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Greenhouse Drainage/ Perimeter Insulation & Flashing: Checklist

  • Greenhouse constructionPerimeter Flashing & Insulation Perimeter insulation is really essential. You want to keep whatever warmth is inside the greenhouse ... inside. A lot of heat leaks out below ground. The Scandinavians developed a system, now widely used, for shallow foundations which relies on perimeter insulation rather than having to go deep into the soil for a foundation. And a layer of flashing or metal outside the insulation keep rodents from happily burrowing inside the insulation. By going deep enough, down to clay, it makes it harder for them little darlin' critters - who will be absolutely delighted to dig up your growing planting area inside.
    • Order your pea gravel and your first load of road stone (see gravel step below) so that they are both on hand
    • Put 24" of aluminum or other metal flashing around the outside perimeter, and then just inside it
    • Inside the flashing, put 24" high 8' sections of 2" foam insulation all around the edge, going to the bottom of that little trench

  • Drainage If you have sandy soil, prob don't need this. If you have clay soil - it's a really good idea
    • Add 2" of pea gravel to the bottom of this little trench
    • Put 4" drain tile (that corrugated black plastic stuff that has holes punched in it) around the edge, curving around the corners, and ending at the lowest corner.
    • If you can figure out a way to join them in a Y at the corner, fine (we couldn't). If you can't just extend one end several feet into your draining trench, and the other as far as needed to that it goes out the daylight.
    • So, for drain tile, figure 2x length, + 2x width + 2' + 10-20' - we needed 20' extra.

  • Backfill perimeter trench So, from the steps above, you've got 24" of flashing with 24" of insulation around the perimeter, you've got some drain tile in the trench, you've got some stockpiled gravel.
    • Fill in pea gravel to cover the drain tile + ~1-2 inches
    • Fill in with some of that stockpiled clayey soil to make the bottom flat again - and this will additionally help keep that insulation in place.
    • Put at least some of that road stone (see below) around the edge to further hold the insulation and flashing in place.

  • If you have sandy soil and/or are skipping the drainage
    • Put in your flashing and insulation and then immediately start putting in the road stone to hold it in place
    • Anything less than about 6" of stone will allow the flashing and insulation to blow around in a good storm. If in doubt, add more - you can level it later.

Overview | Sitework | Drainage, Insulation, Flashing | Stone & Gravel | Foundation | Planting Beds
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