I would like to convert my unheated (attached) garage into a heated workshop. The three exterior walls are already insulated, but the ceiling is not, with only 1' x 1' "tongue and groove" style tiles stapled to furring strips nailed perpendicular to the ceiling joists. After a humid and rainy period, several of these tiles buckled so badly they fell out. I would like to put up an insulated ceiling, consisting of 4' x 8' oriented strand board panels instead of replacing the tiles. Are these the correct materials to be using for such a project? If not, what should I be using for the ceiling material? I don't want to use drywall, because it seems like far too much work. What R value should I be using for the insulation?
Answer:
Let's deal with first things first. The reason the ceiling tiles collected moisture is because there appears to be no attic ventilation nor vapour barrier there and that will do it every time. I would not object to having anything in excess of R-40, blown-in insulation up there but make sure you don't compromise the soffit ventilation when that is being done. You might also look carefully at a baffled ridge vent going the full length of the attic roof (no including the overhangs). You can now use the OSB for a ceiling but make sure it is thicker than 1/4". Why not just staple super 6mm poly to the furring strips making sure it also creates a good seal along the perimeter so you have no vapour barrier voids? Now you can attach the OSB.
