Post 685 –by Gautam Shah
A reveal is a cover strip of wood at the corner (inner or outer) edge of an opening’s frame in masonry. It is often confused (due to very similar purposes) with rabbet, architraves, style, extrados-intrados (for arched openings), etc. The reveal may be formed of wood, stucco, stone bricks or metals. The reveals are placed on all sides of windows or three sides of doors. The reveal may shape-wise merge with the sill or threshold at the bottom. The basic purpose of reveal is to cover up the junction of wall and openings’ frames, but often play important role in framing, masking or enlarging the opening.
Walls are chiefly load bearing entities. The thickness is the third dimension to the nominal planner structure. The third dimension has a functional depth, and architectural character. The Architectural expression of the wall-depth modulates the facade and gives a massing flavour. The functional depth frames the view, and regulates the illumination in the interior space.
Openings in thicker walls have external or internal ‘reveals’ surrounding the frame. The bottom section forms the ledge of the sill. Openings placed on the outer face create deep an inner side or intrados (originally intrados meant, the inner curve of an arch or vault). Similarly openings placed on the inner edge form exterior side or extrados (originally extrados meant, the outer curve of an arch or vault).
The deep interior sides, if ‘square-edged’ (at a right angle to plane of the window), made the perceived size of the opening smaller, then it actually is. This type of setting on interior sides, was not a major issue, where the room spaces were comparatively narrow, and so reflection from opposite walls was available. The narrow spaces were due to the technological restrictions and for functional requirements, such as in long halls and church buildings. In squared buildings the illumination was balanced from windows in the drum perimeter of the dome.
The deep exterior sides, if ‘square-edged’ (at a right angle to plane of the window), made the perceived size of the opening smaller, a desired arrangement to enhance the wall area and de-emphasize the presence of gaps of openings. It reduced the ingress of winds and snow-rainwater. To emphasize the presence of gaps, portals were added as the opening’s treatments.
The ‘square’ edged openings have high contrasting brightness. Such windows require counter illumination to reduce the glare. To distribute the light better in the interior space, inner sides (-intrados with the window fixed on the outer edge) and an outer side (-extrados with the window fixed on the inner edge) were splayed by chamferring. The angled side surface was further carved, fluted with ornate borders or architraves.
Inner vertical sides, window heads and the sill, all were sloped to enlarge the reflective surface area. The chamferred sides on the outer face allowed more light by increasing the sky component, and allowed wider view of the outside.
The effects of square and the chamferred sides of openings were well known to the mural artists (working with different mediums such as tempera, mosaic and frescoes painting), who accordingly composed the stories, shading in the scene, perspective angle, colour’s hue and tone of artwork.
In Romanesque and early Gothic architecture the windows were fixed on inner face, creating a plain and undisturbed interior surface. But by the time this was perfected, the Gothic walls were completely diminished, and windows were as wide as the gap between two columns.
Side walls of Gothic buildings became thinner due to the arrangement of flying buttresses and use of load-bearing columns. But the same advantage was not available in case of un-buttressed Front wall. The entrance doors of Gothic churches were flush-set on the inner face, and that allowed better view across and fuller distribution of light. But the doors set deep in the thick walls, needed chamferring with serrated sides.
In Baroque architecture the depth of opening was concealed with the projected facade elements like columns, pilasters, cornices, or pediments. In Italian Renaissance the facade had an applique lattice like a pattern that united several openings. In post medieval period, windows began to protrude out of the buildings, over into the narrow street. Bay and oriel windows, Mashrabiya openings in the middle East, and Zarokhas in India transgressed out, mainly to gain sideways view and air. The multi sided mass of the projection became a personal statement.
In post medieval period, window projections created serious fire hazards and issues of encroachment of public lands. Both of these were corrected through improved fire laws and defined easement rights. Fire laws required windows to be within the wall (without any projections like ledges or hanging shutters). Later the Window tax curtailed the number of openings in a building.
Gothic architecture had already shown how to divide large openings with traceries of mullions and muntins. Large windows in thin walls require framing and masking, but small depth did not allow formation of integrated architectonic elements, or scooping out for niche creation. Architectural add-on elements such as half columns, extrados, porticoes, etc. were additives placed to frame and highlight the opening.
The surface of the window was strongly stated by articulated divisions, contrasts between glazed and other surfaces like rusticated masonry. Windows were also placed in inward or sunken bays. The mid-wall between the windows was treated as very shallow niche or bordered frame for murals, paintings or placing a fireplace or library cabinet. Building’s facades of thin walls were also undulated by outward bay windows, ledges and other projections.
Thick walls accommodate the shutters of doors and windows within the gap. But shallow window gaps offer no shading. Some form of external shading system is required. Such shading systems have been used for creating architectural facade system, as in Chandigarh Secretariat building.
Glass curtain walls are thin body construction, often without any projections for solar protection. This now sought through the glass technology, and the ventilation through separate HVAC system. Thin walls save floor space, and so are economic in spite of the compulsory recourse to other compensatory facilities. The nominal architectural play of depth and shadows for 3rd dimensional visual depth is not available with openings in very thin walls. This is now recreated by volumetric play of the building mass, or by variegated surface finishes. For such surface modulation, other means include visual reflectance and glows (illumination from within).
The vividness of stained glass windows or the colourful lanterns of Gothic eras are now recreated through see through LED glass. At another level the touch screen provides the same fare. The mix of the two will become part of architectural and interior face of buildings.