Log roof trusses

[Richard Clauson]

What distance should be used between roof trusses spanning 30' with 10" log material? Ridge beam will be 50'----16" log tied into log gable ends. 8/12 pitch with SIP panels and metal roof. Collar ties 1/2 way down from ridge beam. Snow load for Minnesota.

[StressMan79]

the span rating should be on the manufacturers data. The load allowed varies by type (and type of wood, fastener type, etc.

a "scissors truss" will have a smaller rating than a full truss, all things being equal.

If Minnesota is anything like Washington, the snow load can vary hugely across it. I assume that the load at Lake of the Woods is not the same as Worthington. Contact your local building inspector/planning office for local requirements. For instance, the snow load at my place is significantly higher because of elevation. The county recommends (not requires) a higher snow load at elevations above 3000 ft. I am building @ 3008 ft. Not required, but we at LHBA generally overbuild significantly. Therefore the info I got from the local (county) office was of great interest.

For your information, LHBA does not generally recommend trusses. We like the open Cathedral type ceiling and the commensurate usable space. I know of one member building a home now that has scissor trusses, and will still have an open feel and usable space in the peak.

Good luck,

Peter

edit: I see you want to make your own trusses. In that case, I'd go 4' OC and build your trusses to handle the snow load, whatever that may be. 10" logs spaced much closer will not look good, and much further apart will result in inter-rafter bending of the roof panel. Plus, with 4' spacing, you can pick up two with an 8' piece of lumber. I would recommend 12' or 16' tongue and groove over the top, or a mixture so as to produce a staggered roof effect (although ideally, all of your joints will end up on a truss) as far as building them to support the load, 10" poles of DF or even pine will likely carry the requisite snow load over quite a span (even 30'). I'd just use the poles, and not a truss system. my advice for 4' centers still holds however.

[hamchuck36]

The manufacturer of the SIP panels can probably tell you the spacing based on the size of their product and your local Regional Building Department may be able to tell you how much load each truss should be able to withstand. MAY, is the key word as I have found they are not very knowledgeable on log construction.

If you go down to regional with drawings or illustrations, it makes it easier. I have found that most building departments are helpful when it comes to answering questions. Better than second-guessing. Also, most building departments will want to review your plans and may deny your design if they don't feel it's sufficient. Hope this helps.

Jeff

[RockEngineer]

What distance should be used between roof trusses spanning 30' with 10" log material? Ridge beam will be 50'----16" log tied into log gable ends. 8/12 pitch with SIP panels and metal roof. Collar ties 1/2 way down from ridge beam. Snow load for Minnesota.
Any log trusses would need specific engineering. I wouldn't recommend trying to do it without engineering and plans for the log trusses unless you really like your roof sitting on your floor.
Usually log trusses are used for asthetics and to combat log wall settling so you don't have to have center ridge poles and jacking screws. Most of them also use purlins between the trusses to provide a middle support for the SIPs. LHBA method doesn't settle as much so you don't need the jacking screws and installing a ridge pole is much easier for the layman than making and installing a log truss.
If you're talking about having a ridge pole and log rafters rather than trusses, the spacing for 10" log rafters varies depending on your snow load and the species of log you are using. Most common spacing is 48" because LHBA members tend to use 2x decking between their exposed rafters and this works out well with the decking. If you buy the right SIPS which will span between your ridge pole and side wall you don't need rafters.
good luck