Good afternoon, good lunchtime, whatever this is, for wherever you are. Today I'm going to be presenting, as you may know, Material Selection Matters with a focus on six-storey construction and comparing the predominantly materials of wood or concrete. That said, in doing this one-hour short summary presentation, we're going to look at a range of materials from a fundamental perspective, look at some of the structural systems that are commonly used and perhaps why, with also some discussion of issues related to how you build them, material-related questions of how things are built. Again, the focus is concrete and wood. We're taking this sort of information from a bunch of places, that's what they're summarizing today, and I want to point out that although I work at a labs where we do lots of material tests, I also do a fair bit of new construction consulting and forensic investigations. That sort of combination is what's informing this presentation. We see the things that fail, we see the problems that are needed, both in new buildings during construction and buildings that are five or 50 years old. We're overlaying on this some mega-trends that affect all building construction details that I'll go into. The first thing is we're going to look at a little bit of that building science. This is like an engineering building science course for a second-year student, and we'll do it in about 10 minutes because the difference is that you might care, and so you'll learn much more quickly. Four things make most building materials deteriorate. Water and or oxygen are needed for both dissolution and corrosion oxidation. Exterior radiation is a really big deal for exterior components of the building. Either really high temperatures or very cold temperatures make materials begin to fail, and of course fire is sort of a rapid way of destroying a material. So those are the things that make building materials go bad most of the time. There are four categories in which you can put materials, and this is pretty commonly found in material science textbooks and such. So the metallic ones are pretty obvious, the steel, the copper, the lead, the zinc, the aluminum. The way these things fail predominantly is about corrosion, which is an oxygen slash water process. Another component of materials are polymers, and examples of polymers is that they break down under ultraviolet radiation and oxidation. It's not called corrosion in polymers, but they do oxidize when exposed to oxygen, especially at higher temperatures and in the presence of ozone. Natural polymers are actually relatively resistant to high temperature and cold. For example, wood is quite resistant. But natural polymers have a weakness when it comes to moisture. Manmade polymers such as polyethylene or polyester, etc., they get brittle when it gets cold, and they get soft and begin to oxidize quickly when it gets hot. And then the other category we have would be mineral or ceramic-based materials, and they're resistant to many decay mechanisms except freeze-thaw damage and salt. And finally, the fourth category of materials is composite materials, which is made up of a combination. Reinforced concrete is a classic example. The weakest link is what causes a composite to fail. The steel corrodes, causes a failure of reinforced concrete. Or the concrete freeze-thaws, causing a failure of the reinforced concrete. Similarly, glass fiber reinforced plastics. Typically it's the plastic that goes bad, but it can also be the glass. So just to show a few examples, here is a metal corrosion example. I want to point out that although materials have known characteristics, design is often the reason that we see most of the failures. Because one needs to choose the appropriate material in the appropriate design. So on the left-hand side, we see a masonry veneer being attached to a steel stud, and the masonry anchor is obviously severely corroded, and so is the steel stud. And that steel stud is protected by galvanizing, but steel studs in general are not intended to be wet in service. What happened in this project was the screw of that masonry anchor caused water to penetrate through the water-resistive barrier. The moisture that resulted after several years, and this is actually only after three or four years, caused the exterior gypsum board to fall apart and corrosion to occur. So it's hard to know whether this is actually a material failure, or if it is a failure of not appropriately using the right materials to manage moisture, or if you don't manage moisture, use the right materials. On the right side, we see an image of a hot-dip galvanized steel railing. This system obviously has been chosen to be corrosion-resistant, and it's quite appropriate for an exterior application. However, the design flaw in this case was the fact that someone chose to use weld as a connection between the picket and the base plate. And of course, by welding, the zinc corrosion protection was removed, and corrosion resulted. And of course, that corrosion is exactly at the most highly stressed part of the guardrail. Now where many solutions would be available, probably the best solution would be to have a bolted connection at this picket to base plate. Another option would be to shop-weld, then hot-dip galvanize, and bolt the base plate to the concrete as opposed to cast it in. And even another, the sort of least but minimum solution would be to use a zinc-rich primer to paint over top of that weld. So another sort of examples of metal corrosion and their consequences, upper left we see copper corroding, needing a lot of repairs at spots. That roof, however, is 100 years old, or just shy of it, it's 96, 97 years old. And so it's probably done its job. On the bottom right, however, we see a brand new zinc roof, three years old, already showing through corrosion. Zinc is not inferior to copper in terms of corrosion resistance. The difference between the two is that the way that the zinc roof was installed, it was directly applied over a membrane without enough of a gap so water could stay stuck between the water-resistive barrier on the roof and the underside of the zinc roof. And the left, we see another type of failure