The Earth Sheltered Solar Greenhouse Book by Mike Oehler

Permies digital-market wiki page for Mike Oehler’s Earth-Sheltered Solar Greenhouse Book, summarizing claim that earth-sheltered PSP designs are far more effective than conventional greenhouses for year-round unheated growing at higher latitudes. Summary states the book teaches design/build of a greenhouse "six times more effective than the common greenhouse." Argues common greenhouses lose heat from four sides and roof while gaining only from earthen floor; earth-sheltered designs overcome this. Claims Oehler PSP building system allows year-round vegetables without supplemental heat. Sells digital download; points to physical book and bundle with $50 and Up Underground House Book + DVD workshop on Oehler website.

Evidence tier: forum. Sales/wiki blurb, not the full book; performance multiplier is publisher claim.

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