Wooden Greenhouse

[greg@hilltop]

Have been mulling over for some time the possibility of making a wooden greenhouse to my own design and now I am getting to grips with new router table and JessEm lift I thought this might make a nice background winter project along with the oak stairs and finishing the Ron Paulk work bench (how many 20mm dog holes? !!)

Has anyone done this and what advice would you give on timber (Western Red Cedar?) and shape and size of glazing profiles? Any thoughts or opinions would be much appreciated.

 

[Trevanion]

If you're intending to opt for Western Red Cedar you may as well have a look at Accoya, that would be the timber I would use for such a thing.

Accoya Acetylated Wood | High performance, long life modified wood

 

[Ollie78]

Cedar is lovely to look at and also durable but very soft. British grown cedar is quite a lot cheaper but not as tightly grained as the Canadian stuff. I got some grown in Wales, its not so red but smells just as nice and machined up fine.

As trevanion says Accoya would probably be the most durable and it is good stuff. Great if you were going to paint it but it looks crap unpainted or clear finished in my opinion. Trouble is the price is crazy bonkers these days and it makes your workshop smell like a chip shop .

While on the subject of modified timber what about Thermowood or similar, its cooked which changes the nature of the wood fibres for excellent durability, I have seen Pine and Ash, it darkens the natural colour of the wood too.

What about good old Oak ?

Ollie

 

[LBCarpentry]

The timber you chose is based on your budget frankly.
Accoya top but frankly overkill ?
Oak - the biggest swizz of all time
Sapele - decent price but moves a lot and a horrid colour
Personally I think cedar is looking like a good option for this specific job

Frame dims 70 x 55
Casement dims (if any) 45 x 40 ish
Profile - simple bevel internally with bevelled glazing beads for glass retention.

 

[Roberto Flintofski]

This is a project that I am going g to try to sort over the winter. I bought a wooden greenhouse / shed 10 years ago (£1300) so wasnt alot of money but its suffered where the roof glass meets the verticals. The replacement will have full sized horticultural glass rather than the 1/2 sized ones with overlap joints as this makes the bloody thing an arse to clean come the Autumn !

 

[greg@hilltop]

Thanks to all for responses so far.

The timber cladding that I fitted on our recently built passive house and detached garage is locally grown larch with 1 coat of black Osmo wood stain. How would larch compare with WRC from a workability perspective?

Has anyone ever seen a book on making a wooden greenhouse?

 

[NickM]

Following this with interest as it’s something I’d like to have a crack at one day.

I’ve only had a very quick mooch online but couldn’t immediately find any particularly useful resources (e.g. plans, joinery techniques or that sort of thing).

Please keep us posted if you find anything and, if you get started on this, let us know how you get on.

Thanks

 

[Just4Fun]

While on the subject of modified timber what about Thermowood or similar, its cooked which changes the nature of the wood fibres for excellent durability, I have seen Pine and Ash, it darkens the natural colour of the wood too.

I did our decking with that sort of stuff some years ago. Parts of it gets covered in snow in the winter, and it has to cope with a wider range of temperatures than you get in the UK. It has held up fine, and for the right application I would use it again.

There are some caveats though.

It loses some sructural strength in the heating process. I forget the %age loss so let me guess 30%. Depending on your design that might or might not be significant. Having had an aluminium-framed greenhouse collapse under the weight of snow, I would be careful here.

It loses "body" during the process. The end result is like very fast growth timber. Not a problem for my decking but I wouldn't use it for any joinery and maybe not for anything but simple mouldings.

It discolours if not treated. I opted not to treat our decking because this material doesn't need it for longevity but (at least in our climate) if you do treat it you have to re-do it every year or two and I am far too lazy for that. The timber shows no signs of rot or anything but the colour soon changes from a nice rich brown to a dull grey which is not very attractive.

 

[OldWood]

My brother has done a number of wooden greenhouses in his 30 yrs working life; I have a suspicion he would recommend douglas, but I will get that confirmed. As this thread has generated several 'me-toos' there's little point in 'greg' PM'ing me/him, and I will see how his experience can be passed on.

There is a confusion in my mind re. cedar as I'm sure he discourages the use of that outdors and yet my beehives are made of it, and on the basis that I got them from an old beek some 50 yrs ago, they could well be 70 /80 yrs old and are still fine. It may well be that cedar in thinish sections isn't that strong, and certainly one repair my hives have needed is to bond cracks along the grain.

