best timber to use for new windows?

[totallyrandom]

I am totally confused about what timber to use for new double-glazed windows. Any architects/home owners/joiners/others in the know out there?

Quite a few of the better companies (recommended on mumsnet too) have recommended an engineered product called Accoya (it is pickled softwood but meant to last for 50 years +) - it is very expensive. Another company I quite like has recommended an engineered wood called Red Grandis (again quite pricey). Most local joiners like Sapele wood (but I am not sure it can be guaranteed to be sustainable). Then there is the expensive traditional oak or the expensive British Columbian pine (a softwood). I am happy to spend the money and do it window by window/few windows at a time, but I really want to make sure I get the right timber if I am spending all this money and gradually taking out existing windows which aren't necessarily rotten through (but single glazed). So far the only impression I got is that there seems to be a timber fad with most companies/joiners and they switch the product they use every few years which worries me and what is being recommended today hasn't necessarily withstood the test of time.
Sorry for being a house bore, but would appreciate some advice!

Dh is a joiner and he says oak. He recommends to replace all the front in one go then all the back in one go as over time there may be a colour change in the wood so it may be noticeable if you replace windows on the same side at different times.

colour change due to weathering etc..

Oak is good provided it does not get too much direct sunlight - otherwise it can have too much movement ime (confirmed by several joiners I've worked with).

I have gone with a sustainable northern red softwood (sorry, don't know the name). For me it was important that it be sustainable, and I'm not completely convinced about engineered products either, so I have accepted the fact that I will need to be careful about painting to make sure they last well.

I have made that a bit easier by using a paint that doesn't need sanding off in order to repaint.

depending on your house style you could consider aluminium cladding.. possible in almost any colour, looks good and virtually maintenance free

Teak is very good for windows due to the natural oil content and can be coloured down to suit your needs easily as it is light to start with. Very durable as the teak in the Titanic still survives today whereas the metal and other woods have totally disentigrated.

I've done the same as discrete - softwood (good quality) and painted with microporous white stuff - Teknos IIRC. It's on north facing wall so hopefully the UV damage won't be too bad. They look really nice if a bit chunky compared to single glazed sashes.

If we had spent a bit more we'd have gone for sapele and painted it but they were expensive enough as it was TBH. Do you want a painted look or natural wood?

If you are going for a natural wood, iroko can be good but won't take an applied finish well due to the oil content.

Thanks everyone! Our house was built around 1900 - to replace authentically we need flush casement windows (Georgian bars on top section only) which will be painted/stained in white. I have heard that the modern microporous paint is good and need not be sanded down which sounds great! I have also heard that oak can warp badly particularly on South elevations - maybe if I wasn't painting the windows white, it might be worth it, as oak is beautiful. Unfortunately I don't think aluminium would look good/fit in with the rest of the building. I have a few architect friends who always specify aluminium windows (but don't know much about timber as a result).
It is so difficult to make up my mind - DH not interested in the detail:) Agreed that sustainability is an issue.
In Europe, they have been using engineered wood successfully for decades but it seems like a risk if the products being suggested here haven't been around for more than a few years and the better engineered products are just as expensive as a very good quality softwood.
Bureni/Oh Western wind - I love teak and iroko but no window company has yet suggested them so not sure how widely available they are/how expensive for windows and probably not worth it if I am painting anyway (which I should have pointed out in my original post)

Could you stick with the windows you have? The wood in them will be far superior to any modern woods. You could look at increasing thermal capacity in other ways (draft stripping, etc). It will be mich more cost efficient in the long term. English heritage has some stuff on their website about this.

And keeping existing is extremely sustainable in terms of embodied energy etc.