Structural Conservation of Ruins

Kim: Good afternoon. I'd like to welcome you all to today's Technical Tuesday webinar on the Structural Conservation of Ruins. I'm joined this lunchtime by Jon Avent, conservation engineer and director at Mann Williams Consulting Engineers in Bath, Bridget Drake-Wilkes, Senior Structural Engineer in the Structural Engineering Team at Historic England. Bridget recently contributed to the December edition of the Structural Engineer magazine with the Conservation Compendium article titled Another Life in Ruins. The article concentrates on the numerical analysis of ruined walls, and Bridget will focus on structural stability considerations when dealing with freestanding walls. Bridget will follow on from Jon today, who authored the first part of the Life In Ruins series back in 2015, and Jon will focus more generally on the challenges faced when working with derelict structures. Bridget will follow straight on from Jon today, and there'll be plenty of time for questions at the end. So, I will hand it straight over to Jon. Thanks.
Jon: Excellent. Thank you. I guess the starting question is: what is a ruin? And I think everyone here would have perhaps a slightly different idea of what they picture in their mind when a ruin is mentioned, or it may be the sort of grand, national, picturesque ruin, something that we might see as a sort of a window into the past. Today, in the short time available to try and focus more on perhaps the former, the heritage at risk, the dangerous building, perhaps the more rapidly decaying structure where prompt action might be needed as opposed to the more sort of purist types of ruin and conservation. So, if I run through perhaps a few slides that just illustrate the sort of ruins that we've come across over the past few years. It may be barns, ruined barns, it may be ruined manor houses, sometimes in remote locations.
Often very precarious and neglected over many, many years. And coming eventually to someone's attention that it's approaching the point of no return, and needing prompt action. Some may be the more iconic sites. Again, some lost their function from the past, and left ruinous. Some maybe not even surviving very long with a use from day one, Ruined manor houses, mills and mine workings from our industrial past, remote islands, mills, and other industrial heritage. Even more city center-based structures right in the public eye, but sadly neglected, and marine structures, structures even out on the most remotest of locations, on islands, military establishments... Again, a window on the past. So, basically, a very wide-ranging selection of things that might be, well, are classed as ruins, really. And each presenting its own unique challenge.
So, the aim, really, is to run through a sequence of key stages that we would see in any of these particular projects, and looking at the decision process, the thought process, and where we go. So, move on a slide. So, really getting started, key one is pulling together all the interested parties and getting a focus on what are the objectives. And there is often a risk at the start of any project that there's a circle of decisions, and questions, and answers that just continue round in that loop. What work is required? What is the available budget? How much will it cost? Who takes the risk? What is the brief? And the risk that that carries on going round. Because often, no one quite knows how much any of these projects are going to cost, what works are required. It is an iterative process. Whereas often in any project we work on, people want certainty, and the one thing you don't get with ruins is any certainty. And so, the key is defining the brief. I think I've got control back. Did that move on okay?
Matt: Yeah, it did, Jon. Thank you.
Jon: Yeah. So defining the brief and... Defining the brief and understanding with the client what is expected, and having that collaboration to to know where the targets are going to be, what is known, what isn't known. Start with the surveys, information gathering, really important stage. But it's important that it isn't just another survey. I see too many projects where, if in doubt, ask for a survey. And really, the survey needs to be that exercise that moves things forward. So, information gathering, looking at what information already exists, desk studies, using tools and techniques that can help to gather information efficiently. It may be using robot scanning, where a building is too dangerous to enter, the use of MEWPs, even drone scanning, and turning that into reality capture models that can also help look at the building remotely and safely, and understand and build the strategy.
Briefly, ecology is always there, and it is something we should never lose sight of. It can't be ignored. It mustn't be ignored. And being aware of the constraints that it imposes is important as part of that stage of developing a brief, developing a strategy for the site. And obviously, with ruins, the nature is that there's risks involved right from day one, and they can't be ignored. But the tendency to seek to just pass the risk on will not achieve anything. Too many projects where clients pass the risk issues down to the consultant. In their brief, the consultant tries to pass it to the contractor, and ultimately it stops the project moving forward. So, understanding the risk from day one is important, how it can be managed. And this will include things like budgets, and where those budgets can be efficiently used.
