Does anyone know the preferred method for specifing roof pitch? Should
I specifiy it as an integer value of say 6-in-12? Would a truss builder
not like to build say a 6.125-in-12 truss?
...Or is it better to work in integer angle values like 30deg?
I want to draw up plans that make sense for the truss builder, but also
make it easy to mitre pieces like facia boards.
The truss manufacturer will want to see 5/12, 6/12, etc. If you are
drawing plans, one thing to note is that the truss manufacturer will
draw a set of truss plans for you. If it is an existing building,
then the agent will come out and measure for the trusses himself.
This is best due to the fact that any errors in dimensions will then
be his to repair or replace, rather than you.
If this building is in the plan stages, then a floor plan and a roof
plan will give him everything that he needs to know. Typically the
roof plan will be drawn showing overhangs, ridges, valleys, etc and
a spec for the slope (as in 6/12). If you have vaulted ceilings,
pan ceilings or any other special requirements, then they will need
plans showing those, also. A detail of your overhang can be
helpful, too. He will ask all the questions that are needed to
manufacture the trusses, and draw a detailed truss plan with an
engineers stamp on it. Most jurisdictions require this for code
enforcement. Unless you are an engineer or architect, you cannot
draw plans for the trusses. You can draw a set of plans, have the
manufacturer approve them with a stamp and then use them, but they
can do it better and faster than you can. Best to let them do what
they do best. The plan will show placement, bracing requirements,
and any other details that you need to receive a permit and for code
Robert, thanks for your detailed reply. I was just drawing some plans
to get a rough idea of what everything will look like. I have access
to pretty high-end solid modeling software (Pro/Engineer). I will
leave it to the truss manufacturer to come up with the final truss
design as you say. From your reply, it doesn't sound like I have to
assume an exact integer rise vs. run pitch value.
Last year I had to order some trusses for our house. They were a fairly
unique raised heel vaulted ceiling truss. I drew up a simple plan of what I
was basically looking for, with rough dimensions spelled out (i.e. 2' high
raised heel (2x6), 9/12 exterior pitch, 6/12 interior pitch, 1 foot
overhang, extra load capacity).
They sent me back their engineered version of my idea, accounting for
thicknesses of the framing members, something I failed to do. Because this
affected the height of the ceiling peak inside, one company sent me two
plans back, one that used the interior ceiling pitch I had asked for, and
another with the ceiling peak height I asked for (which deviated slightly
from the 6/12 pitch I asked for). Their engineered plan included
specifications for where I should place the bracing.
I included a copy of their truss plans with my building permit. The county
then wanted me to put additional solid blocking between the trusses on each
side for extra support. I also added additional bracing on the center
vertical web during construction.
It was actually all quite simple, and the truss companies contacted me with
any questions they had about my requirements. I was able to review the
truss plans before they actually built them in case there were any changes
to be made.
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