Conrad Speckert got in touch with me following yesterday's post (about single-stair buildings) and he was kind enough to let me know that, this Thursday, Toronto Planning and Housing Committee will be considering this single exit stair item.

Included in the agenda item is a building code report that was done because City Council wanted to know if it were feasible to design multi-residential buildings up to four storeys that wouldn't be detrimental to human health.

Now that the report is done, one of the recommendations being put forward this week is for Toronto to create a guideline that would help people prepare alternative solution proposals under the Ontario Building Code.

Alternative solutions provide greater design flexibility. We almost always have them come up on our projects. In essence, they are a way of saying, "yeah, I know this design doesn't precisely meet the code, but it still satisfies its intent, and it works, so please approve it."

In this particular instance, the idea is to create a public-facing guideline so that more people will be able to figure out how to build 4-storey buildings with a single means of egress. Again, the current maximum is 2 storeys.

Four storeys isn't quite six storeys. But we're getting there. And it has become increasingly obvious that it is now just a question of when, not if. At some point, we won't be calling this an alternative solution proposal. It will just be -- the way.

As I mentioned yesterday, I am not a structural engineer. However, my friend James Cranford is. He is Principal at Stephenson Engineering and he was nice enough to answer a few of my questions about soft story buildings (storey if you're Canadian).

BD: What is a soft (or weak) storey building? And why is it such an important design challenge, even in a very un-seismic city like Toronto?

JC: A soft storey refers to any level in a building that has LESS capacity than the level above. This means it has both less strength to resist loads and less stiffness so that it will move more than the levels above. Soft stories are one of the most significant challenges that many modern building designers face because they are one of the most likely ways that a building can fail catastrophically if not properly designed. A soft storey failure occurs when the building hinges above the weak level and the columns below can no longer support the load of the building above as they become overstressed and loaded in ways they were never meant to act. This leads to a sudden, often pancake type collapse that is likely to bring down the entire building.

We see potential soft storey issues most commonly in mid to high-rise residential buildings that have either amenity or retail spaces at the ground floor. These are spaces that by nature are large and as open as possible. During design, the structural engineer needs to recognize this and compensate for the lost capacity in other ways. This is usually done through a combination of increasing the capacity of the remaining walls and adding new walls at the weak level that fit with the building layouts.

BD: What does the Ontario Building Code mandate in terms of soft storeys?

JC: The OBC generally does not permit soft stories in any form for buildings where people are likely to live, work or play. In critical infrastructure like hospitals which must remain fully functional in the event of a major earthquake, the OBC goes further and does not permit any ‘lateral force resisting elements’ like shear walls or steel frames to be discontinuous below. This means that if you have a wall on the 5th floor of a hospital, that wall must exist with equal or greater capacity on EVERY level below, without exception.

BD: How much more stringent is British Columbia, where there is greater seismic risk?

JC: The requirements in the British Columbia Building Code (BCBC) are almost identical to those in Ontario in this case. However, the seismic design forces will be much higher based on the potential for much larger earthquakes, so while buildings will generally be designed for a higher seismic capacity, they must be proportioned similarly to prevent soft stories.

BD: Speaking generally, what is usually required structurally in order to retrofit an existing soft storey building so that it can properly withstand things like earthquakes?

JC: The most common way to retrofit a soft-storey is to increase the capacity of the weak level. In smaller buildings this can usually be achieved by adding new ‘lateral-force-resisting elements’ like shear walls or moment/braced frames until the overall storey capacity matches or exceeds the capacity of the levels above. On larger buildings this becomes more complex, as the loads are much higher and simply adding capacity may not be either feasible or practical. Therefore a full structural analysis is usually required to find a solution that can be tailored to the unique structural and architectural conditions. This often involves a combination of increased capacity and the introduction of ductile detailing which will allow the building to dissipate seismic energy. This can be roughly thought of as a ‘bend but don’t break’ approach to surviving an earthquake.

In some jurisdictions, the extreme risk caused by (many) homes built with soft stories has prompted local governments to intervene. The City of San Francisco (as well as many other municipalities in California) have enacted ordinances requiring home owners to assess and upgrade their properties, including single family home with garages a the lowest level, to reduce the risk of soft-storey failure in an earthquake.

BD: Thanks for this, James.

I don't usually do Q&As on this blog, so let me know in the comment section below if you found this one valuable and if you'd like to see more of them.

Yesterday it was announced that, starting January 1, 2015, the Ontario Building Code would be changed to allow wood frame buildings up to six storeys. Previous to this, the highest you could go was 4 storeys. 

This change has been in the works for a number of years. And it’s already allowed in most of Europe and in other places in Canada, such as British Columbia. So it’s nice to see this finally happen here in Toronto.

The reason this is a big deal, and worthy of a blog post, is that it changes the cost structure for mid-rise buildings. Simply put, wood frame buildings are cheaper to construct compared to reinforced concrete and other buildings materials.

Some people think this just means developers will make greater returns. But I don’t think that’s the case (see microeconomics). The real opportunity here is to spur mid-rise development on sites that – before this change – would have been previously un-developable. That is, you just couldn’t make the numbers work.

As much as mid-rise buildings make a lot of sense from an urban design standpoint, it’s not always easy to find good mid-rise development sites. Mid-rise buildings are generally less efficient to build compared to towers and you have a lot of fixed costs that don’t scale down just because you’re doing a smaller project.

So what this change in cost structure will, hopefully, do is allow more product to enter the market. And since many big urban centers operate with perpetual supply deficits – precisely because it’s often so hard to build – this should actually help with affordability.

