U value calculations

Forgot to add that from the last change in part L of the building regs about three years ago you have to meet the following:

External walls 0.26 W/m2K Floors 0.22 W/m2K Roofs 0.18 W/m2K

We ended up with around 0.14 W/m2K for a 30 degree pitched roof, which requiring a total of 170mm of PIR (120mm between the rafters and 50mm under) with 600mm rafter spacing and 12.5mm plasterboard. Without the 50mm 'under' we were over the 0.18W/m2K limit

They can't, I'd also worry about some oaf putting a new or screw in one. Suppose you could cover the regular areas with their standard sized panels, then stuff pir/rockwool in the odd corners, and the average would still be much higher.

They seem a very coy about the prices ...

Not sure how 'nail' turned into 'new' ...

I did all my own 35 years ago when dimensioning the CH. Not really needed but it was easy.

Exactly and why I asked him to produce a set of calculations. The drawings accepted by Building Control offer a selection of solutions and I am choosing to use the most practical for the circumstances.

I think BC would like to have seen PIR foam throughout. In hindsight the next thickness of insulated plasterboard might have given a safer margin.

I look at this when time permits. 300mm Rockwool over attic floor is easy enough and might allow for a tighter margin elsewhere.

From

"VACUPOR® is not the cheapest insulation material on the market. However in numerous cases its use will pay back because:

Space is saved ? allowing a project to be realised Time scales are reduced ? alleviating expensive site site set up costs and prelims."

Sounds rather like, if you need to ask.... etc.

My mate the brewer once had an HSE type trying to insist he put in CO2 detectors (worth saying it is a small draughty Victorian brewery and geometry is in his favour). I wrote him a little report based on production rates and air changes, and that did the trick.

And yes, I do know there's a fatality a year in breweries and similar. We worry quite a lot about CO2 leaks in nuclear power stations because these have quite nice enclosed basement type spaces.

Seems a bit like cutting your feet to fit the shoes! OK, perhaps, from design stage onwards but no good for retrofit. I can imagine trying to lay them between existing joists (mine vary from about 14" to about 18" and aren't really parallel in most places). VIPs are also failure-critical - damage PIR and it doesn't leak; damage a VIP and all the vacuum escapes and the panel is an expensive conductor.

Oh - it's a vacuum panel... I've only heard of those in double glazing (vacuum between two panes of glass - Pilkinton IIRC).

Yep - vacuum panels in embedded insulation sounds like a hiding to nothing - one misplaced drill and your insulation goes from great to s**te.

What happened to aerogel?

The figures intended to be achieved from the submitted drawings are :-

Sloping soffits under rafters 0.2W/m2K

Dormer cheeks not specified but design calls for 75mm raftersqueeze between studs and 36/9.5 polyfoam liner board. I am actually using 80mm PIR foam and 25/12.5 liner board.

The cavity walls should be 0.29W/m2K

New floor not specified but 80mm Celotex suggested. I will use 100mm for other reasons.

Exterior glass specified as 1.6W/m2K

One thing of note.. BC was insistent on at least 30mm air gap under the felt. Someone needs to tell the building trade because they are convinced that permeable underlay avoids the need for ventilation!

Will sort you out. You have to register but it took me 1 minute.

The ceiling *may* just manage with the same plus the plasterboard which does have some insulation value - but you'll have double check this.

I feel quite pleased as I managed 75mm between and 25mm under (except for last 2' into eaves) - so my old but reinsulated roof is not that far off modern standards.

New walls?

That should be more than enough - I'm using 50mm as I don't have the space for more.

That's bog standard modern double glazing with K-glass or equivalent.

I was given 25mm as a target (aka 1") but my BCO essentially agrees with yours.

Instruct the builders accordingly and WATCH THEM. I'd be inclined to give the roofing work over to an actual roofer, not a generic builder. A proper roofer would know this as it is a totally standard construction method.