1. The problem statement, all variables and given/known data The ceiling of a single-family dwelling in a cold climate should have an R-value of 25. To give such insulation, how thick would a layer have to be if it were made of each of the following materials? (a) polyurethane foam (thermal conductivity k = 0.024 W/m · K) 2. Relevant equations R = L/k L = length(thickness) k = thermal conductivity 3. The attempt at a solution Rk = L 25(.024) = .6m My homework is telling me that I'm wrong and I have no idea why. This seems like a pretty simple and straight forward question. Can anyone help point out where I'm going wrong? Please!