Embodied Carbon of Roofing Slate

Speakers: Soki Rhee-Duverne, Jim Hart, Jess van der Drift 

Soki  So good afternoon, everyone. Thank you for joining us today. My name is Soki Rhee-Duverne. I'm a researcher in technical conservation and research coordinator for climate change threats and research program at Historic England. 

And sitting with us today is Doctor Jim Hart, consultant. So today we're presenting the findings of a collaborative research project commissioned by Historic England and Historic Environment Scotland. The study focuses on the embodied carbon of roofing slate, and how that impacts the choice of materials for repairing historic roofs. 

So, natural slate has long been the roofing material of choice for many of the UK's historic buildings price rise, longevity, weather resistance and continuity with local building traditions. Yet the domestic slate industry has experienced a dramatic decline since the 19th century, with most slate used in the UK today now imported primarily from Spain. This downturn has been driven by competition from cheaper imports, the closure of local quarries. 

Loss of crafts skills. Changing construction practices, favouring lighter and lower cost alternatives, and regulatory challenges that limit the reopening or expansion of extraction sites. While the idea of conserving historic fabric using traditional materials is well established, the environmental case for these materials has also become increasingly important as awareness grows around the climate impacts of construction. Embodied carbon has become a key consideration in the material choices. 

The motivation was if UK slate could be shown to offer environmental as well as heritage benefits, this could strengthen demand and help sustain a struggling but culturally important industry. The study set out to explore how UK slate compares to imported slate and the alternatives in terms of embodied carbon. It looked at both production and transport emissions, as well as factors such as lifespan, re-use potential and installation practices. 

Traditional materials are key to heritage repairs, but we lack data on the environmental performance. We need reliable data on embodied carbon to enable informed and sustainable decision making, and this work explores the merits of the different material choices. The central question being is whether, and to what extent, embodied carbon accounting supports the case for using indigenous natural roofing slate. 

Embodied carbon refers to the greenhouse gas emissions produced during the lifecycle of a material, from raw extraction, manufacturing, transport, use, and end of life. It excludes operational emissions, but may include potential future benefits for reuse or recycling. It's measured through a data gathering and analysis method known as a lifecycle assessment. 

The study focused on a cradle to site perspective, which are modules A1 to A4 highlighted in the dark blue area on this slide covering production, which includes extraction and manufacturing, and this is often referred to as cradle to gate, followed by transport to the site where the slate is ultimately used. Other modules potentially of most significance to the study, installation, use and reuse potential or shaded in light blue. 

While a full lifecycle assessment would offer a more complete view, this scope supported the goal of comparing products on a consistent basis. 

Production emissions are reported in all Environmental Product Declarations, a standardized document that reports on a product's environmental impact. EPDs were one of the key data sources for the study. In contrast, construction and downstream stages rely heavily on variable assumptions, particularly around installation, maintenance, replacement, and disposal, which differ across EPDs for reasons that are often unclear or poorly documented. 

These inconsistencies limit comparability. Thus, we focus on a cradle to site perspective to enable a more robust and fairer assessment. 

Slate extraction involves cutting large blocks from quarries using diamond wire, which are then split and shaped mostly by hand. For imported slate, up to 85 to 90% of extracted material is discarded. However, it has been reported by Burlington Stone that UK quarries tend to utilize the leftovers turning waste into aggregate or walling stone. This practice reduces the carbon burden of roofing slate as emissions are shared across co products, whereas it is assumed around 85 to 90% of rock quarried in Spain is discarded as waste. 

UK slate production has fallen from an estimated 450,000 tonnes annually in the 19th century to just 25 to 48,000 tonnes today. The most production is in North Wales, around 85%, with smaller outputs in Cumbria and Cornwall. The sector is small but regionally important, and could expand in response to demand for lower carbon materials. Scotland currently has no active slate quarries despite its rich heritage. 

