Based on what I am seeing here, it appears that I have got it wrong when it comes to asymmetric rafter roofs:
My attempt was to keep the ridge centered on the two roof planes, however it appears that the proper way to do this is to actually offset the ridge. It looks like I need to revisit this algorithm and provide for the more correct of the two options, or even eliminate/correct the way I am currently calculating and drawing it.
When I originally programmed this I remember posing the question to the forum as to which method was more correct, here is the diagram I presented:
And in this post I did acknowledge that there were two possibilities/configurations with regards to centering the ridgeboard with the sheathing:
P.S.
About two years after implementing the asymmetric roof I revisited this topic and that is when I posted the possible two configurations:
I didnāt get a huge response or feedback on the question so I guess at that point I dropped it and moved on to more pressing issues.
Current thoughts?
I would want to frame it according to the top illustration. I donāt like all that air. I could see myself shooting a bunch of holes in my sheathing.
Itās pretty small to look at, but it definitely seems like @WALLMAXXās illustration is in accordance with the top drawing.
@WALLMAXX is a real framer, not me.
What I find somewhat interesting with this two configuration problem is that changing from one to the other does not affect the actual roof planes of a asymmetric gable roof in any way (or should not) however it does shift the location of the ridge (lateral and vertical) which in turn changes the rafter lengths on each side roof.
With a hip asymmetric it will have even more implications as the end commons will be affected as well as all of the jack rafters and hip rafters. I will need to manually work through this to understand fully the differences between the two configurations with a fully asymmetric hip roof.
P.S.
Iām kind of kicking myself now for choosing to go with the second option (centered ridge), since I probably chose the incorrect option, but in my defense I think at the time it made more sense to me since the other option doesnāt provide much backing for the sheathing with the higher pitched roof plane.
No, just no ā¦ my experience in the field is, youāre thinking too hard with the offset ridge. I had something similar with a half-ridge beam of sorts, and the contractor couldnāt even fathom that. They understan centered, so I recommend just running with that.
To further complicate things, If you have a cathedral ceiling and need a 1" airspace under the sheathing running from eave to ridge, the ridge needs to be dropped until thereās at least an inch clear to the underside of sheathing anyway. Well, that is until you talk to the structural engineer (cough, cough) and they say that the unsupported edge of plywood pulled back from the ridge (for a ridge vent) needs to be nailed to solid blocking along itās entire length, which of course blocks your vent path. Iāve never been able to reconcile all those demands, at least not easily.
Then again, if you listen to the spray foam people, you donāt need the roof vent or vent space with their product, and that whole issue goes away ā¦ as long as you trust them on that. The roof shingle company doesnāt necessarily accept that, so ā¦ yeah, life is complicated, and the guys who have to build it just want simple.
I donāt know if itās right or wrong, I always put the long point of the rafter flush to the top outer edge of the ridge from each side. At the lengths I was working with it really didnāt matter if I was off by half an inch one way, or the other in the calculation.
As time progressed, I was able to write the equations in my calculator to be perfect and so I started to use that, and my ridge actually is offset. No one would ever notice from the ground. I just like to try and make things as perfect in reality as I can in CAD, because being extremely precise, sometimes helps to make the structure go together better.
I suffer from chasing perfection, but it makes me feel like Iām doing the best I can.
(I often dictate my responses using iOS, Siri. If Iām in a hurry, I donāt always proofread and she seems to think itās OK to drink on the job because she gets things wrong quite a bit. I apologize if somethings donāt make sense.)
To create the air gap necessary on a structural ridge, just add a temporary 2X on top of the ridge and plane all the rafters to the outer edge of that 2X.
The last structural ridge I installed was 3 1/2ā by 18ā at 32 feet long. We just added 2 x 4 plating to the top, tacked in with one or two nails, and once all the rafters were installed, we pulled that plate off.
If you donāt do that, then you have to stop your plywood back from the ridge about an inch, and you start making it nearly impossible to find continuous ridge venting that will span that wide.
I never say that my way is always right. But my way has always worked for me and I will share everything I know if it helps make someone else better at their craft.
Rake walls are an example where you can dimension every piece. If you draw everything to the exact real-world sizes, then just cut all the pieces and put it together and it works perfectly.
Itās much more accurate than trying to pop out all the pieces on the ground at the job site and then measure those pieces.
The hourly rate on a job site is much more expensive than the hourly rate sitting in your pajamas in front of a computer the night before.
I hate having people standing around adding to the pressure that I donāt fat finger a calculation or make a mistake reading a tape measure. Iād much rather draw everything out and laminate it on an 11 x 17 sheet of paper the night before and just show up and start cutting.
Yes, I like to make sure it all works before the time comes. Sometimes Iāve shown up on the site with a full scale template or rafter tale mounted to foamcore.
Here is a screen shot of an asymmetric ridge with a centered ridge board, created with the Truss Plugin:
Note how the sheathing is centered on the ridge and the way the common rafters are slightly proud on the right side.
The devil is in the details with this sort of thing.
P.S.
Moving this discussion on ridge placement back over to the Truss Plugin thread.
Why SketchUp?
Version 1.1.1 - 07.30.2023
- Updated the estimating module to provide more granular data for wall top plates.
*Note: If this updated version is installed then Version 3.2.3 of the Wall plugin is required in order to obtain wall top plate data.
This update per customer request.
Version 1.1.2 - 08.01.2023
- Updated the estimating module to provide location data (within a wall) for windows, doors, garage doors and in-wall columns.
Version 1.1.3 - 09.06.2023
- Updated the scene generator to include gable, shed and hip walls.
Version 1.1.4 - 07.01.2023
- Added complex rafter roofs within the Medeek Estimator.
- Added rafter labels (total length) for complex rafter roofs within the Medeek Estimator.
Version 1.1.5 - 01.23.2024
- Fixed a bug with the Extend Tool for groups (and components) that share the same definition.
Version 1.1.6 - 02.13.2024
- Added foundations within the Medeek Estimator: Slab-on-Grade, Slab, Stemwall, Grade Beam
There is still a lot more work to be done with adding all of the various hardware and items into the estimating for foundations. This is just a start.
Version 1.1.7 - 02.17.2024
- Enabled custom rebar within the Medeek Estimator for Slab-on-Grade foundations
Per customer request.
@LinearGraphs this one is for you.
Tutorial 5 - Estimating Custom Rebar (12:15 min.)
