That's a very ambitious addition to your house and looks impressive from a casual glance. I would say that with all the operable window units and windward door opening in your greenhouse, ventilation should not be a concern. Natural convection should create adequate circulation of any moisture hanging out in the upper areas, considering the relatively low roof pitch.

Upon a closer look however - I'm guessing the gable end to be about 12 ft? If so, I'd be more concerned about structural integrity. I assume in your region, there's some potential for snow and wind loading. A roof with 2x4 rafters spaced 2 ft o.c., no moment connections or corner bracing, and the absence of headers over window/door openings, seems very sub-standard - by any building code standards.

The 2x6 ridge board is obviously not a structural ridge beam. Therefore, horizontal ties should be secured to the top plate - connecting the east and west walls. This is important to counter these walls from spreading, resulting from vertical roof loads. This will eventually cause the rafters to push the outer walls outward. Additionally, without structural headers over the door and windows, will result in the walls deflecting even further - maybe to the point of shattering window and door glass.

Sorry to be so critical of your construction project - it really does look nice and I'm most likely over-criticizing what will be a competently designed structure. Surely the building inspection official mentioned these things when you pulled a building permit, so perhaps you simply haven't completed them yet . . . ;-)

Looks great, but archdiver is correct, you've GOT to tie those walls together, or you will see them start to pull the roof apart in the next few years.

As far as venting use the gable ends. If they are glass now, replace just ONE section with single wall polycarbonate so you can build a shutter / vent / fan to release hot / humid air as needed. A roof vent at this point will be too difficult, and most likely leak. A $20 sheet of poly will be really easy to put up, then you can use 2x4 to frame in a square to mount a fan or vent.

Thanks, archdiver and imstillatwork. Your suggestions are much appreciated. I also appreciate the fact that you ignored the direction our corrugated roof runs. Probably would have been better to set that up so that rain would run OFF. Rather than sit. ANYWAYS...We'll now be putting in corner braces, and horizontal ties connecting the east and west walls. Not sure what "moment connections" are yet, but when I find that out we'll do that too.

With regards to the headers over doors and windows, we only get 10.5 inches of annual precipitation here. Strange with it being a high elevation and the high desert, but that's really it. We're down in the "valley" of the rimrock instead of on the mesas or in the canyons. Your point of getting the pressure off those exterior walls has registered, though. Wind is something I want to look at some more. So, again, thank you for bringing that up.

"Imstillatwork:" I agree with you about the likelihood of leaking if we open up the corrugated polycarbonate roof. The southern gable end isn't glass, actually. It IS polycarbonate sheeting. I love that stuff. As to mounting a fan or a vent...without electricity I'd have to go with the vent. Manually closing and opening it. Is there any particular vendor you can recommend or am I just looking for a basic vent you can find at Home Depot? If we ever do run electricity into the GH, I've heard that fans are more effective cooling agents than vents. Would you two agree?

-High Desert Gardener

My untrained eye is seeing a potential solution to your vent problem, someone here with far more experience, could probably confirm or deny the viability of this.

Given the amount of sunlight coming in, you could remove one of the polycarb panels on the south wall (one of the two trapezoids), and replace them with a plywood panel. Inside the plywood panel, you could mount a solar powered exhaust fan. The fan only operates when the sun is shining! (I found a solar powered attic fan online for about $28! It wouldn't move a ton of air out, but with the other ventilation you have, it wouldn't need to and would be a nice backup for you, if you forget to ventilate some day. Again, it would still get warm, but it would remove the hottest air!)

There are also many solar powered vents or vent openers, you could also install in that place. The amount of sunlight you will lose would be very small compared to the amount of heat that you could easily vent, especially if the vent is mounted as close to the top of the gable as possible.

(Those with far more experience: Is this correct, or am I completely off-base?)

Wow! A solar powered attic fan for $28??? Where in the world did you see that? You mentioned that it was online. Was it a well-known vendor or something like e-bay?