Building a Gazebo from 150mm square posts. Do I need steel to support the roof

[Drew1000]

Hi,  Hope you guys can help.  I am intend to build an outdoor gazebo which will be 4M long by 3.6M deep.  The roof will have a ridge with hips at both ends.  The roof will be constructed from 6 by 2 C24 framing and covered with 11mm OSB.  The plan is to use Cambrian lightweight tiles from Redland which weigh 17kg per square metre.  At a rough guestimate of 16 square metres that would work out around 270kg then add battens, guttering and felt for a ball park 320kg.  My rafters will be spaces at 600mm centres along the roof and for ease of calculation would mean 8 rafters either side at approx 2M.  At approx 3kg per metre that works out at around another 50kg.  So unless I have forgot something I think we are looking at approx 400kg.  My intention is to have 5 supports, 3 along the rear and one at either end at the front to ensure plenty of walk space at front when entering with a ring beam around the top also in 150mm by 150mm.  The posts and ring beam will be of Larch.   My question is.  Will the beam across the front spanning 4M be suffifient to hold the roof weight without sagging or would I need some sort of steel support.  Thanks in advance.  Regards

 

[Russell griffiths]

I plan on doing something similar soon. 
 

can you simplify it. 
hip ends will cause you lots of work,  hips to construct, then 4 hips to cut the tiles to, then hip tiles

 

im going with gable ends as it simplifies the whole job. 
you don’t need 150 x150 as a wall plate unless you like the chunky look. 
I’ve looked at loads of these and an easy way is to notch your uprights and sink in a 50 x200 or something similar and use that as a ring beam around the whole structure. 
 

many ways to skin this cat, have you sketched it up. 

[saveasteading]

The roof ripping off has to be considered too. Uplift is huge when there is a solid roof and open sides.

15 hours ago, Drew1000 said:

Will the beam across the front spanning 4M be suffifient 

I don't think so. A steel would be that size, so timber will be deeper.

Otoh it isn't an occupied building. You won't be in it during the 50 year storm. Would you risk it collapsing every 10 years or so?