Residual Capacity: Finding Unused Building Rights on a Plot

A plot with a building on it is not necessarily a fully utilised plot. What stands there today tells you only what someone chose to build at some point — not what the plan permits. The difference between those two figures is the residual capacity, and that is exactly where the densification potential hides. A villa from 1968 on a large plot in an area since zoned for dense low-rise or multi-storey housing can hold a substantial reserve that neither the seller nor the agent has put a number on.

The residual capacity of a plot is not an abstract quantity — it is a concrete number of square metres of gross floor area that you can calculate, and it determines whether there is a project to be had. This walkthrough shows how to calculate the unused building rights, where the sources of error lie, and how to screen out early the plots where the reserve is only theoretical.

What residual capacity actually is

Residual capacity is the unused building rights: the difference between the maximum building rights the plan permits and the gross floor area already built. The formula is simple:

Residual capacity = maximum permitted gross floor area − existing gross floor area

A 1,200 m² plot with a maximum plot ratio of 40% has building rights of 480 m² of gross floor area. If a 180 m² house already stands there, the residual capacity is 300 m² — provided the other provisions allow those square metres actually to be placed. The base figure comes from a correct calculation, and the full sequence is set out in the walkthrough of how to calculate building rights and plot ratio on a plot.

You find the maximum plot ratio in this order: a current local plan takes precedence, then the municipal plan’s framework provisions, and only if neither says anything do you fall back on the indicative values in the building code — typically 30% for open low-rise, 40% for dense low-rise and 60% for multi-storey housing. Always look up the actual ceiling in Plandata.dk (the national plan register) before you calculate the reserve.

The two figures you have to get right

The residual capacity is only as reliable as the two figures that go into it. Both have their own pitfalls.

The maximum gross floor area

The maximum figure depends on the plot area and the plot ratio — but the cadastral area is not always the area you may calculate from. If the plot has to cede land for a designated road or path, that area generally does not count towards the calculation basis, and lakes, watercourses and protected areas may be excluded depending on the planning framework. Look up the cadastral area in matriklen (the cadastre) and cross-check it against what the local plan says about the basis.

The existing gross floor area

You take the utilised area from BBR (the Buildings and Dwellings Register) — but do so with caution. Two problems recur:

• The registration is not always up to date. Extensions, converted loft storeys or demolished buildings are not necessarily updated. A BBR figure can be both too high and too low.
• BBR’s area concepts do not map one-to-one onto the building code’s definition of gross floor area. What BBR calls footprint or total living area is not the same as the gross floor area on which the plot ratio is calculated. The difference between the concepts is large enough to overturn a calculation — see what counts towards the plot ratio: gross floor area vs. footprint.

So check the BBR figure against floor plans or a survey before you base a purchase decision on the reserve. The other pitfalls of reading BBR are worth knowing in advance — they are collected in the walkthrough of the typical BBR errors and how to catch them.

A theoretical reserve is not the same as a realisable reserve

The mathematical maximum is rarely what you can actually build. The residual capacity can look ample on paper and still be impossible to extract, because other provisions limit where and how high the volume can be placed:

• Building zones define where on the plot you may build at all — the unused part is not necessarily buildable.
• Maximum building height and number of storeys cap how much area you can stack within the footprint. If you cannot build upwards, you cannot realise the reserve, whatever the plot ratio permits.
• Setback requirements to boundaries and building lines reduce the area that can actually be built on.
• Parking and amenity-area requirements must be accommodated on the plot and eat into the space — often precisely the space where the reserve otherwise lay.

This is where the mathematically possible meets the physically possible. A residual capacity of 300 m² is worth nothing if the existing building sits in the middle of the only building zone, or if the height limit prevents the extra storey the calculation assumes. Always assess the placement before you call the reserve realisable.

Building rights after demolition

A special case is plots where the reserve only becomes visible once the existing building is removed. Here it is not the residual capacity on the existing property that is interesting, but the total building rights after demolition — that is, the maximum gross floor area set against a cleared plot.

Two things apply here. First, the calculation does not simply reset: demolition can require permission, and buildings with heritage value or preservation provisions in the local plan can block demolition entirely. Second, you have to calculate on the total new building rights, not on the difference — the existing building’s area is irrelevant when it disappears anyway. A 180 m² house on a plot with building rights of 480 m² gives 300 m² of residual capacity, but after demolition the full 480 m² is in play, provided the plot can otherwise carry the volume.

Rule of thumb: If the value of the existing building is lower than the value of the full building rights minus the demolition cost, the calculation points towards demolition rather than an extension.

Always check the local plan for preservation provisions and tingbogen (the Land Registry) for registered burdens before you assume that a building can be demolished.

What the plan doesn’t tell you

Even a correctly calculated and placed reserve can collapse on something that appears neither in the cadastre nor in the local plan. Registered easements can lay building lines, utility routes or covenants across the plot that in practice restrict where you may build — independently of the plot ratio. A sight-line easement or a protected utility route can consume exactly the part of the plot where the reserve lay.

Always look up the registered burdens in tingbogen (the Land Registry) and read them together with the planning framework. Be aware, too, that the municipality can impose a Section 14 prohibition against an otherwise lawful project while a new local plan is being drawn up — and that a higher level of utilisation than the plan permits requires either a dispensation under Section 19 of the Planning Act or a new local plan. The reserve is only real once it can both be calculated, placed physically, and stand up against easements and the planning framework.

From plot to reserve in minutes

The manual exercise is the same every time: look up the cadastral area, find the current local plan and municipal-plan framework area in Plandata.dk, decide what may be counted, subtract the existing area from BBR, assess whether the reserve can be placed within building zones and height limits, and cross-check against registered easements. This typically takes hours per plot, every step holds a source of error, and the result is often that the reserve was only theoretical.

That is exactly the collation Arcili automates. In Kort (the map module) you can look up a plot and have the public registers — cadastre, plan data, BBR and the Land Registry — laid over one another in the same place, so that the maximum and the utilised building rights sit side by side and the residual capacity can be read off directly. It does not remove the architect’s or consultant’s work, but it saves you the 80–100 hours in the early phase where you screen many plots to find the few that carry a project. Want to see the densification potential on a specific plot? Book a walkthrough.