There are a few super things about your ambition. I agree that you should be better connected with the garden and the total square footage seems small considering the size of the plot.

You need to work out your budget and that will dictate what size you can afford to build. For instance- say you have a £500k budget for the whole house you might well allocate £220k for new kitchen/heating/wiring/flooring/ exterior maintenance such as roof and paintwork. Since your plan involves demolishing a patio you will need another and could well be £45k. This means that there is about £235k for the build and with high ceilings you should probably be allocating £3k/metre square.

If it were my house I would have two basement bedrooms in the extension and then have the kitchen and other new rooms at the same level as the principal rooms., if they are not then likely the current principal rooms will become unused.

Thanks for the reply Jonathan. Good point on having principle rooms level with the extension. On the other hand, we quite like the idea of having a feature stairway beside the wine room glass frontage and the basement rooms are not quite full room height, so they would be tiny bedrooms. We'd also need to think about the access from the sitting room, so lots to ponder.

In terms of budget, the whole house has been redecorated recently and would only need a few carpets changed for better flooring and the rear bedroom windows changed out for modern metal frame windows. The spend would only really be needed on the extension, new kitchen and some structural amendments to the end of the existing dormy room to change it into a semi-outdoor space. I can see the roofing solution being quite high cost with the skylight idea.

Keep the ideas and comments coming!

So what is your budget for building?

We dont have a budget yet. We’re scoping out the total cost vs future value of the home to judge how much we’d like to invest.

For anyone that enjoys a bit of photoshop, this is what we want to do with the archway windows which will obviously be longer down to lawn level

The kitchen extension would be something similar, forming a nice L shape with the arches in the current elongated part of the building:

To do this you will have to demolish the garage block and rebuild it a meter lower. It seems like a lot of expenditure for no gain in square footage.

But I can’t help thinking you have become focussed on building one amazing all purpose room and you are ignoring the rest of the house. I estimate that the extension is about 1.5m lower than the main house and this is a big enough difference for the entry level and the extension to be disconnected.

On reflection you might conclude you would rather have the inevitable change in levels on the patio rather than in the middle of the house.

You might also consider if the extension should include at least one more bedroom. At the £2m price point would buyers expect five bedrooms? Would they expect bigger bathrooms than this house has?

Just for my fun I have played with the plan. I concluded that if it were my house I would want a living room that is wider than the current reception rooms. I also felt that the first impressions could be improved if the hallway received extra light from the former kitchen (from the side) which in turn creates a more impressive hallway and allows valuable storage for coats, an opportunity to have a better guest WC than one under the stairs but mostly a better entry into the largest room in the house.

I put two lower level bedroom and a light well to the side.

And I felt that with a big roof outside the former master bedroom the only Ensuite bedroom could be improved so I took two bedrooms to make a master suite.