Carport structure

[Benpointer]

Hi All, now that the house is done and we have been in 8 months (very nice, thank you) I have turned my attention to something much simpler - a carport. 

 

Broadly what I am looking to do is a 5.25 x 5.75m carport with two open sides, oak post in each corner and a shallow (8.7deg) mono-pitch roof in single ply  membrane or Greencoat on a ply deck, to look like standing seam zinc, echoing the zinc roof on the main house.  

 

We have planning for that as a freestanding structure next to an existing timber workshop but have now put in a new planning app to integrate the roof with the workshop roof, for aesthetics.  But fundamentally the carport needs to be its own structure.  We don't need Building Regs as <30m2 area.

 

Some sketches attached but the question I have now have is how to design and size the posts, beams and rafters to cover the span safely and deal with wind loadings etc?  I am currently thinking a glulam lintel across the 5.25m front opening and open web joists from front to back (5.8m) with the back supported on a timber stud wall and suitable wall plates.  Or possibly a second glulam spanning the opening midway to act as a purlin and then smaller solid rafters from front to middle and then again from middle to back.

• Pay a SE to do the calcs, and if so what do I need to provide?
• Approach a rafter/glulam company with the design constraints and ask them to design and cost it for me?

 

I am very conscious that whatever I build will need to be very well tied down to the pre-existing 6m x 5.5m x 150mm reinforced concrete slab, which I assume is going to be enough to stop it all taking off in a gale.

 

Here are some pics, and thanks for your help!

 

Views of the proposed carport (existing workshop not shown but abuts the west side of carport)

 

Floor plan (not that there's much to see - confusingly West is to the top of this plan(!))

 

Extract of block plan showing the newly proposed integrated roof (North to the top).