Expert: Bruce E. Johnson - 4/11/2011

Question
QUESTION: Hi, I was giving some doublewide mobile home scissor trusses that are made of 2x2 construction with stamped plates. I was planning on using them to build a pole barn but don't know how far apart they can be spaced. The span on the trusses are 24 feet and the pitch is 3/12. I plan to sit them on headers and would like to space them over 2 feet apart if possible. The roof construction would be 5v or some type of metal over 1x4 runners. I live in central NC so not alot of snow but 8 to 10 is reasonable and I have seen more but its rare.

ANSWER: Hi William, mobile home trusses are built to minimum standards.  In their application on a mobile home they are normally spaced 16" apart and in some cases 24"..I wouldn't recommend going beyond a 24" spacing. You also have to be careful about plated trusses that have been improperly handled or taken from an existing home for reuse. The more they are handled the better chance the plates have become loose. Care must be taken to not allow the trusses to flex too much when hanndling as their structural integrity can be compromised. I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: These are brand new so the integrity of the plates and wood should be fine. Do you have any idea if spaced on 24 inch centers what the load rating would be? I would think they would be fine for just about any area since they were for double wides that could be transported anywhere. I was hoping to go just a little further apart to allow for more storage underneath but 24 would probably be adequate especially if I used something other than the trusses for the ends where the overhang will be. These would allow for 26 wide by 30 foot spaced on 24 inch centers.

Answer
Hi again William, I imagine mobile home roofs have a little less load rating than conventional truss roofs mainly because they are made of lighter materials and require less dead load provision.  But, honestly I don't know exactly what that loading is. It is probably published somewhere in the specifications from the mobile home manufacturer if you have access to that.  Where a normal roof truss system is 40 pounds dead load and 20 pounds live load I would venture to guess that a mobile home roof is maybe 20 per cent less.  One thing that we didn't talk about is whether these are two piece trusses (triangles that meet each other in the middle) or actual scissor trusses ( wide upside down V shaped trusses that span the entire distance).  If you have half trusses that attach in the middle you will need a header or ridge beam of some sort for them to hang on.  This will increase your loading capabilities because your span is actually half the distance (from the ridge beam to the outside wall instead of full span from outside wall to outside wall). I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com