Why elevations and not RCP?
A truss manufacturer tells the general contractor of a residential project that the truss design should change in the following ways:
- Heel heights will need to increase from 8" to 12".
- Layout will change from 24" o.c. to 12" o.c.
- Bottom chords will increase from 2x4 to 2x6.
- Truss bearing elevation will not be affected.
The architect is updating the construction documents to show the truss changes. The roof framing plan and building sections have already been updated.
What additional drawing will need to be updated?
| A. | Reflected ceiling plan |
| B. | Exterior elevations |
| C. | Structural general notes |
CORRECT RESPONSE
Exterior elevations
The exterior elevations will be affected by the truss changes, and the truss heel height will change the elevation of the roof.
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David, I agree that RCPs will be affected by changes to the truss specifications in many cases, but I believe the key words to the question are "the architect is updating the construction documents to show the truss changes." Unless exposed, truss changes will not be reflected in the RCPs. From the options available, only the exterior elevations will show changes to the trusses themselves, by changing the profile of the roof.
This question is an example of understanding from your experience other implications that changes like this will have, but you just need to think about it in the simplest, most prescriptive terms. Only answer what the question is specifically asking. Hope this helps.
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I guess NCARB could agrue that the RCP is being done by someone other than the architect, though I agree that the RCP would need to be revised too. In fact, all those drawings would probably need a revision! The elevations would definitely be a priority though, because the height of the structure would be less with 12" spacing instead of 24".
I suggest not relying on these new exams until they are more widely used and edited by NCARB.
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses
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my two (perhaps 3?) cents:
- unless there is no ceiling ("open ceiling"), the truss spacing will not be visible. if there is no ceiling and the roof framing was already updated, there may not be a need for an RCP at all; we are not told that the lighting and other usual RCP items are "ceiling/truss" mounted; they may be wall-mounted instead. not enough info.
- more importantly than the truss spacing, the _heel height_ was increased 4" but the bearing elevation of the trusses stayed the same. this will effectively raise the top chord, and hence the roofline, 4". exterior elevations will definitely be affected by this change.
- the last post mentioned that truss spacing would affect the truss height. this may (or may not) be true for a flat truss, but we don't know if they are flat or pitched trusses (though most residential projects use a pitched truss.) spacing would not necessarily affect the height of a pitched truss, but a deeper bottom chord and increased heel height would allow greater spacing.
make no assumptions, work only with the facts which are presented and like others have said: keep it simple.
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This is definitely a 'choose the best answer' question. Since the heel height is changing and the bearing elevation is not, the truss is going to appear taller in elevation - there's really no way to argue that the elevations aren't affected by the changes.
You could argue that the RCP might be affected, but you could also argue the opposite, making that not the best choice here. Since a roof framing plan exists, the RCPs may simply have a note saying 'trusses above, see roof framing plan' and not show the spacing or sizes of the trusses.
My general advice - if one answer is clearly correct and one could be correct if you apply some assumptions, I'd go with the clearly correct answer and continue on with the rest of the exam.
Chris Hopstock RA
Black Spectacles
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