describes the aluminum extrusion rafter system that will hold the glass. All three of these options can be structural in nature meaning they will span certain distances to be covered and carry the weight of the glass and potential snowload calculations. Some rafters will span further than others without need for a second beam.
Both of these aluminum extrusion options can also be non-structural and used to hold and seal the glass on top of the wood or timber rafters. It is not always recommended and may not be approved by an engineer to place the glass panels directly onto any type of rafter using foam tape and/or silicone but many of these systems are designed that way in order to offer a cheaper product.
Pressure Plate Systems are the most expensive option and are always building code approved when engineered properly with the right thickness of glass which may have to be laminated if the engineer calls for it. These systems use propietary rubber gaskets that are integrated into the aluminum rafter that the glass panel sits on. A non flexing pressure plate then goes over top of the glass that also has integrated rubber gaskets. The glass is secured by screwing the plate into the mating section of the rafter that puts pressure on the glass by pinching the upper and lower rubber gaskets together to firmly hold the glass from glass shifting, wind lift and load deflection. Once the plate is installed a beauty cap is clipped over top for the final finish. Glass pressure plate system diagram
Pressure Plate Rafters are made from extruded aluminum that is shaped into a hollow rectangular box shape rafter that range in height from 2" to 7" depending on the span or distance between supporting ends. The longer the span the taller the profile. Once the glass gets past a certain lenght depending on thickness and width, a purloin cross rafter or butt joint seal maybe required to join the second glass panel to the first in the same bay.
We use Pressure Plate Veneers when we install our glass canopies over wood or timber rafters. They function exactly like pressure plate rafters but rely on the wood rafters for structural support and like the aluminum rafter only stick up above the wood rafter by 3/4" with our low profile beauty caps. Are in stock colors are Bronze, Black and Silver. We also offer many custom powder coated colors for an additional cost and a little longer wait time.
T-bar Aluminum Rafter Systems are usually the least expensive glass roof option. The upside down T is what the bar looks like when looking at the section cut out or the end of the bar. The span strength is determined by the height of the perpendicular portion of bar that sticks above the glass unlike a conventional rafter where the strenght comes from below the glass. T-Bar heights range from 2"- 6" and generally speaking only have 1 vertical piece of metal unlike an aluminum rafter that has 2 so a higher profile is usually required to carry the same load and span the same distance as an aluminum rafter.
T-Bar rafters secure the glass with either a glazing bar or roll bead that essentially is clipped or driven into the mating channels of the extrusion by hand or a rubber mallet. These types of systems utilize either a neoprene gasket or a double sided adhesive foam tape to support and seal the glass transitions that may compress or disintegration over time with heat and may allow glass to metal contact near the glass edge that is the weakest area of the glass panel.
Hybrid Aluminum Rafter Systems are nothing new but are more of an update to the T-bar system that uses a box frame rafter like the pressure plate rafters and usually a glazing bar or roll bead to secure the glass like a T-Bar system. These types of systems use either a double sided foam tape to secure and seal the glass but some use the integrated neoprene gasket like the pressure plate system.
The span or distance the rafters can reach in any scenario will determine the size of the rafter to be used. There are many companies that use off shore (foreign made) rafters and glass that are shipped in containers where the profile and gauge of metal and glass is much thinner and can not support spans longer than 8 or 10ft and may not be locally engineered for our building code requirements. They are usually brought over as one color (white) and then need to be stripped or sanded and recoated for different colors choices that may not be as reliable as powder coating or painting mill finished material (raw aluminum)
Laminated Glass is the safest for overhead deck and patio covers because it incorporates a film between two layers of glass that will keep the glass panel from breaking if tree branches, hail or birds drop objects onto the glass canopy. Glass impurities have also been known to cause spontaneous panel shattering when triggered by impacts or glass edge contact and binding. Many engineers will call for laminated glass and/or a pressure plate rafter systems for permitted deck and patio covers not just for siesmic concerns but for any reason that will avoid a glass panel shattering or falling on someone causing injury or fatality.
Safety is always a good first priority when bidding on a project. Glass panels can shift in the rafters for many different reasons. All deck and patio covers are required to have a minimum slope, so right from the very beginning the glass is contending with gravity. Snow loads, wind lift and uneven deck and concrete footing settling as well as structure expansion and contraction due to humidity and heat all create opposing forces that will test the integrity of all glass deck and patio covers.