The bioclimatic house in Colombia, climate by climate

The same house that works in Villa de Leyva is a mistake in Barranquilla. Not slightly worse: a mistake, with the air conditioning running twelve hours a day to correct what the architecture got wrong. And the other way round: the open, ventilated Caribbean house, built on a highland plateau, is a cold house nobody uses after dark.

This is not a matter of taste. Colombia does not have one climate: it has several, all at the same time, since altitude rather than season sets the temperature. The state has already classified them, mapped them, listed them municipality by municipality and attached mandatory savings targets. Almost nobody says so, and fewer people still know that a new single-family house falls inside the rule.

The country has four climates, not altitude bands

Anexo 2 of Resolución 0549 de 2015, issued by the housing ministry, is a national map of climate classified by temperature and relative humidity, drawn by IDEAM, the state meteorological institute, with a list of municipalities attached. There are four classes: cold, temperate, hot and dry, and hot and humid. Every municipality in the country appears there with its altitude and its class.

Read it twice, because the whole argument is in there. Cartagena and Santa Marta both sit on the sea and fall in different classes. Jamundí, at 975 metres, is hot and dry; Palmira, at 1,001 metres, is temperate. Twenty-six metres apart and a different design regime. Altitude on its own decides nothing.

What the rule requires, and of whom

Resolución 0549, dated 10 July 2015, implements the sustainable construction chapter of Decreto 1077 de 2015, the consolidated decree for the housing sector, and adopts a national guide on water and energy saving in buildings. Its first article sets the object: minimum water and energy savings in new buildings.

The useful question is who it applies to, and the answer surprises a lot of people. The second article carries a table of building type against scale, and this is the row almost nobody quotes.

In other words: your house is inside. With one condition that does narrow it, set out in the third article: the rules apply to buildings put up under a building permit in the obra nueva mode, meaning new construction on undeveloped ground, applied for after the resolution took effect. A remodelling does not drag the duty along with it; the eighth article lets an existing building meet the measures voluntarily.

Passive measures: the part that is architecture

The resolution splits the measures in two, and the boundary falls exactly where the architect stops and the installer begins. Active measures are equipment: air conditioning, boilers, mechanical ventilation, electric lighting. Passive measures are the house itself.

That list is, word for word, the working programme of a properly done schematic design. And it carries a practical consequence hardly anyone uses: if the saving is achieved through passive measures, the certificate is the designer signing the architectural drawings, which under the seventh article amounts to a sworn certification. No extra procedure, no audit, no certifier to pay.

The design objectives, climate by climate

Anexo 1 of the resolution carries a short table worth more than thirty pages of theory: what the design is trying to achieve in each climate. Here it is, summarised and unembellished.

What changes, line by line

Orientation. In Colombia the east and west facades take most of the radiation; north and south take far less, because the sun passes close to overhead. Anexo 1 states it both ways: if you want warmth, you stretch the house along an east-west face; if you want coolness, the long facades are north and south. And in hot and temperate climates a western orientation is avoided where possible, because of afternoon overheating.

Cross ventilation. This is not the same as opening windows: it means the air has a way in and a way out, on opposite faces and at different heights. It appears as a recommended measure in all four climates for housing that is not social housing, but in the hot and humid climate it stops being an improvement and becomes the main strategy, because comfort there comes from moving air rather than from lowering the temperature.

Thermal mass. A heavy wall takes hours to give back the heat it took in. That is a virtue where the night is cool and the day is hot — the hot and dry climate, and much of the temperate one — because the wall stores the coolness of the small hours and returns it at midday. In the hot and humid climate that same mass works against you: if the night never cools, the wall never discharges, and at ten at night it is still radiating the heat of three in the afternoon. There the answer is the opposite: a light, ventilated envelope, and shade.

Eaves and solar protection. The annex separates three families: horizontal elements such as eaves, balconies and louvres; vertical elements such as fins; and the combination of the two. And it makes an observation that strikes me as the most useful in the whole document: horizontal elements are very effective because of how high the sun rides at this latitude, and external louvres are preferable to internal ones, since anything inside offers only partial protection: the radiation is already in.

The roof. It is the surface that takes the most radiation in this country, and the one that gets solved worst. In a hot climate what does the work is less the material than the ventilated cavity beneath it and the shade the eaves cast on the wall. In a cold climate the problem is the reverse, and it is called night-time heat loss. Comparing clay tile, insulated sheet, concrete slab and green roof deserves an article of its own and I am not disposing of it in a paragraph.

Humidity, which rules the coast more than heat does

A thermometer does not explain the coast. Barranquilla and Santa Marta both sit at sea level, less than a hundred kilometres apart, and the official classification puts them in different classes. The variable that separates them is relative humidity, and the reason is physiological before it is architectural: when the air is very humid, sweat does not evaporate, and the body loses its main way of cooling itself.

From that follows the design consequence. In a hot dry climate you can bring the sensation of heat down with mass, shade and water. In a hot humid one that is not enough, which is why the rule demands almost twice the energy saving of a house there than in the other three climates: it knows that a badly designed house in that climate ends up being fixed with equipment.

The architectural answer is the one the houses of the Caribbean and the Pacific coast have been giving for two hundred years, long before any resolution existed: a floor lifted clear of the ground, wide eaves, generous interior height, a ridge that lets hot air out, and a single-room-deep plan so that the air crosses without obstruction.

How this reaches a real project

1. 1Look your municipality up in the Anexo 2 list before you draw anything. The climate class decides the target you will be held to and the direction the design has to work in. It takes two minutes.
2. 2If the site does not match its class, say so. Paragraph 2 of the sixth article lets the builder state on the permit form that the site sits in a climate zone other than the one assigned, and that requires no separate procedure.
3. 3Decide it at schematic design, not at finishes. Orientation, form, eaves and the placing of openings are first-week decisions. After that all you have left is equipment.
4. 4Declare in writing that you are going with passive measures. If you do not say so, active measures are assumed, and that commits you to a consumption you pay for every month.
5. 5Ask that the architectural design answer for the target. The signature on the drawings is a sworn certification: your architect is asserting something checkable, and you are entitled to have it explained.
6. 6Do not buy the word bioclimatic without a section drawing. If nobody has drawn you a section with the eaves, the three-in-the-afternoon sun and the way the air leaves, there is no bioclimatic design: there is an adjective.

None of this makes a house more expensive on its own. A properly sized eave costs what an eave costs; putting it on the right facade is free. What does cost money is the other thing: the house that needs equipment to be habitable. If you are at the stage of setting a budget, the conversation continues in what a country house costs and in what it costs to build per square metre.