However, now Historic Environment, Scotland is supporting revival efforts exploring reopening of certain quarries, for example on the Isle of Longa. A recent study by BGS, the British Geological Society for HES shows that restarting Scottish quarrying could be a viable option, offering heritage, economic and environmental benefits. If you're interested, there is an article about this study in Roofing Today and the link is at the bottom of the slide. 

For the purposes of this study, the imported slate of most interest is that sourced from Spain, China and Brazil. Of these, in 2023, Spain dominated the import market, supplying about 70% of all slate imported into the UK, followed by Brazil with 17% and China at 6%. By value. Spain shows even larger at 79%. This reflects its higher average price compared to Brazil and China in 2023. 

Spanish slate was valued at an average of 760 pounds per tonne, compared with 467 pounds per tonne for Chinese slate and 364 pounds per tonne for Brazilian slate. 

So how did we carry out the study? We set out to understand how UK slate compares environmentally with imported slate and alternatives, like concrete or fibre cement tiles. We carried out a literature review of the available embodied carbon data. This comprised of looking at eight academic papers, grey literature and generic data from various databases. One of the issues we came across was that there are currently no EPDs for UK slate, so we had to rely on older studies that older studies carried out in the UK and had to assume broadly similar quarrying practices. 

We model transport emissions using government greenhouse gas conversion factors, and we assumed slate data to a roof coverage of 39kg/m square for consistency, which is roughly a six millimetres thick. Alternative emissions were reported per square meter, and we also looked beyond production to include installation, maintenance and lifespan factors over 120 years, especially as durability and reuse significantly affect carbon outcomes. 

And now I'll hand over to Jim to present our findings. Thank you. 

Jim Hopefully you can hear me. Can someone give me a thumbs up? Excellent. Thank you very much Soki. Before I get into the numbers, I'll just briefly recap the data we're working from. We had reasonably good information on Spanish roofing slate, as there were five EPDs to inspect. Even though a couple have since gone out of date. 

That said, with most of them coming from the same stable as it were, that's, an outfit called Cooper Pizarro's. It would be hard to argue that the different EPDs offer sort of robust, independent corroboration. However, in addition to those Cooper Pizarro's EPDs, we also have a broader industry, one from the, cluster that Pizarro de Galicia, which is the Galician slate cluster, which is intended to give average for roofing slate light from the across many different quarries and different slate dimensions, also, it was this, slate cluster, one that used the 39kg of slate per meter squared of roof assumption that, Soki just mentioned. 

We took this as a useful basis for normalisation. In reality, the coverage will depend very significantly on the thickness of the slate, which may might be a deliberate choice made by the specifier, for instance, thicker slate for more extreme environments or thinner slate to suit budget. 

The coverage might also be affected by the length and width of the slate and installation practices. Also, the functional unit throughout this discussion is one meter squared of roof. So that's enough slate to cover that area. In theory, that includes whatever fixings are required, such as nails or hooks and potentially timber battens. But these really are outside our scope as they're related to the construction stage. 

That's, lifecycle stage 5, and it's hard to determine whether such choices are specific to the product in question, and therefore whether they usefully inform current comparison between different products. So UK slates, as Soki said, we had no EPDs to draw on, so we were reliant on the. On the 2010 Historic Environment Scotland technical paper TP seven and the associated academic paper by Krishna and colleagues. 

This was based on primary data gathering from UK producers. This provided embodied, embodied carbon values for slate amongst other stone types. If that study were repeated now with the same primary data, it would likely lead to lower values of embodied carbon as a result of the decarbonisation of the electricity grid. So any electricity used in the production of slate, would have a lower, cost in carbon cost now than it did back in 2010. 

Furthermore, as you said, allocation of some of the impact to co-products might lead to further reductions. Also, for Chinese and Brazilian slates, unfortunately we had no data to draw on at all. So we used available all of the available EPDs as a proxy for the, full range of possible, likely possibilities, for the embodied carbon of slate. 

