Roof -- columns

Hi all,

I have to span a square of about 50 by 50 feet with a roof. The roof should have a cupola in the middle.

I am wondering if I can simplify construction of the roof and reduce cost by putting up four columns arranged in a much smaller square in the middle of the larger square. These columns would form the base of the cupola and be tied together by a sturdy wooden square frame.

What I am hoping to do is to eliminate large and complex trusses by having rafters running from the exterior wall to the columns and tying into the frame on the columns directly (somewhat like in a shed roof). The cupola will then be erected above the square frame on top of the columns. The rafters would have to be about 25 feet long
and span empty space.

Can I do this and can I achieve significant cost reduction in the construction of the roof.
Does this make sense?

if this particular construction does not work can columns be used to simplify the construction of the roof in some other way?

What do you think?

i think you are asking roofers an architect question. most of us arent even carpenters.

OK, no problem.
I am reading the other posts and much enjoying the advice.

I would have to agree with marshall on this. You are talking about roof loads and really you might need to consult an architect or an engineer. A 25 foot long rafter is a very long run. Cutting costs might not be such a good idea.

I bet it would be a cool design, though, if it worked.

i read you letter with great interest as cupola’s are used very much in building design in england , and really would need the services of a architect and a engineer as the roof structure needs to be self supporting off your four colunm’s , a roof structure like this needs to be very well planned , and a structural engineer will be advise you what timber size to use because of the load bearing on the roof it self .

hope this helps mate regards john

Two words…steel.




Being a house framer, I might say that the demensions of what you are trying to span is awfuly big. you are going to find that with out using a prefabricated truss a25 ft rafter span will sag over time. around here code says for every 12 horizontal ft a purlin wall , etc must supportthe rafters. The column idea is good. Just pour footers 2ft into the ground. What is the pitch of the rafter going to the copula? What is the actual outside dimension of the copula?