5 ms·

3 is called "soft story" and is something San Francisco now requires be fixed or the building is red-tagged - no grandfathering of existing structures is allowe

3 is called "soft story" and is something San Francisco now requires be fixed or the building is red-tagged - no grandfathering of existing structures is allowed. Buildings like this are all over Turkey, parts of Central & South America, etc and just as you mentioned the soft story (usually the ground story) tends to collapse causing the building to pancake. It's still popular because it's easy to put parking or a commercial (large open space) on the ground floor for density.

wahern 4y ago
The deadline for remediating multi-family soft stories dwellings in San Francisco was 2020. But this only included buildings with 5+ units, or buildings with a commercial space on the ground floor. There are still many residential buildings, including multi-family buildings (< 5 units), with these 3- or 2-wall soft stories, and there's no mandate in place going forward, AFAIK. The fix is moment frames, but the typical cost is north of $100,000 for even a single-family home, largely because of the deep footings required, which means tearing up and rebuilding large parts of the foundation and walls. I really wish there were more economical options available. A lot of engineering and regulatory effort went into developing and permitting cheap but highly effective sheer walls, but when it comes to bridging open spaces the only available option (market or otherwise) seems to be a traditional, bog-standard moment frame developed for large, commercial structures, then scaled down. Contractors don't even offer laminated timber moment frames, only the more expensive steel frames, despite the former technically being available from suppliers and (presumably) capable of passing muster with the building inspector (at least with sufficient cajoling). The premium for steel beams probably only accounts for a fraction of the ultimate cost, but it's an example of the dearth of options, and at $100,000+ those fractions add up. My 3-story house has a window which compromises the sheer strength of the ground floor back wall, and of course a garage opening in front. Even for the back wall the only options offered by licensed contractors were a deep, concrete footing-anchored moment frame; or removing the window entirely so the sheer wall is continuous, without requiring any footing or foundation work. The distance in complexity between those two options seems huge. In principle there must be cheap techniques for strengthing headers, etc, to provide more than adequate reinforcement, but if available or known they're just not in the average contractor's repertoire, even for earthquake retrofitters, and probably unlikely to pass muster as legitimate reinforcement. 3-5 unit residential buildings are described as the critical "missing middle" in the housing affordability debate in the U.S. I would assume that magic figure holds true in Turkey and most other locales, meaning large fractions if not the majority of residential units are in buildings of that size. The dearth of standard, economical solutions for this middle class of building size in SF makes me think Turkey will find it difficult to reform their system. As evidenced in both SF and Turkey, people will go without if the cost is too high; it couldn't be any other way, economically speaking.
- actionfromafar 4y ago
  But what happened in Turkey is probably to a large extent not only that the cost was too high, but that the builders skimped on rules, but pocketed the difference. Now in northern Syria, you could argue the cost would have been too large. The alternative there, in the midst of war, was probably in many cases "build incorrectly, or don't build at all and freeze in a tent".
  - deleted 4y ago
    [deleted]
- thatfrenchguy 4y ago
  > The deadline for remediating multi-family soft stories dwellings in San Francisco was 2020. But this only included buildings with 5+ units, or buildings with a commercial space on the ground floor. There are still many residential buildings, including multi-family buildings (< 5 units), with these 3- or 2-wall soft stories, and there's no mandate in place going forward, AFAIK. The R-2/R-3 neighbors of the city are filled with non retrofitted soft-stories indeed! > The fix is moment frames, but the typical cost is north of $100,000 for even a single-family home, largely because of the deep footings required, which means tearing up and rebuilding large parts of the foundation and walls. I really wish there were more economical options available They do have solutions (Simpsons makes steel strongwalls that are a lot cheaper than moment frames to avoid you having to have a shearwall on the entire front wall), and you'll find structural engineers that will do plans without moment frames that'll definitely get accepted by the city. You'll also find the other half of structural engineers only willing to do moment frames that'll cost you 100-200k$.
- xenadu02 4y ago
  Ouch, it sure seems like reinforcement of a window header, short wall, and the surrounding wall studs would be sufficient... with lots of blocking. You only need enough strength to prevent buckling or deformation right there. I see lots of houses with multiple windows or sliding doors across the back... they seem to treat the vertically continuous wall segments as independent so it's more like several separate back walls. Taken that way you just need enough cross-bracing and reinforced headers/footers no? At least the city is approving those sorts of designs without massive moment frames covering the entire rear wall. (My house fits this with the rear wall being 60% window or sliding door and no steel, but the walls are 2x8 with a lot of blocking and diagonal cross-bracing; the perpendicular internal shear wall connected to it is also built with 2x8s). Garage doors are as difficult as ground floor parking. They often take up the entire building frontage so you need significant reinforcement. My house has a steel moment frame set back from the door opening half the depth of the garage because it has to support a 1.5 car width span and the primary sheer wall for the second floor directly above. The house pre-renovation had none of that, just toe-nailed pillars like lots of SF garages which would have made that part of the house vulnerable for sure.

