Entry
Inclination and Evolution: A Stair Design

Inclination and Evolution: A Stair Design

Thursday, January 05, 2017 | | Mark English Architects

This central staircase rail went from glass, to steel, and back to glass again, in a design transformation aided by hand sketches, computer renders, and actual as-built appearance at the job site. Image: Mark English Architects


Many design aficionados fixate on grand spaces, “great rooms”, built-ins, and other features as design elements, without fully appreciating the importance of circulation. The master suite, the bath, the kitchen, home theaters, and other amenities are touted on design sites for their luxuriousness, but it’s the transitions, such as stairs or passageways, that tie it all together. If stairs are featured in a high-end home, it’s a grand staircase that takes up the entire main portion of the house.

A grand staircase like this one is spectacular, but where does it lead?

A grand staircase like this one is spectacular, but where does it lead?

 

Existing Condition

This particular project from Mark English Architects involved a remodel to an existing three-story home in San Francisco. The building had a basement, a main floor, and an upper floor. We viewed some 3D sections of this project in a previous article that introduced the power of hand drawing. Now, we focus on one particular feature of this home, namely, a central stair as a ribbon, winding all the way from the top of the building to the basement.

The existing stair was a typical wraparound, with wooden rails and a feeling of enclosure. Image: Mark English Architects

The existing stair was a typical wraparound, with wooden rails and a feeling of enclosure. Image: Mark English Architects

 

Phase 0: Glass

The earliest conceptual design for the remodel called for a large glass wall showcasing an interior walkway on the third story. A central glass stair would run down the center of the house. The glass wall concept was rejected by San Francisco Planning, for historic reasons. Without the wall, the glass interior didn’t make as much sense from a design standpoint.

(As it turned out, the original building from 1917 was designed by a female architect named Elizabeth M. Austin of the firm Austin & Sanford. Mark English Architects commissioned an official historic report from Page & Turnbull, Inc. This report established the importance of preserving the original exterior. The final design left the home’s exterior largely the same as before.)

Initial design proposal, exterior. A central glass stair led to a glass walkway on third floor, with light from a long row of skylights. Image: Mark English Architects

Initial design proposal, exterior. A central glass stair led to a glass walkway on third floor, with light from a long row of skylights. Image: Mark English Architects

Initial design proposal, close-up of central circulation under the central skylight. Note the glass floor on the raised walkway and stair treads. Image: Mark English Architects

Initial design proposal, close-up of central circulation under the central skylight. Note the glass floor on the raised walkway and stair treads. Image: Mark English Architects

 

Initial design proposal, interior, showing a glass staircase in the center of the building, with glass rails and interior skylight above. Image: Mark English Architects

Initial design proposal, interior, showing a glass staircase in the center of the building, with glass rails and interior skylight above. Image: Mark English Architects

The final design exterior was a compromise with City Planning, and preserved the original building’s historic appearance. Image: Mark English Architects

The final design exterior was a compromise with City Planning, and preserved the original building’s historic appearance. Image: Mark English Architects

 

Phase I: Steel

With the original glass curtain wall off the table, the architect determined to re-work the interior. A subsequent stair design called for vertical rails made from steel panels. The stair treads from the main floor to the upper floor were to be fabricated from cantilevered steel. The stair from the basement up to the main floor would still have wooden treads.

Although the previous images showed the stair rail panel as a solid sheet of steel, the designers were in fact exploring the idea of perforated steel panels. The clients designed this pattern themselves. Mark English Architects

Although the previous images showed the stair rail panel as a solid sheet of steel, the designers were in fact exploring the idea of perforated steel panels. The clients designed this pattern themselves. Mark English Architects

A physical model shows the stair’s progression through the house, from basement to upper story. Image: Mark English Architects

A physical model shows the stair’s progression through the house, from basement to upper story. Image: Mark English Architects

 

Then, The Client Saw The Treads

During construction, the client saw the treads exposed. They were so excited by the look, that the architect changed the rail design from steel back to glass. “The clients were bold enough to say what they really wanted. They really got it,” observed the architect.

Construction photo showing the stair landings and clockwise ascent as seen from the main floor. The steel treads are welded to a frame that runs along the back wall. Image: Mark English Architects

Construction photo showing the stair landings and clockwise ascent as seen from the main floor. The steel treads are welded to a frame that runs along the back wall. Image: Mark English Architects

 

The client saw the pattern of the steel treads and wanted them to be visible in the final design. The stair panels and rails, which had been designed in steel, were changed back to glass as per the initial design. Image: Mark English Architects

The client saw the pattern of the steel treads and wanted them to be visible in the final design. The stair panels and rails, which had been designed in steel, were changed back to glass as per the initial design. Image: Mark English Architects

 

Phase II: Glass Rail

At this point, the technical problems involved the attachment of the glass panels to the stair treads, the shaping and mating of the panels to one another in a seamless fashion, and addressing seismic concerns. The panels also had to be joined to one another along the vertical seams. The top edge of the panels was rail-less.

