A mathematical model for predicting attic ventilation rates required for preventing condensation on roof sheathing

Presents mathematical model for predicting the heat transfer and moisture- transfer processes in residential attic spaces. Uses model to predict attic ventilation rates required for preventing condensation or frost accumulation on the underside of roof sheathing. Gives attic ventilation charts covering a wide range of outdoor temperatures, ceiling thermal resistances and ceiling air penetration rates. Finds that the addition of a ceiling vapour barrier reduced the required attic ventilation rate by36%, but the effectiveness of a vapour barrier was reduced by air leakage into the attic. Using measured data of Hinrichs, attic ventilation rates predicted by the mathematical model are converted into net free ventilation areas for soffit venting.