Expert: Nazim Nice - 7/15/2009

Question
Hello, I'd like to pick up on an answer you gave to another question.  It concerns the style of gazebo roof.  I'd like to put  simple sloping roof on a gazebo that will be approximately 16x16. The gazebo will be 'free standing' in the middle of the garden.  I feel  that it will be more modern looking and simpler to construct than either a pitched roof or a pyramid style roof.  
I'm concerned, however, about the wind forces and potential problems due to the weight of snow. It seems to me that a sloping roof may be exposure to greater wind stress and snow-weight issues than other roofs (being just one pitch, rather than 2 on a pitched roof, or four on a pyramid roof).  If I'm correct, I presume this means using more robust building techniques and stronger materials (and so the design will probably look 'heavy').

Am I talking sense or nonsense?  Thanks in advance for any comments.

Answer
Hi Peter,

Well, the span of the structural members may be greater in a single sloping roof (usually called a shed roof).  But that depends on how many columns you have.  You could end up with smaller spans if you put in 8 columns instead of 4 (one in each corner and then one between each column).  That would help reduce the size of the members.  If you want a 16' span, yes, you're probably looking at larger members than if you have a sloped roof.  The sloped roof, though would either be made of trusses, or something built on site that resembles trusses, or incorporate a ridge beam (that does span the 16').  If that's the case, the ridge beam will be large and bulky too.  A pyramid is often the most difficult to frame so I think you are wise to look to other solutions first.

As for actual wind and snow loads, that would have to be answered by a structural engineer.  But conceptually you should be concerned about this structure just toppling over.  The joints have to be rigid enough to keep the structure up right.  This can be difficult in a wood structure. You might consider putting 3 columns in the corner (one in the corner with 2 on either side spaced a few feet away)then infill this with a steel fabricated trellis structure to keep the columns rigid.  

Hope this helps.  Good Luck!

Nazim Nice
Principal / Architect
http://www.motion-space.com
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