ADLIan

Remember that SAP rating estimates the energy use and cost of a house under standardised conditions so that the energy efficiency of houses may be compared - in this respect it is similar to the mpg rating of a car and is very unlikely to reflect an individual's occupancy, heating pattern, temperature settings, hot water use etc, etc. The RDSAP system for existing houses is not fit for purpose simply because the fees have been forced down to such a low level. Assessor probably gets less than £50 to travel to the house, do a 'full' survey and then collect the correct evidence to get anywhere near an accurate assessment, hence corner cutting and the easy option of ticking 'default' values. @saveasteading Can you point me in the direction of ASHP assumed to be used for cooling too? I'm not aware of this one.

See this far too often with this type of product, only real solution is to rebuild. What manufacturer is it from? You could ask them for advice on install instructions along with BBA certificate - may give you leverage with contractor. Assume you currently have a U-value of 0.19/0.20 expect this to increase to 0.23/0.24 (the theoretical correction for bad install). SAP assessor will be able to run the numbers and see what insulated plasterboard would get you back to 0.20 or better.

The sound insulation to the intermediate floor looks ok, pretty much straight from AD E. Cavity wall spec will not give U=21! Perhaps nearer to 0.28?

The ACD figures for linear thermal bridges are worst case so would use dense block inner leaf at the floor/wall junction so the 'mistake' is covered in the energy assessment. The use of aircrete would improve things slightly.

It's not a U-value at that point it is a linear thermal bridge or psi-value that is calculated using 2D thermal modelling. Doubt the thickness of the perimeter upstand insulation would have any effect. That detail looks to be very similar to the Accredited Construction Details giving an 'approved' psi-value of 0.16 W/mK. You need to check what psi-value was used in the energy assessment

Moving from aircrete to dense concrete will increase U-value from approx 0.25 to 0.28 (exact wall construction not known). As an area weighted average for the whole wall area the impact is probably negligible. The effect at the floor/wall junction can only be estimated if the psi-value is known and this will depend upon the thermal properties of the materials and the exact geometry of the junction. Only if you know the psi-value that was used in the original energy assessment can you estimate the effect of the different block type.

5.16

Sorry to be repetitive. See appr doc B ( relevant section has not changed for many, many years)

See appro doc B. Not sure what an alternative approach would be especially post Grenfell

Cavity needs closing at top for fire safety - see appr doc B

The acoustic absorption of all mineral wool products will tail off at lower frequencies (less than 600Hz?). Denser and/or thicker product will have a slightly better low frequency performance but as above this will be lost in the noise (pun intended) of the rest of the construction. Someone on here linked to an excellent report (Canadian?) a few weeks ago that covered 100s of stud partition options. Not sure how to search for it.

I'm not sure having the acoustic absorption for the insulation will get you far here - certainly any mineral wool at a given thickness will give similar results, thinner products will be slightly worse. The issue is that any slight difference in this value is totally swamped by the effect of the rest of the construction once installed, for example in a timber stud partition. The sound reduction across a completed partition will depend upon the construction (timber or metal studs) and the density/thickness of the plasterboard each side. Note that 'mineral fibre' is deemed to be a solution in many parts of Approved Doc E. Sheep's wool (not a mineral wool) will need an independent test certificate to show similar compliance.

The SAP rating is based on energy cost. Going all electric with a heat pump will increase the energy costs though offset to some degree by the efficiency of the heat pump. No one really cares about the SAP ratings, important hurdle is getting Building Reg compliance which is made easier with a heat pump

The great Rockwool myth of 'denser = better' busted!! As a bit of background stone wool (Rockwool is a trade name) will always be about twice as dense as glass wool for the same thermal and acoustic performance. Any stone or glass wool in the normal density range, say 10 kg/m3 (glass) to 60 kg/m3 (stone) and at a given thickness will have a similar acoustic absorption value. There will be slight differences in these figures (only picked up in laboratory tests) but they are swamped, once installed in a wall, by the effect of the studs (metal or timber) and plasterboard facings. Look through Appr Doc E of the Regs, the Robust Details, the BG White Book and the above referenced document. Very dense stone wool compressed into a partition wall will have an negative affect on the acoustic performance. Low density products and/or an airspace acts a 'spring' between the 2 (or more) layers of plasterboard. A high density product, compressed, effectively couples the 2 layers of plasterboard so sound energy can be transferred much more efficiently.

The U-value should be corrected for the mechanical fixings securing the insulation & render system to the wall. A few extra fixings will have little, if any effect, but could be included in the correction if you want to be really critical

A 300mm masonry wall will perform better than a 200mm wall simply because of the additional mass and stiffness - doubt the benefit is worth the cost though. Adding any mineral wool in the cavity of 2 masonry leaves will gain very little (nothing?) as again most of the acoustic performance is from the mass/stiffness of the masonry.

A continuous ply/OSB sheathing is relatively vapour resistant and as such there should be ventilation below (above insulation).

Nice gappy insulation - plenty of thermal bypass possible. Also cavity slabs look to have a lap joint edge profile, if this is the case they have been installed incorrectly as the lap joint should ensure water is shed outwards.

I’m not sure the additional cost of 32 grade is justified in a better u-value when installed between rafters or studs. The thermal bridging in this layer means only a very small decrease in u-value (0.01 better?). 35 grade probably at the sweet spot unless you’re really desperate for that very last bit of improvement.

Low density loft insulation is compressed more than cavity/rafter/timber frame insulation. All should expand to stated thickness once unwrapped but over or under expansion should not be tolerated. Complain to manufacturer if this happens.

Earth wool is a trade name. Google ‘timber frame roll’ for alternative manufacturers

Beware of extended lead times and price rises. Knauf I believe are on 6 week or more lead time with 14% price rise due soon.

Part E applies to intermediate floors and certain partition walls within a dwelling. More onerous standards apply to party walls and separating floors between dwellings

External gable wall becomes internal wall in extension. Was a cavity tray installed above the flashing?

PUR for different applications can have different formulations for the core and different foil faces. Check with manufacturer for suitability and if interchangeable. As regards use under screed the MIs and BBA certs will normally require a light gauge polythene sheet.