Help with loft rooms heat loss calculation

[Mmark]

We have just had an L shaped loft conversion done. Builder did not follow the architects instructions for insulation, so now I don’t know what my heat loss is. We have had UFH installed and need to determine if we go for tog 0.5 or 0.8 underlay. I’ve asked the supplier and they say to answer that, they need to know my approximate heat loss. We’d like the King 0.8, but don’t want to risk poor performance. So I’m really hoping someone might be able help?

We have two rooms.
Room 1: 6m x 4m Pitched roof with mansard flat roof section. Two MK06 Velux and one 2m x 2m french doors with side panels.
Room 2: 4m x 3m flat roof. Two sash windows.

Our house walls are two bricks thick, no cavity. The insulation is between wall battens and Roof rafters, with 400 centres for floors and ceiling. We have no insulated plasterboard and both rooms are cold roofs.

 

[^woody^]

Why don't you just assume the greatest heat loss and select the better performing product?

 

[Mmark]

Why don't you just assume the greatest heat loss and select the better performing product?

If I cannot prove that Tredaire King 0.8 tog is OK, then I will have to play it safe with the Ball & Young Olympic 0.5. But the samples of King, that we have, are considerably higher comfort levels the Olympic5.

We used between joists spreader plates with gifafloor. So we are in slightly better position than that if we had chipboard (0.6 tog v 1.4 tog). We had to do this to get combined underlay + carpet under equivalent of 2.0 tog. In theory 0.8 should be ok, but I’m just a little paranoid, unless I can show the figures.