Sloping Insulation On Mechanical Roof

[gnarkill283]

This might be less of a code question and more of a roof design question but since everyone's so helpful here, I thought I'd ask it anyway. We have a large roof that will only be accessible by maintenance personnel. We are trying to keep the parapet heights as low as possible so we are going with the minimum 1/8" per 1' slope to drains if possible. The roof construction is roofing membrane on top of sloped polystyrene boards on top of concrete/metal deck. I'm new to modeling drainage roofs in Revit and what I've noticed when you actually have to model these slopes is that the longest distance to drain decides the edge height of all the drain areas. That's because if say one drain area is smaller than another, it still needs to reach the same height so there isn't a tripping hazard between the 2 areas right? Also should I be using crickets to reduce insulation costs? Its impossible to model crickets accurately in Revit so in some projects I've seen just slopes indicated with line work and no spot elevations (I'm told that the roofers will know how to slope the crickets themselves). Appreciate any help - thanks

 

[gnarkill283]

https://ibb.co/nMfB51S

 

[e hilton]

If it were my project, i would turn off the computer and do it the old way. Looks like you need about 4” of slope, so design your parapet from there. You say the parapet needs to be as low as possible ... how much do you need to turn up the roofing materials, and allow for a cap? A foot? Ok, show that, and then show drain locations, with a note that the sloped insulation to be designed and installed by others. Let the roofers work out the small details.

 

[Yikes]

No opportunity to put the roof drains towards the exterior walls, instead of the center?

Tripping hazard should not be an issue on an unoccupied roof. If it's only 1" you can also add more tapered insulation.

Inside corners can be tricky. Sometimes it's easier to do what you've done, or even add in a 12" high "dam" pony wall to isolate the changes in slope directions.

 

[gnarkill283]

No opportunity to put the roof drains towards the exterior walls, instead of the center?

Tripping hazard should not be an issue on an unoccupied roof. If it's only 1" you can also add more tapered insulation.

Inside corners can be tricky. Sometimes it's easier to do what you've done, or even add in a 12" high "dam" pony wall to isolate the changes in slope directions.

If the drains are against the exterior walls then the distance to slope would be greater making the parapet higher which needs to be 42". Let's say it is an occupied roof, then what I described before is accurate in that the largest distance to drain will govern the height of all outer edges if the drains are done the way I show in the link above - is there a different way like using crickets to avoid this?

 

[Paul Sweet]

IBC requires a minimum 1/4" per foot slope for most built-up and single ply roofs.

You could extend the right hand side of the lower roof to the point where it intersects the upper roof and avoid the offset. Another option is to add a length of cricket insulation where the 2 roofs meet to bring the lower roof up to the higher roof. The roofing sub will probably have his insulation supplier do a layout anyway, and it will probably be different than whatever you draw..

 

[Tim Mailloux]

this is not the right forum for Revit modeling questions. But they can be a down right bitch to model correctly with the correct slopes and crickets. For roof crickets I use an adaptive family that hosts to the roof surface and has adjustable parameters to define slope / pitch. This family is not the easily thing to use but gets the job done and is fairly accurate. For the roof pitch I usually model the roof flat, and then draw in roof 'split lines' to define where and how the roof will fold / warp, I then use the 'Modify sub elements' tool to adjust the roof thickness.

 

[classicT]