Answer: Bitchothane is sold as an ice and water shield and used mainly for roofing; it is a self adhesive rubberized asphalt which makes it suspect (in my mind) as a suitable material for including in a raised bed you plant to use for vegetables. I'm sure it would spark the same kinds of controversy as using treated lumber or railroad ties for the garden beds. Some gardeners use treated lumber but avoid planting root vegetables, others aren't at all concerned about the potential for contamination. I think I'd use redwood or cedar for the timbers and plan on replacing them in 6-8 years. Both redwood and cedar contain natural oils which will help preserve them, even when they are partially buried in the earth.
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