So, in terms of a strategy that manages the budget, what we typically do is try and break the project down into manageable sections. By doing that, you immediately create control over what works are done and in what order. So, dividing the site into key areas, identifying main work tasks, prioritizing, staying realistic, and good communication and collaboration is key. So the matrix on the screen there divided the area into key work tasks, but also focused on what was actually important about the site. Where were the important features, what was significant about the site? So that the decisions were made on where priorities could apply, and which works were perhaps less significant, could be compromised, or could be left out. The key is always trying to get best value.
Funds are always limited. I don't think there's ever been a project where there was quite enough funds, there was quite enough budget. We're always trying to manage tight resources and get the most out of the site. So, one of the keys is to make sure that appropriately qualified professionals are engaged, and all the professional bodies have their own conservation registers where a test of the experience and the test of the knowledge base has been established, and it's important that those valuable resources are tapped in. In the engineering sector, we have the CARE register and that can be looked at online, the ICE or the IStructE, or Engineers Ireland. The other key is that, often, hard decisions need to be made. Compromises are sometimes justified, necessary. It may be that a simple concrete slab goes on a chimney as a capping.
It's reversible, it's honest. It's cheap and efficient. And it can... And it can add stability. Sometimes when you've got precarious structures, adding in a simple concrete relieving lintel, or even replacing and the use of concrete. So, whilst it may be undesirable to use modern materials, sometimes there is a justification, and it is, with all these cases, it's about seeing the bigger picture and where some of these difficult decisions need to be made for the greater protection. And without doubt, collaboration is so important. Again, when I talked earlier on about not just passing the problem down the line, expecting someone else to deal with it, often these projects come with a a very knowledgeable and experienced pool of resources from clients, building owners, funders, consults and contractors, and collaboration and trust always, always gets the best out of the project. Prioritizing work.
Too often these projects are delayed and delayed because there's a desire for more information, more certainty, and lower risk. And it actually never gets that point. There's often a rapidly deteriorating structure. The scope of works will only increase. And so, looking at abilities to perhaps bring out smaller phases of work, focusing on urgent elements, sometimes this is a problem with funding and resources, but in the interests of the building, any ability to get early stages of stabilization work done, is a massive benefit. Again, in the prioritizing works, the couple of slides here was an illustration of a building where a very, very significant collapse was imminent. The main project was quite a distance away, but the aim was to stop this section of masonry collapsing. And the method used was to use nylon cord to simply constrain an area of delamination.
It was very crude. It was very quick, but it efficiently achieved the objective of stopping a major collapse while more permanent solutions could be defined. The use of materials. We're all familiar with the conservation philosophies and the objectives, the key phrases. Knowing when they apply and knowing when they need to be adapted is important. The use, which I touched on earlier, on the use of concrete lintels as concrete capping slabs, they have their place, and again, as part of the big picture, it's important that they form part of the palette of tools that are available to achieve the wider objectives. So, yes, using like for like repairs, stone repairs, accurately matching the historical data. Yes. Sometimes concrete lintels. The message really is, treat each case on its own merits. Repair approaches, again, far too many wide-ranging options available.
But I'll just touch on a couple, some of the decision making. Many projects that we come across have had scaffold put up decades ago even. Still in place. It was put up with the best of intentions, no doubt. But works never happened. And often, the process of putting up scaffolding is not only costly, but it can also create situations where you can't focus on what is important. Whereas the use of crane access on a particular project we did, the bottom right slide, the use of a mobile crane and basket access enabled works to be very, very focused and areas to be attended to much quicker. The other slides, some historic masonry, where instabilities in the masonry had been established, and the approach, one of the approaches that have been proposed was to rebuild. But the loss of historic fabric, the loss of all the pattern of the stonework meant that an alternative solution of masonry jacking was considered and actually adopted successfully.
So, again, no preconceived solutions. Look at each one on its merits. Sometimes getting emergency works and stabilization frames dropped into place is a way. Completely reversible, but a rapid method of bringing in structure. The one here, a stability frame was fabricated offsite and then dropped into the center of the core of the building to enable works to progress. And sometimes simple, bold decisions. The example here is just the use of nylon ratchet straps that were banded around the structure. Again, prevented a collapse, were quick to install and actually bought the time to do more permanent repair and conservation works. Other bold decisions. The example here was a very, very high, precarious chimney section. I think we had something in the order of 50K of works just to try and conserve and stabilize that section of chimney, which was a very, very significant element of the budget for the whole works.
