Insulation choice for timber frame extension

[MasonC]

I was wondering if anyone could help with choosing the insulation for our front extension build. My friend who is an experienced carpenter and is going to be building the front porch with me alongside suggested using Actis insulation. However being technically minded I thought I'd dig into Actis before hand as I had presumed I would go for PIR. However my understanding from this forum is Actis relies pretty much only on the air gaps required in the full system and in itself provides very little insulation qualities. PIR wise my current understanding is that it may not be great from a decrement delay standpoint. Therefore I'm thinking of using a mineral/glasswool product. The extension is currently on the old building regs value requirement but I'm thinking if I can get more in for a similar cost then great but its not a long term home for us so cost is something I care about most. The Actis buildup we were looking at:

BOOST'R HYBRID 35mm
HYBRIS 155mm
HCONTROL HYBRID 45mm

According to their simulator that would achieve 0.12m²k. So if I could hit that U value or better for a similar or less cost then that would be great. The current finish would be ground floor render board and First floor cladding.

 

Any ideas or help would be greatly appreciated.
 

[SteamyTea]

How much room do you have to play with?

 

Mineral wool, blown cellulose or even poured polystyrene beads would all work well.

[MasonC]

I have 150mm between the timbers and was going to have a battened service void internally and battened externally for the render board and cladding.

[Carrerahill]

3 minutes ago, MasonC said:

I have 150mm between the timbers and was going to have a battened service void internally and battened externally for the render board and cladding.

Do the maths on material and time difference, but we just increased the timber size for the frame, think we went 2x7 in the end for our kit. Meant everything was insulation and service void ready in 1 go and gave us nice chunky TF. It saved having to batten it all out, the material costs, nails, time etc. etc. 

[MasonC]

Makes sense going 2x7 to avoid the internal battens, did you do anything in regard to cold bridging with the timbers. Also how did you allow for continuity of the VCL?