Steve Knight

The research on attic insulation shows a declining rate of return after R Values of R-50 (16" of cellulose)have been obtained. This is about the maximum level of insulation I see. After this level is obtained, the cost of insulation and labor to install the insulation will exceed the savings in energy costs over the life cycle of the house. As long as the insulation doesn't block vents there should be no problem caused by additional insulation.

The black staining is commonly called Ghosting. It is generally caused by soot deposits. Typically, when the deposits follow studs or ceiling joists, the deposits are caused by a phenomenom known as thermophoresis where soot particals deposit along a thermal gradient. Because there is less insulation at the stud it is cooler than the surrounding surface and that is where black soot and dust is being deposited. Anything that forms soot will contribute to ghosting. Common sources are candles, smoking, improperly operating gas appliances, pilot lights and cooking greases. Home Energy did an article on Ghosting back in 1998. You can read the article on their web site at http://homeenergy.org/archive/hem.dis.a ... 80109.html Steve