So the apart from the Spanish EPDs, we all had one. We also had one from Argentina for comparison. We also investigated other mainstream tiled roofing products, both ancient and modern, for which EPDs were available. So that's fired clay, which was, first seen in Britain nearly 2000 years ago. I think. Concrete and fibre cement, and we looked at 1 or 2 EPDs from each. 

As it turns out, these were all European producers. I'm aware that since the study was done, EPDs from UK producers may have materialised, but they're not reviewed here. So here are the results for the cradle to gate element alone. That's life cycle stages A1 to A3. We'll, drill into these in more detail and into the transport to the construction site stage. 

Shortly the, the normalised EPDs for slate span a surprisingly wide range. So that's a factor of six. Unfortunately, I have no explanation to offer for this. The highest figure is for the Argentinian slate. But even if we leave that one out and just look at the Spanish slate, the highest valuation value for Spanish slate is almost four times that of the lowest value. 

The value for UK slate from that Historic Environment Scotland study is in the middle of the EPD range, but towards the upper end of the range for the Spanish slate. 

We also looked at other data sources which tended to suggest lower values, but we excluded them from the assessment for various reasons. The Tennessee study from 2008 was for slate products generally, so not roofing slate specifically. And as for the inventory of carbon and energy, the ICE database, there was, no transparency around the values presented for them for slate. 

As for concrete, clay and fibre cement, the cradle to gate values are in the same sort of ballpark as, slate, the range being bookended by fibre cement products of very different thicknesses with the clay and concrete products sitting in between. 

So getting to transport, you might ask why we didn't simply use the values for the transport stage presented in the EPDs. The short answer is that the EPDs don't know where you'll be using the product in question, and therefore the distance involved. Those EPDs designed for use in the UK should have values that are in the right ballpark, at least. 

But to enable a fair comparison across all materials. It made sense for us to remodel all the transport, all the transport emissions from scratch, using a consistent set of assumptions. For this, we envisioned an ideal journey from the quarry to the point of use bypassing any intermediate diversions, for instance, for warehousing. So we assume that manufacturing is co-located with the quarry, and then we have transport from a quarry to a nearby port and then to ports in the UK. 

And from those ports to each of three hypothetical construction sites in London, Leeds and Glasgow. The same modelling assumptions are used in the Historic Environment Scotland stone embodied carbon calculator. And that, as Soki said, that based on emission factors reported in UK Government's greenhouse gas reporting data tables, which helpfully include figures for grams of carbon dioxide equivalent per tonne kilometre for different modes of transport. 

Actually, incidentally, on the Historic Environment Scotland calculator, that calculator does have the potential to be updated with findings from this study to add to the existing data on sandstone and granite, which is already included in the calculator.  

Right. So origins of imported slate. This is where most of our imported slate comes from. The grey flags show locations of quarries admittedly hard to pin down at this resolution. Sorry about that. And the pink ones, the location of, nearby ports. So Spanish slate, from San Pedro de Thrones, in Castelli, León, might take a 500 kilometre journey to the port of Bilbao, followed by a 1200 to 1700 kilometres sea trip to the UK with the variation depending on the port of entry. 

We also modelled the overland route via Dover, which is 1700 kilometres to London, and 2004 hundred to Glasgow. Brazilian slates from the quarries in Minas Gerais. Transporting that the relatively nearby port of Rio. That's approximately 600km. Followed by a 12,000km sea trip. The Chinese quarries in Shaanxi province, much further inland, with a 1500km trip to the port of Shanghai. 

Then followed by a 22,000 km trip to the UK. And then. With apologies to, anyone from Shetland or Fermanagh and a few other places that have been chopped off this map. This is a map of the UK with locations relevant to this study for flagged up. The grey flags mark quarries in Cumbria, that's Kirby, North Wales, Penryn etc. and also, in Cornwall in red. We have the locations of the various ports of entry that are used. 