And so, the difficult decision there was to record and dismantle down to a slightly lower level, and to cap the remains of the chimney. It was a difficult decision to make, but in terms of the available budget, the need to use those funds more efficiently across the site was taken. The flipside of that was that there was other areas of the site where a more recent collapse had occurred on a chimney that was salvaged material that was able to be collected. There was good record, photographs, and we were able to reconstruct that element. The consideration of the future maintenance factored into these decisions. This was an area where the long-term stability could be managed and monitored, whereas the previous one was a much higher and more precarious section of masonry, less significant in terms of its location on the site as well.
So, all these decisions factored into the final solution. This was a case where there was crumbling and decaying mullions present, and the decision on this was to reform new mullions in the window. So, again, another type of decision made, and this was the replacement of some existing structure. Window heads. This was an area where an element of the building was reformed to protect the form and layout of this elevation of the building. So, elements of masonry were reinstated just above the windows. Again, it provided long-term improvements to the long-term management of the structure and protection of the structure. So, adding a bit of structure back, again, was a way of looking at how the structure was going to perform in the future. What we didn't want to do was leave a structure that was any more vulnerable than it already was.
So, in summary, each project, each building is very different. There is no one-size-fits-all. Never go into it with a preconceived idea of what the solutions are. Ensure clear brief understandings and objectives are established as early as possible. Engage experienced conservation advice. And again, with reference to the CARE Accreditation Register for engineers. Establish a budget, prioritize, collaborate. Be prepared to make the bold decisions that need to be made, and be prepared to explain those decisions to those involved with the project. Always try to see the bigger picture, and don't delay, make a difference. And that brings me to a close. I will pass over to Bridget, who will talk about some of the technical design considerations.
Bridget: Thanks, Jon. Very interesting. As Jon says, my name is Bridget Drake-Wilkes. I'm a Conservation Accredited Engineer and a Senior Engineer at Historic England. I'm going to be looking through structural stability considerations for ruins, particularly well-maintained ruins, and just running through the likelihood and consequence of failure when you need to assess stability, the methods of failure, guidance on parameters, guidance on loading, method of assessment, and then on to questions. I'm sure there will be more than one. And it'll probably take about 15 minutes. When does a ruin need to be maintained? This church has been a ruin for the last eight years. And what's likely to happen to it to cause it's fail? Well, one of the things is the self-weight, which, because it's been in this condition for eight years, is unlikely to be an issue unless there's a failure or change in the ground conditions leading to rotation.
Other forms of failure, loading that could cause failure are environmental, i.e. wind and snow, and another one is accidental loading, for example, vehicle impact. And then, the other thing is to think about the consequences of failure. Most of the time as engineers, in accordance with BSEN 1990 basis of design, we deal with medium risk and medium-consequence buildings, so residential and offices. And then there are high-risk buildings such as grandstands, and low-risk buildings, such as agricultural buildings and lighting columns. And in some instances I would suggest that ruins, whether or not open to the public, would fall into this category. But if your business is showing ruins to the public, maybe it's a medium risk. And if you are on a low-risk, you can modify some of the parameters in design.
When should you assess stability? So, basically the... One needs to consider whether the structure has changed. And if it's changed for the worse, then you probably do need to assess the building. Or the other alternative, if the load has changed and increased. And only then you need to do calculations and gain understanding. And again, it's where that feeling of risk and the consequence is significant. In terms of methods of failure, these are the standard drawings of the masonry design codes. There are basically two methods of failure. One is parallel to bed joints, and one is perpendicular to the bed joints. These are for all supported on the two edges. Obviously, with ruinous walls, we tend to be dealing with walls only supported at the base or at one side, and therefore the spans are effectively halved for what applies.
