I want to build a 6 sided gazebo but am having difficulty finding
design details on the roof trusses. Not the trusses so much, but how
to support them all in the center. The roof will be asphalt shingles
over OSB and supported on 6 4x4s. What's the best way to build a
center support? Any useful suggestions will be greatly appreciated.
The framing for a gazebo type structure involves making the rafters
into a "three hinged arch" (using the GT6Z connector Jack talks about)
- these 'hinges' being the connections at the bottom (where it connects
to the posts) and at the peak. That means that the GT2Z connector (see
link below) is equally important as the peak connection. All three
connections - together - provide the strength. Then, by adding the OSB
decking, you create a *diaphram* that also adds stength (think: "What
must happen to the OSB for the rafters to fall?" and you'll be able to
visualize the 'system'). If you were real concerned, you could put in
a temporary support at the peak until you got the OSB installed (I'd
keep it in place until the roof shingles are also installed). It
should be plenty robust enough. Note that the Simpson detail shows
*two* of the GT6Zs (at the peak) - one on top of the rafters and one
However, if you want to beef it up even more, use (as you initially
noted) a *truss* system - making 6 little right triangle truss elements
(made up of a top 'chord' (the rafter), a bottom 'chord' (the 'ceiling
joist', if you will) and a vertical 'king post' there at the center -
all tied together with Simpson clips or some plywood side plates). In
this case, for these trusses to fail, the bottom chords of all 6 would
have to move *out* (towards the posts) from the center point. So, to
stop that, simply use a GT6Z there at the bottom to tie all these
bottom chords in place (this would, in effect, be moving the bottom
GT6Z from the situation in the previous paragraph down to the bottom
plane of the trusses.) Again, make sure to use those GT2Zs out at each
and every post - to tie the trusses to the posts securely. Then deck
and shingle as noted above. This approach would be considerably more
robust than the approach above.
The *important* thing in either of these approaches is the
*connections* - compromise on tieing everything together and you can
seriously undermine the structural integrity of the whole system - and
it is the *system* that carries the loads.
-- john - Registered Architect - GA
(normal disclaimers apply - do it smart, don't compromise, think -
remember, "quality is your friend")
I agree that construction adhesive can help and add some strength. I
generally use it on personal projects as well. The problem is -
*no*body (i.e. the manufacturers) will "put a number" on what the
benefit of these adhesives are - and, without an 'actual number' (to do
a proper structural design), the only rational number is "zero".
Use it? Sure! Will it help? Sure. How much? Nobody knows. (and,
that is somewhat to be expected, because these things generally need a
precise control of the process and that generally doesn't happen in
Therefore, simply consider it as "insurance".
What diameter and roof pitch did you want? Two level roof? Cupola?
There's a lot of guys (at least around here) selling gazebos/kits and have
full sized ones at local garden centres, lumber yards etc.
Why not go check one out for ideas?
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