mechanism. Although the corrosion of that lintel is severe, the reason damage has occurred is because of the expansive forces of corrosion. So I mentioned polymers decaying due to UV radiation, high temperatures and oxidation. Those things completely come together when we talk about roofs. Ultraviolet radiation has enough energy in it and the proper wavelength to be able to penetrate into carbon-hydrogen based polymers and snip those long chains that make up a polymer into shorter lengths. This makes the material weaker and more brittle. At the same time, heating up these roofs, whether it be a rubber roof or an asphalt roof, if you put your nose this close to a roof on a warm summer day, you will smell the asphalt being given off. You will be able to notice the rubber breaking down. Those molecules leaving the roof for every sunny hour mean that the roof gets smaller, literally. It loses matter and hence there's shrinkage. Combine that with a weaker polymer and you get cracking, brittleness, shrinkage, as we see as a common end-of-life condition in an asphalt roof that's exposed to the weather. Of course, one of the ways we've learned to protect asphalt from the weather is to cover them up with a mineral-based material. Typical asphalt shingles or just skip the asphalt entirely, move to, say, concrete tiles or terracotta tiles, and now you have an intensely UV-resistant material, a material that could care less about ultraviolet radiation. The most common polymer, and one of the focuses of this talk, of course, is our wood-based polymers. And wood is a carbon-hydrogen polymer, just like polyethylene, but it is a little bit more complicated, as one can see from the formula shown at the top. So really it's basically a form of sugar that has been made more resistant by adding a couple of hydroxyl ions to the end, and they're still susceptible to UV radiation. That's why, if you look on the right-hand side, that's a fence post in southwestern Ontario, Canada, which has been exposed to the weather for 60 years. Now people who build fence posts in farm country know often to put sloped roofs on their fence posts as a way of enhancing life, and it certainly has worked here. But what can't be stopped is the fact that the UV radiation breaks down the wood and results in a grey patina, as you see here. It also causes some of that shrinking effect, causes some of the material to break down, fall apart, and that's why we see the cracks opening up and the shrinkage. I wanna point out, 60 years exposed fully to the weather. On the left-hand side, we see a building that is less than five years old. It's using wood and a wood product called OSB, which isn't wood. It was wood once, it's no longer wood. It's the Chicken McNugget, I guess, of wood products. And so we've covered that up with a water-resistant barrier, rightfully, to protect it from moisture. However, as is not uncommonly the case, by not having proper design and construction details, water leaking in from the window above is trapped behind that house wrap and being held up against the wood at the bottom of the image. And that's why, within a few years, we can cause much more damaging rot than an exposed fence post after 30, or sorry, after 60 years. So when we talk about mineral-based materials, free-thaw damage in cold climates, mountainous areas, et cetera, is an issue. Not a problem in many parts of the warmer parts of climates in the United States. But it is a problem where you have freezing and thawing in water. And in this case, the reason this brick is failing is not because the brick itself is a problematic product. It's used widely in this area where this photograph was taken with success for several decades. The reason is the lip that you see at the bottom, the asphalt-coated lip, allowed water that ran down the wall or melted from snow to sit at that level to be forced into the masonry. The masonry, therefore, was saturated in fall and early spring, and therefore, free-thawed damage occurred. Had that brick been aligned with the face of that asphalt, no problem would result, which was evidenced by literally the same building in spots where the brick came out. There was no problem. So design and construction details really can matter to how a material responds. So the fundamental principles of the material you can't fix, but we can change our design to accommodate those materials. We often have problems with operation as well. If you're going to be making a concrete today, you will often be using air entrainment to impart free-thaw resistance, and that works really quite well. However, salts can still cause a problem, and salt is something that is applied for de-icing reasons or industrial reasons, and the salt gets dissolved in water. The water with salt dissolved is absorbed into the porous materials, and then at a subsequent time, the water evaporates, and it leaves the salt behind inside the pores of ceramic materials, concrete materials, et cetera. When those crystals reform into solid shapes, they create a massive bursting force, much more so than free-thaw. So you see salt scaling on the left and the right, which is an operational issue of these concretes weren't done badly, but excessive amounts of salt were added along with ponding water to create the issues that we see here. I'm going to go straight into some now trends, given that backdrop of materials and design and operation, to look at what's happening in the world of buildings. There's a number of trends going on, which we could talk about, but I'm going to focus on three of them. Faster construction and design cycles, we're seeing higher density, mid-rise, multi-use buildings mixing retail at ground floor, office, hotel, or residential above, and we're seeing a demand for better energy performance. Codes are demanding better, clients are demanding better, resulting in things like the need for more air-tightness, the installation of continuous insulation, or CI, being mandated in places where it's never been used before, like California. We also see things like congested sites, we're not just building on big open fields anymore, we're actually building urban infill, we're using abandoned industrial lands and