Gotcha. Cathedral ceilings look cool, but they are tough to insulate. One warning: You want a foam that has some vapour permiabiliity, otherwise you have, in effect, 2 vapour barriers on your roof sandwiching the insulation. The strawbale people have discovered that want the cold side of an insulated wall to be about 10 times as permiable as the warm side. Otherwise you get some degree of condensation somewhere in the insulation. You need to be paranoid about the detailing of the vapour barrier too, espeially around electrical boxes and any plumbing that penetrates it.
Given the price of foam, would there be merit in just increasing the cord of the roof truss, then venting the space above the insulation?
Secondly. Blown insulation settles. How do you keep continuous coverage over the ceiling as it settles. I've got a cathedral ceiling in part of my house. There is no way I an get into that space to add insulation, or even check the status of what is happening.
I really really like construction that allows maintenance.
E.g. If you have a flashing that works loose or 20 of the metal screws that hold the metal down aren't down quite tight
enough, and after 5 years the neoprene washer starts to leak -- now what?
My ideal of house construction is that you can replace any one piece without having to rip out 30 pieces, and have a 9 stage repair job. It never works like that, but I make darn sure with my renos that ALL the plumbing is accessible. Anything that will break or wear out in less than 50 years is designed to be replaced without harming the gyprock. (One trick: Buy a square good quality MDF cabinet door, paint the backside well so it doesn't soak up moisture, and mount the bathroom exhaust fan on the door. The door screws through the gyprock into a rough opening. Now the next time I replace it, I have a larger opening to work with.) If I ever build again, there will be some way other than mounting the breaker panel in an outside wall too. Real tough to add a circuit. I like crawl spaces, and suspended ceilings, as it reduces the hidden runs. I love putting the back of a closet adjaent to the bath/shower wall -- then doing the back of the closet with wood paneling held by screws instead of gyprock.
NO plumbing goes in an outside wall, with the exception of outside taps. And they are all long stem valves to get inside where it is warm.
Put shutoff valves on every branch line. You really don't want to shut off all the
hot water for the entire house to replace a washer in the bathroom sink. Especially when you are an hour's drive from town.
Whenever you work on electrical, use a fine point permanent marker, and write down the breaker number on both the electrical box and the cover plate. Saves you grief next time.
Give thought to the height of outlets. Lamps are fine with knee high outlets. But every room should have an outlet that is at light switch height. Makes the vacuuming a lot easier. I used to like computer plugs to be at desktop height, but now I screw a power bar either to the wall or to the desk.
Ok. I got side tracked.