Materials make up a substantial fraction of the costs of new construction. When we previously looked at a collection of 40 different construction tasks, on average materials made up 62% of the cost of the task. And for an average new house, materials make up roughly 50% of direct costs (excluding things like profit, marketing, development costs, etc).
Another important consideration is resistance to infrequent environmental effects. While a very light material might perform the same as a heavy-duty one 99% of the time, it might fail in the 1% case, or in black-swan-like scenarios.
Some of the high tech construction techniques replace materials with complexity. You wonder how long such buildings would last if they were to suffer damage or deterioration i.e., could they be repaired or refurbished and if not do they need to be torn down. A simple example are UPVC windows commonly used in the UK to replace wood often sold as needing no maintenance. True they don’t rot, but they certainly do deteriorate and have a fixed life. A carefully maintained quality wooden framed window may not perform so well thermally but could last over 100 years. There are plenty of buildings in the UK built 600 years ago and which are still reparable using simple methods and with care could last another 400years. Low tech construction techniques may use more materials, but if the building lasted 1000 years, less materials would be used than with high tech buildings if they have to be replaced 10 times in the same period .. and this doesn’t even account for the high complexity/high energy supply chain that accompanies high tech construction.
The more concrete-efficient floor you mentioned from a few years ago has increased height compared to current ones, but the one that I read about and usually think of is the Rippman Floor system, from these articles:
It includes the ventilation and other utilities in the floor cavity so the height increase at that one shouldn't be a problem. But the part that made me think was that apparently 75% of a 20-40 floor building's mass is structure, and half that is floor structure.
So if this design reduces floor mass by 75%, then that represents maybe 25% of the building's total mass eliminated, and the rest of the structure holding that up can be reduced by a good amount to compensate (the effect is disproportionate in the upper floors, which have to be held up by the entire vertical beams below them). Although a tuned mass damper might have to be increased to compensate for an equally tall but lighter building. That saving may easily be worth the extra cost in buildings taller than a few floors.
As a home builder and long time reader of the blog, I was very happy to see this post and a reference to Fernando Pagés Ruiz and his book. Of note is that the book was published 20 years ago, in 2005, and a 25% savings (of $1,000) on lumber would be $5-10k today for a typical lumber package for a 2 story single family home.
Due to the fractured nature of homebuilding, I can confidently say that most small, and even midsized, homebuilders have notable room for savings and material reduction. This is due to both over-building and inefficient floor plans that don't take into account holistic structural design.
To your point, however, saving 10% on a fraction of the materials that make up 50% of the direct costs of the home is not significantly moving the needle.
About circular/octagonal houses: people want to add on to their houses, and you can't do this with a circle or an octagon. Maybe you can add another floor, but nothing onto the side.
Yeah, you can add a square to an octagon and then another octagon.
Heavier construction than is the theoretically calculated minimum is also far better for dealing with the unknown unknowns that always exist in any project (e.g., unknown fault line) both during construction and "oops" later such as a car hitting a vertical in the parkaid or some tenant deciding to remove a wall or put all of their filing cabinets in one room...
Just a minor point. When you discuss percentage of housing cost in the future, please specify whether the total includes or excludes land cost. I know that is implicit in the term “construction costs,” but people often forget that the cost of land is a large percentage of total housing costs, particularly in large metro areas.
I think the only way to make big productivity gains in construction is, as you mentioned, vertically integrated prefabrication.
The major problem in the past century has been transportation cost. With the world moving towards electric self driving cars we can significantly cut transportation costs and enable more prefabrication.
There is also the increasing use of engineered timber. It's lightweight cuts down on transportation costs and hence opens up more room for prefabrication.
An additional cost cutting measure can be telerobotics or remote controlled robots. Although they'll take off in warehouses and some factories like steel mills before construction costs since they will work better in controlled environments.
60 years ago I was told by a co-worker who was an civil engineering student that because in America labor was expensive and materials cheap we designed to save labor, while in Europe it was the other way around. I suppose that's changed now. There must also be considerations of available resources--bamboo being more available in China than in US; wood more available in US than in UK or Ireland.
Context is all--innovations will change the context, as the use of manufactured wood for apartment buildings in this century.
I must admit; the first thing that popped into my head as I read the opener was the notion of a construction worker whose only job was to run around with a hole saw and ruler putting holes in materials in permissible locations just for the hell of it and tossing the scraps into the recycle bin.
If the building is made mostly of platinum it might pencil out?
Another important consideration is resistance to infrequent environmental effects. While a very light material might perform the same as a heavy-duty one 99% of the time, it might fail in the 1% case, or in black-swan-like scenarios.
