ADLIan

Under current Part L in England ALL dwellings should be air pressure tested (was a %age in past).

From memory it’s towards the end of AD L1, section on extensions. Max glazed area of extension is 25% of floor area of extension plus the m2 of any openings made redundant as a result of the extension. With roof lanterns/pyramids the glazed area is based on the area of each glazed section, not just the hole in the ceiling. With big sliding doors and a roof lantern you may fall foul of the ‘simple’ methods and need the SAP calculation route.

Actis require a 200mm airspace to any surface expected to be at 80 deg C or more. This probably conflicts with all of their roofing details!

A few comments: The DIN standard is specifically for Germany and perhaps linked with compliance with their Building Standards so may not be relevant here You need to use BS 5250 Above BS does not accurately model ventilated airspaces. Convention is to do 2 calcs, one including the ‘ventilated’ airspace and another ignoring all elements external to the ventilated airspace (zero moisture vapour resistance). Actual performance is somewhere between these extremes. Allows a comparison to be made to select safest option

Report this sort of product failure to the manufacturer. They may already be aware of the issue. Some form of compensation needed? (But not replacement Actis Hybris!!)

No cill section under door & frame?

No glue = cost saving!!

I used to be involved with injected cavity wall insulation as a system designer. The failure rate, measured by claims on the guarantee scheme was unbelievably low, less than 1%(?) of all installations. There were poor installs/poor surveys many years ago when lots of grants were available but still a very low failure percentage.

You will probably need both an energy assessor and a QS. The energy assessor can undertake the SAP assessment but may not be ‘qualified’ for the costing calculation, this where the QS steps in. Best get agreement from your BCO on the definition of ‘suitably qualified’ and who can be used.

@Mos I understand and agree with you that a simple benefit vs cost is possible. Unfortunately you are wrong here. Appr Doc L does not work like that and you need to read the guidance on the 15 year payback calculation in Appendix A of AD L. Among other points SAP IS used for the calculation and must be done by a suitably qualified person. Looks like you have a strict BCO who will do everything by the book, perhaps a case of picking your battles.

Info is in the European Technical Approval for the product. Took some finding and I’ve lost the link!!

Nothing to back up thermal property claims, lapsed certification and website littered with errors. Appears the 0.037 W/mK is just for the polystyrene bead, finished product is nearer 0.4 W/mK. Either lack of understanding here or playing fast and loose with the claims!

You interpretation on the refurb/upgrade of party walls is correct. There is no mention of 'party walls' in the text and table 4.3 relating to upgrading of existing walls (unlike new build). See also the definition of a 'thermal element' in Approved Doc L. In any case the heat loss from your solid party wall is 0.00 (ZERO) W/m2K (see Table 2.1). The heat loss mechanism for party cavity walls is all related to air movement rather than the temperature difference across the wall, which in theory, is zero. Unfortunately the 15 year payback calculation is more complex and is based on a complete SAP assessment of the whole dwelling - a comparison of 'existing' and with the 'upgrade(s)'. The Approved Doc has more detail on the complexity of this assessment. Perhaps a sledgehammer to crack a nut here and may be easier just to aim for the U-values in Appr Doc L1

It used to be, and I'm not aware of any change, that SAP was specifically not to be used for heating system design.

Membrane behind plasterboard should be an AVCL, not a breather membrane. Also the OSB may be too vapour resistant. Be careful with balance of thermal resistance of insulation between and above rafters. Too little above may create condensation problem within rafters.