attic
My attic only has plywood around our HVAC. The rest is just covered with cellulose insulation. How do people get around their unfinished attics?
I've been up with a flashlight trying to judge where the beams are, but I know it's just one missed step before my legs are hanging through the ceiling (it happened to a friend).
I used a tall plastic bucket once to catch the mice in the garage - I just put a small amount of dog food in the bottom, they could not climb the walls or jump that high to get out. I used a "ramp" made of simple cardboard to the top so that they could hop right in! Safe, no poison and easy to carry out when "full".
This is basically what you're trying to achieve, with respects to ventilation and insulation of the roof.
Start at the bottom of the roof, with soffit vents.
Baffels are used to provide a channel along the underside of the roof decking, to allow air to flow from the soffit to the roof vents. You don't necessarily need baffels, but you do want to provide at least one inch of free space under the roof decking. Baffles simply make providing this gap easier.
You can use either pot vents, or a continuous ridge vent here.
Pot Vents
Ridge Vent
If you don't already have a ridge vent, you'll have to do a bit of work to install one.
Now that you have proper ventilation, it's time to think about keeping the conditioned air in the conditioned space. For this, you'll need insulation. If you used baffles in the previous step, insulating the roof is easy. If not, make sure you maintain a one inch gap below the roof decking while you install the insulation.
You can use whatever type of insulation you'd like, just make sure it will provide the R-value you want in the space available.
Once the insulation is up, you'll want to install a vapor barrier to prevent any indoor moisture from getting up into the insulation. If moisture is allowed to get into the insulation, it could condense and cause mold problems and other water damage such as rot.
You'll want to use polyethylene sheeting, at least 4 mil thick. You're also going to want to seal all seams using house wrap tape, to ensure a good seal.
Now that the space is sealed, it's ready to be conditioned. You'll have to install appropriate heating/cooling elements in the space, which completely depends on what type of heating/cooling you have. If you have forced air, don't forget the returns.
The next item to address, is to make sure you and your stuff don't end up on the floor below. You'll want to make sure the floor of the attic is adequate to support the load. If it's not, you'll have to take steps to beef it up. For this, you might want to contact a structural engineer.
Since you've been getting up and down to do all this work, I'm going to assume you have adequate access to the space. If not, you'll want to install a ladder, stairs, etc.
Best Answer
Since my attic requires maintenance on solar vents and a power vent in the end gable, I took 5/8" plywood, divided it into three lengthwise strips and put a catwalk down the center of the attic. As a prior answer notes, use a small rake to fluff the insulation back over to the proper depth when you're through.
This was after a few years of playing Tarzan, catching the truss uprights and gauging where the feet went. Then you get off by two inches in a partial slip (did I mention hanging onto the truss members?) and find yourself staring ceiling repairs in the face. The plywood's cheaper than figuring out how to replace a ceiling with heating cables embedded in its lower surface.