Depends on the value of your property. How much value will be added. The cost maybe cheap for valuable real estate. We are presently doing an underhouse 2 car garage eastern suburbs. Cost $200k . House value $2M. New house value on completion $2.4M

Thanks all for your advice. Ive included some renders that I made with view along the corridor with and without the bulkhead. I don't think renderst does it justice until you actual walk through @ frame stage. I agree that ceiling height and comfort and look, depends on climate, orientation, insulation, relative proportions of other parts such as windows/doors. Because of the Melbourne climate, we have planned for double glazing, and good insulation with R2.5 batts wall, R6.0 ceiling. We have 2.4m height of windows and door around the ground floor which is btw 3 to 3.6m so I think proportion wise should be ok. In the family where it was always planned 3.6m from the start, we have a band of clerestory windows too. We have decided not to be too excessive with windows ( ie 3m and even 3.6m floor to ceiling - how grand would have that looked though! ) to minimise heat loss during winter. Energy rating for house is 7 stars so far. Thanks for giving me the pro and cons - I have some more confidence to let it stay at 3.6m throughout now.

kelly velvet stools what is the floor to seat height pls

This wasn't your question, but looking at a possible boxed out window in the open plan kitchen dining living it shows just how limited you space is. The following 3D overview shows a boxed out window seat. I have run the kitchen along the same wall as the new window, The Island is 2m x 900 with 1m between the wall base cabinets and the island and 1m between the Island and the wall where your plan shows cabinets. If you have/had cabinets along the other wall as shown on your floor plan they will be 600 deep this would make the island 1400 x 900 which is small. Has your kitchen been renovated and were you considering that, if not. Looking at the overall size of your open plan area I would be considering 1 or 2 large stacker doors to open up to the rear alfresco, that's what I would do but you need to choose what will work for you PS I think that the boxed out window at the front of the house is a lovely idea but possibly not right when it faces West.