The 'Shadow Gap'

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The architects obsession with the shadow gap? OK, so this is a bit of a ‘running joke’ within the construction industry but there are very good reasons for carefully considering imposed gaps, mediating materials and changes in plane, and a lot of it comes down to building and material tolerances and buildability.

Your beautifully engineered smart phone is constructed in a clean environment from high grade materials and has to conform to fine tolerances in order to function, be water resistant, keep out dust and remain robust when being dropped on the dance floor. Hence the design can consider junctions between glass, metal and plastic that are flush, seamless and well, engineered.

Life is not the same on the building site where buildings are constructed in all weathers and will be subject to temperature change, dynamic and imposed loading, changes in humidity and the like. The materials used may be natural, such as timber, straw, earth. Some will be rougher or random in appearance, requiring the judgement of craftsmen on site in order to realise an acceptable quality of finish. Others are more regular but due to manufacturing, will have accepted and agreed natural tolerances. And of course, the process of constructing something as large as a building, over a relatively short space of time, in all types of weather and climatic conditions inevitably means that those carefully considered CAD dimensions that appear in digital form won’t exactly translate into what is finally constructed on site.

Good designers know and understand this and make allowance for this inevitability in their designs. The shadow gap is one way of doing this, by forming an engineered break between two surfaces that might otherwise not meet cleanly.

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Walk around your house and look at the skirtings, architraves, and mouldings for what they really are, they look the way they do for a variety of reasons but are all there essentially for the same reasons. Skirting boards cover the difficult-to-get-to lowest section of the wall where gaining a good plaster finish and termination will always be hard, as well as taking the knocks and bumps of everyday life. They hence create a visual ‘clean line’ more readily than plaster and paint alone. Floor finishes can terminate beneath them, allowing for physical finishing and for cut ends to be hidden. The door frame architraves provide a simple solution to covering the construction gap between wall and frame, making allowance for variations in wall plane and removing any concerns relating to differential cracking between timber and plaster. Over time these devices have changed with fashion, providing future generations the ability to experience historic style and social status in our buildings.

Some of the hardest buildings to both design and build appear to be the simplest because cover strips, skirting boards, architraves and coving have no place in minimalist architecture. And hence every junction needs to be carefully thought through so that it is buildable in a way that provides that finely engineered, effortless final appearance. It’s often deep beneath the construction layers that the thought and planning has needed to go in order that the finished surface is as intended and meets its adjacent surfaces just-so. And this is where a shadow gap might help, a minimal break between one panel or surface and the next, for when a completely seamless look may result in disappointment. It echoes the panel gaps in automotive design or the minimal recesses between materials in appliances and electrical equipment. A recessed junction can generate scale through creating individual panels and hence subdivision of a larger surface. It can be used to visually align separate openings or features, reinforcing the designer’s intent. It can allow the construction and dismantling of a surface or element without resorting to cutting-out and messier demolitions.

Designers hate messy junctions, those that are not consistent, such as when one surface is recessed while further along the seam it becomes proud. It’s generally unappealing because it provides too direct a link to how it had been constructed and often the relative flimsiness of the specific materials used. It hints at inaccuracy and unevenness, the opposite of ‘high quality’. The shadow gap is designed to be big enough so that direct comparison cannot be made between each plane, because first-off, the tell-tale shadow cast by a proud surface is not visible within the designed shadow. This device can also provide a physical end stop to an applied finish, colour or surface treatment, the resultant effect being of a very crisp, straight line. If you’ve ever tried to cut-in with a paint brush against an internal corner you’ll know that it’s not easy and rarely generates a properly clean vertical or horizontal line.

Junctions can also be messy if too many, or too opposing, elements come together. On a larger scale, designers use mediating elements such as glazing to visually break old from new construction, or dramatic changes in plane, height, history, and scale. The glazed ‘slot’ or recessive dark-coloured surface is a neutral background for different things to happen either side. It’s the rice between the Madras and Aloo Gobi. This is the shadow gap scaled-up.

A lot of us have faced conundrums about how to finish things off when completing DIY tasks, especially if you have limited skill and / or equipment. It may be a bit of an in-joke but next time you face such a challenge you might want to reach for a shadow gap.