Technological Artefacts and Separation Distances

{This is something I wrote a few years back. It was an exercise of “killing two birds with one stone”. I was writing VBA macros to export chunks of Excel worksheets to HTML, and I wanted to extend it to include pictures. I also had an idea of writing an article on the problems simple rules can cause, and the evolution of the rules, as then attempt to resolve these problems. The simple rule started with the need to prevent trees damaging houses when they are blown over by the wind. Due to complications of text and image overlap the VBA macro, became dependent on a style to highlight an area as a figure, and then saved such area to an image file. This then imposed need to highlight other areas as text blocks. So the article is mostly comprised of the exported image files.}

Rules are for the guidance of wise men and the obedience of fools

: Douglas Bader

The Basic Rule

An object should be separated from another object by a distance equal to its height.

Separation distances apply to all points on the object.

Reasons For the Rule

Two basic reasons for separation distance. One is to ensure that when one object topples it does not fall on another object. The second reason is to provide open space, and avoid over crowding. The larger of these two distances determines the minimum separation distance. Typically the height of the object will provide the minimum separation distance to meet these two requirements: though a distance 10% to 50% greater than the height would provide better fall protection.

NB: As far as I am aware there are no such mandated rules. Though there are rules for minimum clearances and minimum setbacks: so check local development plan.

Applying the Rule

Separation Between Flat Roof House and Fence
Separation Between Monoslope Roof House and Fence
Separation Between Doubly Pitched Roof House and Fence (Transverse)
Separation Between Doubly Pitched Roof House and Fence (longitudinal)
Separation Between Hipped Roof House and Fence
Separation Between Doubly Pitched Roof House, Fence and Existing Tree. Note that due to inclusion of the fence, the falling tree is constrained to fall on the owners property. If the fence is not included in the assessment, then the tree just needs to clear the neighbours house. However such would prevent the neighbour developing in between their house and the tree.

Alternative Rules

Separation Distance Set Equal to the Sum of the Two Heights
Separation Distance Set Greater than the Sum of the Two Heights
Separation Distance Set Equal to the Sum of the Two Heights: usable space
Notes on Infill Between to Objects
Examples Applying the Compromise Rules
Halving Rule
Proportional Separation Based on Zero At Midpoint
Proportional Reduction in Height Between The Two Control Features
Shortest Object Controls Height at Midpoint, Proportional reduction in Height from Tallest Object
Zero Height at Midpoint, Proportional Increase in Height to the Two Control Features
Zero Height at the Intersection of the Two Separation Distances for the Two Control Features. With heights of other objects no greater than the two control features and meeting their own separation distances.
Another Example
And Another Example, with extra usable space
And Yet Another Example with Extra Usable space

As can be seen the rule itself is simple enough. Have two objects, determine their heights and separate by a distance equal to the taller object. The heights and separation distances are based on the enveloping rectangles of the objects.

This rule caters to the problem of objects falling over, such as trees, and power lines. But maybe considered extreme for technological artefacts which are not expected to fall over, and also with respect to creating open space. So the following condition added.

Condition: The rule to be applied to each point on an object.

This condition means that the ridge of a roof needs to be separated from a fence by a greater distance than the wall. But does not require the separation distance between two objects to match the total height.

When the taller object falls it will fall on the smaller object, unless it collapses in a shorter length than matches its height. A tree for example is likely to be uprooted before it rotates and falls, so it falls in a greater length than its height. A collapsing building on the other hand, may simply collapse into a pile of rubble within its own footprint, or it maybe thrown beyond its footprint.

Having set the separation distances however, the next question is what use is the space between?

If a two buildings are separated from a tree equal to the height of the tree, and the tree is on the boundary between the two properties, then both properties have similar future development constraints. If the tree is more on one property than another then the two properties have differing development constraints. It would seem preferable that a tree be constrained to fall on one property: so all boundary fences need to be set clear of an existing tree by a distance equal to the height of the tree. Whilst new trees should be selected and located, so that their maximum height fits within the boundaries of the property should it fall.

But things other than trees, such as a shed, carport or outdoor kitchen equipment, or play equipment. Typically such would be less than the wall height of the main dwelling, so separating by the height of the object or the dwelling wall height shouldn’t be a problem.

So if a dwelling is 2.4m high at the wall, then a shed or carport of similar height should be 2.4m away from the dwelling, if it is not attached. That then starts looking impractical or waste of space. Thus start looking for variations to the rule to allow infill development between two reference objects.

As we start doing that however, the infill objects are not clear of the reference objects should the reference object fall. The reference objects are therefore feature objects and more important than the infill objects.

In terms of city development, no infill buildings should be between the limits set for the buildings. So an 80m tall building needs to be 80m from other buildings. Small ancillary buildings can be placed in the space but no significant building. Ancillary buildings include bus stop shelters. But existing multi-storey buildings are often separated by a distance less than the width of a footpath. If the issue is separation of buildings produces waste space, then use the space, connect the buildings: bridge the floors and increase access/egress to the building.

Otherwise keep to the separation distances and keep infill to items of less significance and of a more temporary nature.

To avoid rules becoming the problem, rules should be dynamically adaptive, or self adjusting. The purpose of a regulator is to adjust a system and bring it back into control or into desired operating conditions. Most government regulations tend not to regulate, rather they become the problem as changing environment ceases to be compatible with the rules.

I merely created a simple rule, which is clearly impractical to apply to a collection of randomly located objects of differing heights: which is what we already have in both the natural and built environment. For a collection of objects with known locations, can potentially calculate the allowed height for each object: as the height is the shortest distance between its nearest neighbours. None the less applying the rule has potentially undesirable side effects such as waste space: trees in a forest are not separated by their heights.

So think carefully before decide the solution to a problem is to impose a rule on everyone. More than likely will cause even more problems than will solve. {So don’t do it. Ignore that. And This.}

The reason for posting now is I am currently looking at an other aspect of object heights and separation distance. This concerns the material bulk of a building, its dominance over the environment, and the need to create visual space so that people don’t feel closed in. There are certain vague general principles in the development plans, but once actual dimensions are included these become direct prescriptive requirements: no readily observable mathematical model promoting consistency. My project requires justifying a variance from the prescriptive requirements: as the proposed development if allowed to go ahead would breach the requirements. But as the rules are subjective judgement there is also little justification for imposing the rules, where they would cause hindrance, inconvenience and lack of amenity contrary to the intent and objectives behind the rules.

So having side tracked to refresh my memory of similar problems, back to writing about my current problem. I may post more detail about such once the project is over: that is when we are either granted permission for variance, or our proposal is rejected.


  1. [08/06/2019] : Original