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Green roof insulation

LesGreenRoof's picture

I'm building an unheated garage with an extensive green roof. I'm told I should insulate the roof to protect the plant roots from rapid temperature changes (I live in southern Ontario Canada, hot summers, cold winters). I want to use Roxul Comfortbatts between the rafters because their inexpensive for the R value provided. Do I need or want a vapour barrier, and if so on what side of the insulation? It's a sloped roof. From the top down, the construction is:

  1. plants
  2. soil
  3. shovel gaurd
  4. drainage layer
  5. butyl rubber waterproof membrane
  6. OSB roof deck
  7. Rafters & Roxul batts
  8. Typar membrane to reduce air circulation
  9. inside the unheated garage

Do I need or want a vapour barrier between 6 & 7, 7 & 8, neither, or both?

No. The butyl rubber is (post #211324, reply #1 of 4)


The butyl rubber is about as close to a perfect vapor barrier as you will find.  The unheated garage will (presumably) have no significant  humidity sources, so there's no humidity "driving" from the inside.  The 800-pound gorilla is the sod layer, so any humidity "driving" will be from that direction, straight into the membrane.

And you probably want the inside reasonably "open" (what you desribe is fine) in case the membrane should leak.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Thanks Dan. You confirmed my (post #211324, reply #2 of 4)

Thanks Dan. You confirmed my intuition.

My experience with green building (post #211324, reply #3 of 4)

 We built a home and they made sure to install Energystar appliances as well as doors, windows, and lighting. Every bit helps. They made this cute infographic that highlighted some of the green advantages too:

A good solution to lessen the impact of heat or deteriorated air (post #211324, reply #4 of 4)

These days many environmental improvement organizations are emphasing on construction of green building as it is good in two ways: one it improves the appearance and gives a pleasing look and moreover protect you and your house from the bad impact of polluted surroundings and keeps you healthy in all ways...I would like to share one pic which is a good example of green building.