Rooftop Equipment Screens
Rooftop Equipment Screens
One of the things that I didn’t like about my early designs was the way that the engineers screwed up the aesthetics because I didn’t know enough to anticipate the inevitable. Transformers, gas meters, condensing units, rooftop units. If it could go outside, they would find the most inopportune place and, of course, “It has to go there” was the reason.
After a while it dawns on you that there needs to be a discussion about this ‘hardware’ long before working drawings when you often find that you are backed into a corner.
Some of this stuff happens on every project - even houses. Gas meters, electric meters, and condensing units are ubiquitous. Almost no project escapes these exterior ornaments. Propose locations when you are working on the first site plan and get feedback.
What Triggers Rooftop Equipment Screens?
One of the items that creeps into larger jobs is the RTU, rooftop unit. Somewhere around 10,000 square feet, the RTU makes its entrance. The types of HVAC systems that you have in houses are driven by the building envelope. Commercial buildings must accommodate fresh air for the occupants. For an office building rated at 100 occupants (10,000 square feet), the fresh air requirement takes over as the main issue for the HVAC system. The RTU is the most economical way to address fresh air. And as the name implies, it goes on the roof.
Here is a project where a rooftop equipment screen really made a big difference. The approach to the building was from a slightly higher elevation. A rooftop equipment screen took the eyesore away. Below are the drawings that we used to document the rooftop equipment screen.
The screen in place
Site Visit Versus Site Plan For Determining Visibility
Just because you have equipment on the roof doesn’t mean it will be an eyesore. You need an analysis to see if you have a problem. If you are really good at visualization, you can visit the site and picture the building on the site. ‘See’ if you have a problem or not. I need to have the design quite well developed before I can pull this off. I use the Site Plan instead.
By taking a Google map and turning on topography you can see the elevation of various vantage points relative to your proposed roof level. Then make a scaled drawing in CAD to see the relationships. You may have to make several sketches, but it is quick and easy.
Draw a line for the building floor level.
Draw a simple wall and roof line to scale.
Show the RTU as 7’ high (a good guess).
Place the RTU about 1/4 of the building width from the edge, unless you know better.
Now extend the building floor level line as far out as your vantage point lies.
Draw a Vantage Point line parallel to the floor line and the correct distance above or below the floor line.
The vantage point is actually 5.5’ above this line (standing person). Or 4’ if seated.
Now draw a line from the Vantage Point to the intersection of the building wall and roof line.
Finally extend that line through the RTU.
Now you can see if you have a problem with visibility or not. Do you need a rooftop equipment screen?
Sightline sketch
Rooftop Equipment Screens Versus Parapets Versus Massing
If your RTU is too visible for your taste, a rooftop equipment screen isn’t your only choice. If you are making this analysis early enough in the design process, you can play with location of the RTU - move it farther back from the edge. Or add a parapet if that will solve the problem. Or consider the massing of the building itself as a way to screen the rooftop equipment.
Louvered Versus Solid
If you have settled on the need for rooftop equipment screens, there is another consideration or two. Rooftop equipment screens can be solid or louvered. Solid screens definitely block the view of the equipment. They also have a wind load that must be considered. The taller the building the more substantial the wind load. Louvers are less susceptible to wind loads but not entirely. They are also more expensive and have the awkward trait of letting you see through them if the angle is wrong (right?). Often the louvers must be inverted to actually block the view.
Roof-Set - Curb Mounted - Structural
A final consideration is how to mount the rooftop equipment screen. I have never used any method except for structural, but there are two others. Some rooftop equipment screens are designed to be set down on the roofing membrane. This sounds too much like a maintenance problem in the making, but it is an option. The second way to go is to mount the rooftop equipment screen to the curb of the rooftop equipment. This is more viable in my opinion, but can get complicated if there are multiple RTUs. You might spend more design time than the structural solution costs. Of course the curb manufacturer needs to know about this and may need to beef up the curb design. Your structural engineer may need to add strength to the structural support for the RTU as well.