Thu, 07 May 2026 09:04:14 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310585#Comment_310585 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310585#Comment_310585 Tue, 05 May 2026 20:28:22 +0100 Victorianeco
Specifically, I would like to compare:

1. Cavity Fill Only: Filling the cavity with 80mm expanded polystyrene (EPS) graphite beads while keeping new windows (3G) within the traditional layer.
2. Cavity Fill plus External Wall Insulation (EWI): Performing the above and adding a 120mm EPS board external layer.

While the latter is more thermally efficient, it is also more labour and material intensive. I need to evaluate the payback period based on current material costs and research.

Furthermore, I have concerns regarding the impact of the 120mm EWI on the property's interior. Extending the wall thickness may reduce natural light and affect viewing angles from within the room, particularly at the 30 to 45-degree angles we currently enjoy. There is also the potential loss of the window frame's aesthetic "framing" effect to consider.

What are your current thoughts on these two approaches based on up-to-date material costs and thermal performance research? Please let me know if there are any other factors I should consider at this stage.

Thanks]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310588#Comment_310588 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310588#Comment_310588 Tue, 05 May 2026 22:43:58 +0100 fostertom
Tho, as you say, more thermally efficient i.e. saving carbon released during decades of future operation (Operational Carbon), the carbon released at the outset due to oil drilling, processing, manufacture, transportation at all stages, construction, due to that extra bit of work and material (Embodied Carbon) may exceed the carbon saved during operation, leaving the planet worse off eventually. Or even if the Embodied is only half the Operational saved, it still has same effect on planetary heating, as it's having its effect for twice the average duration of the Operational (area under the curve).

This is becoming more and more apparent, as the 'fuel' consumed during Operation (electricity from renewable source) is progressively 'containing' less and less carbon, so less carbon is saved during Operation as a result of the extra insulation, while the initial Embodied Carbon released gets no such beneficial reduction.

The implication is, GBF's traditional emphasis on super insulation (and all of the green building effort for 50yrs) is almost thrown into reverse - minimise the work and materials that create Embodied Carbon, instead throw more heating at it - as long as that's by well optimised electric heat pump, and as long as national decarbonisation of grid electricity continues to progress.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310590#Comment_310590 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310590#Comment_310590 Wed, 06 May 2026 10:54:24 +0100 djh
Firstly the embodied carbon in different types of insulation varies a lot. Consider plastic insulation versus wood fibre, for example.

Then there's the practicalities of operational energy supply. Increasing demand for electrical energy causes all sorts of problems and increased costs. So I feel there's a responsibility to minimise extra demand so far as is reasonable.

And then there's the added questions about airtightness and ventilation that don't go away.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310594#Comment_310594 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310594#Comment_310594 Wed, 06 May 2026 15:09:14 +0100 fostertom I'll add another 'as long as' to my last sentence - as long as the actual Embodied Carbon is properly assessed and minimised as far as possible, by choice of material and/or product, which hopefully themselves have proper EPDs (Environmental Product Declarations) to quantify their carbon content. No broad assumptions, like I implied above. Farage & co will do that for you, once they get wind of all this.

I think it was WillInAberdeen who recently said that woodfibre insulation, once imported to UK, has unexpectedly high carbon content, to rival EPS, which in turn has considerably less than the other, cellular, plastic insulations.

For newbuild, it's a different story. Starting from scratch, or even starting from the shell of an existing building, there's scope for design that fundamentally minimises Embodied Carbon, even sends it negative, while achieving minimised Operational Carbon, even sending that negative as well.

Note the large chunk of Embodied Carbon that can be avoided, by completely eliminating a heating system, not even ASHP, if Passive House standard is achieved.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310595#Comment_310595 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18429&Focus=310595#Comment_310595 Wed, 06 May 2026 18:06:49 +0100 Victorianeco