Modeling roofs for trusses???

[Anonymous]

I’m curious how the rest of the ArchiCAD community models roofs when they are structured with trusses? ArchiCAD’s roof tool is fairly powerful but does not have a good interface for “properly” defining roof planes relative to trusses and/or heel heights.

Modeling roofs for “stick frame” or basic rafter construction is very straightforward. Set the thickness of the roof to match the rafter dimension + roof sheathing – something like 5 ½” + ½” for a simple roof. Now, simply set your reference line to the inside of the stud wall and model away. The plate height (to story x) is easily set at something like 8’ (or 8’1 1/8” for more precision).

However….when modeling roofs for trusses, it’s not so straightforward. Composite thickness does not apply. I set the roof thickness to match the top cord dimension + roof sheathing – something like 3 ½” + ½”. I set the reference line to the outside of the wall stud. Now I need to adjust my (to story x) height if there is a special heel or raised heel condition. Nothing in the roof tool dialogue represents this kind of adjustment so I have to manually calculate the proper (to story x) every time – arghhhh! Its’ never a clean number so its always a problem if I am trying to properly represent the actual roof in relation to the rest of the building.

Note: If I am using a cantilevered truss with the bearing point/height equal to the eave/soffit height, I might place the roof reference line all the way to the outside edge of the roof.

This has always perplexed me…I’m curious what others are doing when modeling roofs for truss conditions.

Thanks,
Dan K

[Brad Elliott]

I do it the same way and wish there was an offset height setting.

[Anonymous]

Hi Dan

I was also wondering how to model the facia and side rakes on a gable roof. If you are using a 4" top cord then your side rakes also come out as 4" but should be 6". Then the facia comes out to about 5" for an 8/12. And changes for different pitches.


Brian

[Steve Jepson]

Personally, I don't fuss with the roof any more than what it takes to generate a roof plan and preliminary elevations, until I have the truss plans.

When I get the truss diagrams back, I use the magic wand to create a few precision 3d trusses. In section I move the roof (roof sheathing) and fascia up or down a little to match it.

I make roofs the same for stick framing as I do for trusses, they are just the sheathing.

Sometimes I use the profiler to add the metal drip edge,fascia, gutter, soffit, frieze, etc...

[Steve Jepson]

BAS wrote:
Hi Dan

I was also wondering how to model the facia and side rakes on a gable roof. If you are using a 4" top cord then your side rakes also come out as 4" but should be 6". Then the facia comes out to about 5" for an 8/12. And changes for different pitches.


Brian

I use a rafter for the gable end fascia and trim sometimes.

What I do most often in create it from my elevation.
In your elevation add a few lines to make the correct outline of your special fascia and trim.
Then copy and paste it into model view.
Set a slab thickness to the thickness you need. Use the magic wand to fill the area of your fascia.

View the fascia/slab in 3d (top view) save as .gsm
Now it is a library part. place it in the drawing. go to elevation and raise it up or down to fit the roof.

the trick to this is to draw a little slab next to your facia/slab and include it in the 3d view so you can click on it to get a true birds eye view of the fascia/slab.

This is basically the same way you make trusses from the manufactures' diagrams.

It may sound a little awkward but it is really quite easy and fast.

[Anonymous]

BAS wrote:
Hi Dan
I was also wondering how to model the facia and side rakes on a gable roof. If you are using a 4" top cord then your side rakes also come out as 4" but should be 6". Then the facia comes out to about 5" for an 8/12. And changes for different pitches.

Brian

Brian,
I use a special object for rake conditions - see attached image. In the image, the roof plane is 4" but the rake and subrake are 6".

Dan K

[Link]

Dan wrote:
This has always perplexed me…I’m curious what others are doing when modeling roofs for truss conditions.

Just whack it on and raise it in section.

Cheers,
Link.

[Anonymous]

Steve wrote:
Personally, I don't fuss with the roof any more than what it takes to generate a roof plan and preliminary elevations, until I have the truss plans.

When I get the truss diagrams back, I use the magic wand to create a few precision 3d trusses. In section I move the roof (roof sheathing) and fascia up or down a little to match it.

I make roofs the same for stick framing as I do for trusses, they are just the sheathing.

Sometimes I use the profiler to add the metal drip edge,fascia, gutter, soffit, frieze, etc...

Steve,
You must be building your own designs - It sounds like you have a modeling technique that works for you.

I explored modeling the roof as sheathing only but quickly gave up on it as the process did not easily reference from (to story x) in the roof dialogue...basically, I think we should be able to model roofs the way they actually "plate" from the structure.

As far as waiting for the truss diagrams to come back, I rarely have that luxury...If you're actually building the project you can probably wait...but if you're only designing it, then you have to "finalize your drawings earlier on.

Dan K

[Anonymous]

Link wrote:
Just whack it on and raise it in section.

Yup....that's pretty much what ArchiCad forces you to do. You would think that such a sophisticated software would have a better way of handling these conditions without having to resort to manual 3D manipulation.

Dan K

[Jefferson]

Dan -

Like Link and Steve, I set the roof as strictly the top skins. Thickness is usually choosen in reference to rafter tail thickness, and elevations are top plate heights. In it's early stages it's thick for visual representation, [read for the client's viewpoint]. The basic form, valley, hip, gable adjustments etc. and then once trusses/rafters are modeled, the up/down in section, [when I'm feeling "on my game", in 3D window.] The "thinning" of the roofs, 5/8" sheathing, + whatever roofing material buildup will be, and final elevation adjustments are a tail end process, once everything else is "set".

This is an extension of my model it as far possible, without going nuts, attitude. It yields nearly completed sections + elevations, plus it's RIGHT. That means no surprises on the job site, and then the only four letters used for my name are the original ones