Browse Forums General Discussion 1 May 13, 2010 9:34 am Our builder has told us that with the type of roof we are having, we will need to have box gutters. I have a feeling these are best avoided ....????? Here's our house .... Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Building on an acre in Macedon ......one day. Re: Opinions on box gutters please.... 2May 13, 2010 10:20 am Box gutter probably aint as reliable as quad gutter(if they are not maintained. In saying that if you design your house properly there is no issue. In my case I made sure I had redundancy in the box gutter. I thought about what would happen if the box gutter blocked and make sure there was other option for the water to travel. You could do the same. Perhaps it may be an option to have a done pipe on either end and perhaps make the downpipes bigger or something to minimize blocking. Re: Opinions on box gutters please.... 4May 13, 2010 1:19 pm So basically what you're both saying is that the issues with box gutters are: 1. they need to be maintained so they don't block up and overflow, because if they do the water will run down internal walls 2. they need to be able to carry large volumes of water in case of a real downpour - again so they don't overflow. Quote: They can work fine but many homes simply don't have the roof drainage designed properly as architects and builders tend to take the same approach as they do with eaves gutters which just doesn't cut it with internal gutters. It has to be done right. So Mozzie, how do we ensure the roof drainage is designed properly? Is there anything else other than what I've said above? (And wouldn't a plumber do this instead of the builder/designer? ) And, my final question is, do I have any choice with the guttering with the type of roof we're having? Or am I stuck with the box .... Building on an acre in Macedon ......one day. Re: Opinions on box gutters please.... 5May 13, 2010 5:30 pm When I went through the trade years ago it was drummed into us that box gutters are a last resort and to be avoided like the plague. Ive seen some real expensive damage done on commercial sites when one's blocked and overflowed. By the looks of your design its pretty much impossible to avoid unless the roof is raised in the middle to fall outwards. I doubt if the designer would do this without significant cost Arfur Re: Opinions on box gutters please.... 6May 13, 2010 7:41 pm Hi Mumagoose, If you really want to get serious you could get a civil engineer to have a look at the design and calculate the gutter size, downpipe size and what sort of design to use but most builders and plumbers would probably use basic rule of thumb. I'm having trouble working out exactly what the roof design is from those elevations as there isn't a roof plan but it looks to me like you are draining quite a large area of roof into a single box gutter - or is it two seperate ones? The rainfall intensity for Melbourne for a 1 in 100 year storm is 186mm per hour. Rainfall intensity isn't actually based on an hourly figure of rainfall, rather its the intensity of rainfall for a given time - say 2 minutes. So lets say it rained that hard for two minutes because thats all it can take to flood a poorly drained roof. Obviously with eves gutters this isn't a problem because when the gutters overflow they simply flow away from the house and no damage is done. With internal box gutters once they fill up the water spills over the edges into the roof space and onto your ceiling or down the walls. This is why internal box gutters are considered undesireable. Areas in the tropics can have up to 600mm/hour rainfall intensity where you can barely see 10m in front of you. In these cases some buildlings don't even bother with gutters as no system is going to drain that fast. Even in Melbourne many large buildings have some serious rain catchment areas and its not uncommon to have a siphonic system draining multiple inlets into a single downpipe at above 200 litres per second - serious stuff that can be catastrophic if it fails. Anyway lets say you were draining approx 14m x 25m of roof area. Based on a Melbourne 1 in 100 year rainfall intensity of 186mm/hour thats 350sqm x .186m = .65 cubic meters. Divide that by 1000/3600 to convert to l/sec and you have 18.6 litres per second to drain off that roof. If you had two downpipes at either end of the gutter then each one has to run 9.3 l/sec. I hope this isn't what your architect has in mind. Nevertheless there are many things you can do to safeguard disaster: GUTTERS: The first one is to use a decent size box gutter. A width of 200mm is considered the minimum for residential properties and hydraulically speaking its desireable to have a ratio of 2Wx1H or in other words 200mm width x 100mm height. I personally think this wouldn't be high enough because 100mm isn't very far for water to rise before it drains over the edge. I'd choose more like 200mm x 150mm. Another thing to think about is water retention - the bigger the gutter the more water it can hold. A 25m section of gutter that size could hold 750 litres of water before it overflows so if it rained very hard for only two minutes that extra retention can buy the system time to catch up and drain the water away. Another thing with box gutters is you need to run a decent amount of fall. This is another area where architects and builders fail miserably with box gutters as over long distances you need a bit of roof space to get enough fall. I can't remember the gutter fall for galv steel but I thinks its 1:200 so over 12.5m (if you're draining from the centre) thats 62mm. If there is not enough fall the gutter will rust out in no time as water will never drain away properly. As it is an internal box gutter is expensive to replace and for the sake of a few hundred dollars I'd seriously consider getting it made from stainless steel so it will last for the life of the house. RAINHEADS: Rainheads are a good idea for