Keeping your home warm / heating / energy crisis / insulation etc

Your right. I will have looked at it, as i skipped over all their options. Must have discounted it due to only 16% light transmission without paying much more attention.

I’m leaning away from solar film and into fitting external solar blinds to our Veluxes.

This is the answer, the Bartlett did a paper on overheating in London lofts which is very relevant to me and external shutters are by far the most effective solution (96% effective at reducing overheating degree hours), followed by night-purge ventilation, then solar control film:
https://discovery.ucl.ac.uk/id/eprint/10072870/1/Indoor%20overheating%20and%20mitigation%20of%20converted%20lofts%20in%20London.pdf

(page 15 has the ranking of passive cooling interventions)

My plan is to order triple-glazed Veluxes with solar control glass (you can get it on special order I think) then fit external solar shutters when we can afford them.

And also actually fit proper insulation to our loft which Dream Lofts who built it didn't do lol.

We cracked and bought a portable air conditioner for the hottest days (it was 30 in our bedroom on Friday night before I turned it on) but according to that paper if we do all the right things we should be ok with passive interventions until 2080 and I'll be dead by then.

Although we're going to fill/cover our house in insulation overheating is a way bigger concern for me than keeping it warm in winter. As badly insulated as it is at the moment, we only set our heating to 18 when we run it so we've not actually been spending that much on gas at all really.

This was a factor in going for wood fibre insulation: it's got high heat storage capacity and better heat protection than conventional insulation, so should buffer summer heat better.

but it’s R value (resistance to heat transfer) is poor compared to others like phenolic foam as is the K value (conductivity). confused as to how that makes for better heat management in summer?

https://www.buyinsulationonline.co.uk/blog/the-ultimate-guide-to-insulation-values

I'd like to shutter our entire roof. Black slate does nothing but absorb heat, it would seem.

When we open the roof windows in the evening, the air blowing in from over the roof is like an oven.

Conventional insulation like phenolic is good at keeping heat in - which obviously you want during the winter - but less good at keeping heat out because its heat storage capacity is poor. Wood fibre insulation buffers heat, which is good when temperatures cycle on a daily basis with an afternoon/evening peak, because overheating is both delayed and reduced, and the stored heat can escape outwards during the evening/overnight.

The poor heat storage capacity of conventional insulation is one factor in why you end up with so many new builds that cost nothing to heat but are unbearable in summer.

Bear in mind that while K-value does represent thermal conductivity , U-value represents heat transfer overall as it considers K-value, the thickness of the insulation and other factors.

Not all wood fibre insulation is the same and the Steicoflex 036 we're planning to use has a U-value of 0.36 as the name suggests. You've got to consider the overall buildup of where you're putting the insulation too - e.g. our external wall buildup for the brick walls will contain 140mm of Steicoflex and give an overall U-value of 0.223.

This is all a bit academic though to be honest! There's no way I'd be using foam EWI on an Edwardian house as it's not breathable, plus the type of insulation will have very little impact on overall overheating factors. As per the paper I linked to above, reducing solar gain via shutters/solar control glass will be key.

Yeah we have that problem with our dark brown cement tiles.

The colour of the roof is 8th in the ranking in that paper, but we're planning on replacing our tiles with white Viroc boards (third down on that page, actually not very white, more like beige) which should provide at least a theoretical benefit!

Should also add that currently our loft is supposed to be a cold roof, but the geniuses who did it didn't actually put insulation in the floor of the eaves storage/ceiling of the bedroom below, or the little wall between that and the loft bedroom. And there's insufficient insulation in the main loft roof.

So even if you found some way to stop all solar gain as is, it just slowly heats up during the day anyway because there's no insulation between the roof tiles and a large part of the loft :/

Plan is to convert it to a warm roof as part of the work but given all the issues it's effectively a re-roof :(

My plan is to order triple-glazed Veluxes with solar control glass (you can get it on special order I think) then fit external solar shutters when we can afford them.

If your Velux are top pivoting, with a handle at the bottom, the support springs may be insufficient to hold up another pane.

If newish centre pivoting, with 24mm thick double glazed units, you could just order a tripple unit to your spec from a glazier. Would probably be a chunk cheaper than special order from Velux.

I obsessed over the build-up of our loft for ages, being terrified of ending up with an unusable sweat lodge in the summer.

Considered various wood fibre products and Frametherm 32 mineral batts, before deciding to use PIR alongside other measures, for the following reasons:

Decrement delay: at the maximum practical insulation thickness of 180mm possible in our loft (without taking the piss with ridge height or reducing room volume too much), using wood fibre would only have gained ~1hr of decrement delay, whilst achieving a significantly worse U-value (~0.18 for wood fibre vs ~0.11 for PIR). I decided that the 8.5 hours of calculated phase shift delay would be sufficient. I also think that too long a delay is a negative, as this will negate the effectiveness of night-purge cooling.

