1960's uninsulated property

Still undecided if I'm going to adopt the fabric first approach (focussing on CWI beads and then EWI with windows in the insulation layer)

or

More later research focussing on reducing embodied energy at source and just use CWI beads and then silicone render over existing.

Just wondering if anyone could share the optimal window fitting detail for each approach and how I could mitigate thermal bridging particularly if I adopt the latter approach?


Property is currently ~20mm render on external reveals and PB and skim internally on the reveals but solid render/skim on the internal walls.

Windows will likely be alu-clad 3G from Allan Brothers, property will be having ASHP and solar.

I know I've harped on about which approach to take but this decision of CWI v CWI with EWI is holding up the project and causing conflict with her indoors.

Property in question linked below for context:
https://drive.google.com/file/d/12ZZsoLmjjSMoA4AW8HBQ_oQzmi9waWuE/view?usp=drivesdk

You're in Exposure zone 4, and clifftop, prob at the severe end of that? so BldgRegs on the face of it bans CWI, unless expert condition survey (esp the render) and OK before doing CWI. But you're intending to EWI as well, which presumably protects from the exposure?

CWI is cheap and easy, as it goes - small embodied carbon I'd a thought. So might think to do that, then thinner EWI to top U-value up to what you want it to be. But if EWI is thinner, can't mount windows in the EWI zone.

I'd say the lo-embodied route would be a 3rd option - CWI alone, which only makes sense if doing the consequent extra heating by increasingly decarbonised electric heat pump incl, for best COP, likely greater or lesser re-engineering of any extg rad system (ideally UFH).

If sticking with gas and extg rad system, then the old approach, concentrating on in-use carbon-fuel saving, is a must. In that case, thick EWI only, simplifying window location.

We have the ASHP - good to go

And will install solar so they're a given.

It is the uncertainty of whether we will go for EWI or not, we really don't want to minimise the viewpoint from inside. Adding another 100mm outwards when sitting within the property regardless of putting windows in the EWI layer will narrow the view if that makes sense - we tend to sit about ~3m away from the window

I think CWI alone could be good but I need to minimise thermal bridges (disc out cavities, replace pillars etc.)

Thanks

Posted By: Mike1woodfibre ... which has fairly low embodied carbon

So you've said but AFAIK that's only true in Europe, close to source, but not after trucking across Europe to UK? EPS (but not any other plastic insulation, for several reasons) wins, for me, not just for much lower price.

Posted By: Mike1Put the windows in whichever insulation layer has the highest thermal resistance - most likely the external

That only works if the EWI is min 150thk, 200 better, depending on the inside-to-out depth of the window frames. Which implies not doing CWI as well.

Posted By: Mike1apply a thinner insulation to the reveals

Make clear you're not endorsing leaving windows within extg masonry zone, with a bit of masonry reveal still outdoors, where you then "apply a thinner insulation to the reveals"?

Posted By: Mike1Or make the windows a little smaller to give space to boost the insulation thickness

You mean boost the "thinner insulation to the reveals"?

Yeah, that question. I don't think we should take that as inevitable - we should account for the ways external air gets in, see if we can fix those.

Obviously airbricks. Gross or hairline cracks in the outer masonry, or in render. Window-to-masonry joint, via cavity closer (if any). Any others? If those entry points were fixed, maybe no need to worry about cavity top open to loft/roof construction voids, esp if the loft space (and wall cavity) becomes part of the indoor volume by continuing EWI-alike unbroken up and over the rafter tops before re-slating.

Then the EWI itself - surely fairly airtight, covering over the above. If that's considered too uncontrolled to be relied upon, then what about the CWI as the answer? How controlled and reliable is that as an air barrier? Far worse than EWI I'd a thought.

Window-to-masonry joint will be taken care of when mounting new windows outboard.

Posted By: philedgewith a sealed cavity any air warmed by the ground floor inner leaf is going to rise within the cavity and warm the upstairs walls to the detriment of the ground floor?

Maybe, probably, but why is that 'to detriment of' ground floor? In a well insulated house the whole volume incl inner skin is evenly heated, so what you're describing is just that desired equalisation throughout. Or maybe you're hoping to zone the heating, so only the ground floor is heated, and any of that 'leaking' to upstairs 'detrimental' to ground floor? Such zoning only made sense in poorly insulated houses.

Posted By: philedgewith EWI as a rain screen there's no reason not to add CWI?

