Notes from Windward: #70

A Metal Roof for PropHouse


      Over the past few years, we've gradually been putting together a small 6'x10' research greenhouse known as PropHouse, which is short for the Propagation Greenhouse. That name refers to our long-term project of working out what it takes to be able to develop a year-round working supply of Black Soldier Fly larva.

Propagation Greenhouse in winter

     People who live in temperate, coastal areas can count on the wild population of BSFs to come in and lay eggs in their waste containments. Unlike houseflies, adult Black Soldier Flies don't have a mouth, so they have no reason to come around bothering people in a search for food or water. Being extremely shy creatures, they only come near human habitation in order to lay their eggs.

     Many areas of the US are either is too elevated, too cold or too dry for them to survive in the wild; Windward is all three, so if we can "domesticate" them here, others will also be able to put a powerful biotechnical tool to work for them.

cutting a shingle from a chest freezer lid

     Since the mature flies lack a mouth, they can't avoid dehydration by drinking dew. As a result, ideal breeding conditions would involve a relative humidity of around 85% and temperatures in the mid 80's. We see those conditions at various times of the year, but never both at the same time. When it's damp enough for them here, it's too cold for them to fly, and when it's warm enough, it's too dry for them to survive long enough to breed.

     It's only within a contained environment that we can satisfy those two requirements simultaneously. But that brings up the next problem, which is that BSFs mate in flight and use the sun to orient themselves during mating. Multiple light sources disorient them, so bringing them inside a controlled environment will only work if it's adequately lit solely with sunlight.

preparing a notched shingle

     PropHouse is designed to meet these needs. As part of that design, the northern wall and the northern half of the roof are insulated and covered with plywood so that the structure retains heat during the winter. But that ability creates problems in the summer in that the thermal efficiency is such that PropHouse can rapidly overheat on a sunny day.

     To prevent that from happening and cooking everything inside, we have a thermostatically-controlled grid-powered fan that kicks in when the interior temps exceed 90°F, something which I've seen happen on a bright sunny day in February when the outside air temp was in the mid-20's.

installing a notched shingle

     In anticipation of taking PropHouse off-grid, we've installed three vents on the north side of the roof with the intent of driving them with the 12 VDC fans that blow air through the radiator on some of the smaller Japanese cars such as Honda Civics.

     Because we live in a forest, we only install non-flammable roof materials, usually a form of corrugated sheet metal. But the three vents made that difficult since the corrugations below the vents are difficult to seal. As an alternative, we decided to give PropHouse a metal roof by cutting sections of enameled steel from some "dead" appliances we had stored up in the Depot where we keep things that are too potentially useful to haul to the dump.

the bucks want to help

     We used a metal abrasive wheel mounted on our heavy-duty handsaw to cut the steel shingles. Using a tub of roofing tar and a caulking gun, the metal shingles were bedded in tar and screwed into place. Sections had to be cut out of some of the shingles to provide space for the vents, but otherwise the task went forward smoothly. The biggest problem was that the two rams in the pen north of PropHouse kept rubbing themselves on the ladder, which made working on the roof a bit more exciting that I usually care for.

     With all the shingles in place, it was time to give the roof a coat of reflective paint to make it even more insulative since reflective surfaces don't absorb heat as much as dark surfaces‒thereby keeping them cooler in summer‒and don't transmit as much heat, thereby keeping them warmer in winter.

the new roof finished with a coat of reflective paint

     Now that the northern roof is installed, the next task will be to mount a photovoltaic panel.

Notes From Windward - Index - Vol. 70