Cost: wood fibre is still several times more expensive than PIR in the UK, and we simply could not afford to spend an extra couple of £K regardless. I’ve however since discovered a new UK manufacturer of hemp-based insulation called ‘Indinature’; their prices are competitive with high-performance mineral wool like Frametherm 32 etc, with all the benefits of wood fibre. Too late for our build.

Mitigations: I used solar-reflective top coat on the flat sections of the loft roof, and raw cement slates (much lighter in colour than usual) on the pitched elements. Low-E triple glazing in all windows and roof lights, external blinds on the Veluxes. Opening windows positioned to allow for cross-ventilation.

All of this seems to have gone towards creating a usable space; the loft felt fine during the recent heatwave.

There is however a lot to be said against the environmental cost of using shit-tons of petrochemical-based insulation products instead of carbon-sequestering bio-based materials… I did use wood fibre to insulate the small section of solid brick parapet wall in the loft however, so remember this token nod when we’re all fucked in a few years’ time.

That sort of makes sense, though that’s my uneducated take not a comment on your reasons/methodology!
I think there’s probably an art to picking the best solution with space/cost/ease of installation to consider along with actually getting calculations right.
Not had a 40° heatwave in our place yet but I’m happy how it dealt with 30° the other week considering the constraints of the building. We do get serious pull through of air though as 3 outside walls and big windows on the 6th floor with the prevailing winds on one side, can be too much at times.

@ectoplasmosis think that’s what my friends have used on their breathable hempcrete house they are designing/building. No membrane and very thick walls with a high resistance to overheating, look forward to seeing it when it’s done.

Thanks that's good to know. Current rooflights are centre pivot but a crap cheap brand so planning to replace with Velux (also because we really want the solar electric ones for various reasons).

All of this seems to have gone towards creating a usable space; the loft felt fine during the recent heatwave.

That's reassuring to know!

I'll probably end up in exactly the same situation with the loft roof as we're constrained by the same stupid planning rules (this is a great example of something Labour could change to make it easier to insulate homes, right).

If so and if we can still afford wood fibre elsewhere we'd have space to go thicker above the under eaves storage and in the vertical walls at the rear.

That Indinature is interesting, I think I came across it when they were just starting out but they didn't have any products you could actually buy then. I'd looked at hemp jute insulation from another supplier but the density wasn't as good which is important for sound proofing, which is important to me, and they didn't give out any dB figures while Indinature's look good. U-values not quite as good though - a big part of the appeal of SteicoFlex 036 is you can't really get better from eco insulation - but could be a decent option for intra-floor insulation where that's not quite as important.

Part of the appeal of wood based insulation for me is the less tangible stuff (smell/feel etc.) so I like the idea of using the SteicoFlex everywhere, but it will add up.

Your low-E triple glazing - that helps keep heat in but not out right? Or have you reversed it?

Buying project spares for PIR makes it cheaper still and it's already been manufactured so you're effectively keeping it out of landfill (or that's how I tried to turn the negative into a positive). That's quite time consuming though...

Condensation/dew point calculations are critical with PIR plus some sort of strategy to keep air moving in all voids. Your building needs to become effectively airtight as any warm air escaping into a colder void will cause issues.

Biggest risk I still have with PIR (internal wall insulation) is joist ends that are now resting on/in colder brick walls, but I've mitigated against this as much as possible (treated). The ideal (but expensive) approach would be to rehang joists inside the warm envelope which would mean any U-Value could be used/attained, so PIR could enable building a passivhaus inside of an old traditional home, although doing this internally is very difficult/expensive and would be reliant on climate/location too.

Working with walls (the breathable approach) is preferred by many, but the dew point above 60mm of natural fibre normally ends up too far inside the building fabric, so you can end up with problems with that approach too. The low risk option internally is ~60mm of breathable fibre but the U-Value of that approach would be above 0.2 W/m²K, although some architects argue the reliance on U-Values for regs needs to be changed anyway (preferring more advanced modeling involving heat storage, lag, etc).

“ Your low-E triple glazing - that helps keep heat in but not out right? Or have you reversed it?”

low-E differentiates between long and short waves so solar heat (long wave UV) is blocked one way and infa red shorter wavelengths are also blocked to stop heat leaving the room, what would reversing it do apart from creating differences between the 2 pane gaps?

Yeah, we sourced all the 150mm PIR that went under the floor slab from Seconds & Co for dirt cheap.

The stuff in the walls of the loft we bought new to ensure intact foil facings, which were all sealed with airtightness tape to form multiple VCL layers.

Against every fibre of my intuition, I also ended up insulating the 2x solid brick external walls in my son's bedroom with PIR, as the cost of using a wood fibre system there would have been £1.5K extra that we just don't have. I used 2x 25mm PIR layers in a 'warm batten' build-up; Illbruck FM330 foam around the perimeter between the first layer of PIR pieces and brick, diligent taping of everything, then another layer of 25mm PIR on top, again foamed and taped everywhere to stop internal air finding its way through.

