ADLIan

Look at the close up shots of other slates. Slates are normally nailed twice towards the edge not once at the very top edge and man made slates normally riveted too. Looks like rivets may be missing in general roof area too as the slates are too far apart to secure the rivet.

Slates are not upside down those holes are for the copper rivets that secure the bottom edge of the slate. Poor roofer if he does not know how to fit these especially in cut slates such as around skylight, probably at the verges too. All needs redoing otherwise roof will last no time at all.

Thanks Jeremy. Not sure if I agree with BCOs interpretation but as long as he/she is happy that's another hurdle crossed.

@JSHarris Jeremy where is the exemption from the water efficiency calculation if you have a private water supply?

Controlled fitting so comes under Appr Doc L as well - FENSA or Building Reg application needed. Min standards for U-values apply.

Adding more acoustic insulation will achieve little. Next improvement is to add mass with 2 or more layers of plasterboard and then to decouple the plasterboard from the joists using resilient bars

Assume this is the floor to the attic rooms and above rooms below. Acoustic insulation required under Building Regs normally 100mm of mineral wool with min density of 10 kg/m3. Loft insulation is normally less than this so does not comply - in reality I greatly doubt there would be any difference in overall acoustic performance if the density is a little low. Using 200mm rather than 100mm would have little effect - case of diminishing returns. You would have to convince Building Control that 200mm offsets the low density or use 100mm of the correct acoustic product.

If attached garage but unheated then no need to insulate roof (or floor or ext walls)

MIs and BBA for EPS, XPS & PUR all require DPM under insulation. All will absorb water to some degree - a search of the manufacturers website should give this info.

Manufacturing tolerance on thickness normally +3mm to -5mm so expect to see bottom of tolerance range for most production runs. 95mm it is!

Will depend on grade of rockwool and polyurethane assumed. Remember to include 15% bridged proportion. Should give approx U of 0.20 W/m2K. Condensation should not be a problem if care taken with the VCL & PUR not sealed though not much safety margin.

Sorry - yes it's Appr Doc F that applies

In England Appr Doc C, Section 7. Looks like BCO is correct.

Be careful with Kingspan TF solutions - in the small print in the brochure tables they often include an insulated plasterboard internal to the studs to improve the U-value.

Monarflex?

Just an excuse for bad manufacturing and poor quality control. The manufacturing spec for PUR is in BS EN 13165, among many other things it gives tolerances on board dimensions (thickness, length, width, flatness etc). A trip to any BM will show their products to be 'pushing the envelope' for these tolerances, especially thickness (100mm thick board for example should be within +/-3mm) and flatness. Remember shortly after Grenfell Celotex were found out not being entirely truthful about the fire performance and thermal performance of some of their product range.

Building Control will probably look at U-value and fire performance of external roof finish - this later requriement is down to building height and proximity to local buildings, etc. Note that Scot Regs strongly advise aginst use of cold flat roofs as do relevant British Standards

@IanLow SAP probably due to use of bulk LPG. Would be very diferent with mains gas.

There is no simple SAP estimator as it is complex with many independant and interdependant inputs. It is not particularly sensitive to elemental U-values especially at the levels you mention. Taking care with air tightness and linear thermal bridges will give better returns. For a new build built to basic Building Reg standards and gas heating you should be acheiveing a SAP of approx 80-85. As SAP is based on fuel COST your choice of heating fuel and heater efficiency will have a big impact - electric resitance heating may reduce the above figure by 10-15 points!

Appr Doc L1A does not give specfifc U-values apart from the backstop, worst case, values - this gives a lot of design flexibility. The U-values in Jeremy's spread sheet are those used in the model dwelling (Table 4 in AD L1A) used to assess compliance using SAP. Remember in Jeremy's spread sheet to always enter cavity width (cell B25) in order to give correct thermal conductivity for use later in each construction. @JSHarrisCould this be defaulted to R=0.18 which would be good enough for most instances and not be so thickness dependant. The spread sheet only gives an approximation and should not be used for Buildng Reg purposes as it does not correct the U-value for thermal bridges, mechanical fixings thru the insulation, air gaps in the insulation etc

Looks as though it must be installed by approved contractor. On timber frame the vented airspace behind the cladding system negates the effect of the insulation.

Assuming in England Appr Doc C gives maximum exposure zones for a range of cavity wall details - fair faced or render? full or part fill insulation? cavity width? etc.

Are those figures correct, MVHR reduces heat loss by a factor of 7? I can see 10-20% improvement when using MVHR provided it is correctly designed. A poorly specified/designed MVHR system can potentially increase energy use!

Depending upon the supplier you may have to cut the mitred boards on site (especially if not 45 Degree mitre). Some suppliers have mitred boards as part of their package

Suggest you check MIs and BBA certs re additional mech fixings when using adhesive or plaster dabs with foam backed boards