Timber choice for a large wooden greenhouse

[RobinBHM]

Have you considered siberian larch?

Brooks bros stock it thicknesses of 1" 1.25" 1.5" 2"
Earlier this year I paid about £900+vat M3 rate.
Thats for U/S grades 1-3 in lengths upto 6metres.

The 2" might have some splits down the middle of wider boards like most softwood.

Bear in mind siberian larch is heavy and dense, around 750kg similar to oak.
Ive had boards where the growth rings are really tight -less than a mm apart.
The boards Ive had are often really straight.....although the odd end of packs Ive had have been a bit donkeys hind leg, but generally really good.

Ive made lots of windows from sib larch and used to import engineered sib larch in joinery sections to build orangeries

Unfortunately 2 1/2" stock isnt available and 3" boards are 5ths

Durability similar to Dug fir.

Douglas fir is a lovely timber although grain can be a bit course. It does tend to suffer with large resin pockets which seem to run diagonally through standard through and through cut boards. Itbmeans the resin pocket appears in both face and edge.

 

[MikeG.]

I hadn't, Robin, but I will.

BTW, Thorogoods say that their Douglas Fir is quarter sawn.

 

[Trevanion]

Not a huge fan of douglas fir, Not very stable (Perhaps the slow-grown stuff is better) and takes on mould like no other timber. I've seen work before where the douglas fir has taken on mould before it's painted and it bleeds through the microporous paint showing up as black dots on the face. I think it works best with some kind of oil-based paint or finishes rather than anything waterbased and microporous.

If I were you I would seriously consider the Accoya even though it's more expensive, Instead of comparing it to the DF try comparing it to the WRC, there isn't much in it. When it comes to machining it there's barely any need for wastage allowance as there's hardly any knots at all it it's usually very straight allowing for dead easy ripping and planing. I dug up a piece of Accoya the other day that I buried a year ago, looked exactly the same as when I put it there and the measurements (L,W,T) were exactly the same as they were when it went in, absolutely no movement at all and no sign of really taking on anything except a little dirt. Did another test with a piece of Accoya and left it in a water bucket for a week, absolutely no change whatsoever, Douglas fir would've expanded 5+ mm easily.

Some reckon you can get 10 years out of your paint (Teknos specifically) before you will need to repaint Accoya, I've definitely seen jobs where the paintwork looks good still after 5 years without any more paint so I don't think it's impossible.

The only real downside is that you will NEED to use stainless steel fasteners and hardware as Accoya eats regular steel for breakfast because of the acetic acid content. Stainless steel hardware and fasteners can really add up on a big job.

An aluminium greenhouse is also great for the money :lol:

 

[MikeG.]

INteresting, Trevanion, thanks. Especially the stuff about mould. The only fastenings I'll be using will be glazing pins and screws for the window hinges, so the extra cost in SS would be negligible. I have an instinctive distrust of pickled wood because of any environmental impact from the chemicals used, but I guess that one day I'm going to have to do the actual research rather than rely on instinct.

As for this recurring notion of aluminium, here is the plinth:

If anyone can point me to a manufacturer who can supply a white mono-pitch Aluminium greenhouse 5455 x 2015 with a 1310 wide double door 1395 from the left hand end that looks Victorian/ Georgian/ Edwardian, with a 37.5 degree pitch to the roof and to finish precisely 1935 high at the plate (on a 775 plinth).....at a price comparable to the material cost of some sawn timber and sheets of horticultural glass, then I'm all ears.

 

[Trevanion]

We had one off this lot not too long ago: https://dovetailgreenhouses.co.uk/lean-to-greenhouse/. It's perhaps not the look you're after as it's quite modern looking design but they're made to measure and you can put them up yourself very easily as it practically all clips together and it held with nuts and bolts. They worked off our measurements and it worked perfectly.

Also in regard to environmental impact with Accoya, there is very little compared with many other timbers. The Radiata Pine is mass-grown out in New Zealand in large plantations and is on a constant 15-year growth cycle, the treatment itself is non-toxic and doesn't harm anything and at the end of it all the byproduct of the process is used in non-brewed condiment which is the faux vinegar they use in fish and chip shops en mass. I was told by the Accoya representative that's why Accoya stinks of the vinegar smell "We sell the byproduct to the food industry" although I've never seen it mentioned anywhere else.

https://www.accoya.com/sustainability/

 

[MikeG.]

Thanks for the sustainability stuff. I'll read that shortly. I'll get a price from Dovetail tomorrow, but it It's going to be thousands, whereas my homemade version will be hundreds.

 

[mr rusty]

I can vouch for the stability of accoya. I made some sash windows a couple of years ago and they haven't shifted a mm - sashes are fairly tight tolerances and all slide perfectly. I used teknos aquatop and primer sprayed with an HVLP gun. I think if you swallow the additional cost at the beginning, you will reap the benefit later.

I will be building a garden room soon, to partially enclose a courtyard with just roof and one facade, and will definitely be using accoya again.

It machines nicely, but is a bit brittle. I suspect you can't wedge tenons, so I would consider modern not traditional jointing methods. I used PU glued dominoes, and again so far so good. Any screws should be SS

 

[MikeG.]

......I would consider modern not traditional jointing methods........

You don't know me very well. I'll be making traditional joints.

 

[RobinBHM]

Ive used accoya extensively in joinery manufacture.

It is a good material, but it is quite weak.

Its only radiata pine fron new zealand grown in about 7minutes.

It wouldnt be my choice for a greenhouse.

 

[Just4Fun]

Re the aluminium v wood comparison, as well as cost and durability you have to consider strength. 3 or 4 years ago I put up an aluminium greenhouse. Last winter it collapsed under the weight of snow. If I rebuild it I will probably use wood to make it stronger.

 

[Woody2Shoes]

As far as durability and dimensional stability of acetylised wood products - here's a brief YT video about Tricoya MDF made by the same process as Accoya which I found impressive: https://www.youtube.com/watch?v=nAIXOLD13Ho also https://www.youtube.com/watch?v=iC5fQ1FPpcw

As far as the environmental impact of the chemicals used in the process. Acetyl Anhydride is the chemical used (together with temperature and pressure) - this is not nice stuff to work with in a factory, but it is essentially alcohol/vinegar and its breakdown products are harmless. Compared to the chemicals in conventional treated timber (far more iffy organic compounds like synthetic pyrethroids), I know which I'd choose.

https://en.wikipedia.org/wiki/Acetic_anhydride
https://en.wikipedia.org/wiki/Acetic_acid
https://en.wikipedia.org/wiki/Pyrethroid

As far as the structural strength of Accoya, yes it's basically fast-grown softwood (so is spruce of course - the most widely used structural timber in the UK) - but it is usually clear grained and you can always make allowances in sizing of timbers.

Here's a mini-greenhouse (skylight!) made from Accoya: https://www.youtube.com/watch?v=sGcF919-B8Q

Cheers, W2S

 

[Benchwayze]

Mike,
I agree with the first respondent. Cedar is the choice. It might not be so strong as Douglas Fir, but I doubt there is much in it. Have a look at Woodpecker Joinery. They make a range of high quality Greenhouses and mostly they use cedar. Their second choice on cost is tanalised timber. I am sure that you won't build with the door facing the prevailing wind, so I think cedar would be fine for strength.

John (hammer)