Roofing Equipment Stands – Part II

Today, we continue with part two a two-part series on roofing equipment stands.   In our last article, we took a look at the functional purpose of why roofing equipment stands are used and some of the problems of not using roof stands for equipment.   We also talked about upkeep and maintenance of HVAC and other types of mechanical equipment on flat or low slope roofs.  Today, we look at why its important to consider how the roof and this equipment work together to avoid conflicts.

 The outline for this two-part article series follows below:

  1. The Functional Purpose of Equipment Stands
  2. Problems Associated with Omitting Equipment Stands
  3. Required Upkeep and Maintenance 
  4. Avoiding Conflicts Between HVAC Equipment and the Flat Roof

Required Upkeep and Maintenance 

Flat roof maintenance is particularly complicated and onerous,  but good flat roof maintenance can save thousands of dollars every year.   The interface area between the flat roof and the rooftop mechanical or HVAC equipment is generally very complicated area.  

The picture below shows an example of a mechanical equipment stand.  Looking at this photo you can see some of the elements of complication.   Overall the roof is so large that there is no way to drain the roof without significant applied slope and / or internal drains.  In this case,  internal drains have been used but overall the insulation or tapered polyiso underlayment is insufficient to get proper grade out to each of the internal drain.  You can see clear areas of pondering which are problematic. This is an EPDM roof membrane, similar but very different than modified bitumen. Modified bitiuman membrane, by comparison has significantly more seams and therefore is more problematic with areas of ponding.

epdm membrane
This particular photo, of a large commercial flat or low slope rooftop, shows the roof is covered with a EPDM membrane.   Dunnage has been placed directly on top of the rooftop membrane but used to dissipate or attenuate the load of that HVAC unit is not as good as separating the membrane from the equipment, but it’s much better than nothing.
broken concrete papers
This particular photo above shows an interesting example of an installer or contractor attempting to do something that is kind of right but overall actually wrong. They installed broken concrete papers underneath the HVAC unit but did not install a slip sheet. At least in this case the concrete papers we’ll slightly lift the unit above the adjacent membrane. However the height is insufficient and a slip sheet is required to isolate the unit.

The picture below shows a HVAC unit set on a custom wood platform between the demising walls of this rowhouse in Capitol Hill, DC.   A rubber mat was installed on top of the wood platform to further reduce vibration from the electric controlled mechanical unit. This particular mechanical unit has both a pump and a fan which causes a significant amount of vibration. Without vibration reduction or isolation, the vibration can transfer down into the building itself.

steel i beams
The HVAC equipment is initially set directly on top of the steel I-beams but the beams themselves are not actually fastened or set in place and can actually spread or shift over time, especially with HVAC equipment like this.

At the same installation as shown in the picture above, another photo shows a different aspect of those items at the tail end. Here where the I-beams bare on the demising walls, the steel has been separated from the aluminum coping with the use of another neoprene separator. 

correct position of steel i beams
This particular photo shows a pair of steel I-beams that are both now correctly coated with a rust coverting primer and two coats of high-performance industrial black finish coat paint, but these particular beams are also set upon a neoprene gasket where they bear on the demising wall. This neopreme gasket absorbs and isolates vibration from the HVAC equipment.

Avoiding Conflicts Between HVAC Equipment and the Flat Roof

The vast majority of conflict issues between HVAC equipment and the rooftop membranes generally occur within a limited subset of areas.  In fact, we often see some of the same issues repeat again and again.  Some of the most common issues that we see, of a repeating nature following the list below:

  1. Improperly sealed penetrations.   Often, line sets, which provide the heating and cooling refrigerant to and from my condenser or evaporated unit on a rooftop Are generally ganged or grouped together with additional elements such as condensate piping, the thermostat or low voltage control wiring, and the line voltage needed to power the equipment.  There are a variety of particular details that are often used and approved for sealing around the penetration of these items through the rooftop membrane, one of the best methodologies is either a gooseneck pipe that runs through the roof and then above the rooftop but has a double elbow set to return the piping downward before it  Is connected to the rooftop equipment.  Another type of approved methodologies is a pitch pocket.   Addition to these 2 approve types of methodologies, yet very few work as good or better than pitch pockets or gooeneck sleeves.
  2. Damage from mounting or lack of equipment stands.   Often, when mechanical or HVAC equipment is set directly on top of a roof membrane damage can be caused by excessive bearing at concentrated spots of the mechanical load.
  3. UV damaged wires or line sets or pipes.   Ultraviolet rays have a tendency to deteriorate the exposed surface of wiring, piping  and or insulation to refrigerant lines.   As these areas of the piping or other elements are wearing away, it can lead to areas of water entry and then that water can follow the areas of the casing or shell or sleeve down into internal parts of the building.
  4. Ponding at lap joint seams where the membrane is depressed by bearing points.   In parts of the article above we talked about the problems associated with bearing point depression in rooftop membranes, but these problems are exacerbated or excenuated where there are seams coincident with the points of depression.   To make it simple, you can basically say that it’s never okay to have ponding areas on a flat or low slope roof, but those areas of ponding or water build up are particularly worse when they are at the location of lap joints or seams in the membrane because those areas have a tendency to leak when they are coincident with areas of submerged water.
condenser on damaged wood
This particular photo shows a HVAC condenser unit set upon pieces of wood dunnage. A slip sheet is missing but yet required by the building code.

The next photo shows a different HAC condenser unit in slow with Clint slightly better quality, but also missing a slip sheet where it is in contact with the single-ply roof membrane.

correct installation
Interestingly,  several elements of the installation are correct, yet still there are details which are incorrect.

Smart and proactive replacement, construction, upkeep and maintenance of low slope roof and mansard roof systems requires an enthusiastic interest and understanding of historical methodologies, waterproofing principles, and building science.   Here in Washington DC, historic and modern residential and commercial buildings are extremely expensive and the roof and related systems provide the shield that preserves the building. 

We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the value of quality construction and building maintenance, and develop a relationship with our company.  You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the roof and related systems of your building in Washington DC, contact us or fill out the webform below and drop us a line.  We will be in touch if we can help.

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