How airtight does it need to be?

ekling211August 16, 2010

So I'm building a greenhouse out of old windows and using some corregated plastic as well. It's turning into one of those nightmare projects that just keeps going and going but it will be fab when it's done. My plan is to use it from Sept-Nov and then March-May. I have no intention of heating it and I'm pretty sure getting it airtight will be impossible. I was thinking I'd probably put a sprinkler with a timer and have it come on once a day, like I do with my garden in the summer. My question is, if I'm watering it anyway why does it need to be so airtight, a little rain inside won't matter, right? Also, how much of the warmth will stay inside if it's not airtight (and by this I mean tiny little leaks here and there)? This is a weekend home so I won't be able to do anything on a daily basis besides the timer. Am I living in a fantasy world with my idea?

Thank you for reporting this comment. Undo
calliope(6)

My biggest concern would be putting a water supply on a timer. Seen them fail and you want water running for a week?

    Bookmark   August 16, 2010 at 6:36PM
Thank you for reporting this comment. Undo
ekling211

Many of us weekenders use them and I admit they are a little scary but from what I can tell from a random sampling, they mostly fail by not coming on at all. Without them I wouldn't have the most amazing crop of tomatoes this summer (some of my plants have 25 each one)!

    Bookmark   August 17, 2010 at 10:19AM
Thank you for reporting this comment. Undo
DrHorticulture_(Z3 Central Saskatchewan)

Sprinkler irrigation during the short, dark days of fall is tempting the gods of fungal infections. Depending on what you plan to grow, you may not need to water more than once every two weeks in November.

How much heat conserved depends on many other factors. Size of GH, exposure, glazing (number of layers), soil temperature. If everything else is optimized, tiny air leaks will be okay.

You can get an idea by putting a max/min thermometer in there, shaded from sun. Place another outside at the same height. Compare the two minima. Also, get a soil thermometer and monitor how it relates to minimum temperatures inside the greenhouse. As a VERY general rule, I find that if
X is the soil temp.
Y is the outside low
Z is the GH low

Z = k(X-Y) + Y
where k is a factor dependent on GH type, location, exposure, weather conditions (clear vs cloudy, calm vs windy), soil moisture, mulch, and depth of soil temp. probe, among others. You should try and get a general idea of what 'k' is on clear nights, what it is on cloudy nights, etc. It will change a bit with season but not much, so start measuring now :)

    Bookmark   August 17, 2010 at 9:36PM
Thank you for reporting this comment. Undo
DrHorticulture_(Z3 Central Saskatchewan)

Just to clarify what I'm saying:

for my poorly insulated, single layer PC greenhouse, k is about 0.25 to 0.3 on clear nights and 0.10 to 0.15 on cloudy nights.

Yesterday morning, the low was 38 degrees (!). Soil temp. at 6" depth was 66 degrees. G.H low was 46. k = (46-38)/(66-38) = 0.29. This approximate trend has held true since installing the GH.

    Bookmark   August 17, 2010 at 9:50PM
Thank you for reporting this comment. Undo
ekling211

Thanks Dr, I get the point, though my question pertains to the building of it so I can't really do that yet. I do hear you about watering though, good thought on that. I guess the bottom line is still get it as tight as possible. Since I'm using old windows, each window is a different thickness etc. No matter how much I try I can tell it'll be far from airtight.

    Bookmark   August 18, 2010 at 11:47AM
Thank you for reporting this comment. Undo
sandy0225(z5 Indiana)

You'd be better off to build your greenhouse at your "weekday house". Once a week tending to it will not be very productive no matter how well your timer works. It would be easier to use the timer two days a week when your not home than 5 days when you're not there. Things go wrong fast in a greenhouse!

    Bookmark   August 27, 2010 at 8:06AM
Sign Up to comment
More Discussions
High hoop greenhouse
Wondering how many of you are growing in hoop houses?...
myfrozenlittlepond
I Need Advice for 1st greenhouse - zone 6
Hi everyone, I bought a small greenhouse from Ocean...
mcolangelo1221
watering pugs
Watering plugs...better from the top or the bottom
kathybesaw
Photo--Jim's chic shack
Not quite finished yet, but thought that I’d share...
James_Shaw_San Francisco Bay Area
Vegetables
What are considered warm and cool weather plants for...
4greenhouse
Sponsored Products
Wilton Desk Lamp by Arteriors
$600.00 | Lumens
Ghost Nesting Tables - Set of 3
| Dot & Bo
Crawfish Kickers with Dipping Sauce - LIGHT BROWN
$60.00 | Horchow
Align Upholstered Armchair in Charcoal
$329.00 | LexMod
Calhoun Leather Single Arm Sofa - Brighton Zinc Beige
Joybird Furniture
Camel & Feather Gray Ornate Bloom Basilica Rug
$299.99 | zulily
Elk Lighting Mount Merrion Decorative Wall Mirror - 17W x 55H in. - 115-05
$230.00 | Hayneedle
Oval Knob Narrow Plate Set - Privacy, Passage and Dummy
Signature Hardware
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™