PlusSpec License: PlusDesignBuild
PlusSpec Version: PlusSpec 23.3
SketchUp Version: SketchUp 23
Computer Type/OS: PC Windows 11
Profession: Builder
Issue/Concern:
Hi there,
In Canada, when we talk to a roof truss manufacturer, we usually have to provide the “heel height” for trusses in the design. PlusSpec currently has an upstand value you can enter into the truss tool; however, as you’re playing with pitch, if you’re used to quoting in heel height, it takes some math and fiddling to get your roof settings set right.
I had a look int the truss tool and I don’t think I saw it in there either.
Thanks, Keith
Hi Keith, in your drawing, you show a bird’s mouth on a rafter, and as a result, the heel height of the rafter is the verticle height above the top plate. You mention significant math to figure out the height, yet the trigonometry is worked out for you. Maybe it is not as evident as it needs to be, but by simply adding in the section size of the rafter plus the sheathing or roof batten thickness in the roof tool :roof-tool3: your roof will be drawn at the correct height.
EG. If you add a 2x4 (3.5") rafter + 0.5" sheathing, the verticle heel height determines the height of the underside of the roof cladding. As a result, if you choose a 6-inch rafter, the birdsmouth will automatically be subtracted from the rafter, ensuring the heel is still the same.
So, to explain, We made a conscious decision when developing PlusSpec pro, PlusArchitect and PlusDeisgnBuild to make roofing easier, as roofing was one of the most common mistakes we see from designers. We did this by enabling end users to add known measurements like rafter size, sheathing size, and roof pitch or ratio to the tool sets to eliminate the need for the end user to do trigonometry.
Keith, I assume you have 4 or 5 standard pitches/ratios you use on the majority of projects and as many rafter sizes. Why don’t you save this as a recipe in your BOQ or as text in your template and choose which one you have used? Here is the math:
Hypotenuse length (heel height) = Adjacent side length (rafter height) / Cosine of the angle. Hypotenuse=Adjacentcosθ or in example, c=acos30°
Keith, in Summary, adds the correct rafter and sheathing height in the roof tool before you draw a roof :roof-tool: :roof-tool3: When you add the rafters, ensure you add the corresponding rafter height in the roof rafter tool or truss tool. If you want a birdsmouth (conventional roof only), increase the rafter size and ensure you have the birdsmouth tick box selected.
Yeah; that’s pretty much where I ended up; making a spreadsheet with all the math, but not after a good day’s worth of not being able to trust the assembly because I had to convert the numbers into the “tool” speak and what I was seeing in the truss vs roof tool was a bit different (compounded by the upstand value).
It would just be nice if I didn’t have to relive my highschool trig class. Even if there was a little box that showed you a summary of those measurements based on what you’ve input, I’m sure it would put at least a few designers at ease.
The reason this is an issue is that I’m designing for a very constrained county bylaw, which means that if the design is a bit off, it means removing a story from the building.
Good work, mate, but you can save yourself a bit of time with the following: BTW it took me longer to double-check the trig and make the post than it did to draw a full house so don’t feel bad
Keith, I’m not sure what you mean; there is no reason to do the trigonometry; it is done for you. All you need to do is select the pitch ratio of the roof and the rafter and sheathing size (which are all off-the-shelf measures). Draw the roof and take a measure. See the video below: I created 4 rectangles and drew roofs with multiple pitches and rafter/sheathing sizes; I cut a section and measured. It took me 2 minutes, and you could save the model as a template or a drag-and-drop component for next time.
You can get to one-thousandth of 1 millimetre of accuracy. I have never met a building surveyor who knew how to measure 1/8 of an inch, so I cant see you removing a full storey if you do the checks initially
so don’t feel bad