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Author Topic: new greenhouse planning  (Read 7111 times)

BajaJohn

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Re: new greenhouse planning
« Reply #150 on: November 06, 2017, 06:37:07 AM »
You can reduce moisture problems by using closed cell foams which are a natural vapor barrier.......
https://buildingscience.com/documents/reports/rr-0912-spray-polyurethane-foam-need-for-vapor-retarders-in-above-grade-walls/view
Many solid and spray/pour insulating foams are not closed cell and therefore allow diffusion of water vapor where it condenses on the cold side so be sure you use a foam that has vapor barrier properties. Apparently mealworms will eat polystyrene foam although it may not be their first choice in a greenhouse.
« Last Edit: November 06, 2017, 06:40:06 AM by BajaJohn »

brian

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Re: new greenhouse planning
« Reply #151 on: November 06, 2017, 12:36:41 PM »
Millet, good to hear you aren't getting mold.  Am I correct in assuming you have a gap between the glazing and the foam board where the frame itself resides?  I worry that moisture would work into this gap and grow mold as there would be no airflow.  Given that you aren't seeing that problem, maybe my fear is overblown.  Perhaps the sunlight betweent the glazing and the foam is keeping mold from growing?  Or, perhaps you've sealed it so well that moisture simply isn't reaching that area.

BadFish and BajaJohn, spray foam is an interesting idea.  I use the canned foam to seal cracks, and it works well despite being an awful sticky mess.  It solves the problem of getting the insulation attached directly to the glazing/frame with little possibility for moisture penetration.  From reading that document you linked to it sounds like using PU foam without an extra vapor barrier is likely fine, as there is nothing that can rot in my greenhouse structure.  I'm not so concerned about it being perfectly flat... my biggest concern is that it's very permanent.  It would be nearly impossible to remove the foam from the frame if I ever need to disassemble any part of the wall frame.  I'm not sure why I would... but it worries me a bit. 

Millet

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Re: new greenhouse planning
« Reply #152 on: November 06, 2017, 03:19:33 PM »
brian, no there is no space between my insulation boards and the glazing.  The insulation boards are attached directly to the north wall glazing.  I sealed the instillation board seams with the silver sided tape.
« Last Edit: November 06, 2017, 03:21:23 PM by Millet »

brian

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Re: new greenhouse planning
« Reply #153 on: November 06, 2017, 03:59:09 PM »
brian, no there is no space between my insulation boards and the glazing.  The insulation boards are attached directly to the north wall glazing.  I sealed the instillation board seams with the silver sided tape.

How is this?  Doesn't the frame get in the way?  Or are your insulation boards fitted around the frame members?  For example, in the photo of my north wall, you can see metal framing that the glazing attaches to.   If I fitted the insulation flush with the glazing it would require cutting foam boards to exactly fit between the frame members.

Millet

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Re: new greenhouse planning
« Reply #154 on: November 07, 2017, 12:20:52 AM »
Yes, I cut the insulation boards to fit exactly in between the frames.  In fact I cut all boards 1/4" longer and wider than the frames, and squeezed them in for a very tight fit.  Being a polyurethane foam product they squeeze down nice and tight, plus I used glue..  Actually polyurethane boards are really very easy to cut.  I use a yard stick and a simple sharp kitchen knife. I did much the same for the back wall, which I put up each night during the winter, and remove each sunny  morning. Doing so greatly helps with the heat bill, which can be high in Colorado.
« Last Edit: November 07, 2017, 12:27:49 AM by Millet »

brian

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Re: new greenhouse planning
« Reply #155 on: November 07, 2017, 09:21:59 AM »
Ah, thanks for clarifying.  Yes, with boards flush against the glazing I wouldn't expect any mold to grow.   

 

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