Architect Notebook ..... ROOF

 Mono Pitch Roof House

The first question to ask is whether the roof should assume a major visual role or whether it should remain obscured behind a parapet wall. The notion of ‘parapet’ generally suggests a heavy wall envelope with a flat roof concealed behind it, whereas the decision to use a pitched roof generates a range of possibilities not only regarding roof form (steep/shallow or dual/mono pitch, for example) but also regarding the nature of the membrane (heavy/light), and more particularly, how the roof and wall effect a satisfactory junction.

Just Asa structural grid can assist in ordering a plan, so can a pitched roof give order to the building’s final form by providing a dominant canopy to which all other formal interventions are secondary. Wright’s prairie houses, with their low-pitched roofs and massively projecting eaves illustrate how a dominant roof can bring together and unify subservient visual incident.

And how will the roof turn a corner? Will the chosen eaves detail be repeated at every corner and re-entrant so that a ‘hip’ and a ‘valley’ respectively are the inevitable result, or will the corner reveal a ‘gable’ and a ‘verge’ ?Will the verge project beyond the wall plane to expose purl-ins and rafters, or will the verge be ‘clipped’, or even concealed behind a parapet? Will such a change in roof treatment at a corner imply an elevational hierarchy and the inevitable consequences in ‘reading’ the building?

roof treatment

If the plan is deep or if internal circulation routes need daylight it will be necessary to penetrate the roof membrane with some form of roof light. Again, the form these roof-lights take will have visual consequences both internally and externally. It is as well to group roof-lights or make them a continuous extrusion so that they are of sufficient visual mass to ‘read’ as part of a design strategy. It is possible to place a continuous roof-light at a roof’s ridge simply within the roof plane, elevated, or projecting one roof plane beyond another to form ‘dormers’ . The latter solution has the benefit of offering reflected light off the ceiling plane.

conservation roof-lights

We have already seen how the choice of wall membrane can profoundly affect a building’s appearance; whether heavy or light, load bearing or non-structural infill to a frame. But the wall must also accommodate openings for access, lighting, views out and ventilation as well as providing aesthetically satisfactory connections with roof, intermediate floors and the ground. The wall must also turn corners so that quoins and re-entrants are significant visual events rather than mere planning expedients.