How do you know there is no insulation up there? Did you drill a hole and check?

I would not tear off the drywall and smash fiberglass up there. The reason fiberglass insulates is it traps air. If you smash fiberglass you lose the millions of tiny air pockets. Instead I would put up 2" of polystyrene (white foam) or the 2" pink foam board between the bare joists. Then just put the drywall back up there and repaint.

Insulating will help you lower your heating costs and you should recoup your costs in 3-4 years, sooner if heating costs continue to rise.

Patrice, as far as finding a roofer who can supply UL2218 compliant roofing...have you picked out a product that you want to put on your house?

Once you do, then go through the manufacturer's website and use their locator to find a certified installer in your area.

Some UL2218 materials are more unique than others and there is a learning curve involved...but some install just like standard 3-tab or architectural shingles, they're a simple nail-down.

I'd be wary of adding isoboard to the roof deck without doing anything to the rafter bays.

Consider having cellulose insulation blown (dense-packed) into the rafter bays. It can be done with access from either the roof deck or from the interior space.

An alternatice would be to install rigid foam board insulation on the interior side of the cathedral and drywalling over that. You'll incur additional costs with that, though.

It's likely that putting isoboard on the top of your roof sheathing will still give you cold rafter bays due to the way the house is framed. Tough to diagnose long distance.

Best bet from my end? Blow in cells.

Just another suggestion:
If there is no insulation and you need to reshingle, you may want to consider a self-ventillating roof, called a "cold roof" by log house people. There are now commercially manufactured, self ventillating, self insulated composite panels that can be simply screwed down on the old roof deck. I had our VERY old house done 1½ years ago and it cured all my problems (poor insulation, inability to vent the eaves and bad icing in the winter).

If you use good hail proof shingles on top of the panels, you'd have it all. One brand name is CoolVent.

Check it out.

Don

Patrice -
A good friend of mine's father own's trela roofing - he's very honest and a great guy to deal with. You might want to give him a ring and see what he thinks. If we ever had a roofing job I'd definitely call him first.