Ascent from main floor to upper floor, viewed from the main floor. The glass panels needed to be shaped and fitted together. Image: Mark English Architects

Ascent from main floor to upper floor, viewed from the main floor. The glass panels needed to be shaped and fitted together. Image: Mark English Architects

 

Ascent from main floor to upper floor, viewed looking down from upper story landing. The stair rail panels would have to be fabricated. In this drawing, the callout explores the interaction between glass panels, where the stair turns a corner. Image: Mark English Architects

Ascent from main floor to upper floor, viewed looking down from upper story landing. The stair rail panels would have to be fabricated. In this drawing, the callout explores the interaction between glass panels, where the stair turns a corner. Image: Mark English Architects

 

Detail of stair from basement to first floor, after changing the stair rail panels from steel back to glass. Although the cantilevered steel stair treads didn’t extend to the basement level, the glass panel rails did. Image: Mark English Architects

Detail of stair from basement to first floor, after changing the stair rail panels from steel back to glass. Although the cantilevered steel stair treads didn’t extend to the basement level, the glass panel rails did. Image: Mark English Architects

 

Siding on stair rail, shown from second story. The stair on the right ascends to the upper story. A raised walkway leads off to the right, with another landing and stair descending to the basement level. Image: Mark English Architects

Siding on stair rail, shown from second story. The stair on the right ascends to the upper story. A raised walkway leads off to the right, with another landing and stair descending to the basement level. Image: Mark English Architects

 

Ascent from the basement to the main floor. In this portion of the stair, the stair treads are wood, with risers. Sketch diagrams of the steel rail panels for the stair helped the architect to understand how transitions between panels, edge of stair, and edge of floor could occur. These early hand-drawn studies developed ideas for possible detailing. Image: Mark English Architects

Ascent from the basement to the main floor. In this portion of the stair, the stair treads are wood, with risers. Sketch diagrams of the steel rail panels for the stair helped the architect to understand how transitions between panels, edge of stair, and edge of floor could occur. These early hand-drawn studies developed ideas for possible detailing. Image: Mark English Architects

Second view of ascent from basement to first floor, viewed from the other side and looking down. This stair sketch diagram shows the landing and its relationship to the steel panels. The details of the transitions between different elements took precedence over the actual dimensional representation in the sketch. Image: Mark English Architects

Second view of ascent from basement to first floor, viewed from the other side and looking down. This stair sketch diagram shows the landing and its relationship to the steel panels. The details of the transitions between different elements took precedence over the actual dimensional representation in the sketch. Image: Mark English Architects

 

Phase III: Full-Size Physical Mockups

Full-size physical mockups built onsite out of plywood were an important part of the process of determining the glass layout. By this point, the stairs themselves were already installed, so the mockups consisted of shaping plywood panels as stand-ins for the glass panels to come. Then, the glass panels could be shaped using the plywood panels as a pattern.

Physical mockups help the architect determine the exact pattern needed for fabrication of custom stair panels. Ascent as viewed from the main floor. Image: Mark English Architects

Physical mockups help the architect determine the exact pattern needed for fabrication of custom stair panels. Ascent as viewed from the main floor. Image: Mark English Architects

Physical mockup of stair rails, showing ascent to the upper story. Image: Mark English Architects

Physical mockup of stair rails, showing ascent to the upper story. Image: Mark English Architects

 

Bolting it Down

To attach the glass panels to the stair treads, a special standoff bolt was used.

Stair detail showing attachment of glass panels to stair treads. The treads are cantilevered steel with wood cladding. Image: Mark English Architects

Stair detail showing attachment of glass panels to stair treads. The treads are cantilevered steel with wood cladding. Image: Mark English Architects

Detail of stair from basement to first floor, showing placement of attachment bolts for the glass panels along the side of the stair. Image: Mark English Architects

Detail of stair from basement to first floor, showing placement of attachment bolts for the glass panels along the side of the stair. Image: Mark English Architects

Detail of stair from basement to first floor. Image: Mark English Architects

Detail of stair from basement to first floor. Image: Mark English Architects

 

Structurally Sound Rail-Free Design

The design called for the glass panels to be attached at the bottom, and caulked together along the seams, with no attachment at the top. How would this work in earthquake country? Would the glass panels experience too much flexion along that top ridge? A structural engineering analysis created recommendations for tempered and laminated glass, showing major stress points and validating the final materials and detailing.

A structural visualization of the flexes and stresses that a rail-less glass stair rail panel could expect to experience during a seismic event. The spots along the bottom represent the attachment bolts, while the single spot on top represents the flexion of the tempered and laminated glass. Image: Triumph Engineering, LLC

A structural visualization of the flexes and stresses that a rail-less glass stair rail panel could expect to experience during a seismic event. The spots along the bottom represent the attachment bolts, while the single spot on top represents the flexion of the tempered and laminated glass. Image: Triumph Engineering, LLC

Flex points show for each of the stair rail attachments along the bottom. The top flex point in the center is how a rail-less glass panel attached only at the sides and bottom could be expected to behave. The panel is attached at either side to other glass panels with a specially rated flexible silicon caulking.

Final Result

The final result has a sculptural quality to it. The stair appears to float in space as an invitation to ascend.

The completed stair with wood-clad steel treads and glass panel rails. LED lights illuminate the underside of the stair with a warm glow that complements the cooler daylighting coming from the skylight above. Image: Mark English Architects

The completed stair with wood-clad steel treads and glass panel rails. LED lights illuminate the underside of the stair with a warm glow that complements the cooler daylighting coming from the skylight above. Image: Mark English Architects

 

This model close-up looks very close to “the real thing”. Image: Mark English Architects

This model close-up looks very close to “the real thing”. Image: Mark English Architects

 

Leave a Reply

Read previous post:
Desert Modern Walking Tour: Palm Springs

The simplicity of Desert Modern architecture finds a natural home in Palm Springs, California. Image: Mark English Architects

Close