shop truss'

[jdtuttle]

Looking for ideas, suggestions for my shop addition. I have an existing 20'x20' pole barn with concrete floor & have poured a 20'x24' pad for an addition. Making the shop 20'x44'. I want the addition to be a timber framed roof. I've been kicking around the idea of using a couple different timber frame truss's. Maybe two hammer trusses in the center and queen truss's for the gables. The truss's will be 8' O.C. with purlins 4'O.C. 2&6 T&G 3" foam, caped with OSB felt & metal roofing. What size timbers should the truss's be? I was thinking 6"x8". I was also thinking 4"x5" for the purlins. What is the minimum slope for timber truss's. I want to keep the profile as low as possible. The span is 20'.
Thanks, jim

[Jim_Rogers]

What is the snow load for your area?

Jim Rogers

[jdtuttle]

Ground snow load is 40.
jim

[jdtuttle]

OOPS! just double checked. Ground snow load is 45. wind speed is 90, seismic design category is B.
jim

[Jim_Rogers]

I think there is a rule on how low a slope you can do with a hammer beam truss. But I don't know it, I'd have to look it up.
A hammer beam truss puts all the roof stress into the posts. So you'll need very heavy posts to hold it up and prevent them from bowing out under that pressure.

Jim Rogers

[jdtuttle]

Jim,
I 'm sorry I wasn't very clear. I think that was my question. I read it somewhere on this site but can't find it again. I have several books on timber framing but nothing about minimum slope for hammer beam truss. I forgot to mention the lumber is white pine I can cut to any size needed. I'm fairly new to timber framing. I built a 24x28 timber frame addition on my house a couple years ago & really enjoyed it. There are three bents with a small loft that's partially open to the first floor. Just looking for ideas to make the shop an interesting & fun focal point.