Wood greenhouse framing - Router Forums
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post #1 of 36 (permalink) Old 03-04-2016, 12:38 PM Thread Starter
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Default Wood greenhouse framing

I'm planning a 6'x6' with 24" spacing greenhouse build.

I don't care for the kits available in my price range so I would like to build it myself.

I would like to use either redwood or cedar but the cost might force me to use treated lumber.

Here lies the problem treated wood around here is very wet, dripping when cutting or screwing into it. I'm afraid if I build it wet the 24" spacing it won't be enough to keep its shape and it will twist like crazy. I may be up for some drying time but I'm not sure how long it might take or how to prevent it from twisting as it dries.

Is there a way I can dry it and keep its shape? Perhaps screw them together with a spacer between for air circulation?

Forget drying and build with 16" spacing and hope for the best? Or keep it at 24" and use scraps for support to keep them in place?
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post #2 of 36 (permalink) Old 03-04-2016, 01:12 PM
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Consider using the PT for the deck frame only, everything above the joists go with 2X spruce framing.

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post #3 of 36 (permalink) Old 03-04-2016, 02:51 PM
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I agree with Ron. There are local wood frame greenhouses that are built with just conventional SPF lumber and they've been standing for years. The inside of the greenhouse will be humid but it shouldn't get wet enough for a long enough period that it will cause rot.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #4 of 36 (permalink) Old 03-04-2016, 04:15 PM
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Otto; I built my 9X15 glass panelled greenhouse out of PT lumber. I think it's about 8 years old now; no sign of algae or rot...but I do wash the interior down with TSP/bleach solution at least once a year to kill spores and insects. This is essential greenhouse practise!
I treated every cut with Copper Napthanate, after having air dried all the lumber under cover for a number of months. My thinking was I was only going to do it ONCE! I've had to tear down too many sheds, greenhouses and garages for clients that hadn't maintained them, over the years.
Whatever size you make it it'll never be big enough... (I wish mine was at least 30' long. *sigh*)

The vertical stud/posts and roof rafters are about 30"+/- o/c to accept the tempered glass patio door panels (single glazed 'cause I'm cheap). The tempered glass roof is about 45 deg. so snow won't pile up...not that it's snowed much in the last couple of years. But if snow's an issue where you are, you might want more rafter support under your glass.
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post #5 of 36 (permalink) Old 03-04-2016, 08:03 PM Thread Starter
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Otto; I built my 9X15 glass panelled greenhouse out of PT lumber. I think it's about 8 years old now; no sign of algae or rot...but I do wash the interior down with TSP/bleach solution at least once a year to kill spores and insects. This is essential greenhouse practise!
I treated every cut with Copper Napthanate, after having air dried all the lumber under cover for a number of months. My thinking was I was only going to do it ONCE! I've had to tear down too many sheds, greenhouses and garages for clients that hadn't maintained them, over the years.
Whatever size you make it it'll never be big enough... (I wish mine was at least 30' long. *sigh*)

The vertical stud/posts and roof rafters are about 30"+/- o/c to accept the tempered glass patio door panels (single glazed 'cause I'm cheap). The tempered glass roof is about 45 deg. so snow won't pile up...not that it's snowed much in the last couple of years. But if snow's an issue where you are, you might want more rafter support under your glass.
That is a nice garden area. Have you had any problems with the PT dripping on your plants? It sounds like you didn't seal the lumber with any paint or stain.

I originally designed the greenhouse to be 8x6 but scaled it back to 6x6 for cost and I'm not sure how much my wife will use it, though I should think about going back to an 8x6 before I finalize the plans. If I use 2x4x12' I should be able to utilize 90% of the lumber with only 16 (? I think that was the count) boards.

Picture of the design at the moment.


I'm planning on wrapping it in clear polycarbonate roofing panels. Hopefully I can get by using 14 of the 26"x6' sheets.

New guy looking for ideas.
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post #6 of 36 (permalink) Old 03-04-2016, 08:07 PM Thread Starter
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I agree with Ron. There are local wood frame greenhouses that are built with just conventional SPF lumber and they've been standing for years. The inside of the greenhouse will be humid but it shouldn't get wet enough for a long enough period that it will cause rot.
What would be your opinion on sealing the wood with a stain or paint of some sort?

I've been wondering about my local SPF lumber and using a decking water seal to help minimize the abuse the wood may take.
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New guy looking for ideas.
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post #7 of 36 (permalink) Old 03-04-2016, 08:46 PM
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Otto; yes, I did refresh the surface with a coat of exterior semi-transparent stain after a couple of years. Again mostly for aesthetics and disease control in the greenhouse. Never had any issue with any PT dripping; it's locked in. Let's not forget that the bad old Arsenic issue is a thing of the past. I'm more concerned with breathing in fungal spores than I am with the PT solution. I try to do a thorough cleaning/sterilizing inside at least once if not twice a year. Takes longer to move all the growing benches etc. in and out than it does to actually do the cleaning.
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post #8 of 36 (permalink) Old 03-04-2016, 08:53 PM
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On the off chance that someone might think I've been partaking of the largest local cash crop...
https://www.emlab.com/s/sampling/env...t-03-2012.html
B.C. scientists to help American researchers study deadly fungus - Nanaimo News Bulletin
And that would be why, at least in part, I'm obsessive about spores in the greenhouse.
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post #9 of 36 (permalink) Old 03-04-2016, 09:19 PM
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If all or most of your glass is facing south your problem will be keeping moisture in the room not removing it. For what its worth, most framing grade PT lumber is warranted for something like 20(+/-) yrs on the ground, prop it on blocks an add yrs to it, maybe decade. The older ACC and the current ACQ lumber treatment, (our area) outside of ACQ eating all fasteners not SST, weighing much more than ACC and having a sort of waxy coating I never got any drippage out of them.

Whatever dripping you may see is probably more likely from rain or snow in your area and or from the area the mills and treatment plants are located. When we were building condos we had a lumber holding area within the development, we got tractor/trailers coming in directly from the mills up north, (usually Maine, Hampster and Canada) much of it frozen, still laden with snow and or rain in late March. Its been a long time since I read up on it, (80s) the problem with PT lumber is off gassing via heat within the 1st yr. On the ground it was something like 17% of the ACC could leach from the lumber into the soil within 2 yrs, so don't use it within enclosed areas or for vegetable gardens.

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post #10 of 36 (permalink) Old 03-05-2016, 01:36 AM
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Otto I think most around here are just painted white. PT lumber should also be painted or stained according to info from the company I bought some decking from for a deck I put in in northern Alberta. I didn't get to it the first two years after I put it in and by the third year it was starting to weather pretty good.
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Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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