ADLIan

Kingspan and ‘higher fire safety performance’ - words I never thought I’d see in the same sentence following the Grenfell Tower fire. All PUR foams burn.

Spax do similar in warm, pitched roofs. Rather than fixing being only in bending, due to vertical load, through thickness of the insulation it’s also part in tension. Makes perfect sense. Good fixings.

Open perpends, mainly to drain the cavity, are not normally classed as 'ventilating' the cavity as they are too small to actively promote mass air movement

The bright foil face works both ways in improving the thermal resistance of an adjacent airspace. There is no difference in U-value if working from outside to in or inside to out. Black bodies (equivalent to most construction products) both absorb and emit 'large' amounts of energy. Reflective surfaces (such as these reflective AVCLs and breather membranes) do the opposite. The rate of heat transfer by radiation is proportional to the emissivity of the surface and the fourth power of the absolute temperate in kelvin. A temperature difference of say 5K across the cavity is insignificant compared to the absolute temp. Some very complex physics above my pay scale.

An unvented void without reflection is around 0.14 R value, without the reflective your U value moves from 0.13 to 0.14. But is also directional, so is reflecting heat from outside, so in summer useful (?), not sure about any real use in winter as it cannot reflect heat back in to the house because of it's position. Take the marketing blurb with a pinch of salt. Standard unvent cavity has R of 0.18 m2K/W can be as high as 0.80 (ish) with highly reflective surface. Product is directional in that only bright finish on one side, MIs show product internal to insulation with reflective face onto airspace, in this case works as stated.

Too many years in the industry! Timber/steel frame good practice guides & MIs. Building Regs, Appr Doc C (or equivalent)

The VC Foil only has a thermal performance if there is an airspace present next to it - if sandwiched between other products it adds nothing thermally. In timber frame construction with masonry outer full fill insulation should NOT be used, a 50mm clear cavity needs to be maintained behind the masonry leaf.

Render direct onto insulation direct onto timber frame is not accepted practice - see Building Regs and any good guidance on the design of TF. I believe this is a result of failures observed in the USA and Canada that took many years to become apparent. Should be a rainscreen system using render board with ventilated cavity behind. Not sure I’d want polystyrene in this system however due to fire risk.

Cold flat roofs are frowned upon now. Not sure how you can cross vent your roof. Warm roof is safer option

Won’t comply with relevant BSs or Building Regs. Architect should know this. In a cold roof 50mm cross ventilated void is required above the insulation, can’t see how this can done here. Warm roof is the best (only) option.

OP is in Preston.

Flat roof needs redesigning, cannot fully fill the joist void with insulation!! Correct insulation to flat roof and packing void between 1st joist and steel insulation marked ‘A’ should minimise thermal bridge.

Therm is not very intuitive and great care is needed in building the model. The results need further manipulation to get the psi-value and the added bit of maths varies with junction type if I remember correctly. Also refer to BR497 from BRE on the calculation conventions. I use Psi-Therm 2D and 3D - expensive but easy to use.

Replacement doors or windows is notifiable work under the Regs. Building Control application or use FENSA registered installer. There again who’s going to know, who’s going to police it.

Door and window openings are a separate input input SAP - area and U-value of each opening. A roof window does not degrade the average U-value of the roof, same applies to walls.

If there are roofs (or walls or floors) with different U-values they are normally entered into the sap software as different elements along with associated area and U-value. The software will check the area weighted U-value and ensure that worst case U-values are not exceeded. The sap assessment allows a degree of ‘trade off’ between elements.

There should be a new EPC as part of the Building Reg sign off. Search the epc register for the address.

No need for AVCL in a cavity wall, full or part fill - not sure how it would be installed! Wall may show slight condensation risk but will still comply with BS5250 on condensation & moisture in buildings. Stop worrying about it.

It's all to do with risk. Typical 1 or 2 storey house is not particularly high risk - fire is probably internal and any damage will be limited to the dwelling itself. In high rise, over 11m, this chimney stack effect and risk of fire spread to other properties/flats is just too great. Open state cavity barriers (expensive!) are used in this scenario - an intumescent strip on the front of the cavity barrier expands in the heat to block the ventilation path and stack effect.

Modern mineral wool formulation is much nicer to handle. Older types, normally yellow colour, tend to be worse

Even if a cavity batt product is Certified for use as a full fill insulation in any exposure zone there are caveats that should be read, normally in conjunction with the Building Standards, Approved Documents and associated British Standards. Wall may need to be rendered or clad in more exposed locations.

I believe the Scottish Regs for cavity closers around openings are more stringent than England & Wales hence the caveat

Thinking of it as a balcony floor is missing the point. It’s a flat roof to the room below and as such should have proper waterproofing, correct falls & drainage and be insulated.

Greenguard is an extruded polystyrene thermal insulation. Compressive strength of 500kPa is ultimate ie at failure. Safe long term static load may only be 1/5 of this value. Not sure it’s the correct product here and doubt manufacturer would stand by this application.

The SAP energy rating is based on energy cost - being all electric (resistance) for space & water heating looks to be part of the issue as it is the most expensive fuel option. Even lots of insulation, triple glazing etc, etc may not be enough to change the numbers significantly. Beware that MVHR if poorly designed and/or installed may use more energy than it saves! Did the surveyor use default values for the MVHR? I note the house is timber frame - the low thermal mass parameter may also be a factor. The efficiency of a new ASHP for space & water heating should help to improve the rating considerably.