use on parapet walls either end of the box gutter. These are used externally and can actually look attractive despite many architects not liking them. Heres an idea of what they're like: http://www.stratco.com.au/products/Rainheads_Sumps/rainheads_sumps.asp One of these either end of the gutter and the appropriate sized downpipe is the best way to go. Make sure as is in the pictures they are fitted with overflows. The picture shows some pretty small ones which are no where near big enough. If you want a system that is close to fullproof then you want 100% overflow capacity. In other words if all of the downpipes block the overflows whould be able to flow just as well. So if you have a 100mm downpipe then two pops out the side of the rainhead about 75mm each are barely going to cover it. For aguments sake if you actually did have a downpipe running 9l/sec then at a very rough guess 150mm is more like the size you want. Downpipes never run at full capacity as they suck in air as well as water. Some inlet designs use a funnel shaped body that helps to encourage better flow and baffle air out of the system such as these: http://www.marley.co.nz/webfiles/MarleyNZ/files/rainwater_roof_outlet.pdf If you are using downpipes internally then you can run a sump and this sort of inlet which will work quite well. For your house it looks like all of the downpipes would be external on the outer wall so it would be rainheads. Another thing with a decent rainhead is that they often have the downpipe sitting higher than the base of the sump so leaves tend to fall to the bottom and not block the downpipe. So without trying to confuse the issue any more I'd recomend large stainless steel box gutters with rainheads that incorporate decent overflow capacity and adequate sized downpipes. Never run a single downpipe for a gutter no matter how small the gutter is and the more downpipes the better. Also make sure that the area around the overflows on the ground drains away from the house (a stormwater pit nearby is even better). I wouldn't leave it up to the plumber to decide all of this for you - get it specified on the plans and have it okayed by someone who knows what they are doing. Then make sure it is installed as per the drawings. I hope this gives you a better understanding of roof drainage and what to look for. For me personally I wouldn't have a problem using interal box gutters as I used to design roof drainage and I know that if its designed and installed adequately you have nothing to worry about. Re: Opinions on box gutters please.... 7May 13, 2010 8:00 pm Hmm, one-in-one-hundred-year storms? We had one of those late last year with a stupidly huge amount of rain dumped on us in a 15-minute period. The box gutter at the front of the house was fine. We had water running into the roof cavity from all the standard gutters though, and dripping through fans and light fittings. Re: Opinions on box gutters please.... 8May 13, 2010 9:15 pm Good info mozzie I'd like to add : turn the top edge(s) of the vertical sides inward to stop fast flowing water from going over the sides... sort of like 'weathering' the 'box' guttering. I am all for Box gutters they are EASY to clean, and rather than having guttering all around your house you can have 1 well made one doing the job. Onc Where you are coming from is where you are going to... Re: Opinions on box gutters please.... 9May 13, 2010 10:11 pm Awesome info Mozzie, thank you - that is exactly the sort of information I was after Yes, we are draining a large roof into a single box gutter - which I was liking the idea of because, as Onc said - it's only one gutter to maintain then. Also we are building in Macedon so obviously we will be living with the risk of bushfires and we were trying to have a simple roof so there weren't any nooks and crevices for embers to hide in. I was thinking a box gutter filled with water would be quite a handy thing in the case of a bushfire.......hmmm , but now I'm wondering if there are regulations around having to have gutter guard or something with a high BAL assessment - anyway, that's another issue for another time. Quote: If you had two downpipes at either end of the gutter then each one has to run 9.3 l/sec. I hope this isn't what your architect has in mind. So far it's me that's designed the house Mozzie - and I'm a physio not an architect, so maybe it's time I got some professional help on the design front! But .... what is a reasonable amount of water to expect a single downpipe to run? (Or does that depend on the product/size etc of the downpipe?) Anyway, thanks heaps for all the advice, I now feel happy to keep the "box" rather than change the house plan! Building on an acre in Macedon ......one day. Re: Opinions on box gutters please.... 10May 15, 2010 1:23 pm Not sure I can answer that question as it has been a long time since I was involved in this stuff. Your design so far is unusual for a residential propery - you are running two downpipes in place of what would normally be more like 6. It calls for a commercial type solution where you would have it engineered and use larger size downpipes that feed into open stormwater drains that can be cleaned out and also used for water retention. I would think that you will need to check some of he regulations as you mentioned but if you can change the design to incorporate more downpipes then that can only make things easier and cheaper. I'd be waiting until your design is finalized then contacting a civil engineer - may not cost that much as it shouldn't be a big job for them. Re: Opinions on box gutters please.... 11May 15, 2010 3:39 pm You should be saving heaps by having a flat roof('batwing' actually.)(no hips or valleys) the only thing is unless you want it you will end up with a ceiling on the 'rake'. ...or have a low ceiling or very high roofline at the high point. ...and the lowest part of your home will be the middle.