rejuvenating them to create new buildings, but again, not a lot of room to work. We're seeing demands from both the cities and municipalities and some owners to create things that are resilient in the face of things like Hurricane Sandy in New York, Hurricane Katrina in New Orleans, and this means that we start thinking about buildings differently, how will they respond to floods, windstorms, long-term power outages, et cetera. As owners hold on to buildings for longer, this is particularly the case in institutions, but even some long-term institutional investors, we see an increased focus on how much does it cost to maintain, upgrade, and renew these buildings, and this is becoming more of an issue in North America as our building stock becomes older, becomes more needy of upgrades and changes. So that design becomes important, and many people can talk about other trends that are going on, and many things are changing in the industry. So to look at the faster construction, one of the things obviously that does is it puts schedule pressure on, so we have to build more quickly, and as a consequence, we tend to build all winter, we tend to build all summer, we tend to build in the rain, but we tend to build in all kinds of weather. In the past, our forebearers often knew to say, this is crappy weather, I'm going home, but we're not allowed to do that anymore, we have to keep going, and as we build in these all kinds of weather, too hot and dry, too cold and wet, we then quickly close up the building because we're in a hurry, and as a consequence, substrates such as concrete and wood get covered over with finishes that are vapor impermeable, like rubber flooring, or ceramic tiles, and we've seen a tremendous increase in problems with things like that, which go back to a change in practice because of faster construction demand. With higher building density, we see that there's more of a challenge for all types of building enclosures and interior separators. We need better acoustic separation, we need better fire separation between us and the building that now may only be 20 feet away, or maybe 6 feet away, or maybe 0 feet away. As we build higher density, we build taller buildings, and this means that we have to worry more about fire protection during construction, so as we know the build time will be longer for a 20-story building than a 3-story building, that means there's more time during construction that fires can occur, and it's harder to do fire protection because you can't just reach it from the street. We see more challenges with wood shrinkage, as you go from a 2-story building out of wood to a 6-story building out of wood, your shrinkage increases by a factor of 3, and so movements that in the past could be ignored today result in windows being bent out of shape, toilets being pushed off their flanges, fire risers causing gypsum board to crack and crush, and of course we also, because we're building taller, see higher rain and wind loads, and that means that the technologies, materials, and procedures we use to build a 3-story building are no longer applicable for a 6-story building, which sees more wind and rain. So an example of the kinds of housing density we're seeing, this could be made out of pretty much any commonly available building material, but it does mean that we have more challenges with fire separation, setbacks, and so on. And then there's obviously energy performance as an issue, demand from codes and customers, and what's interesting now is as we see more complex and larger buildings, they are also worth now doing computer modeling, hourly annual energy modeling, to show code compliance. This means that owners are starting to get information during the design phase that says this building will use X amount of BTUs or kilowatt hours. Then they operate the building and they find out that they're not using X, they're using Y and it's a very different number than X. And this feedback loop has started to occur with owners getting a better sense of, well, what did we actually think we were going to achieve and why is it so different in actual practice? And so that's turning some of the questions to not just how do I meet the code, but how do I make a building that actually delivers performance? Of course, energy performance, much like durability of materials, is both a system and a design issue, not a material issue. It's not about how much insulation, it's how you install it, where you install it. And this is why the terms like continuous insulation and air barriers have gained such prevalence because we know those are the low hanging fruits as a way of improving energy performance. Now, one can't talk about energy and concrete without mentioning thermal mass. And there are real benefits to thermal mass, particularly in climates that are milder with temperature swings that are wide or temperature swings that are close to interior room temperature. So a lot of desert regions in California, regions in New Mexico, Arizona can see some pretty tremendous benefits from thermal mass. However, the challenge is it's hard to understand and predict. And it depends intensely on the building occupancy and the outside climate's variations as to how much of a benefit you get. So the building codes, ASHRAE 90.1, for example, Title 24 in California, do benefit mass walls a priori. You don't have to do a lot of detailed calculations, but it's often hard to see that benefit outside of the code numbers without detailed modeling. Another thing that has raised its ugly head over the years has been an increasing interest in embodied energy and embodied carbon. And this is because as people become more concerned about energy use and carbon emissions, they ask rightfully, so how much energy is used, how many emissions result from the manufacturing and construction of the building? So this has created a whole bunch of studies. It's often too onerous to do this for an individual project, but as research studies of generic buildings, there's lots of information in literature that's out there. And general answer tends to be that given the relatively high energy use and the lifespan of 25 to 50 or more years of operating a building, the