For the importation of slate. Going down the left hand side of the map and then up the right, we have Greenock near Glasgow, Belfast, Liverpool, Avon mouth. That's Bristol, Southampton, the London ports of Tilbury and Gateway, Felixstowe and finally Immingham on the Humber Estuary. Also highlighted are the locations of the three hypothetical construction sites London, Leeds and Glasgow. 

The modelling, of course, deals with transport from ports for imported slates and quarries for domestic slates to these three cities. 

This is what we found, for transport of slate to construction site. So this is for life cycle stage A4 alone. This graph, it's presented in six groups of three. So each set of three is the three sites of London, Leeds and Glasgow. And it's for each of the six slate categories. From left to right, these categories are Welsh slate, Cumbrian slate Spanish slate. 

Transported by sea Spanish slate with the via the overland route, Brazilian slate and Chinese slate. So, the key takeaways from this in my view. Firstly, and obviously the values for UK slates are comfortably the lowest in the region of one kilogram of carbon dioxide per meter squared. That's not completely negligible but is clearly significantly lower than the cradle to gate emissions. 

Note that for cases where slate is used locally, e.g. Cumbrian slate within Cumbria, emissions will typically be less than the smallest bar on this plot, which is just 0.5kg of carbon dioxide. So the less favourable options the transport emissions are high enough to match, exceed or, in the case of China, comfortably exceed the likely cradle to gate emissions. 

Recall that the cradle to gate emissions for Spanish slate were in the range of 3 to 11, whereas this figure for transport from China is in the low 20s. As you see here for imported slate by. See the difference between the values for the different construct construction sites is basically noise. It's pretty negligible. This is on the, assumption that slate is landed at a port relatively near to where it is needed. 

That might actually be a bold assumption. We're not sure if we took did a rand took randomised picture. This would result in in higher values all round. For UK produced slate and for slate imported by overland routes. The location of use is clearly quite important and it's helpful to get an accurate measurement. So for instance with slate transported over land from Spain, it is of course, as I mentioned earlier, a much longer distance to Glasgow than it is to London. 

Putting it all together. Here's a summary of embodied carbon for cradle to gate. That's the first column of numbers. Transport to construction site. That's stage A4, the middle column and the total of the two. 

As discussed for the UK. We only have one number to go on for the cradle to gate, and this number may well be an overestimate, but the transport emissions are very low, leading to a relatively low overall total for Spanish slate. The cradle to gate greenhouse gas emissions span a surprisingly high range. As mentioned, and the range associated with the transport stage reflects the difference between overland and maritime options for Brazil and China. 

We have no specific information on the cradle to gate, so we can only assume that it's somewhere within the range that we see in other EPDs. And for transport. Brazil is at the bottom of the range indicated in China at the top. 

Looking at the alternatives, fibre cement, etc. This is the data from four EPDs that were examined from the left: fibre cement from Belgium, fibre cement from Ireland, concrete tiles from Denmark and fired clay from Germany. The cradle to gate figures, which as expected, make up the majority of the life cycle emission, in each case. That present that's the lower part of each bar. 

They are they are as reported in the EPDs. They're in the same ballpark as the numbers already discussed for slate, although the figures for fibre cement tiles from Ireland are rather high in comparison to everything else. The reason for that is clearly the greater mass per metre squared of roof, which in the in the case of the Irish product, it's, it's more than twice the mass of the Belgian product. And we can assume that it's a much thicker product, than the four millimetre Belgian tile.  

As for transport, the emissions shown here are as modelled in this study, not as presented in the EPDs as by and large. These EPDs are not aimed at the UK market, so transport from the factory in Europe has been modelled. Arguably, then, the transport figures may be presenting a bit of a worst case scenario, as although we did not include a market study, we know that at least some similar products are manufactured in the UK. 

Clay and concrete are both quite heavy. The mass per meter squared of roof being about the same, a slate and sometimes more. So local sourcing would clearly be advantageous in terms of transport emissions. 

