I recently built a pole building. I used the 6' wide fiberglass/vinyl insulation on the roof under the metal. I want to heat a portion of this building year round and need to increase the R-value. Should I use fiberglass insulation between the roof purlins or a reflective insulation (foil/bubble) hung from them or both. Live in Spokane, WA. Thanks.
The fiberglass insulation should have a decent rating. You have two easy options though, use rigid insulation between the purlins like you spoke of or build a ceiling down lower to reduce the cubic feet that you are trying to condition.