Concealed dunnage?

Has any one concealed the dunnage beams in the roof? ie used the beams in place or in addition to roof joists. I assume this could potentially allow the vibrations from the compressors to travel across the roof.

Guest User | 4 years and 3 months ago

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Guest User | 4 years and 1 month ago

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Thanks Ed!

agdipierro

in General Discussion 4 years and 1 month ago

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Allocate 20K for steel dunnage running from bearing wall to bearing wall including stairs with railing over it and roofing repairs
.

Guest User | 4 years and 1 month ago

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Can someone who has installed dunnage recently give me some idea for the fabrication and install of steel? Thanks in advance.

Guest User | 4 years and 2 months ago

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Kemper is a good choice.

brooklyndempsey | 4 years and 2 months ago

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Similarly, ours was done for landmarks (even if it is just a few inches lower, those inches may be critical to getting approval) and FDNY clearance. As has been pointed out above, this is not an inexpensive option.

The penetrations don’t seem to be an issue at least with our membrane (Kemper), which is bonded right up the metal posts. We’ve had them for 5+ years and they are very solid seals–whatever issues we may have in the future, I don’t think the dunnage posts will be a problem. Other membrane materials may be different.

Guest User | 4 years and 2 months ago

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dow, are you referring to the dunnage? There are two options – put them in the yard or the roof. It’s unsightly to have them in the yard. If you put them on a roof, by code there are limited: dunnage or parapet/built up parapet. Fire code requires stairs if the dunnage goes across the roof. By putting the dunnage to the side it’s smaller, lower, provides a clear path for fireman and not visible from the street (Landmarks). I am still on the fence and my hvac guy is also advising against this route. I will price this out vs. switching to radiators. At some point my compressors also wear out as they have been used a while. Not rushing into spending $$ on dunnage only to find out in a few years that the market will be flooded with lighter units.

dorkofwindsor | 4 years and 2 months ago

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These seem marginally lower than the parapet, add roof penetrations (the bane of my existence) and then there’s the cost. Are people primarily doing these for aesthetics or usually only when necessary for landmarks? I couldn’t fathom more penetrations than I already have with ductwork, electrical etc.

Janedrew, during a fire you are almost certainly going to walk onto your neighbors’ roof(s) whose building is not burning. Having said that, your roof aesthetics seem important to you so best of luck.

Guest User | 4 years and 2 months ago

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lmiller thanks again – SO HELPFUL! @restoratin contractor – also thank you. The dunnage is elegant and relatively more contained than spanning a roof and then having stairs over it which can be a tripping hazard especially during a fire. I waited to do roof work in order to figure this out all together.

restorationcontractor | 4 years and 3 months ago

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The entire installation can be done from the roof deck. Because you are opening/reclosing the deck and the additional difficulty in installation it’s obviously going to cost more than just throwing dunnage across the parapets. It will result in a much nicer job though.
If your ceilings are open below even better.

The beams can be fabricated in several pieces with bolt together connections and assembled on site if you have space issues getting a 20′ + I beam into your building.
We have done these down to small passenger elevator size (with engineered connections) and bolted together on site.

Imiller very nice work guys.

brooklyndempsey | 4 years and 3 months ago

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Here are some pictures from our installation. One shows the equipment mounted, one before the equipment was added, and finally a detail of how the I-beam under the roof is supported by the masonry. [3 dunnage under roof beam](//muut.com/u/brownstoner/s3/:brownstoner:Xt46:3dunnageunderroofbeam.jpg.jpg) [1 dunnage with equip](//muut.com/u/brownstoner/s3/:brownstoner:kZbF:1dunnagewithequip.jpg.jpg) [2 dunnage empty](//muut.com/u/brownstoner/s3/:brownstoner:ZbQK:2dunnageempty.jpg.jpg)

barc | 4 years and 3 months ago

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[IMG_5439](//muut.com/u/brownstoner/s3/:brownstoner:28rl:img_5439.jpg.jpg) this is an example of steel from party wall to party wall that is under the roof. steel tubes are stubbed up from those beams to support the dunnage that supports the condensers. the HVAC was placed here to keep it out of LPC site lines. but the steel solution can be used on any flat roof.

Guest User | 4 years and 3 months ago

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On a landmark building, units cannot be visible from sight lines on the street

dorkofwindsor | 4 years and 3 months ago

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lmiller is this a requirement for a landmarked building?

Guest User | 4 years and 3 months ago

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Genius! Happy to find a kindred spirit. I very much appreciated the detailed explanation – thank you. Would you mind sharing a photo or a photo of plan (without any personal info) so I can share with my structural engineer. He didn’t want to do it this way and drew it the “typical way” jdbrooklyn19@gmail.com if you prefer not to post. Thanks in advance.

brooklyndempsey | 4 years and 3 months ago

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We have concealed dunnage constructed this way.

I-beams were set directly across the house supported by the walls (involving opening the roof, masonry work, and a crane). These beams sit below the roof surface. Then a separate welded structure of I-Beams was placed on top, held up by a foot or so of pipes so it is above the roof surface—this structure is not full width of the house presumably for FDNY clearance. Then the roof was sealed up and the membrane (Kemper) bonded to the pipes that support the structure.

This way the beams are significantly lower than they would be if they were on top of the parapet wall, which we needed to keep our mechanicals low enough for landmarks. Our AC units are isolated with rubber, but we have a generator which is supported by spring isolators. No vibration issues—the beams are massive and very solid. Nothing is sitting “on” the membrane—all of the weight is supported by steel-steel-masonry.

It isn’t a simple installation, but works well for our house.

Guest User | 4 years and 3 months ago

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Thank you for the thoughtful response.Yes that’s exactly what I was after. I agree about not sitting on the roofing membrane – would have to use sound isolation. With this approach you get rid of raised beams and the stair for FDNY. Is building up the side parapet and attaching the compressors an alternative to dunnage?

dorkofwindsor | 4 years and 3 months ago

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Not sure what you are asking. If you concealed the I-beams into the existing roof (much harder than it sounds) then the equipment would sit directly on the roofing membrane? That would make no sense and it would be very difficult. Perhaps it is done somehow, but you would not want it sitting directly on the roof membrane in any case. Perhaps someone else could chime in if this is a thing. I would guess that it would significantly increase the cost unless it was part of a total gut.

The dunnage will sit on the parapet anyway, same wall / same structural support. Same vibration.

They make specific spring and rubber isolation pads for equipment to sit on. Many residential contractors will not put those on – usually they will put on a $2 cork/rubber sandwich that will flatten in a few years and you will likeley feel vibrations. No matter where you put your dunnage.

In your quote I would recommend specifying that a spring vibration isolation mount for the appropriate size of the equipment be installed. Not hard at all but they don’t do it residentially afa ik. I think places like mason industries will recommend the correct size for free if they call them and give them the equipment / weight.

EDIT: I know commercial buildings will do a “curb mount” for heavy equipment but I’m pretty sure those already have very well supported roofs (ie high rises with cement floors) for all the equipment. That would seem to be overkill to me for a residential job.