Help me plan my Colorado sunshed

9 years ago

This spring I'm converting an existing shed into a sunshed. I live in Colorado at 6000 feet elevation, about 40 degrees north latitude

The shed is 8 feet by 12 feet (on the south side), with wood framing, a wood/plywood floor, and currently has plywood/asphalt shingle roof. There's an existing shelf all the way around the inside of the shed between walls 2 and 3 where indicated.

I plan to remove two of the roof panels indicated, and replace with triple-wall polycarb (if I can afford it)

My intention is to use this as a passive solar greenhouse for seed starting, jumpstarting tender vegetables, season extension, and winter harvesting.

I plan to addthermal mass and fiberglass insulation/vapor barrier/drywall eventually on the north and east/west walls

I attached a rough diagram of the profile of the shed.

My original plan was to replace the asphalt shingle on walls 1 and 2 with polycarbonate panels, and leave wall 3 as plywood construction with some added insulation.

After speaking with my knowledgeable mother-in-law she suggested I may want to leave wall 1 as asphalt shingles, and consider instead glazing walls 2 and 3 or wall 2 only, due to the difficulties of keeping a greenhouse cool in Colorado with all our sunshine here.

So I have some questions:

I'm concerned that glazing wall 2 only would provide insufficient light for plants. Is this something I need to worry about? Is my MIL right about glazing the side and not the roof?

Will keeping the uppermost panel (wall 1) shingled reduce my solar gain significantly?

The shed has an existing plywood-on-2x4 floor. Is there anything I can do to insulate this, or should I not worry about it until it rots, later?

Thanks for any advice, I'm going to cross post this to RMG.

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Comments (3)

fruitnut Z7 4500ft SW TX
9 years ago
I'd side with MIL. 1 glazed will increase summer heat and light when it's least needed. But 1 won't increase winter light or heat gain much at all. So partly it depends on when you will be using the greenhouse most. The added summer heat thru 1 can be vented with a power fan in the peak and inlet down low. Don't under estimate the need for ventillation on any sunny day. Here at 30N my sunroom will hit 120F+ on a sunny day right now unless heat is vented into the house. That's a heat gain of 60-70F over outdoors.
Golden David
Original Author
9 years ago
Thanks fruitnut, the rear western wall of the shed abuts a large masonry retaining wall that runs N-S so I will place the inlet vents down low by that wall, and the outlet on the eastern side. Even though the wall is about a foot from the shed, i think it will still serve as a bit of a heat sink.

I am currently researching viability of solar fans but I will have power running to the shed, too. Old solar fan threads in this forum seem to think its not worth it but the price of solar has plunged in the last five years.
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Golden David
Original Author
9 years ago
So I've completed the rough construction And I'm in the process of installing insulation and ventilation. The insulation is a rigid foam R-13 with foil lining. I will literally cover every non glazing part of the inside structure with this eventually and seal all seams with caulk and foil tape.

A photo below but more at

http://forums.gardenweb.com/discussions/2811423/help-me-plan-my-colorado-sunshed

I settled on a 1250cfm powered thermostat roof fan and I purchased about 600sq inches of louvre vents.

The idea is to have vents that will seal easily in the winter with foam cutouts.

Am I making any mistakes by not automating the intake vents? Would a passive flap lifted by the exhaust fan be inefficient ?

Will leaving the roof vent unsealed during winter be a problem? I was thinking I could automate only one third of the louvre vents during the winter and that 200sqin would create a passive convection with the uncovered roof vent to keep the power fan from kicking on most days.

Thanks for reading I may have worked this out by writing this post but as always I welcome any feedback.