And for final display of the results, the this graphs give gives an overview of the cradle to site emissions for the main slate and non-slate options. What we have here is for each product a range for the values we have found for cradle to gate added to the values modelled for transport to site. So for UK slate with only one data source for the product stage and relatively short transport scenarios, the band is very tight and it's more than likely that an up to date true value in inverted commas would be outside the range indicated and in fact hopefully, below it for reasons discussed already for the alternative products here. 

The top end of the range uses the modelled transport emissions as already discussed, but the bottom end of the range uses the lower transport emissions reported in the EPDs. We've done this as a proxy for the possibility of being able to find similar products manufactured locally. So on its own, this plot doesn't provide a compelling case for domestic slate at all costs, but it does make a strong case for avoiding import from distant sources. 

And it also shows a reasonable likelihood that domestic slate and to be fair, Spanish slate, if shipped by sea, will at least be competitive with alternative options, and further investigations could double down on the case for domestic slate. 

An obvious feature of slate is its durability, and it's generally reckoned that a well-maintained domestic slate roof might easily last for a century or more, with failures in the past being associated with the poor quality of metal fixings rather than the slates themselves, and these days we use more corrosive, more corrosion resistant nails and clips and things. Obviously, this would be an environmental win if the slate is lasting longer than comparable products, albeit an environmental win that takes a long time to arrive on material installed. 

Now, as this is about avoiding emissions in the distant future. But how do we calculate that advantage? Unfortunately, things get a little bit sketchy at this point, as pretty much all of the EPDs here identify a reference service life of 60 years, which conveniently matches the standard reference study period for building life cycle assessment. To be fair, if you took a walk around a 1960s housing site estate now, I think there's a high chance that you would see a lot of houses still sporting their original roof tiles. 

That said, the Royal Institute of Chartered Surveyors, RICs, they have the guidance on whole life carbon and this does leave a possible opening in that they recommend that buildings are assessed over 120 years, as well as over 60 years. And if it could be shown that the slate roof is good for 120 years plus and other routes, roofs will need replacement well before then. 

This would present a significant carbon account advantage for slate. Currently, however, my assumption is that the evidence for this, both the domestic slate surviving that long and the top and the alternate is falling short. I think the evidence might be missing on that. Finally, just to recap on a few of the limitations, I think I've touched on pretty much all of these already, but essentially and sadly, no EPD. 

So UK roofing slate. So putting this up against more recent data on Spanish slate does not make for an ideal comparison. This is, of course, something that might easily be rectified, and doing so would also deal with the issue of allocation. So that's the fraction of the impact that can be. Allocated to co products. 

The absence of data on slate imported from China and Brazil would be harder to address. I think, inconsistent EPD scenarios. This isn't really a problem when comparing cradle to gate emissions, but really is an issue when digging into emissions associated with subsequent stages. Which, necessarily rely on assumptions about where the material is used and its subsequent fate. 

This is why we did our own modelling of transport emissions. As an example and other example assumptions about the installation process and materials involved might differ for important reasons to do with the slate itself. Or it might be. Or they might vary at the whim of the modeller. And it can be very hard to disentangle this. So, and similarly, assumptions about what happens to the materials at the end of life, 

Finally, I should mention that while consistent assumptions were used for transport modelling, which gives a level playing field comparisons, they are not necessarily accurate assumptions. So some research and logistics would be needed to resolve that. And at that point, I will hand it back to Soki to wrap up. 

Soki Thanks, Jim. So just to conclude, indigenous slate offers significantly lower transport emissions compared to imported slates. More analysis is needed due to data gaps. But that but in general, natural slate shows a lower carbon footprint that imports and common substitutes and UK slate could potentially have lower production emissions. But without more, specific data. EPDs, we can't do, further, more accurate comparisons. 

