Do I Need a Vapour Barrier When Insulating a Shed?

Your shed does not need moisture or vapor barrier unless you plan to heat or cool it. The plastic should be 6 mil poly, but 10 mil to 20 mil is better. If you heat your shed, the barrier goes on the inside of the wooden frame. If you cool your shed, the moisture barrier goes on the outside of the building.

Does insulation work without vapor barrier?

To work effectively, the vapour barrier also must be warm enough to stay above the dew point on the exterior side, which means sufficient insulation must be installed over the barrier to maintain the temperature no matter the weather outside. (Source: NRCA.) ... (Source: NRCA.)

Do I need breathable membrane on shed?

If you're insulating a shed for use as a home office or cosy garden building, then it's worth installing a breather membrane between the shed walls and the insulation to help with moisture. This is especially necessary if there is no other ventilation in the shed (e.g. a roof vent).