(least thermal insulation[good for stove not for fridge]) Just a thought or 2 Where you are coming from is where you are going to... Re: Opinions on box gutters please.... 12May 15, 2010 8:47 pm Yeah Onc, we did want a raked ceiling - at least in the living area, but not over the bedrooms etc...hmmm, may have to look at that further. I don't want low ceilings or a stupidly high point..... I kinda just wanted a flat roof with the minimal angle required for drainage over those areas The "batwings" (I was calling them butterflies ) are just at either end on the house. Here's the floorplan (so far).... http://i874.photobucket.com/albums/ab301/mummagoose_2010/FloorPlanPrivate.jpg So the box gutter would actually be on an "outside" wall over the kitchen/laundry/study area - does that make sense? So would it be possible to have another couple of downpipes here somewhere? Or is that just a silly suggestion? Onc, can you explain your point about thermal insulation? So do you mean the lowest point of the roof will have the least insulation (because of roof space?) .... or have I totally missed the point? Anyway - thanks for your input Mozzie and Onc. If I ever get a planning permit I will definately be needing some more "professional" help on this. Not saying you guys are not professionals - but I certainly am not! Building on an acre in Macedon ......one day. Re: Opinions on box gutters please.... 13May 16, 2010 5:03 pm I don't have much knowledge when it comes to the designs of roofing, guttering and drainage, but I am well experienced, having seen the all-too-common results of poor designs! I do water damage restoration as part of my job. I'll mention two of many jobs I've been to since the big storm we had about 8 weeks ago... One was a $5 million architect designed home. The owners had been in the property for one year. It had taken 3.5 years to build, and they've had problems whenever they have heavy rain. The quality wool carpets had wet patches throughout the home in about 20 places. She explained they have a skillion roof with box gutters and water overflows into air conditioning ducts and the ceilings. The carpets had already been replaced about 6 months earlier at a high cost to the builder. It seems its a design fault, and I'm not sure how they will address it. Another job, I have removed carpets from three rooms and dried out the building. A long skillion roof again, and box gutters overflowed. The internal wall beneath took a LOT of drying over about 20 days. New carpets are being fitted this Tuesday. People renting the house are crossing fingers it doesn't happen again. Seems to be that building designs are not adequate when it comes to minimising risks of water damage! But its all good business for me! Ash. Re: Opinions on box gutters please.... 14May 16, 2010 6:33 pm royalblue I don't have much knowledge when it comes to the designs of roofing, guttering and drainage, but I am well experienced, having seen the all-too-common results of poor designs! I do water damage restoration as part of my job. I'll mention two of many jobs I've been to since the big storm we had about 8 weeks ago... One was a $5 million architect designed home. The owners had been in the property for one year. It had taken 3.5 years to build, and they've had problems whenever they have heavy rain. The quality wool carpets had wet patches throughout the home in about 20 places. She explained they have a skillion roof with box gutters and water overflows into air conditioning ducts and the ceilings. The carpets had already been replaced about 6 months earlier at a high cost to the builder. It seems its a design fault, and I'm not sure how they will address it. Another job, I have removed carpets from three rooms and dried out the building. A long skillion roof again, and box gutters overflowed. The internal wall beneath took a LOT of drying over about 20 days. New carpets are being fitted this Tuesday. People renting the house are crossing fingers it doesn't happen again. Seems to be that building designs are not adequate when it comes to minimising risks of water damage! But its all good business for me! Ash. Our next door neighbours have boxed guttering, they have had at least two overflows that I am aware of in recent times, one of our deciduous trees' leaves goes into their gutters, so I am told, and they would have their own plant life that ends up in there and they don't clean it out often enough. But even when they do they still have problems so they say. I am sure they would like us to remove the tree but since it's been there longer than them - it ain't going to happen. Their house is about 30 years old. Re: Opinions on box gutters please.... 15May 16, 2010 8:33 pm We have a box gutter as part of our new extensions/renovations. We actually have a roof sloping back from the front, then 2 roofs sloping inwards from the sides - so 3 roofs draining into the box gutter (with one smaller box gutter as well). The main gutter is about 200mm wide and maybe 200-250mm high. We have just installed a rain water head and I am concerned it will not be adequate, dare I mention that to my DH though?. We have no trees nearby to mess the gutter and it is the perfect size to get up and simply sweep out with our standard kitchen broom. Re: Opinions on box gutters please.... 16May 19, 2010 1:12 pm Can I give an opinion from an unhappy previous box gutter owner-avoid at all costs!!! We have just sold our house because I just couldn't trust the box gutters to not overflow yet again. We had the water run down internal walls several times-the worst being during a"รถnce in 100 year" event in which all of the internal ceilings collapsed and we were out of the house for 3 months while insurance fixed the place. The other concern we had was that we had previously tried to have the gutters repaired (that had rusted from old age) and had lots of trouble finding someone to even quote on replacing/repairing them. 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