There is whole-house MVHR, so that should go some way to controlling internal moisture, and I ran the build-up through a few dew-point calculators which suggested that it would not be too much of a problem even if moisture did somehow find its way past 2x VCLs.

Sounds similar to me, I got 200mm (from Wales!) for floors for ~£50 a sheet as the business was closing down and then lots of 100mm for walls more locally (leftovers) for ~£30 each.

I built 2x4 stud walls inside every external wall and insulated between (25mm cavity), then foam in the small gaps, taped the foil, then added a VCL too(!), mainly to pass the airtight layer between floors more easily. I also have a whole house MVHR.

I removed the foil from the cavity side to further reduce the chance of condensation, but that only made a small difference in the dew point calculator and was a bit of a faff!

I used a 5kw 'eco' wood burner in the lounge last winter and if anything it was too warm (~60m³).

low-E differentiates between long and short waves so solar heat (long wave UV) is blocked one way and infa red shorter wavelengths are also blocked to stop heat leaving the room

So you reckon it helps stop overheating? Because there seem to be completely contradictory opinions on that and I've struggled to find a definitive answer.

The accepted orthodoxy seems to be that it can cause overheating, that's what it says if you google "low e glass overheating"

Low-E glass can trap solar heat energy, which can be beneficial in the winter, but it can also lead to uncomfortable temperatures in the summer. To prevent overheating, installers may recommend using solar control glass in combination with Low-E glass for south and west facing windows.

Which is also what Pilkington say:

https://www.pilkington.com/en/global/knowledge-base/types-of-glass/energy-efficient-glass/low-emissivity-glass

The use of low-e glazing helps to retain heat even in winter, allowing you to comfortably use these rooms for more months of the year. Low-e glass is also recommended for north or east facing windows, where a larger proportion of heat loss would be expected. For south and west facing glazing where overheating can become a problem in the summer months, your installer may recommend the use of solar control glass.

By reversed I meant having a setup which keeps out not in, but I think that's basically solar control glass...

I had a long back and forth with Velfac about this before finalising the glazing order, and they helped spec low-e glass with a low G-value which works to reduce solar gain, with the 2x argon-filled cavities reducing the U-value and preventing heat loss in winter.

I can dig out the written spec later if that helps.

So you reckon it helps stop overheating? Because there seem to be completely contradictory opinions on that and I've struggled to find a definitive answer.

The accepted orthodoxy seems to be that it can cause overheating, that's what it says if you google "low e glass overheating”

It stops some of the uv solar gain I can feel that just by having my hand behind the glass and then sliding the pane across, i can also feel the slight difference when there is one pane in front of the other (we don’t have double glazing just old crittall windows and secondary glazing). it definitely works for us but every case is different. SE facing so get a fair bit of sun up to about 2 pm in summer but there is a small projecting lip round the whole window (5m long) so when the sun is at it’s highest the sun only hits a small section of floor as this lip and the wide window sill means the rest of the room isn’t in direct light only reflected.
what the glass also does is stop some heat loss in winter, it seems to work very well then as the sun is now in a lower and shorter arc in the sky so if it’s clear we get winter sun coming into the room all day and in autumn/spring it can mean the heating doesn’t come on. so the glass is helping to keep that solar gain in.
We also have thermal foil backed blinds so when it’s heatwave time these are closed along with the windows around lunchtime until 2pm and this way the temps remain stable until opening windows around 5-6pm. my partner opened them early last week when it was 32º outside and the Tado plot showed the temp rise immediately

TLDR: in our use case it makes a significant difference and i’m glad we specced it.
I know the next flats on the SSW and W sides overheat as they bake in the sun right to sundown so another option might work there, they have their blinds drawn most of the day whereas ours are open after 2pm.

Pilkington make different versions of K glass to suit different usage requirements.

This is all fascinating stuff, I’m educating myself vicariously - thank you!

so on that 30º+ day Tado shows it’s only gone up .4 of a degree from the morning until partner decided it was better to open the window in the bedroom where it goes up nearly a whole degree which is the steep line. I closed the blind and the heavy curtains late morning, can see where the window was open and the sudden change when everything was closed.
This made it the coolest room in the house despite being in full sun from about 6am to 3pm. this isn’t all down to glass as the internal insulation plays a big part too. in fairness to her though the breeze and drop in humidity mean’t it didn’t feel much hotter. impressed with how slow the increase was during the day though.

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Here's a link to a Velux data sheet, which lists their various glazing options, how each one is constructed and a table to rank their usage

https://cdn-marketing.velux.com/-/media/marketing/uk/technical/bimcad/external%20product%20info%202020/external%20product%20info%20july%202020/external%20product%20information_ggl%20july%202020.pdf

Who on here has insulated under floorboards - any recommendations on what to use + whether it is realistic for me to hope I can salvage / reuse the lovely 1920s floorboards in the house at present, or will they all split and be useless?

We've done it, used 100mm PIR. Crawled under the boards rather than lifting them. Our place is 1930s and a lot of boards have split when we've lifted them. Might be able to save yours better but be prepared to find some reclaimed replacements.