These are based on slender walls in accordance with the current standards. So, for a 100-millimeter thick wall, these give a slenderness ratio between 24 to 27. And if we think of a 600-millimeter thick rubble core wall with the same sort of heights involved, it would give a slenderness ratio between 4 and 4.5. If you want to get a more realistic, slenderness ratio, you'd need a massive, ginormous test rig to build a test wall, kind of in the region of 14 to 16 meters, which is unrealistic. The earlier [26:53 inaudible] tended to give guidance that a slenderness ratio of 12 was the maximum, which gave about, for a 600-millimeter wall, about 7.2 meters high. So, greater than a domestic house. It should also be noticed, as we've gone to the [27:11 inaudible] with walls that are mainly subject to lateral loads such as [27:15 inaudible] walls, there is no absolute limit as there was in the earlier [27:19 inaudible], but capacity understandably does reduce as you're becoming very slender.
So, if we consider failure parallel to the bed joints on an ashlar, or a 600-millimeter wall with a central core, the alignment of stones varies along the length, and there are some instances where you could perceive an area of weakness. But it's also important to remember that just behind that, the rubble will have a different alignment, and therefore the weakness will vary. And then, if we consider the failure, failure in kind of absolute terms of ruins, not failure of your plaster finishes or anything else, only occurs when the center of the wall goes pretty much almost to the face of the wall, with some local crushing occurring at this point. So, either the foundation is softened on one side, causing rotation with the centroid, then beyond the face of the wall, or there's a vehicle impact, or a gust of wind with significant sufficient duration, i.e. kinetic energy to activate the mass, lift the centroid up to rotate it to this point of no return. Otherwise it just rocks back into position.
And the signs of vulnerability to this type of failure, horizontal cracking, or signs of horizontal cracking in bed joints, and on the opposite face a horizontal crushing of the mortar and/or the units. In terms of failure perpendicular to the bed joint, I've used the same piece just stretched out to show a plan of a rubble wall. Again, it depends on the alignment which is here, but probably if you've got [29:24 inaudible] facing, it will have a staggered joint. The strength of the mortar in the facings and the core may vary slightly to be stronger on the facing, and failure, in terms of the drawing we looked at earlier, is this rotational failure. But, in terms of a ruinous wall, is this actually a failure? Does it matter that it's opened up this much? Or does one element just become a freestanding wall?
The other thing is that, if it's a vehicle or something that has caused this impact, it must, again, have significant duration to activate the mass, to cause the rotation and the crushing of the face to the masonry. Signs of vulnerability to this type of failure are vertical cracking in the mortar joints, or possibly through some of their facing stones, and vertical crushing of the mortar, and/or the masonry units. Guidance of parameters. This is a really boring slide, so I'll just whizz through it really quickly. So, there is very limited guidance in the current standards regarding the use of lime mortar which relates to random rubble masonry. And it suggests that one uses, for newbuild construction, one half of the value for M2 mortar. M2 mortar is a mortar of strength, two Newtons per millimeter squared at 28 days. Because there is limited information on lime mortars, some testing and reporting was undertaken in 2009, and this shows that NHL5, which has a compressive strength of five Newtons per millimeter squared at 28 days, has a classification between M4 and M6, which kind of makes sense really.
And that with a quick climb, even though it was masonry units rather than random rubble, the strength aligns with the guidance above, which is always reassuring. But what we need to consider is, for most of the readiness rules we're looking at, these have already stood for an extended period of time, and newbuild values should be enhanced to allow for the additional curing of the mortar over time. And this is best addressed by CS 454, related to appraisal of bridges used by highways. And another paper by the same people. So, this is an extract of the highways paper, and this has compressive strength of the masonry units on the right in stone, and to the same scale on the left is brickwork, and it identifies different types of bricks and different types of stone. And then, because we're looking for a pure- like a lime mortar, historic lime mortar, we're actually looking at this lower curve here.
But this is a good starting point for assessing the strength of the units whilst they're actually in use. Depending on the findings and your feeling about the sensitivity, it might be necessary to recommend testing to gain more confidence in your assessment. And then, I'm sure every engineer on this call knows all about this, but our current methods of modern standards uses characteristic design. So, we use the 95th percentile of a load as our characteristic load, and the fifth percentile strength for the resistance of materials. And provided your fifth percentile strength is greater than the 95th percentile of your load, your design is a success. So, just with that, what one needs to consider is, for the most processed materials, such as steel, we have a very low factor of safety. Oh, and apologies on this.
