timmy123 Posted July 10, 2014 Share Posted July 10, 2014 Does any one know how to design flat modern roofs as in the attached image? How does drainage work? How are they constructed with wood framing house? Regards, Tim Link to comment Share on other sites More sharing options...
MPDesign Posted July 10, 2014 Share Posted July 10, 2014 Tim, IMO The construction can be in lumber, I-joist, steel bar joist, poured concrete, to name a few. The bottom line is what spans do you need for the design and geographic location for specific load calculations. As far as drainage is concerned it usually is on the low side of the roof pitch. but seriously it depends on the finished look of your design. Do you want gutters to show or not? that dictates how the drainage will be designed weather external or hidden. regards, Michael Link to comment Share on other sites More sharing options...
HumbleChief Posted July 10, 2014 Share Posted July 10, 2014 From the attached picture it's really hard to say what's going on behind the fascia of the flat roof. If I were designing/building it and it truly was a flat roof or at least designed to look like a flat roof, there would actually be small parapet walls around the flat interior roof area and that flat interior roof would be filled with crickets that would channel the water to either exposed scuppers or an in-wall drain system. The crickets would be hidden by the small parapet walls and the actual roof would not be flat at all as where I live it would not pass code as we need a minimum of 1/4" per foot fall. That's probably why the picture shows such a large fascia. If you really want a truly flat roof check to see if you can build one in your area then be ready to waterproof the heck out of it and await a call in a couple years when it starts to leak. Oh, and as Michael says you can build out of any building material you choose. 1 Link to comment Share on other sites More sharing options...
rlackore Posted July 10, 2014 Share Posted July 10, 2014 Parapets are an option. Either way, the roof will need a slope, typically 1:96 or 1:48 as minimums (check codes). You can achieve the required slope of the roof plane through the roof structure, or with tapered insulation. Of course, choice of membrane and proper detailing of flashing is essential. Link to comment Share on other sites More sharing options...
Nicinus Posted July 10, 2014 Share Posted July 10, 2014 Perhaps Chief can make the plan available? After all it is used for marketing. Link to comment Share on other sites More sharing options...
Kbird1 Posted July 10, 2014 Share Posted July 10, 2014 This Style is pretty common especially Downunder , so I am sure Glen and some of the Kiwi guys will chip in too , often called a Monoslope ,( or Skillion Roof in Oz) but basically built like a big Shed Roof. There is no need for crickets really , it can be done with the edge Flashing, it has a vertical edge standing up about 1 - 1 1/2" above the roof surface to channel water down the roof to the standard gutter at the bottom ( similar to the shed roof edge flashing actually). On a large project it may still be advisable of course ( commercial Job approach), but the upstand stops water rolling off the edge and "dripping" and causing staining etc. on larger built up Fascias. The rest of the detailing is pretty standard as far as Soffits, venting, Low Slope roofing ( Torch-On) etc. Last one I built was a small Art Studio but I only got a couple photos with the edge showing ( and the Client's painting ) Link to comment Share on other sites More sharing options...
HumbleChief Posted July 10, 2014 Share Posted July 10, 2014 I thought the OP was referring to a 'flat' (looking) roof, not a roof with a visible or perceptible slope. If he was referring to a sloped roof, or a mono slope roof, then of course just slope it and be done with it. If he wants it to look flat (not be flat as that's some guaranteed future pain) then I'm not sure how to build it other than what was suggested above. I'm thinking that a monoslope roof is indeed flat - it's just not level. I think the OP wanted a FLAT AND LEVEL roof - could be wrong. Link to comment Share on other sites More sharing options...
raltd9245 Posted July 10, 2014 Share Posted July 10, 2014 Tim, IMO The construction can be in lumber, I-joist, steel bar joist, poured concrete, to name a few. The bottom line is what spans do you need for the design and geographic location for specific load calculations. As far as drainage is concerned it usually is on the low side of the roof pitch. but seriously it depends on the finished look of your design. Do you want gutters to show or not? that dictates how the drainage will be designed weather external or hidden. regards, Michael Tim is correct, I've done all of the above at one time or another. In Az "Flat Roofs" usually have a parapet either sloped one way or with crickets and Scuppers. IMO flat roof is a misnomer you can't have a flat roof and take care of the water. The trick is to make it look flat. Link to comment Share on other sites More sharing options...
Kbird1 Posted July 11, 2014 Share Posted July 11, 2014 Parapets and scuppers as suggested, if you want it to look flat from the street but the image on the Chief Website doesn't look flat to me , hence my response re the Mono-slope but maybe I interpreted the question wrong , wouldn't be the 1st time today Link to comment Share on other sites More sharing options...
Joe_Carrick Posted July 11, 2014 Share Posted July 11, 2014 As someone who designed my own home 25 years ago with a "Flat Roof System" I can say that it's not that big of a problem. My method was to have a Rafter System with a 1/4" per ft slope to internal roof drains and overflows. The Ceiling joist wer then scabbed on to the sides of the rafters perfectly level. The waterproof membrane is the key element. Generally, a good torch-down 2 ply system is good for at least 20 years. Even better would be a decking system which will probably last for at least 30-40 years. I designed my home with just a 6" curb around the perimeter and sloped the roof to the center where the drains were located. As far as modeling it in Chief - I just use a floor with short solid railing walls for the parapets. The actual slope & drainage are handled with details and notes. Modeling it as perfectly flat isn really a problem -it's close enough and the actual construction isn't that difficult for the builder. Link to comment Share on other sites More sharing options...
dshall Posted July 11, 2014 Share Posted July 11, 2014 JC, I've been doing a few decks lately. Using area drains, trying to limit max. Change in drop to 2", IOW, max 8' run to a drain. Using multiple area drains in lieu of scuppers for overflows. I am finding I am putting the drains I centers of decks vs at perimeter walls. Any comments? Link to comment Share on other sites More sharing options...
