ADLIan

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.

To clarify, above standard is for blown in mineral wool. No equivalent* Standard for eps beads but same BBA standard and test methods for manufacture & install *there is an equivalent BS! BS EN 16809.

This work is notifiable under the building regs. At the least the manufacture and install should be in accordance with BS EN 14064. Product needs to be CE/ UKCA marked as there is a designated/harmonised BS EN. Not sure how you would even confirm the thermal conductivity, once installed, of random beads bought from eBay never mind all other declared physical properties and weather resistance. Building Regs require these products to have 3rd party certification (BBA or similar) for both the manufacture and installation. Approved systems installed by approved contractors are generally deemed to comply with the Approved Doc without a building reg application. In short DIY is a non starter.

Do NOT inject any insulation in the cavity between a brick/block outer and the timber frame. Simply not a recognized system/method of insulating walls. Cellulose cannot be used in external masonry cavity walls.

Remember SAP is not intended to be a deign tool for the space and water heating systems.

A = GF area. P = perimeter length as you look at the plan view. In above 36m (not 3.6m, no thickness involved). P/A for most houses is approx 0.4

Is Ubakus treating this as a suspended ground floor? Does not appear to be.

Therm won’t do it as it’s a 3D analysis rather than 2D.

Back in the early 2000s (cannot remember exact dates) there was a loophole in the Building Regs that allowed the efficiency of heat pumps to meet the CO2 emission standards whilst allowing cr*p levels of insulation and airtightness perhaps as bad as the backstop values. Heard of developers using this method and dread to think what bills the house owners were left with. The additional costs, compared to gas heating, was very obvious in the EPCs.

Bear in mind blown in cavity insulation (new build or refurb) is notifiable under the Building Regs. Product should carry 3rd party certification (BBA or similar) and be installed by approved contractor.

Can be modelled using 3D thermal modelling (not THERM) but frankly it's such a localised and discrete piece of metal and no doubt will surrounded by insulation it's not worth worrying about.