actual energy upfront is a relatively modest amount. Now as we move to really energy efficient buildings, or if you're doing really energy efficient in a mild climate, the embodied energy and carbon does become more important. Although for the vast majority of buildings in the vast majority of locations, 80 to 90% of the total energy and emissions occurs during the operation of the building. What that tells us as designers is that we need to focus on making sure the building is energy efficient without having to worry as much about the energy embodied in its construction. So with that background, let's start a little survey of the materials and structural systems we have available. It's hard to have a conversation about what structural systems to use and why without understanding that different occupancies have different needs. Residential buildings, by their very nature, have relatively modest size of compartments, maybe 20 feet in one direction by 50 feet in another direction. And those compartments, called apartment units or townhouses or whatever, want to be separated from their neighbors, from fire, sound, and odor. And so the actual structural system choice is often driven in multi-unit housing to say, how do we get great internal partitions? And the performance of things like concrete and concrete masonry units versus lightweight hollow systems of framed steel and framed wood studs. In office buildings, wide open flexible spaces are valued, big chunks for flexible installation of services that can be added and removed as the tenants change, results in very few vertical partitions and pretty good horizontal partitions between floors. Concrete or steel floors with concrete on top of them to provide fire separation, acoustic separation floor to floor, and almost nothing laterally other than stairwells and elevator cores, again, routinely done with concrete. In retail, we have very few partitions and we know that we're going to have lots of churn and therefore we don't really want a lot of fixed heavy duty walls and we don't care too much about sound separation. And as a consequence of those sorts of different drivers for different occupancies, we've seen wood frame housing being used for low-rise single families with occasional three-story type multis. We see masonry construction for low and mid-rise institutional and when it gets to higher loads, we see a lot of concrete, especially in institutional investor-owned buildings, and steel frame tends to be in low to high-rise commercial with much less in the institutional market. And these choices really were made for a lot of good reasons if we're talking about the average choice made over thousands of buildings over the last few decades. So because high-rise buildings are exposed to higher wind loads, higher earthquake loads, require higher fire resistance because it's further from exits, and because it's more difficult to repair and replace, we have higher durability expectations. All of that has driven materials and systems that can meet that. Now none of the material properties I've talked about with respect to mineral-based, metallic, or polymer-based have really changed in the last hundred years, they're sort of fundamental to nature. So why are we seeing people re-evaluating the choices they make? Well primarily this has to do with those big trends we talked about at the beginning. People want to build faster, higher speed, they're worried about dwindling labor and more expensive labor, more demanding energy requirements, and higher performance expectations over the long term. And so these changes mean that building designers need to modify their structural systems and partition choices to meet more labor-efficient construction. Often that means things like prefabrication, to limit the amount of work on congested high-intensity sites where we don't have a lot of room to work, and to be able to get better speed and more weather insensitivity. Of course, precast concrete was the first and original prefabricated system that did all of this. That was one of its reasons for existence. And that need of a prefabricated weather-insensitive assembly system is greater now than it has been before, and so precast is well positioned for that. Similarly, with taller buildings we have better need for fire and sound, for more efficiency we need more insulation. And so those types of things also lend themselves well to what the precast industry has to offer. So obviously with single-family housing, the solution to a fire is run away, and that's actually quite reasonable given it's easy to get out of a two-story building, and the fire in that two-story home won't spread to the neighbor because we provide a large enough gap. Similar solution to sound, just provide 12 feet, and as we get to higher density, we are seeing very few buildings with 12-foot separations, they go down to 6, then they go down even less, and then you have to start worrying about fire separations. And eventually in the townhouse, you actually start needing to use things like concrete walls between the apartments if you want reasonably competent fire and sound separation. We use hot-rolled steel frame in a lot of low-rise buildings, but one has to realize that a steel frame does not provide any separation. You have to build all the partitions, exterior enclosures, and interior partitions. And that means that we also have to add the cost of fire. So if you're comparing apples to apples, you have to realize it's not just the steel frame, it's also the steel frame plus the enclosure, plus the interior partitions. Now in low-rise, say office building, speculative office building, one can build such a system and may not be as worried about long-term durability of the system. You don't have to worry about fireproofing because we're far enough away in a suburban setting, and so we have a lot of options that may be low-cost. Where one needs better fire protection, because we're close to our neighbors or we're building taller, we can use site-cast concrete or concrete of any type. And those sheared walls that we would often use for concrete separate vertical bearing walls and the floors that we would often use for partitions