Low Slope Roofs w/ Drains - Is it possible?

[jamesd10181097]

I am attempting to create a roof that would consist of metal deck placed level then place tapered insulation at 1/4" per foot originating from a roof drain location out to a complicated perimeter with a parapet. To complicate this further I also need crickets between the roof drains.

Someone told me to simply draw the roof plan using detail lines but I wanted to model it so I could see the roof slopes in section without guessing what the insulation thickness will be at the section cuts. Also with the powerful modeling tools it makes sense (to me at least that) that this would be possible and would simplify the process of calculating insulation thickness.

[sbrown]

You will just need to model two roofs on top of each other, one the structure, one the tapered insul. If your drains aren't in the center, you will break it up even further. Lets say there is one drain offset from the center 1/3 of the way to one side of the building, it will take 5 roofs total(still no big deal) 1 roof for the structure, then 4 triangular shaped (in plan) roofs where you use a slope arrow on each defining the highpoint on all of them and the low point(drain). If you want to use slope, then just make the 4 roofs trapezoidal in shape with the part around the drain a very small straight line so you can use the slope defining line.

A tip I learned from a structural engineer is to actually slope the structure to the drain, this means you don't need any tapered insul, except for crickets. You can just use 3" thick insul on most of the roof. If you go this route you just need 4 roofs instead of 5 in my example.

[jamesd10181097]

Thanks for the information, I will give it a try right now.

The only reason I did not slope the structure, is that the client wants this building planed for an additional story. So we are keeping the deck level and handeling all slope strictly with insulation.

[jamesd10181097]

One additional question, how do I make the insulation roofs flat on the bottom & sloped on top?

[beegee]

You would use an in-place void to cut the roof.

[jamesd10181097]

I was using roof tools to generate the insulation. So creating an in-place void form can not modify a roof can it?

[beegee]

First create the roof.

Then create a generic family using a void blend ( or other tools if suitable ).
Set the base of the blend at the top of the roof ( for example ) and the top at the level of the drain ( ie -200 mm or whatever ).
Before finishing the void family, select Cut Geometry and select the roof and the void, then finish.

The result will look something like this.



I was using roof tools to generate the insulation. So creating an in-place void form can not modify a roof can it?

[SCShell]

Hi Beegee,

I am following this thread with great interest. I happen to be doing the exact same thing, only back wards. (what's new!)

I have a flat canopy section of deck with framing and I am then putting tapered insulation above it, sloped 1/2" per foot upward to form a gable roof profile. (Simple way to get level roof edges and fascia trim on all 3 sides of my overhanging roof canopy.) I already have the roof deck modeled as my lower roof, locked to my canopy roof level. I have a rigid insulation roof above that, set with an offset above the level so that the bottom of the rigid sits on the deck and the top of the rigid is at the peak of the ridge based on my slope. And, I have a third roof (the roof membrane and finish) modeled as a sloping roof, which is currently "inside" of the rigid insulation. Now I just need to cut out the upper portion of rigid insulation to complete everything. (I was waiting for the weekend to do some tutorial searching/reading.)

I have not played with voids, blends or void families much; however, the ones I have done in the past were simple and effective. As usual, I now don't remember how I did them! I was wandering if your approach works the same way, or is there a better way for cutting the top of my rigid insulation with a void. Can I use an in-place void? is it a "roof based" family? And, what view is best to do this type of thing in, roof plan, 3d isometric, section or elevation?

As usual Beegee (as well as all of the other "family" gurus here on AUGI...) thank you in advance and thank you very much for sharing your time and experience!

Steve

[tatlin]

Interesting topic! And one we'd like to make easier to do in the future.

BTW, There is another (possibly easier) way to do tapered insulation currently that does not require an inplace cut at all.

1) create one roof that is the flat 'structrual deck' (T.O.Slab/T.O.Deck). This roof type has all layers up to top of stucture or the bottom of the rigid insul.
2) create another roof type that has your membrane, sheathing, and insulation. Make the insul the bottom most layer.
3) Create new instances of this type on top of the stuct deck. Slope these roofs via slope defining lines or slope arrows to the low points you need. Worry about the 'main' sloping areas first, don't worry about crickets yet. You might need to make more than one of these roofs to pitch to multiple drains.
4) Now the insulation roof overlaps the struct roof. Use Join Geometry to cut the stuct roof from the insul roof.
5) Voila, you now have tapered insulation! Join Geometry will also get rid of the thick line inbetween them.

Extra credit:
6) You could actually use the cut tapered roof to extract the quantity of rigid insul...
7) crickets can be added via detail lines or little insulation roofs joined to the main roofs
8) roof drains can be added as roof-hosted families or just level-hosted families.

[jamesd10181097]

Thanks for the advice Tatlin, sounds alot better than what I was doing.

The way that I was doing it before I saw your post was to just make roofs for the membrane itself leaving the thickness at 1/8" so the space the I intend to be tapered insulation (between the structural deck and the membrane roof) is actually empty, same with crickets. Then I plan to represent the insulation in section by drawing a filled region using the membrane roof as a guide. A little cumbersum when it comes to the sections but that was all I had at the time.

[jamesd10181097]

OK I tried your method Tatlin, but I think something is not working the way that you suggested. I made the insulation layer 12" thick so that it would intersect with the 2" steel deck. This causes the insulation to extend well below the 2" steel deck. When I join the to it merly cuts the 2" out of the 12" and leaves the potion below the steel deck. it also removes the insulation hatch for some reason.

It works great if I make the insulation layer thin enough that it would not extend beyond the steel deck. But I have some long runs that require quite a bit more thiskness than the 2" steel deck can cover up. take a look at the images.

[Steve_Stafford]

OK I tried your method Tatlin, but I think something is not working the way that you suggested. I made the insulation layer 12" thick so that it would intersect with the 2" steel deck.I think you just need to make sure the insulation roof is sitting on the structure roof. Use the Base Offset from Level parameter to move it up...

[beegee]

Hi Steve Schell,

I imagine you will use Tailn's method rather than mine ( I know I will ! ), so you won't need a detailed response about void blends etc now.

[SCShell]

Hey there,

Thank you Beegee, Matt and Steve. I like this approach...simple! I assume it will work for my "backward" situation. (I got to admit James, I did like your workaround.)

This forum rocks!
Steve Shell

[tatlin]

It works great if I make the insulation layer thin enough that it would not extend beyond the steel deck. But I have some long runs that require quite a bit more thiskness than the 2" steel deck can cover up. take a look at the images.
jamesd101,

My approach will work better if you make the lower roof thicker than just the roof deck. For the bottom roof it would work better if it was not just the 2" metal deck but also a thicker layer (8" to 2'-0') to represent the 'structural zone' where the beams or joists would be.

[SCShell]

jamesd101,

My approach will work better if you make the lower roof thicker than just the roof deck. For the bottom roof it would work better if it was not just the 2" metal deck but also a thicker layer (8" to 2'-0') to represent the 'structural zone' where the beams or joists would be.
Hey Matt,

I have tried that approach; however, if you model your bar joists say, the 'structural zone' masks your bar joists.

Thanks
Steve

[Markitekt]

Interesting procedure. Does anyone know where I may find Revit 3D roof drains for the "cherry on top".

[gsHoeflinger]

Hey Matt,

I have tried that approach; however, if you model your bar joists say, the 'structural zone' masks your bar joists.

Thanks
Steve


Very good point. I run into that same issue. Any ideas?