ADLIan

Re the air pressure test. 0.3 has been assumed for the as designed dwelling. Agree this may be a typo so get it checked. 5 is used in the target calculations as this is used in the ‘model’ house that is the comparison dwelling.

The 0.006 W/m2K only applies to the wall construction outlined in the 1st post. Change the thickness of either layer of insulation and the number will change. Still nothing to worry about!!

It’s specific depending upon the type and number of fixings penetrating the insulation and the construction of the floor, wall or roof

It’s a known issue in the rainscreen industry so is always accounted for. The effect of the brackets on the U-value is assessed using 3D thermal modelling

The correction factor does mean more insulation is needed to offset the effect of the fixings. With wall ties and small screw fixings the effect may be minimal. An extreme case would be aluminium brackets used in rainscreen cladding that may add almost 0.1 W/m2K to the uncorrected U-value. An uncorrected U-value of 0.15 W/m2K becomes a corrected value of 0.25 W/m2K in this instance so additional insulation is needed to compensate and get back to the 0.15.

EN ISO 6946 give u-value calculation method including correction factor for mech fixings.

Correction to the U-value for the fixings adds about 0.006 W/m2K to the U-value in this instance. Bigger things to worry about!!

Less than 50m2 & no heating/cooling then exempt from Part L energy efficiency requirements. Simple!

I doubt the difference in density or mass/m2 makes much difference acoustically. I thought duraline was just more robust for heavily trafficked areas

Flow restrictors? Under Approved Document G to reduce water use - been part of the Building Reg for may years. Depending upon the type of tap it may be possible to remove the restrictor - otherwise its new tap time.

Mineral wool slabs are treated with a water proofing agent. They have to pass a very extreme BBA test to prove they work, do not allow moisture to pass and get certification. They can normally be used below dpc

This is down to brick and/or block type. Manufacturers will advise, 10m(?) for brick, perhaps only 6m for block (and render?).

Do not use a hybrid flat roof unless insulation between joists is minimal (which becomes almost a waste of time & effort). Old rule of thumb, if you had to go hybrid, was at least 2/3 of thermal resistance above the deck/joists. Not sure with current insulation standards if this still applies. Also requires an highly efficient AVCL at ceiling level which is very difficult/impossible to achieve. BS6229 on flat roofs and BS 5250 on condensation and moisture in buildings both advise against use of hybrid flat roofs. Problems can take many years to become obvious as all well hidden within roof structure.

Lintel, concrete or other, will not affect the U value. It will affect the psi value (linear thermal bridge) which is used to assess the heat loss from this, and other, junction.

There is nothing in the latest Regs on thermal performance that prevents the use of standard catnic type lintels.

IIRC phenolic foam should not be used under timber (ply/chipboard) flooring. Floor would need battening throughout to take it out of load bearing path.

Latest Approved Doc L has U=0.18W/m2K in extension wall. Looking at approx 150mm of mineral wool or 100mm PUR

Might be better spending your money on lower conductivity insulation, 0.032 W/mK. Look for ‘32’ in the product name/reference. Also check that your wall tie with its small cross-section is suitable for 250mm cavity, you may have to look at a heavy duty tie with larger area. Teplo tie may offer little benefit bearing in mind the cost.

Adding insulation under a beam & block floor changes it from a suspended floor to a ‘solid’ floor. This is OK provided there is a correctly detailed DPM under the insulation - possible in a new build but impossible in a refurb or upgrade. The Energystore system is approved for new build only, not upgrade work. As above, an expensive solution looking for a problem.

Why not 175mm mineral wool batt at 0.032 W/mK? Will give U=0.15 W/m2K with aircrete block inner.

Appr Doc L limits the glazed area of an extension, go slightly over and you will have to use high performance glazing/improved fabric insulation and use the area weighted average u-value method to show compliance. Go a lot over and you’ll be using full SAP calculations to show compliance. This may give an idea of overheating but SAP is not a very sophisticated tool in this respect

Full SAP output is used to show Building Reg compliance and create the EPC for new build dwellings. Full SAP calc is also needed for new dwellings created by conversion but normally only to issue the EPC (sometimes needed for Building Reg compliance too). EPC is needed as part of BC sign-off.

Under the 2021 version of Approved Doc L intermediate floors with heated floor systems require thermal insulation (as well as acoustic requirement).

May be yellow glass wool. Waste product was ground to make fibres that were injected into cavity walls and blown into lofts. Can you see individual fibres?

Don’t do it!! Frowned upon by BS6229 & BS5250 and doubt insulation manufacturer would support it without lots of caveats. On your head be it.