We didn't realize until this morning that Greek lettering isn't working, so the Gs that you can see here in a funny script are actually gammas. So, the partial factor for steel, which is very processed, is one, and then this increases as there is more uncertainty about the quality control and processes. So 1.5 for concrete, increasing for timber, and then masonry is at the highest level here. The variation in the masonry levels are to do with the use of category 1 and category 2 units, and the same foot for mortars. And with a historic building, you're never going to have a category 1 unit or mortar because it is to do with quality assurance and probably the paperwork. If there ever was any, it has long since been lost. But really, saying it's unrealistic, one also needs to look at the time served element of what you have, and whether it's working. And what you do if a brick has failed on the facing and crushed, you tend to replace it.
So, there's some element for thought on what one uses as one's material factor of safety, and the same for mortars. And then, there's further guidance on this in the IStructE's appraisal of existing structures, which again states that with sufficient testing you can review the partial safety factors. But quite often this doesn't happen, and it's eliminating a really large potential benefit. And then, it also reminds us that there's the opportunity... So, some of the factor of safety relates to chases and to the breaking out of repointing of mortar. So, there are potentials, particularly for ruinous wide walls of taking some benefit as chases that are less likely to be significant. Right. I'm quickly going to progress to guidance on loading. So, the main loads that we tend to worry about is wind loading.
So, here we have a stable block where there was a building in front of this wall which was removed, leaving a slender wall which initially was unmaintained, but has been maintained. And at the point where it was repaired, someone asked whether it was stable. Unfortunately, in a rural or country location, you can't consider the benefit of adjoining walls, even though it's clear to see that this garden wall to one side and the retaining wall on the other side are shielding the wall. But it is also possible with the ruin that you know the orientation and the size of it, and you can take those benefits if you wanted to do more, and have more certainty about whether it's stable, because you actually have the wall, you could monitor the wind speed and orientation, and the scale of movement at the wall tops to develop the actual relationship, which would eliminate the need to make assumptions in your design.
In terms of the changing environments, we're experiencing more frequent and intense storms, but there's little change in the maximum wind speeds. And whilst excess rainfall will have an impact on inadequately maintained ruins, if your ruin is well maintained, it should shed the water. Another thing just to reflect on with this is what we talked about earlier, about being able to activate the mass of the wall. And it's really how long a duration of a gust of wind you need to activate that wall to cause it to tip over. Our current standard uses a 10-minute mean wind velocity, but given that the density of brickwork is in relation to the density of air, the air is 0.07% of the density of the brickwork. So, how much do you need, how much wind do you need to activate it? Which I'm not quite certain about at this point.
Another area is plant action. And whilst abrasion and growth through a wall is really a maintenance issue, there are also below-ground elements, where if one has what to modern standards is perceived as inadequate foundations, you can end up with issues such as in this location on the left, where you can see the diagonal cracking, which on investigation was due to a tree root that had gone underneath the wall and was causing it to crack, and the wall to split. And another thing, which is earth pressure. Historic retaining walls are a whole different topic, but generally, with stability of walls, the main failure with earth pressure is the fact that ground levels have changed. In this instance here, it's probable that when this wall was built, the ground level behind it was at the same level as the pavement in front.
But over time the slope has flattened, leading to an earth pressure being exerted. And then, the last of the loading ones is verticality. In our modern design standards, we have a contingency for verticality which we use and tend not to think about. But actually, when you've got a ruin, you can measure what your verticality is. And you can either use a long spirit level, or if it's not very windy, you can use plumb bob, and then other alternatives are an EDM or laser scan. Laser scans are particularly useful where you've got elements such as this chimney on the right with a changing wall section, that's difficult to quantify just visually looking at it, the scale of movement. Right. Progressing to the method of assessment. What is important to remember when we're considering the stability of ruinous walls is that this is not looking at preserving finishes and other serviceability issues.
This is either it's failed or it's still standing. And so, on the left-hand side, we show a vertical wall imbalance. So, the stress underneath the wall is rectangular. As the wall starts to rotate, either due to wind loading on the side of it or softening of the ground under one side of the wall, the stress distribution goes trapezoidal, and ultimately, when it gets to the third the engineers often talk about, you get to a triangular stress distribution. Once you go beyond this point, it still stands, but one ends up with a very peaky stress, which in fact yields and gets more squared-shape at the characteristic compressive strength of the wall. This is shown on the left in figure 5.24. The IStructE masonry for the design of plain masonry and building structures, which I kind of struggle with. But this is showing an anti-clockwise tipping wall.