floor-to-floor are excellent fire and sound separation. Of course, pouring concrete on the site is sensitive to cold weather, sensitive to hot and dry weather, sensitive to rain, etc., and you need a fair bit of repetition and formwork to be economical. That said, this is widely used as a way of doing buildings that last a long time while providing good fire and sound separation. And you can see in this picture, the top floor under construction is tarped so that we can provide winter heat at a time when the temperature might be dropping to the 30s and so needing a bit of extra heat. Concrete masonry provides all of the benefits of concrete with perhaps more flexibility because the units are smaller, but this results in labor and it still has weather sensitivity. One of the new kids on the block are insulated concrete forms, which try and manage the weather sensitivity of pouring concrete in cold or hot weather by using insulation as lost formwork, protecting the concrete core from excess of cold or drying, and also then allowing the insulation to be part of the finished building enclosure. These systems can work for relatively high-rise buildings. I mean work technically and economically, provided there be some rigor applied to the architecture to not have very large horizontal openings in the form of windows, etc. Of course, architectural precast, as I mentioned, one of the original prefabricated system, allows one to provide a fire-resistant, UV-resistant exterior finish that is actually also part of the full enclosure by adding windows and insulation. We don't have to have a certain textured finish. There's a wide range of finishes, including metallic paints, very interesting laser-cut form liners, and of course, brick and stone finishes, as shown here. We know how to build those prefabricated panels in such a way to ensure really good air-tightness and pretty much any R-value that you could practically want. And because it's prefabricated, this type of system can be erected in very tall buildings in pretty much any kind of weather very quickly. So sandwich panels take that architectural precast one step forward by actually making sure there's an interior concrete-wide as well as an exterior concrete-wide with insulation built in. This is an example in northern Canada where labor is very expensive and the building season is only about three months long, and so this was an obvious solution to this owner's need to get some high-density, multi-unit residential buildings built. And so within that tight window, with a limited amount of labor on site, these panels, which were cast with windows and finishes in situ, in the factory, I mean, so that they could just be lifted into place, meant that the total precast system could be erected very quickly and meet those constraints. Now, total precast as an architectural panel, single-wide, is also effective. You can see here, this is a building in my hometown where we have a concrete load-bearing exterior skin with punched windows, shear walls, elevator core, stairwells. The whole nine yards is done as a precast panelized system. And so this provides good fire and sound separation, provides a structural solution, as well as providing the partitions and enclosure. So this can be done and built pretty much all year round, even in a climate where we will often get snow, rain, or sun, sometimes in the same day. So when we talk about tall wood buildings, these are the new sort of high-density responses. Cities want to have higher density. Cities want to see more buildings built that are three, four, five, six stories high, as opposed to one and two. And they want them closer to their neighbors. So one can try and use wood, and that's the new thing. So there's a number of categories of tall wood. We're gonna focus on the wood-framed systems, which go four, five, six stories high. And those have been now accepted by some code jurisdictions as structurally okay. You just need a structural engineer to sign off. For newer types of systems, over six stories, we have something called cross-laminated timbers, which I will demonstrate to you. I'll just give you some quick photos. This is quite a different animal than six-story wood frame, although it does let one build as high as you pretty much practically wanna go. RDH is currently involved in the 18-story building in Vancouver that's just finishing construction right now. Post and beam was used in the turn of the last century. We would have 16-inch square Douglas fir columns, or at least 12-inch square, and that would let us go four, five, six, seven, eight-plus stories. Today those 16-inch square Douglas fir are not available, and so now we can make them out of glue-laminated timber, although that adds to the cost and increases moisture and fire sensitivity. And, of course, we could use a concrete frame with wood infill. This is done in places like, say, New Zealand or Germany, but rarely done in North America. So as an example of a standard, classic, new development, here we have a concrete podium, which contains a combination of retail and parking, and that is a fire and acoustically separated from the wood frame residential up above. And that concrete, of course, is deliberately chosen to provide a solid base that is fire proof and fire resistant so that the wood framing above. So four stories on one-story podium. We're seeing buildings like this being built pretty much everywhere urban development is occurring in North America right now, whether it's Austin, Texas, or Washington, D.C., San Francisco, Seattle, Portland, Calgary, you name it, that's where we're seeing it. So we've also now seen buildings going as two stories of concrete with five stories of wood on top, and almost every combination thereof. And this trend started maybe about 10 years ago, and lately there's been a fair bit of it and we've gained a lot of experience about what works and perhaps more experience in what does not work. First warning to provide is that this is not like building a three-story townhouse. It is actually quite different, and this means different for everybody, whether it's the framer, the code official, the moisture consultant, energy consultant, the