ADLIan

Hybrid flat roof is never a good idea. Depending upon calculation inputs it’s possible to show the design is ok but look at the input data very carefully!

EPS/XPS behind mech fixed plasterboard is acceptable (if not ideal). Marmox is XPS with thin (2mm?) cement facing. Mech fix this to rafters and it will melt (perhaps as low as 120 deg C) leading to product failure, showering anyone below with molten/burning polystyrene!! Having seen fire test of this it’s not nice and you do not want to be in this sort of room fire.

I agree the burning furniture is the issue but the structure has to be safe too. Fire fighters have a tough enough job and deserve medals as big as bin lids - if persons are reported in the building there is the further risk of molten/burning ceilings falling on them!

In respect of U-values the 'Regulations' do not drill down into detail hence the guidance in the Approved Documents. Unless otherwise stated the maximum U-values for floors, walls and roof is an area weighted average. This gives some flexibility but note however there is a back stop for roofs of 0.35 W/m2K. @Nickfromwales I have read the OPs post and pretty sure I understand what a 'chalet bungalow', 'ceiling' and' rafters' are. I stand by my original point that a combustible XPS ceiling to is not fire safe! The Building Regs/ADs on fire and fire safety would not allow it. On a more general note whilst this work does fall under the Regs unless you tell them I'm not sure how any Building Control Body can enforce and police such upgrade works.

I would question the fire safety implications of a Marmox or Jacoboard ceiling and doubt the manufacturer would promote this application.

'Non-combustible' is normally defined as a reaction to fire of Euroclass 'A1' (to BS EN 13501-1) so this gives the starting point. Check MIs - they will state minimum distance to combustible materials and may give a reduced distance if shielded by a non-combustible product and an airspace.

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.

Photo evidence of insulation, detailing, junctions etc has been part of latest Regs, in force for last 3 years. One of the reasons I got out of energy assessments - SAP assessor is now seen as the bad guy when it is really a BCO issue. You need to take it up with your BCO to see if he’ll offer some form of waiver/relaxation of the Regs

if the house is too exposed, which sounds as though may be the case, any form of retrofit cavity wall insulation is probably not suitable and would not follow the design & installation guidance for these system. The problem is filling the cavity with any form of insulation increases the risk of wind riven rain penetration in very exposed areas. Find a reputable CWI company nearby and check with them - they should offer a full survey & design package and if too exposed advise you against CWI. External insulation may be your only option but probably needs the cavity insulating to avoid thermal bypass - Catch 22 situation!!

Binder is added just after glass fiberisation (web search will show process in detail). Binder is heat cured to bond fibres in a ‘loose’ matrix hence air can be trapped. Any irritation is primarily from the fibres though newer technology produces ‘nicer’ fibres. URSA and Knauf probably take the lead here.

The 2 products are the effectively the same, glass mineral wool. The difference being the processing additives, binder & colour (which only accounts for something like 5% of the product). @SteamyTea The thermal conductivity of basalt, as a rock, is 2 W/mK (ish). Basalt is also much denser then glass which is part of the reason that stone wool is approx twice as dense as glass wool for the same thermal and acoustic performance. The mantra of 'denser = better' from one of the stone wool manufacturers is bullsh*t. They're just different mineral wool products with similar applications.