So, you've got the self-weight coming down the center, and then you've got the thrust block resisting it at the face of the wall. In my mind, I find this easiest to understand in the right-hand picture, which is from earlier guidance, which shows a clockwise failure with the lateral force and the gravity, and then the thrust block resisting just on that face. So, it's a tilting or toppling approach, not the design moment of resistance, which we normally use for more serviceability-type aspects. If one has a perpendicular failure, it's the same, but the only issue is that there is no gravitational resistance in the wall. Hence, whilst it works, it becomes difficult to prove at greater spans, which was why I said, what is a failure with this type of perpendicular rotation, and how does it affect your ruin? Right. Which leaves us on to questions.
Matt: Bridget, thank you so much. Okay, let's go over to the Q&A session. I am aware that we have little time left, so we will get through these as quickly as we can. For those of you who can't stay with us beyond 2:00, we apologize. But obviously, the session is recorded and you'll be able to catch up on the Q&A via the recording. If I could ask our presenters to turn their cameras on, please. Thank you, Jon. And Kim. And Bridget. Okay, Kim, I will hand over to you to field the questions. Apologies that you got a number of comments that are about the Venice Charter, which were comments rather than questions. So, we may or may not have time to reflect on those. But over to you, Kim. Kim, you're muted.
Kim: Sorry. So, I'm going to start right at the beginning, if that's okay. So, Jon, the point of no return, is this technical, financial or philosophical? And to what extent do you think that this phrase is a reflection on the observer rather than the observed?
Jon: I think it's probably a reflection on the observer, I think. Is there ever a point of no return? We could probably debate that for an hour. Is there always something that can be done to help it in the right direction? I would say generally, yes. I think it's a phrase that gets probably used and abused. I don't think there... I think there's rarely a point of no return. I think it comes back to this issue of: do something, don't do nothing. Because. Yeah. How do you define the point of no return? I don't think you can, really. It's a phrase that gets misused.
Kim: Super, thank you. So, concrete elements next. Does this not present issues with moisture movement within the heritage materials?
Jon: I think the... Again, one that could be discussed for a long time. I think the simple answer is no, because it's not used in such a wide spread. We're not pouring in, we're not advocating pouring in, flooding in concrete to historic monuments. It's areas where a clearly defined element of concrete has been used for particular reasons. So, in terms of its effect on the moisture, it is minimal, and in some instances can be actually beneficial by controlling where the moisture is going. It might be protecting it from getting to a retained timber element. So, I think no. I mean, any change affects moisture movements and moisture patterns. But again, with…
Kim: It’s a very small…
Jon: For the right reason and the informed reason, it's okay, but it's not advocating the use of concrete. I think the point of the talk was... It's looking at the whole palette of tools and techniques that can be used, and finding the right one, and informing why that one is the right one to be used.
Kim: Brilliant. The stability frame that you showed early on in your presentation, fixed to a ruin structure, how was that worked out?
Jon: Again, another one for a talk in itself. But it was- the issue with the building was a lateral stability issue through the central core of the building. There were four-story, very slender brick flank walls in the center area. The actual vertical capacity wasn't a concern. There were basements in the building. And the issue was that the two walls were independent and able to sway and move, and by dropping this braced frame down the central core, this four-story steel frame that was made and literally dropped in, we were able to stabilize, provide improvements, significant improvements to the lateral stability. And in the first instance, we were able to just hang the wall- hang the frame on the central walls, because there was a lot of collapsed material in the lower ground floor area and basement area, which we were then subsequently able to clear out and start moving forward with an overall stability scheme. So, I hope that answers that.
Kim: Brilliant. Thank you. Did you want to say a bit about contingency as well? And that was sort of a point rather than a question.
Jon: Yeah, contingencies.... Contingencies are… I mean, everyone wants to have a contingency, but actually, the key is using the total budget efficiently. I'm not a big subscriber to this, keeping a secret contingency, you know, away from the contractor, and being able to- I think the whole issue of collaboration and honesty, and everyone working to a fixed budget and getting the most out of that six budget is important. So, I'd almost say I'd rather not have any contingency, just know what the available funds are and use them efficiently. And this idea of splitting the project down into phases, which is what we've done on a few projects, and then knowing how each section of the work is going as to what you can then... You know, the confidence level of how the budget is being used and whether you... So it's almost the works themselves, elements of the work become the contingencies. If you've got to admit something to, you know, to pull back funds, if you've got something that you think, “Right, if that phase went well, we could actually do a bit more,” I find that that tends to be a better approach.