city, we have different concerns and there's quite a bit of a learning curve to figure out these different things. And let me give you an example. These are the first floor of six-story wood frame buildings in Seattle. And you can see that although theoretically I only need to use a double two-by-six every 12 inches to take the structural load, if I wish to have windows and patio doors, just say that were to happen, I actually have to put more wood around those openings. And you end up with, as you can see here on the left side, seven pieces of wood with an eight-inch spacing followed by five pieces of wood and five pieces of wood, eight-inch spacing, seven pieces of wood. The reason all that wood matters, well first it's just a lot of work to put it together, but also if water gets in between those laminations of wood during construction, it dries out quite slowly. And of course people don't want to wait for it to dry out. They want to line the inside with gypsum board, paint it, and put some cabinets on the wall. That kind of thing can trap moisture in those laminations and cause structural decay. The other challenge is that on the right-hand side, you'll see that those red dots there is that we've had to come up with ways to anchor these tall but narrow wood frame walls to the foundation. In the past, the buildings were never tall enough for their width to need too much anchoring. Now we have all these structural connections so that the building will not rock off of its foundations in windstorms and seismic loads. And when we started this, the industry started using threaded rods, and the loads were high enough that as you can see they would use these squash blocks of four by sixes sitting on a couple of two by sixes to transfer the load from that threaded rod into the wood frame. However what was quickly noted was that when wood shrinkage occurred the originally tightened up threaded rod suddenly was no longer tightened up and so several companies created structural springs which is what that red stuff is. So you torque up that threaded rod to a certain number and when the wood frame shrinks it moves downward that spring continues to keep the same force on that rod so the building doesn't rock and roll. So this is an extra level of concern that the structural engineer has to apply and people have to check to make sure it gets done otherwise you get creaky buildings with cracked drywall. Attaching things like masonry cladding to buildings becomes difficult. You have to start now interfacing between say steel lintels and steel beams over wide openings to be able to get the capacity that you want in the thickness you have and the connections become challenging and oftentimes people are relying on bolts into solid timber that are not very reliable if those bolts were ever to get wet or if the wood was to ever shrink too much you will split the wood. So there needs to be a lot of focus as soon as people start attaching pieces of steel to pieces of wood the wood moves the steel doesn't. Lots of challenges there. We also find that we need to be quite a bit more careful about how the building responds to wind and rain. The experience in wood frame construction and there's lots of it has been two stories three stories and now when you get to five and six stories there's a lot more wind and a lot more rain. What that means is that the the systems used for air tightness and water control that were developed and we have experience of in low-rise housing no longer apply. When you get to those higher wind loads and they're in the order of a of two to five times more so quantifiably a two-story building with an overhang in a suburb will have maybe one-fifth the wind and rain loads as the top story of a six-story building with a low slope roof. So there's a big difference in what kind of materials what kind of quality assurance programs you need what kind of systems you're going to design for. So this is only a four-story building but already you can see that the membrane that was installed for air and water tightness is getting ripped off and torn apart by wind exposure and this is actually turns out to be a relatively expensive problem during construction. So we would recommend we use a fully adhered membrane like one would use in commercial construction to deal with this of course that cost more money and so then the first time they build these buildings it's always all do the same thing we do for houses and she have a loose laid membrane like this and then it gets windy and then they find that the cost of going up on a lift truck to fix these types of problems is quite extensive it's not like a house where you get a ladder and throw up against and put some tape on it and so doesn't take long before the builder says you know I think it's cheaper if I use a fully applied membrane but it changes the materials and cost structure. Now I mentioned that if we wanted to go quite a bit higher or deal with much higher loads the wood framing doesn't really make a lot of technical or economic sense and so we start seeing cross laminated timber which is kind of like sheets of plywood on steroids instead of 1-8 inch lambs that go cross each way we see you know three-quarter to one-and-a-half inch laminations of solid lumber going in alternate directions these panels typically up to say 8 by 40 some feet long are actually a lot like precast concrete slabs and you can cut out openings for windows and doors and structural connections they are also much more expensive than using wood framing but they have to they have a really some interesting challenges that go with them one has to be a little bit careful not to get them too wet looking at the photo on the bottom left there you can see that there are cracks between each of the boards that are used as these laminations and when that slab on the right gets rained on because occasionally people build buildings and they get rained on the water instead of running off the side will actually run into each of those cracks into the wall into the floor and then laterally to the next crack and then down and laterally crack so they basically soak up water into the CLT and so one has to have a good construction