You never mentioned your budget that you're willing to spend. You could add a thicker fill backed insulation blanket - 50mm, 75mm or 100mm are the common thicknesses. Steep roof pitch so would need scaffolding, harnesses, etc.. which adds up quickly. Probably still not enough insulation though but probably cheapest option. Insulation under existing timber linings then reline over the top of that as some have suggested. Working at height though so would need scaffold set up again and working overhead is not fun nor easy. You could replace the roof with a sandwich panel roof. Try Versiclad or Kingspan or comparable. They have a polystyrene type of insulation between an outer metal roof sheet and a metal inner sheet. These are heat laminated together. Again different thickness available from 50mm up to 180mm is common. The 180mm has a R rating of 4.7 which is quite good. Again steep pitch, etc., probably need new ridge capping, etc.. Probably most expensive option...... Keep us all posted on your decision though!

From what I can see, the only way to enter and exit the laundry is from the outdoors. Is this intentional? Would you never see yourself or someone else in family popping into the laundry to run a load of clothes? Or wash a dog in the laundry sink? Maybe this is the way it is there?

I'm sorry to say that I have only negative input also. This floor plan does not look as though the house would flow at all. Have studied Interior Design & have been involved in a lot of house plans, but sorry to say I don't think you will be happy in the long run. You have a Laundry right at your front door. This is where all your visitors will be entering. You have no external door from your laundry , so will you be carrying clothes outside through the house or will be there be a door in the garage to the outside? Bedrooms 3 & 4 need to go through the rumpus room to get to the toilet and bathroom. You dont want bathrooms & toilets to be seen from your front door, its not a good look. Your bedroom quarters should all be grouped together with access to bathroom & toilet, so you dont need to go through other rooms to get to them. Your area of your kitchen and breakfast bar seems to be too narrow if you are intending to have bar stools across there with doors opening out to a deck. If your most beautiful views are along the south & west I would consider flipping the design. Try to get your designer to put all 4 bedrooms, bathroom & toilet on the East side and make that the bedroom wing. Make the rumpus room from the internal garage wall towards the west. Move your balcony from that same point and wrap it around your rumpus room with big bifold doors that open to one side. This will give you the views and entertaining space in & out. Move the laundry door from the front entry to where the cupboard is at the moment. Leave the garage/Laundry door where it is and seen if you could get cupboards for storage along that garage/laundry wall. In your kitchen area I would extend the doors on that balcony out which will give you more room for stools along the breakfast bench. Move your toilet to the back wall of your living room near the stairs. I know that wall is long but your designer should be able to fit in a toilet and basin comfortably and what ever area remains you could either make it into a wet bar for entertaining or inbuilt shelving and cupboards below? or maybe even the piano, which will not be in a walk way now but in nook overlooking the living area; where it can be used on special occasions. I would also do the same with the balcony as below and wrap it around the living room with big bifolds opening to one side which will give you that indoor/outdoor living space especially if you have the wonderful views you say towards the south/west. Get rid of you french doors leading into the living room and open up all the space so it feel airy and roomy. With the toilet gone from where it is, the piano moved and the balcony moved out a little, your walk way is opened up, there will be a better flow into your dining and library areas without walls and obstacles. You will get a much better view out from your kitchen area, (which lets face it is where you will spend a lot of time) as you will be able to see the views to the south and west whilst standing at the sink. Where as it stands now you have a toilet and french doors blocking the view from your kitchen.

Very chic. That bar cart is fabulous. I need a martini now!