Kim: Brilliant, thank you. And then, if money were no object, how far could you go with an intervention? So, could you bring a ruin back to a usable building? But I think Notre Dame is the best example of that, isn't it? Bringing a ruin back into use.
Jon: I dream of one day having a project where money is no object, and time's running out. It's hypothetical, isn't it, really? And again, the whole philosophy of what you're trying to do, I mean, finding a use for buildings, someone had said about, you know, what is a ruin? You know, again, I touched on that at the start. You know, everyone has a different view of what they see as a ruin. You know, I looked at the... I think when I looked up the dictionary definition, it described it as a large white house falling into gentle ruin as the- as an example of its use. Well, you know, we know it's a whole range of different things to different people, so...
Kim: One for Bridget. What is the effect of core washing/loss on these failures, and how can they be assessed?
Bridget: Yes. That's part of the reason why my talk dealt with well-maintained walls, because core washing is an issue associated with where you get water ingress into the core, which leads to the washing out of the material, and bulging as it exerts a lateral force on the sides, which aren't tied back. So... It can't be assessed in that way, and does present a significant issue. I know our colleagues within the Building Conservation Team are looking at these bulging-type failures and how to identify them earlier. If it's a case where tying action needs to be reinstated to address it. So, it's more of a maintenance issue.
Kim: Brilliant. Brilliant. Your point about breaking out, could you just say that again?
Bridget: Yes. So, with the raking out of walls, of the masonry, obviously, that gets to a point where mortar is a sacrificial material. And once it's recessed by two and a half times the width of the joint, one needs to look at renewing it, otherwise, effectively, you're reducing the cross- sectional area of the wall, which is particularly relevant on modern buildings which have slender construction, and therefore the material factor of safety, a part of it being such a large factor in comparison to other materials, allows for that material to be renewed as part of its sacrificial use.
Kim: Does HE have guidance on vegetation removal and management? I think we do have a page on the internet. Maybe we can put that in the chat.
Matt: We will find that link and post it with the recording.
Kim: Super. Thank you, Matthew. And should we always remove vegetation, or can it be left in situ in some instances? And that's one for both of you, probably.
Jon: I would say, yeah. I mean, again, there isn't one-size-fits-all, and I think types of vegetation, we shouldn't see ruins just being cleaned back to some sort of pristine... There's a whole range of reasons why a level of vegetation is probably necessary and important. So, in simple terms, yeah.
Bridget: There's also balance. Like, if you've got an extreme head of vegetation that you then get windage issues associated with increased surface area for the wind to catch on. But as Jon says, if you've not got the opportunity to maintain, vegetation does help hold things in place, provided it's not being compromised and started to grow into your structure.
Kim: Super. And then, masonry anchor systems, did we want to talk about that, or is that potentially one for another day as part of a…
Jon: I mean just very briefly, it's another one of the range of tools that are available. You know, often ruins have elements of masonry that were in configurations that they were never intended to be in. So, you know, overhanging sets of masonry half a window is gone, or... So, there is some argument for using anchors to help stabilize those. But that's one for a talk in its own right, really.
Kim: And then, the final question: would you recommend that a program of maintenance should be included as part of any program of repairs?
Jon: Yeah, definitely. I think any works that are done, it is important that we don't walk away from the works at the end and then, you know, two years, three years, five years, it's back in the condition it was. And I think even during the works, an eye on how the building is going to be maintained. I think there was elements in my slides discussing where that thought process... It's no good leaving an element of structure that is almost impossible to maintain. That's not going to achieve anything. And particularly, the fact that it doesn't get maintained is going to lead to accelerated damage in the future. I think future maintenance is a really important part of any main phase of works. And it is part of our responsibility as designers anyway to have an eye on future maintenance, be it conservation, or any sort of construction project.
Kim: Super. I think we’re at the end of the questions there.
Matt: Absolutely fantastic. Thank you so much, Bridget, Kim, and Jon, for an absolutely wonderful presentation.

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