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Old 05-28-2005, 03:14 PM
pricer pricer is offline
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Default Curbs, Curb Adapters and all the Possibilities in Between



Curbs, Curb Adapters and all the Possibilities in Between


As many of you know, I have a keen interest in the design and fabrication of roof curbs and curb adapters. I do not claim to have all the answers and I have much still to learn. I have been working on new ideas and I have a great deal of time invested in studying the many possibilities. I have posted many photos of one of my most current projects in the photo gallery here if anyone is interested in viewing.

This project was unique to say the least. We had to replace the old package units with new equipment and not disturb the customer’s productions below. This lead to many design ideas. The existing factory curbs had to be removed and the new units installed in as quick of time as possible. The old curb had served its time well but needed to be replaced.

The existing unit’s footprint was considerably larger than the new Carrier package unit we were going to install. One of the first ideas proposed was to just tear out all of the old stuff and fill in the hole on the roof with decking and basically start over. To have done this, it would have taken many days, involved other trades, disturbed the customer’s production and cost more money. I initially thought of building a new pitched factory curb to replace the existing flat curb. This would take care of the problem of having to cover the big hole in the roof. The cost of building the new pitched base curb was far less expensive than reframing the roof structure and replacing the roof deck. Having to stop production in the machine shop below would not have been very good either.


Once the new curbs design was conceived, there were a few more unknowns that had to be worked out. The first was how to efficiently remove the existing curb. I was sure that the old curb’s bottom flange was welded to the I-beams in the roof structure. The initial plan was to build the new base curb in the same fashion as the original. When the existing unit was installed thirty years ago, it was never set to be level. The new base curb had to have 1 degree of pitch built into it to make the new equipment level.

The second unknown was the actual size and location of the duct drops that were installed in the old curb. I could not get up to the bottom of the unit very easily, the building is 45 feet up to the roof line and a great deal of equipment was sitting under the unit on the roof. I traced one of the ducts down the wall and was able to measure its width and depth. Using this information, I took a series of photographs of the bottom of the unit and surrounding duct work in hopes I could print them out and enlarge or decrease the photos size on a copy machine and compare that info with the field measurements. This worked very well. I also measured the photo before altering it in the copy machine. Using a pair of dividers and knowing one of the duct sizes in the trunk line I was able to find the size of the duct drops using an aspect ratio. The information from this was confirmed by resizing the photo to a particular scale and measuring.

Once the data and theory were established, the design of the curb’s adapter to the new unit was achieved. Now construction began much like the fabrication of any other curb adapter. Drawings were established and the parts were cut, fitting, welding and other processes were moving forward. You can see many construction photos in the “Pricer” gallery here at the shop. What made this adapter unique was the fact that the new units base dimensions, especially the length, was about 2/3 the length of the existing unit. A standing seam roof was built into and onto the curb adapter making it about 17 feet.
We had planned on setting one new curb and unit in a long day. There were still some small unknowns and we would test out skills on the first one. Once the old unit was removed, we found that the existing duct drops were not secured to the old curb and the big one, the existing roof curb was not welded to the buildings structure in the way we had anticipated. A few decking spot welds held the ends in place. The job moved on very well and we were thankful for it. We completed the first curb in one regular day; the other two were installed in a twelve hour day by the same crew that installed the previous. All of the theories were proved true and the job was a success and I am thankful for it.

Maybe this info will help someone out there and if anyone could use any help, I would be happy to consult. Photos and model numbers are helpful.



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Old 05-28-2005, 03:19 PM
pricer pricer is offline
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Photo of the pitched base curbs during early construction.
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