Conrad Speckert got in touch with me following yesterday's post (about single-stair buildings) and he was kind enough to let me know that, this Thursday, Toronto Planning and Housing Committee will be considering this single exit stair item.

Included in the agenda item is a building code report that was done because City Council wanted to know if it were feasible to design multi-residential buildings up to four storeys that wouldn't be detrimental to human health.

Now that the report is done, one of the recommendations being put forward this week is for Toronto to create a guideline that would help people prepare alternative solution proposals under the Ontario Building Code.

Alternative solutions provide greater design flexibility. We almost always have them come up on our projects. In essence, they are a way of saying, "yeah, I know this design doesn't precisely meet the code, but it still satisfies its intent, and it works, so please approve it."

In this particular instance, the idea is to create a public-facing guideline so that more people will be able to figure out how to build 4-storey buildings with a single means of egress. Again, the current maximum is 2 storeys.

Four storeys isn't quite six storeys. But we're getting there. And it has become increasingly obvious that it is now just a question of when, not if. At some point, we won't be calling this an alternative solution proposal. It will just be -- the way.

As I mentioned yesterday, I am not a structural engineer. However, my friend James Cranford is. He is Principal at Stephenson Engineering and he was nice enough to answer a few of my questions about soft story buildings (storey if you're Canadian).

BD: What is a soft (or weak) storey building? And why is it such an important design challenge, even in a very un-seismic city like Toronto?

JC: A soft storey refers to any level in a building that has LESS capacity than the level above. This means it has both less strength to resist loads and less stiffness so that it will move more than the levels above. Soft stories are one of the most significant challenges that many modern building designers face because they are one of the most likely ways that a building can fail catastrophically if not properly designed. A soft storey failure occurs when the building hinges above the weak level and the columns below can no longer support the load of the building above as they become overstressed and loaded in ways they were never meant to act. This leads to a sudden, often pancake type collapse that is likely to bring down the entire building.

We see potential soft storey issues most commonly in mid to high-rise residential buildings that have either amenity or retail spaces at the ground floor. These are spaces that by nature are large and as open as possible. During design, the structural engineer needs to recognize this and compensate for the lost capacity in other ways. This is usually done through a combination of increasing the capacity of the remaining walls and adding new walls at the weak level that fit with the building layouts.

BD: What does the Ontario Building Code mandate in terms of soft storeys?

JC: The OBC generally does not permit soft stories in any form for buildings where people are likely to live, work or play. In critical infrastructure like hospitals which must remain fully functional in the event of a major earthquake, the OBC goes further and does not permit any ‘lateral force resisting elements’ like shear walls or steel frames to be discontinuous below. This means that if you have a wall on the 5th floor of a hospital, that wall must exist with equal or greater capacity on EVERY level below, without exception.

BD: How much more stringent is British Columbia, where there is greater seismic risk?

JC: The requirements in the British Columbia Building Code (BCBC) are almost identical to those in Ontario in this case. However, the seismic design forces will be much higher based on the potential for much larger earthquakes, so while buildings will generally be designed for a higher seismic capacity, they must be proportioned similarly to prevent soft stories.

BD: Speaking generally, what is usually required structurally in order to retrofit an existing soft storey building so that it can properly withstand things like earthquakes?

JC: The most common way to retrofit a soft-storey is to increase the capacity of the weak level. In smaller buildings this can usually be achieved by adding new ‘lateral-force-resisting elements’ like shear walls or moment/braced frames until the overall storey capacity matches or exceeds the capacity of the levels above. On larger buildings this becomes more complex, as the loads are much higher and simply adding capacity may not be either feasible or practical. Therefore a full structural analysis is usually required to find a solution that can be tailored to the unique structural and architectural conditions. This often involves a combination of increased capacity and the introduction of ductile detailing which will allow the building to dissipate seismic energy. This can be roughly thought of as a ‘bend but don’t break’ approach to surviving an earthquake.

In some jurisdictions, the extreme risk caused by (many) homes built with soft stories has prompted local governments to intervene. The City of San Francisco (as well as many other municipalities in California) have enacted ordinances requiring home owners to assess and upgrade their properties, including single family home with garages a the lowest level, to reduce the risk of soft-storey failure in an earthquake.

BD: Thanks for this, James.

I don't usually do Q&As on this blog, so let me know in the comment section below if you found this one valuable and if you'd like to see more of them.

Yesterday it was announced that, starting January 1, 2015, the Ontario Building Code would be changed to allow wood frame buildings up to six storeys. Previous to this, the highest you could go was 4 storeys. 

This change has been in the works for a number of years. And it’s already allowed in most of Europe and in other places in Canada, such as British Columbia. So it’s nice to see this finally happen here in Toronto.

The reason this is a big deal, and worthy of a blog post, is that it changes the cost structure for mid-rise buildings. Simply put, wood frame buildings are cheaper to construct compared to reinforced concrete and other buildings materials.

Some people think this just means developers will make greater returns. But I don’t think that’s the case (see microeconomics). The real opportunity here is to spur mid-rise development on sites that – before this change – would have been previously un-developable. That is, you just couldn’t make the numbers work.

As much as mid-rise buildings make a lot of sense from an urban design standpoint, it’s not always easy to find good mid-rise development sites. Mid-rise buildings are generally less efficient to build compared to towers and you have a lot of fixed costs that don’t scale down just because you’re doing a smaller project.

So what this change in cost structure will, hopefully, do is allow more product to enter the market. And since many big urban centers operate with perpetual supply deficits – precisely because it’s often so hard to build – this should actually help with affordability.