Attic spaces get very hot in the summer months. This heat can take years of life out of a roof. It is very important that your roof is vented properly. If you are installing insulation in your shed roof you need to install soffit vents to allow air to flow from the soffit area in the evest and go up into the attic space of the shed.
There should be a vent in the eves between every truss. This vent should have a clear space above it to allow the air to travel from the vent to the ridge of the attic. Often, especially with blown insulation and lean to or modern shed roofs, the area on top of the wall, just inside of the vent gets loaded with insulation and it stops the air flow. Insulation companies and large home stores sell a rigid baffle that sits between the insulation and the roof decking to allow air to flow by. They are easy to install because they are held in place by the insulation.
Tools and Materials
Using a facemask respirator when in the attic is important to reduce the amount of insulation dust you will breath in. Be very careful to only step or lean on structural rafters or other supports while in the attic. Drywall willl not support body weight, there is a danger of falling thru it when you are in a attic space. You should also wear long pants and a long sleeve shirt when working around insulation.
The hardest part of figuring out how many baffles you need is getting into the attic and climbing around. It may be easier to measure the lineal feet of the wall that you will be installing them on from the outside of the house and dividing by 2. The result is how many baffles you need for that wall. Gables do not need any baffles. Baffles are available at larger home stores and insulation suppliers.
You just slide them into place making sure that they are not filled with insulation. A good way to tell if air can get thru is to turn the lights out in the attic in the day time and see if there is day light coming thru the gap made by the baffle. The insulation will usually hold the baffle in place. It is wise to put staples into the sides securing it to the shed roof truss.
If you are building a modern shed or lean to shed you will need to install baffles when you install the insulation. This is typically done just before installing the drywall on the modern shed ceiling.
Images courtesy of Ownes Corning.