And unfortunately, as Jim has mentioned, the only available UK data is actually from the Historic Environment study from 2010 and a separate study by Krishna, which, from 2011. And these may not reflect, modern practices for decarbonisation of the of the grid. And from where we are now in 2025. That translates long lifespan up to 100 years or more. 

And these potential mean fewer replacements over a 120 year period. In contrast, alternatives like concrete tiles or fibre cement may need at least one full replacement, increasing the total embodied carbon, and UK slate has significantly less waste and associated carbon emissions due to co product allocation. So in terms of future research directions, what we've identified so far, that we need up to date sector wide UK EPDs to assess the emissions accurately and to fairly compare UK slates to imported products. 

More empirical evidence is needed on the long term performance. More research is needed on waste during installation, treatment, at end of life and the assumptions used in model D, we need a better understanding of how quarry waste and coproducts affect carbon accounting and could lower UK slates reported emissions. And we need to carry out detailed modelling of A4 impacts using real transport data. 

The modes, the distances, number of stops, whether there are storage implications along the way to refine UK versus overseas comparisons. And we need to carry out a market study to study the potential for scaling up indigenous slate use supply chain, understand supply chain dynamics, and consider the regeneration of local economies. So lastly, just to say thank you all for being here and listening. 

Our thanks go to the steering committee who gave us really invaluable advice and direction. The report is now on our website. That's the first link. And there is also a summary article in the latest issue of context. 

So that's it. Thank you. 

Jess Brilliant. Thanks Soki and Jim, that has been, an incredibly, interesting, 40 minutes. And I think that's reflected by the questions that are coming in in the chat. Are you guys happy to pop your camera's on and see if you can provide some answers to these? 

Soki So my camera, is it working? Is it working out? Is it working now? Okay, great. 

Jess You've got it both, I was going to say loud and clear, but I don't think that's quite the right words. So, I think, firstly, people want to know more. I think about, you know, embodied carbon in other building materials. Do you know, are there any plans to mandate EPDs in the UK building sector? 

Soki I yeah, I doubt there will be a mandate that's coming from the government. Because the commercial implications, step in Jim any time. But the commercial implications of producing an EPD will depend would lie with the manufacturer and there, they are very expensive to produce. But despite that, I think, increasingly within, local authorities, when you consider the embodied carbon or the whole life carbon of buildings and what, local authorities are requiring at a planning level, they, they will be moves, I think, in the future to make some case for, a whole life carbon under planning regulation, which would only mean that that will also put pressure on the industry to, produce UK EPDs. So those parts Z, for example, which is the embodied carbon whole life carbon proposal for buildings, but it obviously hasn't been is not passed into law and there's no compliance with it. But it is on everyone's radar within the construction industry. 

Jim But yeah, I would just say and in in Europe it's move. In Europe at least it's moving a bit faster as well. So, in Scandinavia there it's actually obligation to achieve certain, embodied carbon levels or whole life carbon levels when with new construction products, projects. So yeah, it's moving in that direction, but quite slowly here. 

Jess That said, it's nice to hear, I guess, there is movement, but always these things could be faster. I hesitate to say. In terms of what's next? The research that we're doing, well, Historic England doing into, embodied carbon. Are there any plans, to look at, things like natural stone slate versus imported materials, GRP, fibre cement, slate. 

Soki We don't know what the next stage of this particular research strand will be. I think at the moment, we are probably if we do, we will be doing more work on embodied Carbon. Will we will be doing more work on whole life carbon. But I think, at this stage we will be looking at whole buildings or building elements rather than a specific material, despite the need. 

Jess But it sounds fascinating. I'm looking forward to the, to the next webinar. So, someone's written here as a practitioner over four decades. I would have no hesitation in stating that Welsh slate is of a superlative quality. How do we harness the justification on this? 

Jim Well, I mean, it's I mean, this study adds to the case for using Welsh slate. I mean, that that's, one thing I, I would save and if, if we could actually get better data on, on Welsh slate and its embodied carbon, then that would improve the case even more. So what else does it take to get people to use the best quality slate? 