wahern 4y ago

The deadline for remediating multi-family soft stories dwellings in San Francisco was 2020. But this only included buildings with 5+ units, or buildings with a commercial space on the ground floor. There are still many residential buildings, including multi-family buildings (< 5 units), with these 3- or 2-wall soft stories, and there's no mandate in place going forward, AFAIK. The fix is moment frames, but the typical cost is north of $100,000 for even a single-family home, largely because of the deep footings required, which means tearing up and rebuilding large parts of the foundation and walls. I really wish there were more economical options available. A lot of engineering and regulatory effort went into developing and permitting cheap but highly effective sheer walls, but when it comes to bridging open spaces the only available option (market or otherwise) seems to be a traditional, bog-standard moment frame developed for large, commercial structures, then scaled down. Contractors don't even offer laminated timber moment frames, only the more expensive steel frames, despite the former technically being available from suppliers and (presumably) capable of passing muster with the building inspector (at least with sufficient cajoling). The premium for steel beams probably only accounts for a fraction of the ultimate cost, but it's an example of the dearth of options, and at $100,000+ those fractions add up. My 3-story house has a window which compromises the sheer strength of the ground floor back wall, and of course a garage opening in front. Even for the back wall the only options offered by licensed contractors were a deep, concrete footing-anchored moment frame; or removing the window entirely so the sheer wall is continuous, without requiring any footing or foundation work. The distance in complexity between those two options seems huge. In principle there must be cheap techniques for strengthing headers, etc, to provide more than adequate reinforcement, but if available or known they're just not in the average contractor's repertoire, even for earthquake retrofitters, and probably unlikely to pass muster as legitimate reinforcement. 3-5 unit residential buildings are described as the critical "missing middle" in the housing affordability debate in the U.S. I would assume that magic figure holds true in Turkey and most other locales, meaning large fractions if not the majority of residential units are in buildings of that size. The dearth of standard, economical solutions for this middle class of building size in SF makes me think Turkey will find it difficult to reform their system. As evidenced in both SF and Turkey, people will go without if the cost is too high; it couldn't be any other way, economically speaking.

actionfromafar 4y ago
But what happened in Turkey is probably to a large extent not only that the cost was too high, but that the builders skimped on rules, but pocketed the difference. Now in northern Syria, you could argue the cost would have been too large. The alternative there, in the midst of war, was probably in many cases "build incorrectly, or don't build at all and freeze in a tent".
- deleted 4y ago
  [deleted]
thatfrenchguy 4y ago
> The deadline for remediating multi-family soft stories dwellings in San Francisco was 2020. But this only included buildings with 5+ units, or buildings with a commercial space on the ground floor. There are still many residential buildings, including multi-family buildings (< 5 units), with these 3- or 2-wall soft stories, and there's no mandate in place going forward, AFAIK. The R-2/R-3 neighbors of the city are filled with non retrofitted soft-stories indeed! > The fix is moment frames, but the typical cost is north of $100,000 for even a single-family home, largely because of the deep footings required, which means tearing up and rebuilding large parts of the foundation and walls. I really wish there were more economical options available They do have solutions (Simpsons makes steel strongwalls that are a lot cheaper than moment frames to avoid you having to have a shearwall on the entire front wall), and you'll find structural engineers that will do plans without moment frames that'll definitely get accepted by the city. You'll also find the other half of structural engineers only willing to do moment frames that'll cost you 100-200k$.
xenadu02 4y ago
Ouch, it sure seems like reinforcement of a window header, short wall, and the surrounding wall studs would be sufficient... with lots of blocking. You only need enough strength to prevent buckling or deformation right there. I see lots of houses with multiple windows or sliding doors across the back... they seem to treat the vertically continuous wall segments as independent so it's more like several separate back walls. Taken that way you just need enough cross-bracing and reinforced headers/footers no? At least the city is approving those sorts of designs without massive moment frames covering the entire rear wall. (My house fits this with the rear wall being 60% window or sliding door and no steel, but the walls are 2x8 with a lot of blocking and diagonal cross-bracing; the perpendicular internal shear wall connected to it is also built with 2x8s). Garage doors are as difficult as ground floor parking. They often take up the entire building frontage so you need significant reinforcement. My house has a steel moment frame set back from the door opening half the depth of the garage because it has to support a 1.5 car width span and the primary sheer wall for the second floor directly above. The house pre-renovation had none of that, just toe-nailed pillars like lots of SF garages which would have made that part of the house vulnerable for sure.