I'm now talking insulation with the architect and their view on insulation appears to be Celotex, Celotex and more Celotex, but I need value for money. So think through the problem I recall a tread dealing with insulation costs at thickness/m2.

Can anyone point me in the right direction?

Oh, it looks like we are going down the timber frame route, if that makes a difference.

Triassic,
Try 'Xtratherm' PIR, just as good as Celotex XR4000 PIR, but a lot cheaper!
Good luck

I used dritherm and fg quilt in the roof

Posted By: Ed DaviesThe way I compare insulation prices for different sized materials is by multiplying the area by the R-value to get the total resistance and dividing that into the cost to get the price per resistance.

A fair way, but not the whole story. Having to use twice the thickness of insulation to get the same U-Value (if I have read your figures right) that will have a knock on for cost in other areas and the construction method used.

Also, PIR is air tight where any fleece type insulation is not and that must affect the insulation efficiency (have we discussed that at all?).

I think more of the question is 100mm PIR or 150mm (if you go for PIR). In terms of VFM difficult to argue as pay back is a long time. In terms of reduced CO2, that depends on your philosophy.

I tried to tread a middle ground and ended up with 130mm PIR on the outside of the frame.

It seems like the next big step up in insulation products is just around the corner but probably not soon enough for you Triassic.

Rockwool have a product called Aerorock ID which is a hybrid of mineral wool and aerogel but due to production limitations it appears that it is currently only available on the German market and no doubt at a premium price.

I'm pretty sure that aerogel hybrids will be the way forward once they become more widely available.

There is a lot of research being carried out in this area, one EU funded project is http://aerocoins.eu/ but they have yet to report.

Another one is http://www.hipin.eu/

and http://nanofoam.eu/

The reason that PIR/PUR sells so well is that builders are reluctant to change their practices/designs. The required thickness of mineral wool or EPS/XPS can normally be accommodated with a bit of forward planning. PIR/PUR & phenolic should only be used where space is tight.

I would work out what thermal resistance you need to reach you target heating load & look at how you can accommodate the required amount of mineral wool or EPS/XPS in your structure. If the structural cost is prohibitive then look at using a mixture of mineral wool/EPS/XPS & PIR/PUR.

If you're really tight for space then use only PIR/PUR or phenolic. However, I would say that there's something wrong with the design if you end up in that place. For example, using a high performance insulation in a floor means the overall thickness of the floor insulation is reduced. This makes it much more difficult to mitigate thermal bridging at the floor-wall junction because the relevant path length through the wall is also reduced.

David

Its only best for most builders because they can carry on doing what they are used to. Cavity walls fully-filled with mineral wool can easily reach U values of 0.12W/m2K. The additional cost of cavity ties & separate lintels is marginal.

David

What cavity width are you suggesting for 0.18W/m2K with PIR?

You'll need about 125mm of PIR with a lambda of 0.023 W/mK, but most PIR solutions need a 50mm ventilated cavity, so that means a 175mm wide cavity. Fully-filling with DriTherm32 will achieve the same U value at that cavity width.

Lower grades of mineral wool can be used, but as you say, this may impact costs for lintels, cavity ties, footings, etc & reduce room sizes for a given footprint. However, this decision can be made on a site by site basis. Especially given the higher risks of thermal bypass with PIR/PUR in cavities, I don't think it is so clear cut.

David

Posted By: DarylP
smaller rooms,

Sorry but this makes me laugh. I am planning my new build and deciding what size the rooms will be, then putting the walls (whatever thickness) around the outside. You only end up with smaller rooms if you IWI existing buildings.

I am planning to copy Tony, 300mm cavity with mineral wool full fill. Regarding the window reveals, we are planning a cottage so thick walls will look correct, my next task is to design rounded/angled window reveals to look in keeping and also let in more light (hoping to start a thread on this soon).

Posted By: DarylPPIR with a lambda 0.022 gives a U-value 0.18 with 6"/150mm cavity (100mm PIR & 50mm clear), but full-fill '044' batts needs 8"/200mm...You could spec '032' batts, but then the cost of the batts is not far from PIR!

I didn't know you could buy mineral wool cavity batts with a lambda of 0.044 W/mK. That sounds more like cheap loft insulation. The normal options are 0.037, 0.034 & 0.032 W/mK. If the issues you describe are enough to drive you to PIR/PUR cavity boards then 0.032 W/mK mineral wool cavity batts are the only sensible alternative. I don't see an increase of cavity width from 150mm to 175mm being a game changer, especially when looked at in the round.

Posted By: DarylPIf you count the effect of the foil-faced PIR producing a low-emissivity cavity/air space, then the PIR can be even thinner.

This seems to be already taken into account in the example you gave. Are you also assuming a lightweight aerated concrete block to the inner leaf?

The latter makes wet plastering difficult. Where would your air barrier be in that construction? How do you tackle thermal bypass of the cavity boards? How do you deal with cold bridging caused by steel cavity lintels? Don't you need separate lintels in any case? Or will you be insulating the soffit/reveals?

Posted By: DarylPI do agree that up to 100mm, full-fill is the best.

I don't think there's a hard threshold. I think you need to look at the whole solution.

David

No brainer is one way of describing it. I can think of others.

David

I found the following quote interesting -

"Specification of insulation products is often based upon the minimum requirement of the Building Regulations AD (Approved Document) Part L and their relationship with manufacturers performance data, ...........

and it has been suggested that legislation is driving the production of a range of products that ‘just work’, presenting little apparent difference between them.

In order to specify insulation correctly however, the specifier needs to understand the reasons why it works, and apply the correct technology to any given construction detail. In understanding more fully the processes that make insulation work, and indeed the factors that stop it from working, specifiers will be in a far stronger position to specify the correct material for the correct application.

The installed performance of an insulation product is reliant upon not only performance characteristics and the adherence of contractors to manufacturers and general best practice workmanship requirements, but also the suitability of the insulant specified to its installed location. "

From - http://www.designingbuildings.co.uk/wiki/Thermal_insulation_for_buildings

Building regs allow it, but its still not standard here & so comes at a premium. In addition, many people (including planners) prefer bricks to render.

David

Posted By: joe90my next task is to design rounded/angled window reveals to look in keeping

Our rounded reveals will be designed with a chainsaw on the day

Posted By: Peter_in_Hungary

Posted By: davidfreeboroughBuilding regs allow it, but its still not standard here & so comes at a premium. In addition, many people (including planners) prefer bricks to render.

David

OK but does the premium cost out weigh the savings taking into account speed of construction and avoiding poor workmanship in cavities causing thermal bypass and unwanted convection currents sapping heat.

There's a school of thought that cavity construction is cost competitive, promulgated around the Denby Dale house IIRC. I never took enough interest to understand the details or veracity.