ADLIan

Following last changes to the Regs many manufacturers have introduced their own psi-values that can be used in the SAP process in place of the old ACDs. Elmhurst keep a register of these companies that assessors may use. Available to Elmhurst assessors - copy attached. Remember under the new Regs photo evidence is required to show the exact detail has been followed on site Elmhurst Thermal Bridging Scheme List v3.xlsx

If we assume a floor with perimeter 50m and area 100m2 with a U-value of 0.15 W/m2K. The rate of heat loss associated with the floor and perimeter would be as follows; Floor only = 100 x 0.15 = 15 W/K Perimeter heat loss(using SAP default psi-value) = 50 x 0.32 = 16 W/K Perimeter heat loss(using dense block psi-value, insulated cavity) = 50 x 0.17 = 8.5 W/K Perimeter heat loss(using enhanced psi-value, with aircrete block inner, insulated cavity) = 50 x 0.08 = 4 W/K The exact geometry of the floor/wall junction may change the psi-values but above are the right order of magnitude.

The detailing of the floor/wall junction does not give a SAP 'fail'. Some details will be better than others but this is only one of many (40+) linear thermal bridges that must be accounted for within SAP.

Get a new build SAP assessor on board asap. A sap calculation should be done at the design stage to show the proposed dwelling complies with the regs. This is updated on completion to reflect the ‘as built’ house and to generate an EPC that is required as part of BC sign off. The Regs now also require a lot of photo evidence of the insulation and its installation. Your sap assessor will advise further. Without this evidence the assessor will use default values with the risk the completed house fails the Regs.

At the edges of a flat roof the VCL should be continued up through the thickness of the insulation to join with the waterproof layer.

Depends upon what’s in their BBA Cert. May be limited to max ‘severe’ exposure zone with masonry inner and outer. 50mm cavity still applies with sip and framed construction.

compliance with a BBA cert is an alternative way of complying with the Regs rather than using Approved Docs. Most built in cavity insulation will be approved for severe or very severe exposure zones but look at the small print for the need for render or have flush/weather struck mortar pointing. Has nothing to do with insulation being breathable or not. Above applies to masonry. Sips, timber frame or metal frame must have 50mm clear cavity between insulation and brick/block outer.

Note SAP is a method of assessing energy use in a house in a standardised way; it should not be used as a design tool for hot water or heating systems.

Insulation of pipe work is in building regs too, for the same reason

Because you are only altering the area weighted average u-value. The correction for fixings is a separate calculation (based on type of fixing, number of fixings and construction/insulation thickness of the element) that is then added to the basic u -value.

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.