What Reflective Surface?

One must never use shiny metal for reflectors.  Rows of flat mirrors can be used, but not the wonderfully reflective aluminums, unless they are adhered to an absolutely flat or convex surface.  Dr. Frank Nordstrom of Farmington, New Mexico set fire to his roof with a drum door that used specularly reflective aluminum.  The door, which sagged slightly, was still open in May when the sun climbed high enough in the sky to focus on the edge of his roof.  Fortunately the whole house did not burn down.

 
At Zomeworks we have used shop grade aluminum in flat panels and also curved in arcs.  These have never caused a fire.  The dull finish scatters the radiation. I think a large parabolic dish, even covered with dull aluminum, could start a fire.  I have heard that some white paints on parabolic dishes can.

We have made many reflectors such as those used by Alfred von Bachmayr on the Fountain Valley School (Fig.8) or by Don Felts on a house in Albuquerque (Fig. 9) with four rows of ordinary 12” x 12” mirror tiles, and had good luck with this for 30 years. I would not try five rows; too many suns could focus in one place.

Fig. 8

Mirrored Sunbenders in winter position. Fountain Valley School,Colorado Springs, CO.Al von Bachmayr, Architect 1979

Fig. 9
Mirrored Sunbenders lowered in summer position. Albuquerque, NM c. 1985 Don Felts, Architect

 
White paint can work well as a reflector.  Today we sell Sunbender reflector/ shades that use painted steel roofing panel reflectors that bend over the ribs and can be purchased by the customer locally. Zomeworks manufactures and ships only the ribs, poles and brackets. (Fig. 10)

Fig. 10

 New style Sunbenders using ribbed steel roofing panels.
Zomeworks Roof 2006

The back side can be any of the many available colors while the front side is the standard white primer found on the underside of metal roofs.

Aluminum or mirror reflectors are not suitable for all skylights.  They may irritate by glaring brightly through clear glazing.  White reflectors are less offensive, yet still do their job adding considerable heat and light. Skylight lenses that diffuse the light can help.