 5deg sloping roof facing west. Also see http://www.uq.edu.au/solarenergy/pv-array/st-lucia-multi-level-carpark-1 ----------------------------------------------- http://pab34newdigs.blogspot.com.au/ ----------------------------------------------- Re: Is good drainage possible with a flat(ish) roof? 5Sep 17, 2013 6:17 pm I have a box gutter over my garage (house is tiled roof). Box gutters are prone to flooding as water has no where to overflow, plus the fact that silicone is waterproofing the joins. I'd recommend to avoid them if possible. Re: Is good drainage possible with a flat(ish) roof? 6Sep 17, 2013 7:04 pm mesophyte So what would you recommend, from a drainage point of view? Not all box gutters give problems but if one does, the results can be severe and that is the problem. It also has to be considered that all gutters will eventually need replacing. I would never buy a house with box gutters and I know many others, particularly those in the industry, who feel the same. As to whether this would impact on resale value...I don't know. It would be interesting to hear the opinion of others. The obvious alternative is to design for eaves gutters. There are many styles now available. The half round has a superior flush/drain function but the aesthetics need to suit. The link below takes you to a recent thread about a proposed box gutter. viewtopic.php?f=53&t=66839&p=1067108#p1067108 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: Is good drainage possible with a flat(ish) roof? 7Sep 17, 2013 7:19 pm With all box gutters there should be a built in overflow to allow for any potential blockages. We've installed quite a few over the years and were quite pedantic about their design and installation. Sometimes we have kicked the roof plumbers or roofers off the job and installed them ourselves because of poor work practices. It's not rocket science as they say and if they are designed correctly with the aforementioned overflow as part of the design and installed correctly then you won't have any problems. That being said I've also seen a lot that were way undersized and fitted woefully. Stewie Re: Is good drainage possible with a flat(ish) roof? 8Sep 17, 2013 7:44 pm Thanks for the replies guys. It seems to me that putting in something that requires extreme care in design, installation & maintenance is just an unnecessary risk that'd be best avoided - especially if/when it's easy to do so. I can't imagine an eaves gutter solution would cost significantly more either - could even be less, or what do you think? Re: Is good drainage possible with a flat(ish) roof? 9Sep 17, 2013 8:33 pm Our change from standard house plan with a flat roof to a skillion style roof cost an extra ~$30K. (Might not be so harsh for you, since it is custom designed anyway.) We did it purely for aesthetics, but it has a few other advantages too. http://www.housebythewater.wordpress.com From blank block to new home in Mandurah, Western Australia. viewtopic.php?f=31&t=65564 Re: Is good drainage possible with a flat(ish) roof? 10Sep 20, 2013 6:51 pm Colorbond has a requirement for a minimum 5 degree roof pitch if you wish to maintain their 30 year warranty. Re: Is good drainage possible with a flat(ish) roof? 11Sep 20, 2013 9:09 pm That's good to know, Dukecaddy, thanks. 5 degree pitch visible would probably just look dumb, so would have to put in parapet walls to hide that - or get a bigger pitch.. Re: Is good drainage possible with a flat(ish) roof? 12Sep 20, 2013 10:59 pm If his architect is thinking of using Colorbond Kliplok then you can install that down to 1º pitch although it isn't the prettiest of roofs in my opinion and a parapet to conceal a lot of it wouldn't be a bad thing. Stewie Re: Is good drainage possible with a flat(ish) roof? 13Sep 21, 2013 10:10 am mesophyte That's good to know, Dukecaddy, thanks. 5 degree pitch visible would probably just look dumb, so would have to put in parapet walls to hide that - or get a bigger pitch.. ...and... Stewie D If his architect is thinking of using Colorbond Kliplok then you can install that down to 1º pitch although it isn't the prettiest of roofs in my opinion and a parapet to conceal a lot of it wouldn't be a bad thing. Stewie A couple of things. mesophyte, I don't quite understand your reasoning as to why 5 degrees would look 'dumb'? Also, in another post you have uploaded a photo of your site and a plan. Do you have any elevations of the house you are planning to build as I just can't see how practical a house with a near flat roof and parapets will be in such a leafy environment. Stewie, you're right Cliplok looks a bit average but Custom Orb Accent is good down to 2 degrees which is just a 'standard' looking wave profile. ----------------------------------------------- http://pab34newdigs.blogspot.com.au/ ----------------------------------------------- Re: Is good drainage possible with a flat(ish) roof? 14Sep 21, 2013 12:32 pm I think a lot of flat roofs look ordinary and associated with commercial or cheaper houses. The other issue of flat roofs is access in the roof space for maintenance, repairs or even things like running cables or air cond ducts. If there is a leak, how are you going to find it? Also don't forget architects may like to design different looking houses to make a statement, but they aren't the ones who have to build, pay for or live in it. Re: Is good drainage possible with a flat(ish) roof? 15Sep 21, 2013 3:20 pm The flat or skillion type roof seems to be a favourite at the moment amongst a few designers. Almost invarably their will also be celestory windows that go along with this. It seems the current trend for passive solar design. The last I can remember this style was in the 60's and soon went out of fashion. The were mostly associated with "beach style" houses as they were simple and cheap to construct. It seems designers have now modified this with parapets around to hide the roofing style making it appear commercial in style. In our new estate their are 10 houses. Three of these have "flat" roofs. All roofs have some problems associated with drainage but with some luck and good design it hopefully might work well. Settlement 1/2/12 New Shed 23/3/12 Slab poured 27/3/12 Frame complete 4/5/12 Roof complete 1/6/12 LOCKUP 29/6/12 Our new build blog http://kareenhillsownerbuild.blogspot.com/ Re: Is good drainage possible with a flat(ish) roof? 16Sep 21, 2013 8:46 pm Thanks for the comments everyone. PAB_34, just thinking that a visible slope of only a few degrees will not look great; it wouldn't look flat, but not purposefully pitched either, just a little crooked. But that's just me No elevations yet, but it'd be a split level design in any case. Not sure what you mean about it being practical or not; you're going to have the clean the roof anyway from debris (yes there'll be leaves) and at least on a flat one you could walk. JB1, true, roof space / access could be an issue. Although I'm not planning on having recessed lights (prefer indirect) or ducting there, but still. delatite13, how do you think the ones with the flat roof look? Commercial? I'm not so worried on the aesthetics - a flat roof could work very well in my location - but more on the practical side.. Re: Is good drainage possible with a flat(ish) roof? 17Sep 22, 2013 9:38 am 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: Is good drainage possible with a flat(ish) roof? 18Sep 22, 2013 2:35 pm SaveH2O A related thread. Thanks. I had seen that actually, but not entirely relevant here as I get to choose the insulation levels + types, put solar PV on the roof etc. Building Standards; Getting It Right! It's all good. You can get both wye piece and the coupling with or without thread. The cost difference is negligible and means the plumber only has to carry the single… 1 4898 yes it is possible but watch for noise transmission, decouple as best you can. Maybe wider top and bottom plates with 70mm studs to allow the cabinet to be recessed fully 1 6634 You can wash over existing pavers with 10% solution of water and hydrochloric acid, then wash off. The acid will provide for required bond key with new concrete. 1 36950 |