# Timber choice for greenhouse and sheds



## TFWS (6 Apr 2021)

hi

i've been around lots of timber over the years doing diy and now i am starting out on my own but i am still confused about timber choices for garden projects.

i am constructing a timber greenhouse now and i've gone for treated timber which has the rounded corners and green tinge to it. the timber hasn't got a particularly natural finished but it will be painted eventually and the rounded corners challenge accuracy. 

now, when you buy a B&Q shed for example the timber often looks like prepared planned finish but stained being brown on golden in colour so what's going on? can anyone "shed" some light on things?

i suppose what i am asking is, if you a constructing something in timber for outside and the timber is on show and exposed like a greenhouse or shed what would you use?


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## gog64 (6 Apr 2021)

I think the brown stain on sheds is just a bit of preservative slapped on. You are normally instructed to properly paint it straight away if you want it to last any time.

When I've made tables for outdoors, I've just used planed timber (of whatever type the project called for) and then carefully finished it with exterior grade paint or timber treatment according to the manufacturers spec. I happened to see a large table I built a few years ago at the weekend and it was still perfect, all mortice & tenon joints still in perfect nick, all of the legs (laminated in this case as it was a really chunky table) still perfect, despite being out 24/7 on a patio. It would have been nice if the blighters had given it a coat of something every year though, it was looking a bit weathered!


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## Blackswanwood (6 Apr 2021)

There was a post a few days ago where someone was repairing some decking (I cannot find it) which quoted BS8417 .. I think you are looking for Grade 3 for sheds: 

BS8417PreservationofWoodCodeofPractice.pdf

Hope this helps!


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## Cabinetman (6 Apr 2021)

Very tongue in cheek, for a Green house it should be Green wood


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## TheTiddles (6 Apr 2021)

You can get sheds in dip treated and pressure treated. Dip is just that, the treatment is on the surface and you need to protect it repeatedly or it’s toast. Pressure treated the treatment goes into the wood more (ideally totally) and you don’t have to keep repeating it, but as it ages it does kinda help prolong its life.

For a greenhouse I’d be looking at a timber that doesn’t need regular painting as that’ll get un-fun very quickly. So cedar, larch and Accoya are often used.

Treated CLS is never going to be nice wood for building nice things, it’s for frames etc it’s often fast grown and soft.


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## thetyreman (6 Apr 2021)

canadian western red cedar is what I'd use, it isn't cheap though! but definitely durable.


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## TFWS (6 Apr 2021)

thanks everyone

@TheTiddles are we saying that "dipped" could be some sort of cheap planed prepared software?


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## johnnyb (6 Apr 2021)

yes I was confused about my decking repairs. the majority I'd had sawn and treated especially. one joist was from b and q. that one joist had almost totally rotted. the others were perfect.
a wendy house was brought from a well known shed supplier. few years down the line its just disintegrated. the floor has holes everything's loose. whereas as she'd we brought in the late seventies is still fine and has been moved several times. structural strength has a part to play as well as preservative.


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## MikeJhn (6 Apr 2021)

Use a micro pores's exterior stain, don't paint it will crack and let water in with the sunshine that obviously a Greenhouse will be in all the time.


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## TheTiddles (6 Apr 2021)

TFWS said:


> thanks everyone
> 
> @TheTiddles are we saying that "dipped" could be some sort of cheap planed prepared software?


Yep. I know a guy who works at a joinery shop making gates etc... 3 of them make several hundred gates a week and dip them on site


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## Billy_wizz (6 Apr 2021)

Dip treatments are mostly little more than colour these days


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## mikej460 (6 Apr 2021)

I suspect the timber you have used is KD (Kiln Dried) pressure treated. As a greenhouse if left unpainted it will last 5 years or so as long as rain doesn't get into joints or allowed to pool. If you paint it with Garden Shades this will extend the life considerably and more so if you repaint every few years. I speak from experience here and am just about to build a new greenhouse from the same timber.


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## Awac (6 Apr 2021)

I have praised this stuff before, it works, and it is so cheap, not often that happens! Apply once, that's it.

UK Agent.








 Eco-Wood Treatment - Harrod Horticultural (UK)


A non-toxic wood preserver which gives a rustic, aged weathered look and only needs applying once sounds like the stuff of dreams to wooden raised bed gardeners and DIY enthusiasts Ð but Eco-Wood Treatment is a reality!Supplied in



www.harrodhorticultural.com





Manufacturer (more info and pictures).