Joe_Carrick Posted July 11, 2014 Share Posted July 11, 2014 That should work fine as long as the edge of the deck (2" high point) provides a way for the water to get out if a drain gets plugged. I would opt for one of the high end membrane deck systems and make sure the bond between the drains and the membrane is positive so that any standing water can't get thru into the structure. Link to comment Share on other sites More sharing options...
raltd9245 Posted July 11, 2014 Share Posted July 11, 2014 JC, I've been doing a few decks lately. Using area drains, trying to limit max. Change in drop to 2", IOW, max 8' run to a drain. Using multiple area drains in lieu of scuppers for overflows. I am finding I am putting the drains I centers of decks vs at perimeter walls. Any comments? You are possibly making the framing much more expensive doing a center drain in lieu of a one way slope. IMO Link to comment Share on other sites More sharing options...
Joe_Carrick Posted July 11, 2014 Share Posted July 11, 2014 Ron, I think you're right, but it really depends on the structure. In Scott's case I believe he has a span of about 16' so if he sloped in just one direction at 1/4" per foot he would have a total drop of 4" which could be a visual problem. There are basically 3 ways to get slope on a "Flat Roof": 1. Sloped the Rafters and add level ceiling joists if needed. 2. Level Rafters and add wedged shaped strips on top to create the slope 3. Level Rafters and a LW Concrete Topping sloped as needed. My preference is #3 Link to comment Share on other sites More sharing options...
dshall Posted July 11, 2014 Share Posted July 11, 2014 Ron, I think you're right, but it really depends on the structure. In Scott's case I believe he has a span of about 16' so if he sloped in just one direction at 1/4" per foot he would have a total drop of 4" which could be a visual problem. There are basically 3 ways to get slope on a "Flat Roof": 1. Sloped the Rafters and add level ceiling joists if needed. 2. Level Rafters and add wedged shaped strips on top to create the slope 3. Level Rafters and a LW Concrete Topping sloped as needed. My preference is #3 4rth way is to build flat roof with ply over and then put the rippers with more ply on top. More plywood but maybe easier to build. I like this method the best because at the last minute you can change how you want to deck to drain. And Ron, Yes, JC's point about a large differential between highest point and lowest point gets to be extreme. I think I like the idea of the lowest point being no lower that 2" from highest point. If this is the goal, a max of 8' at 1/4"per ft means a 2" ht. differential. This way you can avoid scuppers if you want as long as you put in one extra drain that would meet the overflow requirements. I know this might not be this most cost effective approach, but it seems to give the most flexibility. I can't wait to retire. This frickin business somehow has become rocket science out here in California. Ask JC how much his burned out kitchen is costing the insurance company, it will blow your mind. It is such a frickin battle to get permits these days. I go down to the city and look at plans from major architectural firms, and I don't know how they got a permit. Boiler plate details that barely apply to specific conditions. These cities are essentially forcing homeowners to do things without permits because going through the permit process is such a costly exercise. I have neighbors who are redoing their kitchen, poor contractor, has met with these people probably 6 times too many times and we are going to meet again at 3:00 to discuss..... I don't know what. Tough to make a buck these days. Link to comment Share on other sites More sharing options...
DRAWZILLA Posted July 12, 2014 Share Posted July 12, 2014 blow your mind. It is such a frickin battle to get permits these days. I go down to the city and look at plans from major architectural firms, and I don't know how they got a permit. Boiler plate details that barely apply to specific conditions. They bribe the plan checker, simple as that. Went in to the city the other day and the plan checker said it will be 4 weeks before he could get to it. He also said that he could do it during his off hours for $500. The city of Yorba Linda fired their inspectors and plan checkers (cleaned house) for taking bribes. about a year ago. That's what we have become. Does anyone just do their job anymore?. They become too busy at work doing who knows what and take all the plan checks on the side, double the money, why not. Link to comment Share on other sites More sharing options...
dshall Posted July 12, 2014 Share Posted July 12, 2014 Perry, probably over half of what I charge is for dealing with the nonsense we have to thru these days. Link to comment Share on other sites More sharing options...
smitty Posted July 13, 2014 Share Posted July 13, 2014 Hi tim Thought l would throw my two bob's worth in. Built a few of these down under (Sydney) as they are becoming popular. Similar to the description given by ds hall. Basically use I beams ( hyspan) or LVL's straight onto level wall top plates. The underside of these serve as fixing for the ceiling sheets. The I beams ( depending on span) maybe upto 360mm deep or more? On top of the I beams (that are level) place ply sheeting ( 16mm) would do. This allows the carpenter easy access and to work easily. Then construct the parapet wall around the edge of the roof at desired height ie maybe 400mm depending on pitch and high point of roof. This is constructed as per normal stud wall. For the roofing material we would use metal (clip Lok) sheeting that can be use d at a minimum 1 degree pitch. This would sit on stud walls of varying heights spaced at approx 900mm to 1100mm across the roof span in place of standard roof battens. The lower stud wall or batten needs to be high enough to allow for a box gutter (say, 135mm) three lengths of 90 x 45 mm on top of each other. The upper stud wall (batten) maybe 300mm high etc depending on span. The metal sheeting is fixed to the batten walls. Then it is a simple matter of flashing the parapet wall down onto the metal roofing. Drainage pipes can run between rafters/ceiling joists, above eave/soffit. Hope this helps. Smitty Link to comment Share on other sites More sharing options...
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