Masonry or prefabricated: which one, and when

The question nearly always arrives in the same words: "would masonry or prefabricated work out better?". And it is the wrong question, not out of technical pedantry but because "prefabricated" does not name a structural system: it names a degree of industrialisation. Four different things shelter under that word, and they behave, cost and remodel differently.

The same holds on the other side. "Masonry" is not one thing either: the Colombian building code recognises seven types, and treats them in seven ways. This article sells none of them. It puts the comparison in order and ends on the question almost nobody asks in time.

What "prefabricated" means in Colombia

In the Colombian housing market the word covers at least four separate families, and not one of them is simply "prefabricated". All of them are in the code; none of them sits outside it.

The seismic zone rules several out before you choose

Before comparing prices it is worth knowing that the list of options is not the same across the country. The code assigns each system an energy dissipation capacity — special, moderate or minimal — and then says, zone by zone, which one is allowed and up to what height. These are the rows that matter for housing.

Read it with your own municipality in mind. In a high seismic hazard zone — which is where Cali, Jamundí, Palmira and Bucaramanga sit — confined masonry, the standard Colombian house, is capped at two storeys. That is not advice: it is what the table says. If your project is three storeys in a high zone, the conversation about the system has already begun, whether you have had it or not.

And there is one title of the code cut to the measure of the small house. Título E covers one- and two-storey dwellings in confined masonry and in cement-rendered bahareque, a traditional cane-and-earth wall, in use group I, within programmes of no more than 15 dwellings and under 3,000 m² of built area. Outside those limits, or with another system, the house is designed the long way, through Título A.

Time, cost, maintenance: what can honestly be said

My reading of that table is short: the systems that win on speed lose on flexibility, and not by a little. What industrialisation buys is a repeating cycle, and a repeating cycle demands that the design be closed before the first pour. That is good business across two hundred identical houses. In a single house it almost never is.

The question nobody answers: taking a wall out ten years later

This is where the comparison stops being academic. Nobody builds a house thinking about the remodelling, and almost everybody ends up doing one: a child arrives, another leaves, the closed kitchen stops making sense, the terrace becomes a study. The right question when choosing a system is not what the square metre costs today. It is what can be taken out tomorrow.

And the answer turns on one thing alone: which way the load comes down. The code defines it in two lines, in the title covering one- and two-storey houses.

And here is the point that gives this section its title, because it runs the opposite way to what almost everyone assumes. In structural masonry and in industrialised concrete, every wall that matters is structure: the system is cheap and fast precisely because it did away with the columns and beams, and what it did away with is what would have given you freedom later. In a frame with infill walls the reverse happens: it costs more at the outset and leaves the plan open for good, because the load never passed through the walls.

Confined masonry sits in the middle, and it is the most confusing case of all: a wall confined by small columns and tie beams is part of the seismic resisting system, while a partition wall in the same house, built from the same block, does nothing at all. Rendered and painted, they are identical. Nobody can tell them apart by looking.

The test for whether the work counts as minor comes from the code itself, and it is the one an engineer will apply: the structural system is deemed not to have been modified where repairs and minor changes are made that affect neither the seismic resisting system nor the structural integrity of the building. The whole difficulty lies in deciding whether that wall belongs to that system, and neither the owner nor the site foreman gets to decide it.

And what the permit rules say

The legal consequence is as clear as the technical one, and it sits in the decree on planning permits. There is a mode called modificación, defined as authorisation to vary the architectural or structural design of an existing building without increasing its built area, and another called reforzamiento estructural, for intervening in or strengthening the structure to bring it up to adequate levels of seismic safety.

On the other side sits what needs no permit at all. The definition of a repair of the kind called locativa is explicit about what it excludes, which is why I quote it in full.

Translated into real life: removing a partition wall in a frame building is a modification, needing a design and a permit but no major structural calculation. Removing a load-bearing wall in structural masonry or in an industrialised system means intervening in the structure, and that calls for a structural design, an engineer who answers for it, and the corresponding permit mode. The subject has an article of its own: structural strengthening, what the code requires and what the permit costs.

How to choose, in the right order

1. 1Start from the seismic hazard zone of your municipality, not from the price. The table of systems has already ruled options out before you looked at a single quotation.
2. 2Ask yourself how many houses you are building. Industrialisation wins when the project repeats. In a single house the advantage in cycle time rarely offsets the cost of the formwork or the rigidity it forces on the design.
3. 3Decide whether the plan is going to change. If the answer is "probably", a frame with infill walls is worth the extra it costs. If the house is final, structural masonry is hard to beat.
4. 4Look at the climate before the catalogue. High mass where the night cools; a light, ventilated envelope where it does not. The structural system and the thermal behaviour are chosen in the same conversation.
5. 5Ask for the structural drawing with the load-bearing walls marked, and keep it. It is the document that decides, ten years on, whether the remodelling takes two weeks or two months. Asking for it today costs nothing.
6. 6Check that the labour exists in the municipality. An excellent system with nobody able to build it properly is a bad system.

There is no best system. There is one that is best for your site, your municipality, your number of houses and your tolerance for a plan that stays fixed. If what you are putting together is the budget, carry on in what it costs to build per square metre; if what you are putting together is a house in the countryside, in what a country house costs.