Eco Wood Treatment | Call (888) 738-5516







ecowoodtreatment.com


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## MARK.B. (6 Apr 2021)

A little tip if you go to a timber yard and buy treated timber and select from the pack , don't be tempted to pull off the top couple of layers to get " the good stuff underneath "  the timbers on the outside of the packs tend to absorb more of the treatment and those towards the middle less and also those from the middle can contain a fair bit more moisture as it takes a long while to dry out inside . If you do pick your own timber do yourself a favour and restack what you don't want , trust me when i say ,you will get more help from the yard staff next time you visit ,leaving a mess on the deck will have you're name on the naughty list and it is suprising how quickly all the staff become to busy to help


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## TFWS (12 Apr 2021)

@Awac what sort of projects are you using this eco product on? the blurb suggests to be applied on previously untreated timber and cannot be over-painted for example


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## TFWS (12 Apr 2021)

so i've persevered with building this greenhouse/potting shed from the kiln dried pressure treated timber on the basis that it will be painted over and i must admit even with my limited experience the timber is rough, bowed, knotted and you name it....

i have done areas of cladding in redwood timber shiplap so what should i use as preservative on this before painting?


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## johnnyb (12 Apr 2021)

screwfix do a water based preserver about £22 for 5 l. I spray it on twice with dry time. then it needs sealing otherwise it leaches out. making then spraying creates a barrier. whereas using pressure treated allows weak endgrain( unless well treated) coating wood has been the same process for years(until teknos et al) make..preserve...prime....undercoat...gloss.


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## robgul (12 Apr 2021)

I'm just completing a garden project - horizontal cladding on battens on a blockwork wall - using Thermowood ("baked softwood") that's about 25% of the price for Western Red Cedar and, they say, will outlast the cedar even with no finish. Have to say it's easy to work with and looks good - at the moment it's almost cedar coloured but will fade to a silver/grey which is what we want. Fixed with Spax stainless screws - by gum they're expensive!
We're also getting a traditional greenhouse that's also made from Thermowood.


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## Awac (12 Apr 2021)

TFWS said:


> @Awac what sort of projects are you using this eco product on? the blurb suggests to be applied on previously untreated timber and cannot be over-painted for example


I would expect clean untreated timber is always the best, but in a mad artistic moment I handmade a window frame for my wife's workshop and carved it. I thought then some linseed oil which I had (spoon carving y'know...lol) would maybe give it an interesting look ( yeah, yeah)....jeez the sun in France laughed at me and started drying out the frame, so that's when I found this stuff, applied it over the top of previously oiled frame and it has worked well. As long as it can get to the timber it will work. Under £20 for a gallon. Worth a try, not much to lose eh? Have applied it on top of pressure treated wood, no problems, looks great in my mind.

Oh, and it's the green alternative, which I will always use if possible.


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## TFWS (13 Apr 2021)

@Awac thanks for that. useful to know. i assume we're looking at it as a treatment as you describe and a final finish ie. the blurb suggests it cannot be painted or stained over?


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## Awac (13 Apr 2021)

TFWS said:


> @Awac thanks for that. useful to know. i assume we're looking at it as a treatment as you describe and a final finish ie. the blurb suggests it cannot be painted or stained over?


I have never tried painting over it, I try to leave the wood showing where I can. You can buy a stained version, or maybe try mixing in some pigment of your own?


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## topchippyles (13 Apr 2021)

Use larch and no need to treat it either if you prefer natural look. Good for 20 years and i am lucky enough to have a good supply locally to me.


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## Billy_wizz (14 Apr 2021)

MARK.B. said:


> A little tip if you go to a timber yard and buy treated timber and select from the pack , don't be tempted to pull off the top couple of layers to get " the good stuff underneath "  the timbers on the outside of the packs tend to absorb more of the treatment and those towards the middle less and also those from the middle can contain a fair bit more moisture as it takes a long while to dry out inside . If you do pick your own timber do yourself a favour and restack what you don't want , trust me when i say ,you will get more help from the yard staff next time you visit ,leaving a mess on the deck will have you're name on the naughty list and it is suprising how quickly all the staff become to busy to help


You leave a mess at our yard sorting through packs you don't come back period! You need to work round the air gaps for the best chance of uptake but generally the wetter heavier bits are the ones that have taken the most in so take longest to get the water back out


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## Benpointer (16 Aug 2021)

I am looking to build a 'cedar' greenhouse. 

I say cedar, but Canadian Western Red Cedar has got ridiculously expensive so I'm now looking at alternatives. It would actually be cheaper to build the frame from European oak but I fear it will move far too much and cause issues with the glazing. 

I might look at UK grown WRC which is not as durable but probably durable enough (I plan to cap the rafters with aluminium capping and take care to avoid water collection spots). I can get green WRC cedar from a local sawmill but how long would I need to let it air dry? The posts and rafter are likely to be 90 x 45mm section, so the old rule of thumb would say if I start with 2" boards I need to leave the two years. Then again the green UK WRC I have used in the past for featheredge cladding has been remarkably stable as it dried.

It's all getting a bit complicated - I can see why people have aluminium greenhouses!

Any thoughts suggestions?


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## johnnyb (20 Aug 2021)

one year per inch is probably over the top on softwood. I've had large chunks of green larch dry in 6-12 months.


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