A property myself and my wife are looking at has approximately 300m2 external wall area.

The build is a 60s cavity construction right on the sea front.

I assume EWI would be best but at ~£110m2 it just seems it outweighs any energy savings in the long run...

£30k plus scaffold, roof extensions and so on.... we'd also like to renew the windows at a great expense.

What are people's thoughts? It's a bit of a 'slightly' different project compared to my previous mid terraced renovation....

The EPC value I find has little to no impact on value in the UK of a property...

People are more interested in property size, location, garden size, proximity to amenities and so forth.

I don't think spending ~£40k would increase the value of the property by £40k and certainly wouldn't save £40k in energy over my lifespan....

Just my thoughts...

Agree with you (VEco) that most people aren't interested in the EPC, or insulation etc when buying. Does it look nice, nice surroundings, nice kitchen and bathrooms. Perhaps you can combine the EWI, windows, other external alterations, to improve the look of the house, so that some of the "invisible" insulation spend, is re-couped by virtue of the appearance of the house being improved (curb appeal).

An example of before and after, where EWI was added (with cavity filled walls), then over clad in timber. Floors insulated, loft insul improved. New windows also, etc. There will be a lot more interest when the time comes to sell, due to the visual improvement, which will drive up the selling price...plus it will need a fraction of the heating energy.

In terms of thermal improvement per £, 'low hanging fruit' like loft insulation, cav wall insulation, draught stripping pay very well. Once that's done, what next? you obviously want to go further.

Then, next step is typically new (plastic) windows, which can pay back in property value, but has small benefit in overall thermal improvement per £. Piecemeal things like internal wall insulation even less - a lot of money, fiddly work, disruption, loss of floor space, can't safely be really strong insulation and is riddled with thermal bypasses.

For thermal improvement per £, full EWI incl new windows can't be beat - tho it's a lot of money, it's even more thermal performance pro rata, by a long chalk. Plus far less internal disruption. It's also sufficiently 'thermal' to make expensive upgrade of heating system unnecessary - save that money and spend it on insulation/airtighness instead. That is, no need for UFH, ASHP, instead the clunky old inefficient existing heating will be called upon so infrequently, that it can stagger on for some years perhaps, with two thirds of the old rads removed. Still need water heating of course.

Yes, there's a payback-justification gap, between the 'low hanging fruit' and full EWI+windows. I discourage clients from spending money in that gap.

Posted By: VictorianecoA property myself and my wife are looking at has approximately 300m2 external wall area.

The build is a 60s cavity construction right on the sea front.

I assume EWI would be best but at ~£110m2 it just seems it outweighs any energy savings in the long run...

£30k plus scaffold, roof extensions and so on.... we'd also like to renew the windows at a great expense.

What are people's thoughts? It's a bit of a 'slightly' different project compared to my previous mid terraced renovation....

What is the plan for the house? Short term and sell on, medium term or the last one before they cart you off?

Short term - make it look pretty and add a bit of insulation in the loft

Medium term -

Posted By: fostertomIn terms of thermal improvement per £, 'low hanging fruit' like loft insulation, cav wall insulation, draught stripping pay very well.

and plastic windows (maintenance free(ish) especially on the sea front)

Long term - As medium term but perhaps more loft insulation and better quality plastic windows, perhaps EWI on the coldest side (unless the walls have facing bricks) but EWI all over is IMO difficult to justify the ROI at 40K especially as you will be doing CWI anyway - which will be needed before EWI.

Posted By: fostertomWhy? To prevent air blowing about in the cavity?

Yes

Posted By: fostertomNo need to cavity fill before EWI, as long as it's well sealed. If it's not sealed then much of your EWI money's being wasted, even if you have CWI.

But it is my understanding that CWI Mineral wool blown in at a density of at least 18 kg/m3 is normally enough to prevent air movement in a fully filled cavity and probably the easiest way to stop cavity draughts. Mind you getting someone to install CWI properly could be a challenge in itself.

Our 60s cavity construction house had:
Cables in cavities
No cavity closers at the top
3cm dia holes in inner and outer leaf in places (out of sight between floors or behind cladding)
We had it CWI with glass fluff then EWI.

Foam fill if done well (the mix must be perfect) likely gives lower air leakage than fluff.

Posted By: VictorianecoIt needs new windows anyway, so we are off the opinion plastic would be better than timber or alu-clad? Any recommended supplier for plastic windows?

Personally I'd choose alu-clad. And always avoid plastic which aren't very green and have multiple drawbacks:

- environmental & health impact - toxins and pollution are inherent to PVC - see https://www.greenspec.co.uk/building-design/polyvinyl-chloride-pvc-environment-health/
- surface degradation and discolouration through UV light & surface deposits
- susceptibility to impact damage (depending on location) & cracks through thermal cycling
- questions over the long-term availability of suitable spares - replacement glazing beads, hinges, etc.
- overall unremarkable life expectancy - typically 20 to 30 years, but depending on quality
- uValues not always great, depending on construction
- clunky visual appearance
- limited recycling facilities

I'm with Mike1 on this. Check uPVC durability in a salt environment.

Posted By: VictorianecoIs that real world experience or taken from a sales blurb?

Real world experience and academic research.

In respect of the latter, the RIBA webiste provides a quick overview, with comparisons to other window materials, here (it is sponsored by Valfac, but they do provide the academic references):
https://www.ribacpd.com/articles/velfac-windows/7834/cradle-to-grave-the-comparison-of-window-life-cycles/200009/

There is still a huge variation in whole window U value, and I don't think it is fully captured by 2G versus 3G. You'd like to think a high end window manufacturer would fit the best glass as there's hardly any price difference - I would suggest trying to get warm edge, argon fill, soft coat (Planitherm One or similar).

Pilkington make a free calculator (Pilkington Spectrum), which shows differences (light, heat, acoustic, etc).

FWIW we have 35 yr old uPVC, all still fine with zero maintenance except retrofitting planitherm U=1.1 glass and foam filling sections. My parents had a massive 1890 ish house - after that (and my own Victorian starter home) I'm not so enamoured by rattling rotten wooden windows which seem to constantly needing painting. If uPVC didn't have bad environmental credentials it would be the perfect window frame material IMHO.

Posted By: Mike1In respect of the latter, the RIBA webiste provides a quick overview, with comparisons to other window materials, here (it is sponsored by Valfac, but they do provide the academic references):
https://www.ribacpd.com/articles/velfac-windows/7834/cradle-to-grave-the-comparison-of-window-life-cycles/200009/

A good comparison, whilst probably outside of the remit for the article, it is a pity that there was no price comparison.
For many replacing windows comes at a time when general upgrading is done, often when just moving in. At such times budget limitations often play a large part of decision making.

Would you go for 2g or 3g? Isn't the modern thinking you would go for 2g on the warmest side of the home and 3g on the coldest? Or am I imagining reading this somewhere?

Is there a near passive House spec I can read up on somewhere?

Definitely softcoat glass, warm edge, argon/similar and 12-16mm gaps whether 2 or 3G for sure - lower spec hard coat is often used, I have no idea why. 2G lets in more light, but a bit more heat out, and has a lower embedded CO2. I can understand that 2G might be all that is technically needed on a southern face in temperate climates (uk), but I think 3G is nicer than 2G everywhere. The embedded CO2 of windows, as other building stuff, is high, so repair rather than replace, and buy to last.

For me, 3G always. Without any fancy coatings etc I get condensation on the *outside* of the window (which always makes me smile) and still loads of solar gain. I can comfortably sit next to my 3G windows in the winter without any curtains - never could do that in a previous house with 2G.