Greenhouse design - Clear or Solar?

EvaP(USDA Zone 8)February 27, 2013

Hello, I am in the process of building a 10x16 foot greenhouse (or I should say my husband is), it will be wood framing with polycarbonate corrugated panels used for roof and sides. Originally my plan was to have the plastic on all exterior walls but now I am questioning if a better plan is to only have the plastic on the roof and south facing wall and insulate (and finish with white paint) the north, east and west walls? I plan to have planting beds along the north wall too so want to be sure that they will receive enough light.

The sixteen foot length will have full southern exposure. I live in the Pacific Northwest and plan to use the greenhouse for my vegetable garden; planning on two foot high raised beds three feet wide and a total length of about 33 feet. An article I read said, that âÂÂThe North wall transmits very little light, so minimizing heat loss is a trade-off for lightâÂÂ.
I appreciate any insight on the best design for our area.
Thanks for your help.

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George Three LLC

my guess is that having the north wall insulated with rock is not going to significantly increase the nighttime temperature in the greenhouse. R value is cumulative for the whole structure, and the majority will be very low.

if you want to get tricky, I would encourage you research trying a N wall and lower 3 feet of S E W wall with a high thermal mass construction.

    Bookmark   February 27, 2013 at 10:59PM
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Twin-wall poly is a very durable material.

How are you going to ventilate and summer-day-cool the greenhouse?

    Bookmark   February 27, 2013 at 11:20PM
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EvaP(USDA Zone 8)

Thank you! Planning to do the lower 2 feet of exterior walls wood as the inside will have 2 foot high garden boxes built around most of the perimeter. Does this sound like it might help keep things warmer?

Right now researching automatic venting, fans and vents. Have an old house fan thinking of using too.
Thanks much,

    Bookmark   February 27, 2013 at 11:37PM
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Embothrium(USDA 8 Sunset 5 WA)

I would not go overboard - so to speak - with wood, it can be problematic in a greenhouse.

    Bookmark   February 28, 2013 at 12:38AM
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George Three LLC

jus sayin' wood is not good for thermal massing either. if you don't mind the permanence i would go CMU as much as possible.

    Bookmark   February 28, 2013 at 2:24AM
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EvaP(USDA Zone 8)

Ok thank you, this is what I need to learn.

The cinder block foundation is done with 4x4 wall posts for 6' walls and gravel floor is in. Ready to finish framing.

So what I hear you saying is that three insulated walls would not give enough solar benefit to be worthwhile; better to use clear panels for light. Is this correct?

Appreciate your help.

    Bookmark   February 28, 2013 at 12:01PM
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sundevil(z7 WA)

Have you considered of a pvc pipe frame covered with clear greenhouse film?

    Bookmark   February 28, 2013 at 7:55PM
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EvaP(USDA Zone 8)

Yes we did consider the hoop house style but decided we wanted a more permanent structure.

    Bookmark   March 1, 2013 at 1:10AM
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A good reference book about building greenhouses in our climate is
Gardening Under Cover: A Northwest Guide to Solar Greenhouses, Cold Frames, and Cloches by William Head.

It discusses siting, styles, and heat sinks. Also shading during summer if you want to use it year round. You need clear for winter use as we have such low lighting to keep things growing.

The KCLS has it if you're in King County. I scanned the greenhouse structure page, so email me if you'd like me to share it. It talks about pitch of roof, type of roof & functions.

Best wishes & post a photo for us to see.


    Bookmark   March 1, 2013 at 11:13AM
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EvaP(USDA Zone 8)

Thanks Corrine,
Yes, I just purchased that book; it has been a great reference.
Never used a greenhouse before so hard to imagine needing to provide shade:-)
Probably be another month or two but will be sure and post pictures...will have to show it off!!!
thanks Again

    Bookmark   March 1, 2013 at 7:18PM
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