Adrian Lowenstein, P.E., MBA’s Post

Is this overlap enough? What is the need for Rock wool?

For one, ventilation is a consideration not just for climate but also type of curtain wall system used: if unified, the vent can be provided with a weep hole to the exterior of the chicken head (outside the primary air/water seal) to bith pressure equalize and drain any condensation, but venting also raises risk of something (dirt, bugs, etc) getting into your shadow box. Have to get a little more creative with venting a stick built. Since it's a spandrel cavity we typically see mull wraps to increase thermal performance, but whether they're used depends on a number of other factors (cost, construcability, total building/ glazing energy performance, interior humidity, etc). Can't say I've ever heard of spandrel glazing used at a shadow box and not sure why you would? Unless I'm missing something that'd kind of defeat the point of a shadow box, no?

For decades I've tried to educate the industry NOT to use shadowboxes. They are unmaintainable solar ovens. Our testing has recorded temperatures >120 degrees C in shadowboxes. Hence we vent our shadow boxes (to vent or not to vent is a long argument with pros vs cons) into the mullion cavity to reduce energy demands in the predominantly building cooling environment of Australia. There are many potential defects of shadowboxes that can be solved with expert design & manufacture: - outgassing of shadowbox materials staining the inside of the glass; - air-side blooming discolorations to the glass; - buckling of the backpan; - imperfect cleaning of the glass before shadowbox assembly; - Moire effect; - contamination entering the cavity through the ventilation holes. But shadowboxes have inherent issues that physically can not be solved: - condensation forming on the inside surface of the glass; - the repeated wetting/drying of the glass causing long term corrosion and staining of the inside surface of the glass. Refer Chris Barry & Peter Hartog's paper "Shadow-box panels: Risk and unexpected outcomes" from 2015 GPD. G.James solution is to use a stepped IGU with a 50mm or 100mm spacer with ceramic frit to the inside.

Thank you for sharing the detail for the UCW shadow box.  1. Consider using a thickness of 1.5 to 2mm for the GI sheet in standard sizes for the shadow box. It might currently appear thicker than necessary. 2. It is advisable to maintain a 2 to 3 mm gap between the shadow boxes to ensure proper sealing. 3. For securing the shadow box, screws with angle with Touch-up painting 4. as per UAE regulations that favor GI (Galvanized Iron) over aluminum, particularly for fire safety between floors. 5. Optimize airflow by strategically placing ventilation holes in front of the shadow box. 6. To prevent color reflections, it is advisable to place the shadow box on the outside if its color differs from the system profiles.

I’ve been looking at this detail for awhile now. How do you install? First -galv. Back panel with continuous caulking ( no air flow) , caulk screw heads Second -install insulation Third- alum panel with double side PSA glazing tape - how do you silicone? Heat build up would cause the tape to fail over time. Great detail , but hard to execute

managing the thermal qualities of the assembly is so critical- there are lots of buildings around ATL with spandrel conditions that demonstrate external condensation during the shoulder seasons, because the surface temp of the spandrel glazing drops below the dewpoint. In addition to mitigating heat buildup, ventilating the shadowbox helps warm the glass surface with the ambient temps in the building to address this.

Expanding on what Mr. Vladimir Sheverya wrote, the risks caused not only by falling temperature (condensation), but also by rising temperatures should be carefully analyzed. In addition to the temperature in the cavity between the sheet and the IGU, the temperature between the two panes of the IGU should be checked (dynamic modeling). Remember that the 1st seal can be butyl (2nd seal silicone), and its critical temperature is lower than that of silicone or glass! PS.I don't like unventilated spaces, 100% tightness everywhere is difficult to achieve.

Nice post👍, but.....so many deatails explain the physics...of course it's important and it could be done in variousa ways. Sometimes much easier using plain ventilated facade materials...treating the air space in that manner with drain holes to evacuate condesation. Dew point is crucial but often, in reality, not as calculated. On the other hand, rarely companies pays attention/explains how the shadow box intersection with mullion's brackets are handled....dealing with complex gap formes, looses not to mention fire proof etc. It would be nice to se this for change

Thank you Adrian for bringing this up. Thermal design of shadowboxes is indeed tricky as the thermal bridging effect for the spandrels has always been overlooked. I have done some simulations as shown below: a) It is interesting to note that the R-value of Case 1 is only 3.5% worse than the current scheme, which means that the contribution of the mineral wool is very minimal. This is because the position of the mineral wool is closer to the warm side, where there is less heat flow. Replacing good insulation (air) with better insulation (mineral wool) is like increasing the wall thickness of a bucket, but the holes in the bucket are not plugged. b) Case 2, improving the frame (increasing the thermal break and adding insulation properly...) is more effective. This is because some holes in the bucket are plugged, but somewhere else becomes relatively weak. I am sure there are many ways to plug the holes and am happy to see the discussion going on... Cheers!

The topic is interesting, but the given drawing is far from the best example. In this system, there are many not quite successful solutions both from the technological side and from the side of physical processes. From the point of view of safety, the unit of structural bonding the IGU to the frame is the most responsible in this system. This system accumulates significant thermal energy in a closed space. In turn, the place for bonding on the frame involves three-sided bonding of structural silicone. This means that there is potentially designed tear or shear in the structural silicone. Modeling and calculations of similar elements showed the possible temperature of the parts in the cavity behind the IGU up to 120°C\248°F (This shadowbox is an analogue of a solar collector but without energy extraction). In this case, what would be the temperature on the surface of the façade system from the room side?