Some of the high tech construction techniques replace materials with complexity. You wonder how long such buildings would last if they were to suffer damage or deterioration i.e., could they be repaired or refurbished and if not do they need to be torn down. A simple example are UPVC windows commonly used in the UK to replace wood often sold as needing no maintenance. True they don’t rot, but they certainly do deteriorate and have a fixed life. A carefully maintained quality wooden framed window may not perform so well thermally but could last over 100 years. There are plenty of buildings in the UK built 600 years ago and which are still reparable using simple methods and with care could last another 400years. Low tech construction techniques may use more materials, but if the building lasted 1000 years, less materials would be used than with high tech buildings if they have to be replaced 10 times in the same period .. and this doesn’t even account for the high complexity/high energy supply chain that accompanies high tech construction.
What percent of building materials are recycled after demolition? I can imagine that industrial recycling has the potential to actually be profitable.
The more concrete-efficient floor you mentioned from a few years ago has increased height compared to current ones, but the one that I read about and usually think of is the Rippman Floor system, from these articles:
https://www.noemamag.com/concrete-built-the-modern-world-now-its-destroying-it/
https://designbuild.nridigital.com/design_build_review_dec21/concrete_floor_low_carbon
It includes the ventilation and other utilities in the floor cavity so the height increase at that one shouldn't be a problem. But the part that made me think was that apparently 75% of a 20-40 floor building's mass is structure, and half that is floor structure.
So if this design reduces floor mass by 75%, then that represents maybe 25% of the building's total mass eliminated, and the rest of the structure holding that up can be reduced by a good amount to compensate (the effect is disproportionate in the upper floors, which have to be held up by the entire vertical beams below them). Although a tuned mass damper might have to be increased to compensate for an equally tall but lighter building. That saving may easily be worth the extra cost in buildings taller than a few floors.
As a home builder and long time reader of the blog, I was very happy to see this post and a reference to Fernando Pagés Ruiz and his book. Of note is that the book was published 20 years ago, in 2005, and a 25% savings (of $1,000) on lumber would be $5-10k today for a typical lumber package for a 2 story single family home.
Due to the fractured nature of homebuilding, I can confidently say that most small, and even midsized, homebuilders have notable room for savings and material reduction. This is due to both over-building and inefficient floor plans that don't take into account holistic structural design.
To your point, however, saving 10% on a fraction of the materials that make up 50% of the direct costs of the home is not significantly moving the needle.
About circular/octagonal houses: people want to add on to their houses, and you can't do this with a circle or an octagon. Maybe you can add another floor, but nothing onto the side.
Yeah, you can add a square to an octagon and then another octagon.
Heavier construction than is the theoretically calculated minimum is also far better for dealing with the unknown unknowns that always exist in any project (e.g., unknown fault line) both during construction and "oops" later such as a car hitting a vertical in the parkaid or some tenant deciding to remove a wall or put all of their filing cabinets in one room...
Excellent!
Another great article.
Just a minor point. When you discuss percentage of housing cost in the future, please specify whether the total includes or excludes land cost. I know that is implicit in the term “construction costs,” but people often forget that the cost of land is a large percentage of total housing costs, particularly in large metro areas.
I think the only way to make big productivity gains in construction is, as you mentioned, vertically integrated prefabrication.
The major problem in the past century has been transportation cost. With the world moving towards electric self driving cars we can significantly cut transportation costs and enable more prefabrication.
There is also the increasing use of engineered timber. It's lightweight cuts down on transportation costs and hence opens up more room for prefabrication.
An additional cost cutting measure can be telerobotics or remote controlled robots. Although they'll take off in warehouses and some factories like steel mills before construction costs since they will work better in controlled environments.
60 years ago I was told by a co-worker who was an civil engineering student that because in America labor was expensive and materials cheap we designed to save labor, while in Europe it was the other way around. I suppose that's changed now. There must also be considerations of available resources--bamboo being more available in China than in US; wood more available in US than in UK or Ireland.
Context is all--innovations will change the context, as the use of manufactured wood for apartment buildings in this century.
I must admit; the first thing that popped into my head as I read the opener was the notion of a construction worker whose only job was to run around with a hole saw and ruler putting holes in materials in permissible locations just for the hell of it and tossing the scraps into the recycle bin.
If the building is made mostly of platinum it might pencil out?
Section modulus. In flexure, the primary effect is thickness, or distance from the neutral axis.
Section modulus goes as the ^3 cube of thickness.
This is how I-beams work.