A Checklist Can Help Multiple Trades Coordinate Their Work on Pipe Curbs

It never ceases to amaze me the way pipe penetrations through the roof are flashed or integrated into a roof cover. It’s as if there is a contest to see if everyone can do it differently — roof cement, membrane pitch pans, pourable sealer, lead, sheet metal covers, pre-molded boots, roof curbs penetrated in every which way, and on and on. Ninety percent leak within a few months, only to then be caulked, covered in roof cement or duct taped. (See Photos 1-6.) Most of these conditions relate to roofs that have been re-roofed. What’s a designer to do?

The Solution

Photos 2-3. The thinking here appears to be, “Let’s save time and goop up several penetrations at once.”

To deal with these conditions, I decided long ago to isolate the pipes from the roofing by having the HVAC piping come up through a prefabricated roof curb with a pipe curb cap with sleeves for each pipe — thus, making the pipes fully independent from the roof. As such, the pipes could then be replaced or removed, and additional pipes added, without affecting the roof membrane and possibly the warranty.

I would suggest that when multiple pipes all grouped together penetrate the roof cover, the standard of care for architects, roof consultants and engineers is not a pourable sealer pocket, but a pipe curb.

Design items to consider when moving forward with a pipe curb on an existing roof to be replaced include:

• Purpose: isolation of the pipes from the roofing.

• How many and what type of penetrations are you dealing with?

• Disconnection, rerouting and reconnection of the piping.

• Understand that the work of these details will most likely require coordination with mechanical and electric contractors.

• And let’s not forget the owner, who may be without air conditioning for several days.

• Vapor drive from the interior into the curb: How to seal the interior of the curb?

• What type of deck is there, how open is it to allow the pipes to pass, and how can it be closed off?

• Separation of the pipes placed close together.

• Waterproofing of the interior of the curb.

• Ability to at some time in the future to gain access to the pipes.

• Material that will not rust (copper and stainless steel).

The Detail

Photo 4. This article is not about these kinds of roof curbs.

The proper detail will involve a roof curb and a sheet metal cover with sleeves that only allow one pipe to pass though. The height of the curb should be 12 inches above the roof surface — remember that tapered insulation. This condition of course requires specific detailing.

Construction involves disconnecting the pipes (and re-capturing Freon where it exists). The detail should encompass a vapor retarder, roof curb, insulation for the interior of the curb, and a solderable sheet metal hood with sleeves and a removable top. The last steps of the construction process include reconnecting the piping and sealing the pipe to the sleeve.

A very specific detail should be created to convene what is required. (See Figure 1.) The construction of the pipe curb requires coordination of several trades.

Photos 5-7. These photos show the right way to do it: clean, isolated from the roof, and not a tripping hazard.

As with other details, the pipe curb detail can involve a complex set of steps. In addition to the contractors having difficulty being able to decipher the steps, our observers did too, and so we created the following Quality Assurance Checklist.

The Checklist

Pipe Penetration Quality Assurance Compliance

1. Have the existing curbs been removed, pipes disconnected (and any Freon captured), electrical disconnected?

o Yes  o No

2. Has a new insulated roof curb of the correct height been installed and properly secured?

o Yes  o No

3. Is the vapor retarder attached to the curb with an additional piece of vapor retarder material?

o Yes  o No

4. Have the gaps between the pipe curb and roof insulation been filled with spray foam insulation?

o Yes  o No

5. Has the roof deck on the interior of the roof curb been closed to the pipes to allow for the application of spray foam?

o Yes  o No

6. Has the opening in the roof deck for the pipes to pass been closed off with a sheet metal plate and spray foam been installed to seal the bottom of the curb from air exfiltration and to support the concrete?

o Yes  o No

7. Has the inside of the curb been filled with a minimum of 2 inches of concrete?

o Yes  o No

8. Has the curb been filled with a minimum of 1-1/2 inches of pourable sealer over the hardened concrete base?

o Yes  o No

9. Have the copper/stainless steel enclosure and sleeve(s) been fabricated with fully soldered joints?

o Yes  o No

10. Has the copper/stainless steel enclosure cap been fabricated with fully soldered joints and have a cross break on top?

o Yes  o No

11. Have the pipes been modified to fit through the sleeves?

o Yes  o No

12. Has the inside of the curb been filled with loose batt insulation?

o Yes  o No

13. Have the proper stainless steel screws with EPDM washer fasteners been used to secure the metal cap?

o Yes  o No

14. Have the pipe penetrations been centered in the sleeve and shimmed with a foam rod?

o Yes  o No

15. Have the primer, then foam rod, then polyurethane sealant been installed around the pipe to the metal sleeve?

o Yes  o No

16. Have all sheet metal debris been removed from the roof surface?

o Yes  o No

Figure 1. Pipe Penetration Curb Detail

The Result

By planning, properly illustrating the detail, and working with a good quality set of contractors, long-term success can be achieved. (See Photos 7-9.)

With pipe curb details, as with so many other elements of sustainable and resilient roofing, assisting the crew in the field as well your staff is the key to providing long-term benefits to our clients.

About the author: Thomas W. Hutchinson, AIA, CSI, Fellow-IIBEC, RRC, is a principal of Hutchinson Design Group Ltd. in Barrington, Illinois. For more information about the company, visit hutchinsondesigngroup.com.

About the Author

Thomas W. Hutchinson, AIA, CSI, Fellow-IIBEC, RRC
Thomas W. Hutchinson, AIA, CSI, Fellow-IIBEC, RRC, is principal of Hutchinson Design Group Ltd., Barrington, Ill., and a member of Roofing’s editorial advisory board.

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