Saturday, December 03, 2011

Ecoroof Grant Report: Addendum

See Ecoroof Grant Report for the main write-up. This is an addendum to that post.

During a site visit from Portland BES staff to see the ecoroofs, Tom Lipton suggested two changes to our ecoroofs:

Mulching exposed pond liner

On the garage and carport roofs, we had left about half the pond liner exposed. (See original report for details.) That makes the liner vulnerable to degradation by sunlight, making it last only 20 years instead of the 40+ years expected from a liner covered by soil media. Tom has been experimenting with douglas fir needles as a thin mulch on a light-weight ecoroof of his own, and has been having good success, so he suggested that we apply something similar.

In some areas we moved soil media over the exposed liner in a very thin layer. In the rest, we applied a thin layer of pine needles or bamboo twigs with leaves. Both materials should decompose slowly, providing an effective sun blocking mulch, without holding water and thus adding excess weight to the roof. They will likely require periodic reapplication as they decompose, though perhaps some of the hardy sedums will eventually colonize the areas and act as permanent cover over the thin layer of organic matter.

Expanding sunspace roof drainage channel

We have ~290 ft² of metal roof from the rest of the house draining into the sunspace roof. I created two small channels using 4” diameter drainpipes. Tom mentioned potential problems he'd seen in similar situations in winters when we get alternating freezing and thawing weather, creating ice dams around the drain. He suggested enlarging one of the drain areas to minimize that risk. I removed the drainpipe from the western channel and dug out the soil media to leave just a thin layer for pond liner protection.

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