I know little about the strength of larch but its tendency to move is against it, as is its weight. I built a hive roof of larch and regret it everytime I take that lid off!!

 

[AndyT]

Has anyone ever seen a book on making a wooden greenhouse?

I've got an old pamphlet from The Woodworker, published just after WW2. It describes how to make a timber greenhouse in just three pages, so no dumbing-down there!

Here's a scan in case it helps.

 

[AndyT]

Also, have a look at this thread for a longer discussion of timber choice.

https://www.ukworkshop.co.uk/threads/timber-choice-for-a-large-wooden-greenhouse.119042/
What a pity Mike's not around on this forum to post pictures of his build.

 

[Benchwayze]

Western Red cedar is the traditional choice for wooden frame greenhouses. If it ain't broke why fix it? Especially if the alternative is crazy-price.

John

 

[greg@hilltop]

I think the general concensus is WRC but I am confused by the grades available. Can anyone explain this and tell me what I should aim to use? As ever I'm very grateful for all the imput received.

 

[johnnyb]

I'm loving that woodworker article btw. just reading it makes me want to decipher and build it!. the 2 things I can suggest are the roof simple rafters are very vulnerable and lead or a patent system are preferred to this design.the bigger the greenhouse the more the tendency to spread. also dwarf walls with dpc are really sensible and allow the vulnerable timber to be off the deck. I've seen many greenhouse built using redwood last over 50years btw. not that I would recommend it for that but cedar was and is an expensive product and greenhouses after the war were utility essentials. I wouldn't be surprised if woodworker had articles for greenhouses and cold frames every 2 years!

 

[NickM]

What a pity Mike's not around on this forum to post pictures of his build.

Hear hear

 

[Benchwayze]

My first workshop was a repurposed,
dilapidated timber framed greenhouse; half brick construction. More than just a few panes of glass were missing and the weather had taken toll. That was in in 1964 and it must have been been at least 30 years old then. The framing was made of cedar wood, and had been painted. There was still rot, especially in some of the joints. There was evidence of repairs that had been made with deal. It would not have been difficult to restore the greenhouse. However I was a woodworker and not a gardener. If you catch my drift. Nine feet square and 'gave issue' to a house full of rudimentary furniture.
Happy days!

Jphn

 

[OldWood]

I checked with my brother this morning (my original post at 10.38 yesterday).

His opinon is that cedar is the traditional wood to use as it goes a nice uniform colour with time; however it is not a structural wood and in reality needs to be increased significantly in cross section to obtain any strength. Further if you have to any glass repair work on the roof then cedar becomes a concern because of its lack of structural strength.

That leads onto the next element which is cost - cedar is expensive and so increase in timber size leads to even greater overall cost.

The only time I've used cedar was for a small turned bowl - lovely item but my memory is that the wood was difficult to turn as it was so soft.

It is douglas fir that my brother recommends - good structural strength and significantly cheaper than cedar. He has done a greenhouse in cedar under pressure from the customer, but he had deep enough pockets that looks over-rode material cost, and the long term diffficult maintenance.

 

[Jameshow]

Out of interest how does DF compare to larch in terms of strength and durability??

Cheers James

 

[Trevanion]

Western Red cedar is the traditional choice for wooden frame greenhouses. If it ain't broke why fix it? Especially if the alternative is crazy-price.

John

There really isn't much between Accoya and WRC these days though when you're buying larger sections, maybe a couple of hundred pounds per cubic metre if that. At that point, you may as well go for the timber which has a 50-year above ground guarantee (25-year underground) and have peace of mind that you know you won't have to coat it as often as WRC and that it's not going to twist or move at all which could potentially break panes. Especially with the lower quality of softwoods in general as of late.

 

[Benchwayze]

Hi trevanion.

I see where you're coming from but I'm afraid I cost by cubic foot and I have to convert it later to suit the timber yard. Lol!
As I said the greenhouse referred to was at least 30 years old in 1964 . I wouldn't have said it was at the end of its life, had I wanted a greenhouse, but there was some rot to contend with. I just reduced it to the brickwork, repointed and added windows, a roof and of course a door.
Only had one item stolen from it in ten years: my fault leaving the shop unlocked while I had my lunch break!

Cheers

John