floor area ratio

Form and figures (7) Irregularity and project


1906. Noisy le Grand, some 13 km east of Paris




A new, somewhat artificial, combination of city block and open blocks, in a wider urban core project for a metropolitan municipality. Almost exclusively housing, but by the market square, near supermarkets and a big regional mall


Form and figures (6) Regularity and densification


The images in this post correspond to a Spanish city; but I will not say which one, as this is not relevant; in a certain way, it could be anywhere in the world, as urban tissues evolve over time, as it is so well explained in the Biblio post of this week.

The extension grid, conceived in a given moment for a height and a building type (here individual homes on two heights, with a lot courtyard on each and reduced dimensions) is substantially densified through the use of multifamily housing, bigger lots (everyone wants his parking slot to be in the building) and with 3 times the original height. As the city block is narrow, no central courtyard was present and none is expected to appear now with such densities. Double aspect apartments are also far from possible, and in general the housing units are far from optimal. But this density allows a feasible retail base in the buildings, a chance to walk to work, or other advantages of density. Take two more elements: the city is an organism with a substantial inertia, as buildings can easily stay for 50 or 100 years, and the urban planning rules can change several times over that period, so chances are you will never see all the buildings in the block with the same height…


So we face an urban landscape whose plan view can be regular, but in which separative walls between lots and height differences can be not temporary, but permanent features; a cartoon artist, Ibañez, always rendered as a background images with these height changes and fractured skylines so common in the Spanish cities of the last century. But this is not exclusive of Spain: if you are in Paris, some areas as the southern XVth district show well the brutal stop to “business as usual” that WWI meant, with city blocks in which changes in height and regulation are clearly visible…


Forms and figures (5) Opening the block

Opening the block has been a recurrent idea since the begining of the 1900s. But how and how much? As ever, Rotterdam is a zoo full of missing links…

Opening through a setback in the façade plane: the street gets diluded

Opening through a setback in the façade plane: the street gets diluded

Opening through a setback from an internal division: the street keeps its shape, and the block is equally open

Opening through a setback from an internal division: the street keeps its shape, and the block is equally open

Please, as previously, if the animated gif does not display properly, try opening it in a different window

Biblio (49). The evolution of the urban tissues. Impact of the urban frame and architectural form

Biblio 49-evolutivité tissus urbains

This publication by the Institute for Regional and Urban Planning of the Region Ile de France concerns a relevant matter: how will the urban tissues conceived now according to contemporary ideas evolve in the future. It is known that when you visit the Ensanche in Barcelona you are seeing a much denser  tissue, quite different from what was designed in 1860, and a similar thing has happened in nearly all cities. Authors state that it is possible to embed into the urban project flexibility elements to allow a better future evolution. Their analysis concerns three items:

–           Urban frame (streets grid, size and arrangement of lots), property structure and public space.

–           Architectural form, including uses, bulk and architectural typologies adapted to uses.

–           The juridical aspects coming from diverse norms and the relation between properties.

An annex includes a study of real cases in the region.

Biblio 49-evolutivité tissus urbains-interior

Form and figures (3) Setbacks and fences


If the upper animated gif is not visible in your browser, click on it for an independent view

Usually the setback from the lot line is limited. Making the setback equal to the backyard does not seem so smart, as 2 small gardens are probably less fun than having a larger land tract. If the setback increases to reduce the backyard to the smallest dimension, good treet would make for a better landscape street but the “freedom” is lost to do whatever you want in a space hidden from the street (but not from your neighbors or google earth…). But some do it, ending with a parking or a storage in the façade…

A case in Madrid

A case in Madrid

Form and figures (2) Floor area ratio 1 on an urban development zone

3jul 2013-1m2m2sectorBuildings can be developed on a net lot, as in the previous case; i.e., without changing the initial lot, or changing its shape but without changing the overall area. But in some cases there is a need to include in the operation not just the lots land, but also that which will be needed for non private uses, according to the legal binding conditions in each case.

In Spain, for instance, if you are building on previously undeveloped land, you must create the streets and allow for the location of gardens and other public facilities that will be used by the new dwellers (in Spain it is usually compulsory to locate public gardens, even if all homes are individual and with their own private gardens). There is also a certain amount of on –street parking, which requires also a certain space. Each planning law and each plan set a different quota for each of these surfaces.

To produce a rapid back of the envelope calculation, you can consider that a floor area ratio of 1 requires a surface for public facilities and streets that is the same as that of private lots. So, if FAR is 1 overall, FAR on the net lots, which will be just 50% of the land, will be 2, as usually any building on public facilities is not taken into account (FAR is calculated for floor spaces that are lucrative for the developer). So, you will not understand the full meaning of FAR unless you know the scope on which it is calculated…. And it must be acknowledged (there form based codes are right) that the figure itself doest not allow to kwnow the resulting urban form: just reminding yesterday and today’s posts, 1 sq m/sq m as measured on net lots allows for individual housing on rows, but 1 sq m/sq m (or 1 sq ft/ sq ft, which is absolutely the same thing) on a larger area usually asks for a different urban morphology.

Form and figures (1) Floor area ratio 1 on a net lot

A form based code has usually some numbers behind, explaining the formal result. The following images show how the same floor-area ratio can have different consequences in formal terms.

fbc-A-parcsolas-10p6fren25fon-0pl-1 m2m2

As a begining: 20 lots, 10 for each street frontage, with 6×25 m (150 sq m), a common real estate product (at least in Europe). The sidewalk is not counted on these calculations, having considered it is a part of the public right of way.

A floor area ratio of 1 would mean covering the whole lot with 1 level


If half that surface is put on top of the other half, gardens appear. Still 20 homes with 150 sq m of built-up area, but much better as there can be windows…

fbc-D-parc+viv-5p12fren25fon-2pl- 1m2m2

If lots have twice the lot line length (12×25 m, 300 sq m lots), you reduce the number of homes by half, each with 300 sq m as built up area. Open space is on the lateral setbacks, but it is not necesarily attractive…


If lots become 20×25 m, with a floor area of 500 sq m, you get just 6 lots, and each home, with 500 sq m of built up area, is in the center of its garden… but 500 sq m are a bit too much for such lots, or it is perharps better to think about multifamily housing (each floor has 250 sq m).


The same layout with 500 sq m lots can become quite different with 4 floors, each with 125 sq m, so  two appartments can fit inside. 48 homes on the same land initially subdivided for 20…