Hot Tub Roof Installation (in San Francisco)
June 6, 2013 8:56 PM   Subscribe

Hello! I noticed a deck being built on my roof (4 stories tall) in San Francisco. I think it is highly possible that they are putting in a hot tub (which I am stoked about) because there are drainage holes in the tiled floor of the deck they built, as well as plumbing. Anybody here experience the process of installing a hot tub on a roof? How do they get a hot tub up there? Are there any resources that talk about installation of hot tubs on existing roofs? I tried flexing my Google fu to no avail and this subject matter intrigues me so.
posted by nathanm to Home & Garden (8 answers total) 1 user marked this as a favorite
A cubic meter of water weighs a metric tonne. Hot tubs typically weigh two or three tons when they're filled.

The first step is to get someone who knows what they're doing to evaluate the structure of the house to see if it can support the weight. The answer is mostly likely "no".
posted by Chocolate Pickle at 9:28 PM on June 6, 2013 [3 favorites]

The drainage holes and plumbing don't necessarily mean there's a hot tub going in - large flat roofs will typically have roof drains in the middle of the roof, and those drains require plumbing to carry water to ground level or the storm sewer. So, a tiled roof deck would just sort of need those things anyway.

Chocolate Pickle is absolutely correct about the weight issue, and beyond just the "will it fall through the roof" factor, there's also the fact that it's on top of a 4 story building in a heavy seismic area, so there would need to be a whole lot of structural bracing going below any hot tub installation because all that weight will really cause problems in an earthquake. Unless they've addressed all that and had a roof hot tub installation approved by the building department, this would definitely not be something to get stoked about - it's more of a "move before the building collapses" thing.
posted by LionIndex at 9:37 PM on June 6, 2013

San Francisco is very particular about permitting. I very much doubt that a permit for a hot tub would be issued, and I would not want to live in a building that had one on the roof unless real structural engineering surveys had been done. I'd blow the whistle.
posted by anadem at 9:51 PM on June 6, 2013

Slightly off-topic: I was in a Haight-Ashbury apartment in the '87 earthquake. My apartment neighbor had a planter on her roof, and when she felt the earthquake she was quite sure it was the planter coming through the roof from over-watering. I'm pretty certain she'd have been right if it had been a hot tub.
posted by anadem at 9:55 PM on June 6, 2013

Hi, it's probably not a hot tub going in... but if it was, it would go in via crane.

an empty hot tub isn't crazy heavy, but even modern 4 person tubs hover around 500 gallons, i.e. 2.1 tons and change.

it can be done, but it would take at least engineered beams below and additional safeguards.

the plumbing may be for container gardening
posted by bobdow at 9:55 PM on June 6, 2013

Let's use this Jacuzzi J-465 as a typical hot tub. It weighs 5, 382 lbs when full and has a foot print of 55 square feet for a load of just under a 100 pounds per square foot. Put a rigid sub deck under the hot tub 4' wide all around and the lbs/sq ft drops to 23 or just over the design load for snow for many places in the US.

So a roof top hot tub (or one on a deck/balcony) is quite do able though care should be taken. Where I live an engineer might not be required; span and column tables go high enough. Though an insurance company might want to see it signed off on especially on a strata building and a long span would require engineering. A support column/wall under the foot print could make design trivial.

Installation would be via crane or a simple roof mounted winch (often semi permanently installed to allow for lifting of HVAC units). Some buildings this size will have a freight elevator that will handle the volume. Heck a more modest 6x6 tub might fit in a regular elevator.
posted by Mitheral at 10:08 PM on June 6, 2013

Put a rigid sub deck under the hot tub 4' wide all around and the lbs/sq ft drops to 23 or just over the design load for snow for many places in the US.

Yeah, roof dead load even in SoCal with no snow load is 20 psf, but that's for a roof that isn't going to be occupied. Floors are generally designed to 40. So, part of the deal would be whether the roof was originally designed to be occupied or not.

But still, seismic. Even a column or wall under the tub wouldn't help in that case unless adequately braced.
posted by LionIndex at 10:28 PM on June 6, 2013 [1 favorite]

It shouldn't be possible to legally build a roof deck in SF without going through the Planning Department and/or Building Inspection for permits. If they have a permit, they should have a Job Card with the permit documentation posted somewhere. Maybe start with DBI and search for a building permit for the address? Obviously, the work may be all happening without permits, which would leave me somewhat concerned whatever they're building.
posted by zachlipton at 1:35 AM on June 7, 2013 [1 favorite]

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