moisture management protocol to a make sure that you get the water off the surface as quickly as possible before it goes into the cracks and be checking with moisture pins to make sure that the wood dries out before people try and put flooring on the top and drywall on the bottom. University of Waterloo where I teach in the School of Architecture and Civil Engineering we we've got a research hut and one of the projects we did recently in response to the industry needs was testing a bunch of little chunks of CLT which we pre-wetted to levels that were observed in the field and then investigated different membranes that could be put over them in different insulations that could be put over those CLTs to see if we could develop a way of predicting drying of these CLTs and it totally demonstrated that there's a right way to do it and a disastrously wrong way to do it and so one has to be careful of just putting vapor barrier type membranes over top of CLTs that have exposed to rain but one can use vapor permeable membranes and vapor permeable insulation and get away with this in most places. Now many people have probably heard of the 7, 8, 9, 10 story CLT buildings but there are actually very few of them. Most countries have like one or two showcase examples. One of the reasons is that it really isn't that easy and it really isn't that cheap but we definitely can do it and it's certainly an engineering challenge to be able to sort out all of the construction and technical issues but although we can build these buildings the real question is should we and that's a question that's got to be answered on a per project basis but we should go into it with eyes open which is part of what this presentation is trying to provide is that there is definitely complexity to manage in all of these pieces. There are new things to learn about like hold downs. There's a lot to deal with in terms of construction moisture, shrinkage movement immediately after construction and fire control during construction. So another picture from Seattle here. One of the ways to manage moisture is to remove the sheathing and replace it with something mineral based like in this case glass-faced gypsum. However as you can see the framing inside this building you can imagine if you have a heavy rainstorm right now that water is going to go from floor to floor to floor wetting all of that framing both in the floors and in the walls. This is less of an issue when you're building two-story buildings because the window during which the roof is not installed was limited. You only had to build two stories and the building was smaller. Now that you build four, five, six stories by the time the roof gets on you've had a much longer time span, often months of course, in which case it's almost a certainty you're going to get rain. The only question is how much, how often. And even in places where it snows this becomes a problem because the snow sits there, the sun comes out and you end up with the same problem. So some of the examples we've seen in the field in forensic investigations, this is an example of a building in the Pacific Northwest where two layers of three quarter-inch plywood were used as a way of providing a strong structural diaphragm. And during construction this roof floor got rained on and so the water would go into the joints between the plywoods, run laterally before it would run out the other side soaking up all the plywood. And of course it was finished and within a year people knew there was mold growing in between the pieces of plywood because it was built quickly, without sufficient control of water getting in during construction and getting out afterward. As a consequence of these moisture concerns there is a push in the countries that are trying to build these bigger wood buildings to provide better site protection during construction. So on the left-hand side there's a couple of photographs from Finland that demonstrate a system where they actually put an entire tarped structure over the entire building and then use a lift frame to lift it up as construction goes on. Now while this is not inexpensive, it claims that it actually greatly improves construction speed because they have fewer lost days and they have fewer construction drying needed and so on, moisture defects and so on to repair. So but again in terms of comparing apples to apples one needs to know that this kind of a approach may become necessary particularly in places where it rains a lot like the Pacific Northwest and along the East Coast a fair bit as well. On the right-hand side there's a project RDH did the building enclosure for in Prince George, British Columbia and Canada, a place where it actually does rain a lot when it's not snowing. And so here the effort was put into tarping all the walls as you can see in the bottom right but it was still we still didn't have the ability to convince people to put a floating roof over top of it and moisture management of the CLT floors was a challenge and needed to be kept on and did change construction cycles and construction techniques to ensure that we had good performance. Now it's important to recognize that wood can shrink a lot across grain. Along the grain, e.g. along the length of a wood stud, there's very little shrinkage but across the grain the shrinkage is quite a bit and so if you're putting in wood that is in the 18 to 25 percent moisture content range and then having it dry out in the middle of summer you should expect some significant shrinkage and the 3 to 5 percent is quite normal. That means that turns into if we look at a typical floor joist double top plate single bottom plate into half an inch to as much as an inch of movement and so if we stack up multiple floors that means that we end up with multiple inches of movement between construction wetted lumber and dry operating conditions. The right-hand image shows what happens if you were to say put balconies on posts on the outside of the building. You install it with a 2% slope out and you end up with a 4% slope in after two years of operation and that sloping in means water gets driven into the patio doors the joint between the wall causing water to rot and decay and