Contractors have traditionally struggled with the best way to support HVAC ductwork on commercial and industrial roofs. Traditional support systems take two forms—H-frames fabricated from Unistrut channel that is connected to a rubber or plastic base, and steel supports that tie into the structure beneath the roof deck.
If you have ever spent time combing through the Engineering Catalog, no doubt you have seen examples of non-penetrating Unistrut duct supports, an example which is shown below:
Although traditional Unistrut duct supports are simple in design and offer a good deal of adjustment, we often field questions regarding wind load ratings. The Unistrut Catalog doesn’t offer wind load rating data, and folks who go down this path often get questions from their engineer of record. Click to learn more about wind load ratings.
As mentioned above, the other option to support rooftop HVAC ductwork is to fabricate a steel H frame that is welded or mechanically attached to steel beneath the roof deck. Fabricated steel H frames lack the adjustability of Unistrut duct supports, but their design can be stamped by a professional engineer (PE) when wind load rated to meet local building codes. The downside to this type of duct support is that you’ll be making large penetrations in your roof.
There are times when roof penetrations can’t be avoided. That said, roof penetrations can cause several problems. Each time the roof membrane is penetrated there is another added weak link to the roofing system. Even with flashing complete, the seals aren’t always flawless. Over time, sealants can dry out and crack allowing moisture and mold build-up. If the flashing fails, in some cases, severe leaks will damage the building and the expensive equipment below. Penetrations can also void the roof warranty, and the labor time and materials used to flash each penetration add to the overall project cost.
With this in mind, Unistrut Service Company challenged its engineering staff to come up with a new approach to avoid the common pitfalls associated with fabricated H supports and Unistrut duct supports. Our solution comes in the form of a pre-engineered kit that saves contractors (and owners) time, effort and money.
Each kit contains pre-cut Unistrut and the related hardware to achieve variable height, but the feature that sets our kits apart from the competition is a pair of concrete bases and rubber pads to create a protective barrier between the weighted base and the roof surface. Each base weighs in at 38 lbs. and features pre-cast stainless steel threaded mounting studs for long service life, and the entire system is wind load rated at 120 MPH (the wheelhouse of category 3 major hurricane force of winds). Each kit size is offered in pre-galvanized, hot-dipped galvanized, and stainless steel. We also offer custom sizes and heavy-duty custom engineered solutions to match any size ductwork, with optional PE stamps for a nominal charge.
Be it round or rectangular ducts, Unistrut duct supports are customizable to accommodate wind loads in any region of the country. Be sure to check out our roof duct support detail drawings, which are downloadable in PDF format.
Round
Rectangle
Unistrut duct supports can be ordered online and have standard finished of hot-dipped galvanized or pre-galvanized. If needed, there is also a stainless-steel option that can be ordered.
| Part # | DS01HG | DS20HG | DS03GH | DS04HG | DS05HG |
| Dimension A | 48" | 54" | 60" | 66" | 72" |
| Dimension B | 45 1/2" | 45 1/2" | 45 1/2" | 45 1/2" | 45 1/2" |
| Dimension C** | |||||
| Dimension D | 3 1/2" | 3 1/2" | 3 1/2" | 3 1/2" | 3 1/2" |
| Max Distance Between Supports | 5' | 5' | 5' | 5' | 5' |
| Max Load | 400 lbs | 400 lbs | 400 lbs | 400 lbs | 400 lbs |
| Max Wind Load | 120 mph | 120 mph | 120 mph | 120 mph | 120 mph |
**Dimension C is provided by Customer**
| Part # | DS01PG | DS02PG | DS03PG | DS04PG | DS05PG |
| Dimension A | 48" | 54" | 60" | 66" | 72" |
| Dimension B | 45 1/2" | 45 1/2" | 45 1/2" | 45 1/2" | 45 1/2" |
| Dimension C** | |||||
| Dimension D | 3 1/2" | 3 1/2" | 3 1/2" | 3 1/2" | 3 1/2" |
| Max Distance Between Supports | 5' | 5' | 5' | 5' | 5' |
| Max Load | 400 lbs | 400 lbs | 400 lbs | 400 lbs | 400 lbs |
| Max Wind Load | 120 mph | 120 mph | 120 mph | 120 mph | 120 mph |
The days of penetrating roofs to install wind load rated duct supports are over. Unistrut Service Company’s pre-engineered mechanical equipment supports not only save time, money and effort but they bring peace of mind. Say good-bye to worries about high winds damaging rooftop ductwork…and leaky roofs! To learn more about our game-changing approach to supporting rooftop ductwork, contact Unistrut Service Company for further assistance today.
