External Glass Floor roof as viewed from the inside
External glass roof floor corner, maximising daylighting potential
Glass floor roof glazing dividing new and old: vertical to horizontal floor detail.
Walk on external glass floor roof with anti-slip detailing.
Glass floor roof design:
Glass floor roof glazing solution:
When we were approached to design this external double glazed glass floor roof glazing , the client’s brief and architectural intent couldn’t be more precise “a walk on glass rooflight”.
This glass floor roof glazing solution adds value to the contemporary architectural design in two ways.
Firstly, this glass floor roof design draws natural light daylight deep into the existing house and new build extension,secondly this glass floor extends the surface area of the terrace located at first floor level.
This glass floor roof-light glazing solution is bespoke and unique to the building form, merging new and old, it is critical to the daylighting and environmental strategy within the building footprint, acting as a natural light filter to living spaces within the existing house.
The form of this snaked glass floor roof glazing wraps itself around the existing Georgian wall,it has a vertical end and an internal/ external corner.
Glass Floor Roof Configuration
The outer pane of the clear spanning double glazed units sit on a perimeter steel frame, the internal pane sits between the steel and is structurally bonded to the outer pane.
The outer ADT face pane consists of 4 sheets of 10mm toughened laminated together with an ionoplast interlayer. Each pane is individually heat soaked tested (HST). The glass is fritted to face two of the fourth pane along the perimeter outer glass step detail and intermediate glass joint details.
The inner ADT face pane is 12mm toughened /laminated consisting of 2 pieces of 6mm clear glass, toughened resin laminated together. The K glass is located to the inside of the cavity. The use of a hard coated low e glass enabled fritting to face 3. Black was picked as the most suitable colour to conceal the black edge of the spacer bar and un-slightly silicon line.
Project Risk Management
At the initial design, we sought specialist advice on the design of the glass floor roof configuration and how to manufacure the double units..
Glass risk management became a vital component in our design approach. Investing in the design enhanced product longevity service life.
Key glass risks to be considered in detailing a glass floor roof Design:
- The laminated interlayer had to be u-v stable, resistant to solar gain and aesthetically pleasing. Degradation along glazing edges as a result of wetting been critical and a decisive factor in selecting the ionoplast laminate interlayer.
- Possible degradation of IGUs along its edges from ultraviolet light had to be managed so had the use of materials such as sealants. Fritting been the critical factor in the resolution of this issue.
- Nickel Sulphide Inclusions, always a problem and very difficult to risk manage, each unit weighed in excess 350 kg. Spontaneous facture would result in excessive glass replacement costs. Heat soak testing (HST) reducing the risk, adding cost to glass procurement but adding value to the project longevity in service.
Glass Floor Roof Procurement
Typically this type of project takes time to procure as the glass floor units are individually prepared to suit bespoke on site conditions.
In total there are 6 layers of glass, the glass manufacturing sequence includes:
- Cutting, polishing and cleaning.
- Fritting to specific faces of certain layers to suit bespoke interface detail.
- Laminating each outer pane three times and the inner pane twice.
- Assembly of the units.
Durations typically takes from placement of order depending on the level of architectural glass detailing 12 to 16 weeks.
Glass Floor Roof to Vertical Wall detail
The vertical end gable to this glass floor roof solution was the most difficult to detail. The façade solution had to work with a number of unique interface conditions. These included:
- An existing wall which was neither plumb in either direction or incorporated a vertical dpc. This wall was not insulated.
- A new wall to the left side which had a primary steel structure and was externally clad in stone. Tie back fixing, weathering and thermal details been critical to over come.
- The top of this wall linked to the roof upstand creating a difficult interface condition to weather between the horizontal glass floor and vertical structurally clamped solution.
The constructed frameless glass solution that takes each of these interface conditions, the solution is a simple three sided stick curtain wall frame with no head transom. The framing members are recessed behind the external fabric, the rhs jamb internally is insulated to reduce the risk of thermal bridging. The frame is fixed along each side and across the bottom.
The face glass is structurally clamped into situ using a concealed vertical toggle, the vertical glass joint between the edge of the face glass and the stone is silicon sealed using Dow corning 791.
Stepping Glass roof detail
The external 40mm thick glass edge of the roof outer pane extends 150mm over the inner pane forming a minimalist glass overlap detail with the vertical face pane. The inner pane set back in line with the inside of the face glass, nthe outer pane forming a neat architectural glass joint detail.
Glass Fins detailing
The two external glass corners are supported by a glass fin. This fin is 20mm wide by 300mm high. Its ends are captivated at each end by a bespoke 316 stainless steel-bracket. The fins are fabricated to suit each interface conditio, its plates concealed behind the plaster board.
All other intermediate glass joints do not require glass fins.
The toughened/ laminated glass fins supports the 40mm outer pane, each pane stepped over it by 15mm allowing the imposed weight to be transferred to the fin. The inner pane sits in between the fin and does not take on any dead weight.
Other Interface conditions
The three external edge conditions of fundamental importance to the overall performance include:
- Upstand detail between paving slab and roof unit.
- Junction between existing wall and glass floor edge.
- Glass floor detail to parapet wall.