all kinds of mayhem. But we also get problems with elevators stops not lining up so you got a six-story building with an elevator in it, top five floors are wood, the wood shrinks four inches between start of construction and end, well the elevator no longer will work and you have to come in and adjust it three times in the first year to get it to actually stop at the landing. Or fire hydrant risers so you have a six inch steel pipe runs full height of the building if the building shrinks four inches you better allow it to move or it'll punch right through the roof and it'll rip hose cabinets off the wall. I know this because I have seen this. So there are some interesting things that will happen if you have a plumbing riser without swivel joints you can cause the toilet to be pushed off of the floor ripping the caulking off of the ceramic tile and the toilet will rise up off the floor by an inch or so or more depending on how you manage that movement. So there's a lot of things to really think about as we go to these taller buildings those movements accumulate from being handled by normal details to not being handled by normal details. So we need to develop new and better details. So another challenge that we have faced is that if people switch cladding over the height of the building and in today's architecture I'm not sure which building doesn't change cladding over the height of the building. The classic example would be a masonry veneer for the first three stories to avoid structurally connecting it back and then maybe another two stories of fiber cement panels or something like this and the flashing at the bottom normally detailed to direct water over the masonry veneer turns from being sloping and ripping water off to turning into a gutter that collects all the water in the top story and feeds it into the joints in the flashing with obviously disastrous results. As an example of some of the details that we've needed to actually develop this is a detail from a Seattle project where the masonry is held down from the window several inches and the architect needed to design how to make that look good in the end it really did but that allowed for a sliding joint so that at the top floor or the fourth floor the amount of shrinkage that occurred at that wood framing would be accommodated by a sliding joint that would maintain its water tightness even though it would shrink in the middle of summer and probably grow a half an inch or more in the middle of winter. During construction fires never were much of a problem until recently with these wood frame buildings. We always had a problem with asphalt roofs being installed with open torches on wood frame buildings but as we started to see four, five, and six story wood frame buildings we've seen some pretty interesting fires happening and so you know people are starting to come up with fire plans which are kind of common sense as soon as one recognizes that this is a difference between a concrete building and a wood building and so this sort of, in these images here, what we would do would be well first of all you need 24-hour fire watches, secondly you need to make sure your standpipe goes up with the building so we have access to standpipe water, it's useful to break buildings in large buildings of spatial extent into phases so that if a fire occurs in one phase there's a fire block to others that can survive a construction. Once the building is built the fire risks go down quite a bit provided that the gypsum board and the fire sprinklers and alarm systems have been put in. However, that said, a recent study for the insurance industry of mid-rise wood frame buildings and concrete and steel buildings and their insurance costs do show quite an interesting result. If there is a fire in a building, ten percent of steel buildings and seven and a half percent of wood buildings are damaged and or demolished, sorry, they can't be repaired, they're demolished, whereas only a little over one percent of concrete buildings are demolished. So this tells us a fair bit about the resiliency and the asset value that you might have and there are also, this report is available online, there's also some interesting numbers in there about how sensitive some buildings can be to say plumbing leaks. So when you have a plumbing leak and the water runs down three stories, how much gets damaged? You know gypsum board will always be damaged but what about the wood framing? How much does it cost to dry that out? And that kind of insurance costs are slowly being recognized by the insurance industry and will result in higher premiums and often premiums for first time multi-unit residential building owners, people who buy condominiums or need homeowners insurance and rental that didn't know about this in the past. So, you know, summary is that there's a lot going on in these changes and a lot of reasons for these changes but what we can say for sure is that let's understand that different material categories have different properties and because different kinds of projects, residential, commercial, institutional, retail, etc. have different needs, we should be trying to find the best solutions for them. Combining those, understanding the materials, the designs and the different projects and so although we have the technical ability to mix and match any kind of material with any kind of occupancy, that doesn't mean that the best material is the one that you could make work. There are alternative choices we have to think about and so design is an important aspect and design will have to change for six-story wood frame buildings but we also need to make sure that municipalities, owners, code officials, inspectors, etc. recognize there are fundamental differences between a concrete structure and enclosure and a wood one and they require different levels of attention and detail, different levels of quality assurance control and different levels of insurance operational rigor, etc. So that's it for me right now. We have a few minutes for questions and I was going to

material selection

wood

concrete

six-story buildings

structural systems

fire resistance

construction speed

wood frame buildings

emerging trends