wall insulation - feedback and alternatives

MizMix

I understand wall insulation is just one part of the picture but would appreciate any feedback on this. I do plan on seeking independent advise from an energy advisor before finalising construction plans but I have a meeting with arch early next week and would appreciate some input on this (I also want to get as much knowledge on this as possible before dealing with the energy advisor).

Arch has proposed:120mm kingspan K6 full fill cavity on the ground floor (block inner leaf, brick outer leaf) and 120mm Kinsgpan K5 on the first floor (block inner leaf, cladding externally) which would achieve a u value of 0.16 or so.
He hasn't proposed alternatives and seems to prefer it that way so I want to do my homework on it! The more knowledge I have the better!

Is this basically kingspan insulation boards and beads on the ground floor and insulation boards and external cladding on the upper (no beads)? Or am I interpreting it wrong? U values sounds great to me BUT I would like to validate my research:
- This is an expensive way (probably the most expensive way) of getting these u values?
-Risk of: thermal looping, difficult to control quality, can't do thermal imaging

Or is the proposed actually a good way to insulate?

The alternatives seem to be:
-Wide cavity with full fill beads (from my research here this seems to be best practice?). 175mm cavity with full fill should give a similar U value I think (about .17?) but would cost a lot less than the proposed? If this is the case is there any reason I am overlooking that he is proposing the above?
Would the alternative of wider cavity fully filled not only be a lot cheaper but also be more effective/less risk (e.g. less chance of cold bridges and less risk if the builders are not complete perfectionists- to note this is not a simple house design with 4 corners so this is why I'm thinking full fill with bead only is less risky?). And on top of this is it worth going even wider? .17 though in a fairly air tight house (2 m3 target - well this is what I will be asking the arch to stipulate in the tender) sounds good to me- note we're not aiming for passive but we do want a good level of air tightness, insulation, comfort etc.

Feedback would be appreciated

Rabbo

The kingspan boards are similar to eachother and are basically high density pu insulation. He isn't proposing to install any beads. The boards would have better insulation qualities than the beads so you would require less of a cavity. This is an advantage as wide cavities require larger foundations and structural sign off by engineer. The downside of the boards is that quality control can be a bit of an issue however I would argue that full full board insulation is less likely to be installed incorrectly than partial fill board insulation. Another disadvantage to the full fill boards is cost, they generally work out more expensive than equivalent bead insulation. I would favour full fill boards myself over bead as long as you can find decent blocklayers, make clear with them the standard of work expected and keep a close eye on work. There's potential for the beads to be incorrectly installed aswell and for uninsulated areas left in walls. I know that you can geta thermal survey done after but in practice I've never seen it happen.

MicktheMan

MizMix wrote: »

Feedback would be appreciated

OP, have you considered block on flat and ewi?

MizMix

No haven't considered ewi due to the house design - ivory brick lower and fibre cement cladding on upper

sydthebeat

It sounds like the architect might be used to "farming out" the insulation specification to kingspan.
The k boards are phenolic foams, the most expensive standard insulation.

MizMix

Thanks sydthebeat I thought they were the most expensive- does that however take into account the fact that while wide cavity wall fully filled may be cheaper in itself there may be associated costs such as getting a structural engineer to sign off (or perhaps I need this anyway?!), more expensive foundations etc....plus more precise and complex detailing in the construction plans to avoid thermal bridging. Whereas the standard 120mm cavity walls is a more 'straightforward' build.