Gambrel Roof Modeling Issues


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Using manual roof planes to create a gambrel roof on top of the second story floor, I locked the pitch and the ridge top height so it calculates the other values. This roof plane screenshot shows the correct top of plate at 197 15/16".




This roof plane screenshot calculates the Top of Plate at 198 1/8" despite the other values being correct. I took the correct roof plane above and copy reflected it with this result. I Also drew it as a manual roof plane. Still get the same incorrect value. How does this happen with symmetrical reflected roof planes? Or manually drawn symmetrical roof planes?



I drew this in cross-section in AutoCAD to double check the numbers and math in Home Designer. There is some error in the decimals, I even typed the decimals into the ridge top height to reduce error. It seems to take the decimals but displays the nearest fractions. Otherwise the numbers calculate correctly.


I am left with mismatched top of plate values and the way the roof generates at the connection between upper and lower pitches is a mess. 





Any ideas on how to fix this?


Thank You,



Home Designer Pro 2021



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24 minutes ago, wranch said:

I am left with mismatched top of plate values and the way the roof generates at the connection between upper and lower pitches is a mess. 


Did you Join (with the Join tool) those 2 roof planes?

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Thank you David and Eric.


The join tool helped, but bumped the geometry around a bit. I got that kind of sorted but I am still seeing the same issue with a lack of symmetry in the roof plane specification as I posted above and in the 3D model, screenshots below.


I started this as a new model to try to reduce variables from things I had tweaked previously. It is just exterior walls, the second-floor hip walls and an asymmetric gambrel roof. I am confused why this won't generate symmetrically.




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26 minutes ago, wranch said:

I am confused why this won't generate symmetrically.


Not something anyone can answer without knowing exactly the steps taken.


Attaching the plan file (close Pro first) will give someone something to experiment with.

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In order to obtain symmetry in a roof design, especially a gambrel roof system, each pair of roof planes side to side, must match in terms of their pitch and baseline heights. This is also true for the other two roof planes that are opposing pairs. Until they are made symmetrically on both sides you will not have a useable product. The roof plane baselines must also be laid out in plan view symmetrically as well as having matching pitches and baseline heights.


The easiest way to get a gambrel roof is to properly set up your structure in plan view and then follow unerringly the steps and settings described in the Build Roof Dialog - Roof Types Tab - Gambrel Roof settings placed by you in the opposing walls on the wall's Roof Tab, the opposing walls set to "Full Gable Wall". Only if the geometry of your floor plan and its pre-settings being correct will you then get a product. It can be done manually but whatever method used must be precisely and methodically laid out.



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I think I have isolated the problem. The attached plan has all the correct roof geometry and symmetry, yay! The issue is where the two pitches meet and the detail of that rafter connection is creating a weird roof plane joining and rafter connection. It is terminating the upper pitch rafter at the lower pitch instead of the other way around. Seen in this screenshot: 




The lower pitch uses 2x6 framing, the upper pitch uses 2x8 framing. This AutoCAD screenshot shows the correct as-built detail with the 2x8 in green and the 2x6 in red.



If I use join roof planes it destroys the geometry. Is it possible to fix this detail to match the as-built?


Thank You




Gambrel Roof

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