Except unnecessary cost and embodied carbon.

Well there's other stronger routes, like up the stairs or thro the floor, that puts poss transfer via a filled cavity in the shade! So that's not a relevant point in the 'fill cavity or not with EWI' debate.

Posted By: fostertom

Posted By: Mike1woodfibre ... which has fairly low embodied carbon

So you've said but AFAIK that's only true in Europe, close to source, but not after trucking across Europe to UK?

Woodfibre comes out top in this paper from Sheffield Uni, but there may be something more recent that says otherwise:
https://www.sciencedirect.com/science/article/abs/pii/S036013231400393X

Put the windows in whichever insulation layer has the highest thermal resistance - most likely the external

That only works if the EWI is min 150thk, 200 better, depending on the inside-to-out depth of the window frames. Which implies not doing CWI as well.

Yes, it would depend on the thickness. Ideally model it in software...

apply a thinner insulation to the reveals

Make clear you're not endorsing leaving windows within extg masonry zone, with a bit of masonry reveal still outdoors, where you then "apply a thinner insulation to the reveals"?

Correct.

Or make the windows a little smaller to give space to boost the insulation thickness

You mean boost the "thinner insulation to the reveals"?

Correct.

Posted By: philedgeSurely even with a sealed cavity any air warmed by the ground floor inner leaf is going to rise within the cavity and warm the upstairs walls to the detriment of the ground floor??

I think so, and I'd fill it as well as sealing it.

It's not a cavity wall, but taking double glazing as an example, the optimum cavity width is between 14 and 18mm*. Go wider and the u-value gets a little worse (because convention accelerates). Expand that to 50mm and I'd guess it would become significantly worse.

*16mm & 18mm for some specs. Register and play at https://spectrum.pilkington.com/

Posted By: philedgeRe different temps through the house, that's pretty standard design principle...AFAIK?? We run 21 degrees downstairs and 18 degrees or less upstairs.

You can't do that unless you're heating the house (or actively cooling the upper part) so not really a possibility.

You can prob assist answering your own question by asking the rendering company to quote for render only and also EWI with render (at say 100mm EWI just as a bench mark). Somtimes the need to prep the existing surface to take render-only can be at least partly mitigated by adding EWI, reducing the cost uplift of adding EWI.

We speak with certainty of how energy costs and carbon weighting of that energy will be in the future. We have really no idea of what lies ahead, esp with malign "world leaders" influences taking control of the diretion of international trends, and all the meteorological consequences (eg US pumping more Venezuelan oil, and now meddling with Argentinian oil). Change tends to happen much faster and to greater extremes than any modelling or predicitions.

"We're all doomed Cpt. Mainwaring!"

We prefer to keep bedrooms a couple of degrees cooler than living rooms. Our layout has only one doorway between the two floors that we keep closed, and separate ventilation systems. This makes a big difference, if the door is left open we can feel the heat rising from downstairs.

Posted By: WillInAberdeenThe Sheffield study is 11 years old, which might as well be from a different century. It's really worth checking how the world has changed since then.

Back then UK electricity was 310g/kWh and heatpumps were still an oddity, so avoidance of energy loss was the big thing . But electricity is on track for 50g/kWh with the wind/solar farms that are now in construction, nevermind the bigger ones coming through planning.

So any EIA more than a couple of years old is basically chip paper now!

There are 2 ways of calculating this - 1) standard embodied carbon, which takes into account the front end - production, manufacturing, distribution, installation & installation waste; 2) whole-life carbon that add 'in use' and 'end-of-life' impacts too - but most of the carbon is still locked-in up-front.

The future carbon intensity of the electricity supply therefore isn't a factor in the first case, and is only a small one in the second (where a lower carbon intensity has probably been used anyway).

However there has been a significant change in intensity between the date of the study in 2014 and now, which may have changed the rankings. Wood fibre still has a head-start - timber absorbs carbon from the atmosphere as it grows, so the raw material has a negative carbon balance - but that can be negated by shipping it long distances by road. Nothing is simple.

Does anyone envisage that plastics will be reprocessed into virgin feedstock at end of life? That's bound to come, when/if plastics feedstock (and numerous other essentials) can no longer be a cheap byproduct of oil-for-fuel. Then old hydrocarbons will be as valuable as lead and their %age recovery will be as high as aluminium.

Parex