I don't know it needs. The trouble is, it needs a very sort of long term view to, to specify the best quality products does not. 

Jess Yeah I think. Yeah. Absolutely. Right. You've sparked a discussion now in the slate in the, in the chat about the best where the best slate in the UK comes from. I don't know if now's the time to er to venture into that kind of. 

Soki I don't think so. You know. Make those kinds of judgments. 

Jess And, you know, say going back to looking at, you know, the embodied carbon of different roofing materials. Do you know if there's any figures available for fired clay manufactured in the UK? 

Jim I didn't find any. So, I haven't looked again since doing this study. And so, I, I actually don't know who supplies fired in the fired clay in the UK. I but there is somebody, but no, I didn't find an EPD. I, I've, I did a very quick search. Dug up another EPD from a British supplier of, concrete tiles, which was in the same sort of ballpark as the, as the Danish one that I mentioned. But know that I don't know about that. I just looking at a question about Brazilian slate, which I can see is highlighted in the box that I can see, which somebody asked is it a mudstone? And yeah, I'm not a technical expert, but that's yeah, I understand it is a mudstone. It's not a true slate. And I think the importers themselves, say that it has to be handled differently to slate. And it has to be, you know, it has to be sawn raw chip for wire. So that would actually have implications for the installation phase. And, you know, the, the embodied carbon of the stage A5 might be higher than for other slates. 

Soki So it's a sedimentary rock, isn't it, rather than the metamorphic rock, I believe. And so because of the differences in geology, I think the, the Brazilian slate, which is. Yes, I'm not saying will have reduced, structural, performance. And so therefore handling and working with it. You have to do it differently because of the increased risk of breakages. 

The use hooks, for example, when you're installing it rather than, nails. That's what I, that's what I understand. 

Jess Very interesting. So not all slate is the same and on that line, what grade were the Spanish slates in this study. 

Jim Grade. Well, the EPD from the Galician slate cluster, covered all roofing slate. Produced in the in the region by the by the members of the cluster. So that would have been quite a wide range of roofing slate. 

Jess That yeah. And someone's put here presumably quarries producing, producing random widths resulting in less wastage. 

Soki Could I pick up on a thread a conversation that's been happening in the chat about, solar tiles. I mean, I think you have to consider, several factors, especially when you're thinking about historic designated assets. The first is the visual and the architectural impact. You also have to think about the durability, longevity, repairability. 

So solar slates, obviously, you will have to repair maybe every 30, 40 years compared to if you were to use natural slate, which you use good quality natural slate. It is, known to last over 100 years, 250 years. Also, I think a key thing here in our conversation about embodied carbon is the embodied carbon trade off. 

So while solar slates will help reduce the operational carbon, they will have typically have a higher embodied carbon, upfront footprint due to the materials and the manufacturing processes. So, I think you have to think about it in the big picture. And obviously the planning permission and all and all of that, 

Jess Yeah. It's never straightforward. Is it? 

Soki But, you know, unfortunately. 

Jess I think, you guys have done a great job at picking up on most of the questions that have been asked in the chat and not going, you know, too deep into the nitty gritty. I don't know if there's anything you've seen that you'd like to answer before we wrap it up today? 

Jim I can see a couple of which I'll just do very, very quickly. Do we know that the discarded waste of Spanish slate quarries? No, we don't know that for a fact. But it is reported that way in academic literature. And also, it's an assumption given in at least a couple of the EPDs. 

Jim So, you know, I think it's a safe assumption. Next one, does this study consider Canadian slate. I did I did come across Canadian Slate whilst doing this research. But it's not a significant import. So in terms of volume and value. So it's not included. 

Soki I think when we looked at the import data, it, it was like a 2 or 3% or less. Oh, less. Okay. Yeah. So we didn't really consider Canadian slate for the UK market. Any case.