Best approach for suspended floor

[Tetrarch]

The 1917 house refurb has a decision point and I am receiving conflicting advice.

 

The new extension (25% of footprint) will of course be insulated. The 1990 (old) extension  (35% of footprint) is completely lacking any floor insulation and so I am happy to have it dug up and relaid simultaneously with the new extension. So far, so simple.

 

My builder has advised that I could/should remove the suspended floor (40% of footprint) and infill with hardcore, concrete and insulation to create a floor like the rest.

 

The other option, is to insulate between the floorboards and either use spreader plates to drop the UFH pipes below the joists or (height-dependent) put floor trays with a screed (liquid FL if that saves some height) on top.

 

Is there a huge difference in efficiency between my builder's recommendation and the latter idea? One advantage is that I can do all the insulation myself as a job before he even starts on site

 

Regards

 

Tet

[Onoff]

My downstairs Bedroom, Hall and Dining Room are all suspended floors over dirt. The lounge is a weird suspended floor construction above a "concrete" floor (who knows how thick!). They'll all be coming up and get the hardcore, insulation and UFH in slab treatment. D'stairs Bathroom already has had this treatment with UFH loop in place (but going nowhere at the mo). Stairs room is concrete, that's coming up for the dig down / build back up treatment. The UFH manifold will sit under the stairs and all UFH pipes go off from there. I'll be putting in at least 150mm PIR + 25mm EPS. Kitchen and Utility are concrete but way too high.....tba! ?

 

 

The one thing that always sticks in my mind is @Jeremy Harris saying even with his super insulated house sitting in 300mm of EPS, he estimated his heat losses to the ground as 8% I think it was. That really puts things into perspective!

 

@oranjeboom in here dug his whole ground floor up and built it back up. 

 

All I need to complete mine is money and time!