I need to build a pergola / brise soleil along the south wall of our house, partly to shade it from summer sun. I plan to build it from timber but I want large spans between the uprights in order to maintain our views from the windows. So I plan to make engineered girders for the horizontal pieces - probably a couple of timber flanges, some timber uprights to separate them and some wire diagonals to provide racking resistance.

I want to keep the timber reasonably slender and I'd rather use a durable timber than treated softwood for appearance sake. We have some timber cladding that is cedar. Windows and doors are dark brown ali-clad and the render is cream.

What are good choices for the timber to use, without breaking my bank?

FWIW, for clearest view, could you consider a suspension system using uprights ("made of anything") (masts) sited well clear of your FOV, then stainless cables supporting a (lightweight) /modular screening structure.

FYI, mask-calculation SW here...
http://susdesign.com/overhang/index.php

gg

The "large spans" may be the problem coupled with the "slender" timber sections. For that reason Western Red Cedar "Thuja Plicata" wouldn't be my choice. It has low bending strength unless you go for larger sections which you don't want. UK cedar timber can also be suspect in larger sections,- sometimes rotting/hollowing from the inside. It, like Oak also may limit your choice of fixings, - corrosion. I'd go for Glulam for ease of working, or possibly Oak if you're feeling ambitious.
You could also look at bark stripped timber rounds although that may not be the architectural look you want, and may involve too much of a design change.

Thanks for the ideas everytbody. The spans are about 4 m; two spans between three supports. I like the idea of cedar but wasn't sure of its suitability. I know I'll need stainless fixings and fittings. What sort of glulam would you consider to survive unprotected outdoors? I'm not particularly worried about the bending strength because that should be taken care of by the wire diagonals I think.

Green oak or larch are possibilities

With three supports you effectively reduce the spans if you can use the cantilever bu using very long bits of wood or clever joins.

The wires are clever and I like that idea

Larch

If bending no problem, then what's against untreated ('semi-durable' meaning it's fine if able to drain and dry freely) local doug fir? Selected of course - no knots. I'd be intertested to hear why not, exactly.

Posted By: tonywires are clever

How will youn ensure equal tension in all, so some of them don't end up doing all the work/tearing out fixings? And what fixings - adjustable for tension? How to prevent any of them 'giving'? I've found informal use of wire for bracing e.g. rough n ready rose arch, many go slack and after a while the rose 'trunks' end up propping it all up!