Wall construction choice for additional first floor above existing garage

Hi,

I've recently joined the forum and have some questions on the first phase of our build which will be to convert the integral garage into living space and add a first floor to it. The existing ground floor walls are ~270mm cavity walls with yellow fibreglass insulation between (I think slumped or missing in places from what I've seen at the top of the walls of another part of the house).

 

I'm considering what construction method to go for currently. The exterior finish we are planning is a mix of render and cladding on different elevations. It will also have a pitched roof.

 

Below are a few options I have been considering (U values from quick inputs into Vesma calc). My plan is to add 150mm EWI to all existing walls of the house, so all the options include that.

 

1. Match downstairs and continue the 150mm EWI up from groundfloor (0.15 W/m2K) 

2. Side laid thermal blocks and continue the 150mm EWI up from groundfloor  (0.17 W/m2K)

3. Timber I-beams with frametherm insulation (~220mm) and continue the 150mm EWI up from groundfloor  (0.1 W/m2K)

 

Though I would like to do it all myself, I don't have the time, so I'll need to employee either the builder I have used before or others. So that will need to come into my comparison.

My assumption is that the foundations are capable based on some original construction photos, but I need to dig a test hole or two.

 

Any comments on performance, material costs, time and complexity, or other considerations would be very welcome.

 

Thanks,

Andrew