Green Roof Reno: April 2008
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April 26, 2008
Go Green Expo
Just a quick note to say that if you are interested, you should check out the Go Green Expo this weekend. . . .
There will be some green roof and green wall suppliers on hand with their products.
The Hilton New York
Saturday 10am-6pm • Sunday 10am-3pm
See the project below from Seoul, Korea by Mass Studies Architects using G-Sky Living Wall Panels . . . A similar product by Green Living Technologies will be on hand at the expo . . .
April 22, 2008
Into the Ceiling
So even though Spring is here . . . We're still inside trying to figure things out. Our next step was to determine the structural load capability of the roof in order to determine how to proceed with getting the deck and green roof built. So we had to go into the ceiling and look at the beams.
I was excited to inspect the roof from below – to see the size and condition of the beams holding up our roof and measure their spacing. I choose the side of the skylight to cut into the drywall so that it would be least intrusive. It would also allow us to look above the ceiling without actually cutting into it. After removing a 10” x 18” drywall piece in the side of the skylight niche, I caught a faceful of some really old air. I mean who knows when this space was last open?
What we found was true 3” x 7” beams that are spaced 24” apart on center. From what I understand this is not great news . . . the depth of the beam is the key number here and seven is just not that impressive. New wood decks are often framed off of 2x12s spaced 18” to 24” on center . . . in other words with a lot more load capability.
On the positive side, the quality and integrity of the beams seemed intact; with no dampness etc., though one of the beams looks like it had some water staining at some point. Everything up there now seems dry as a bone. We actually have about 12 inches of space between the ceiling and the roof, which means we could raise our ceilings if we wanted to. Right now, it’s not even a consideration, with all our money and resources devoted to the green roof project.
One key thing to note, the load-bearing walls do not extend to the ceiling (12 feet) but stop at the fourth floor ceiling (11 feet). In this case, the load-bearing walls are the interior walls that run down the center of the building separating our apartment from our 4th floor neighbor. So what that means is that we will consider cutting into the roof and building up that load bearing wall to form a 2’ high parapet in middle of the roof. We would then frame the deck, and if need be, the green roof off this parapet and the side parapet.
But, we still have a lot of questions - What can we expect to pay for building up a 2’ parapet from the load bearing wall? How does this differ price-wise from using steel? We would like to still consider using steel, but want to know the price differential between these options. Is steel two times more expensive or ten times more expensive? Will the 3x7s at 24 inches on center be enough to support the 17 lbs/sq ft of the green roof modules?
April 2, 2008
The Meeting
Finally we met with our structural engineer, “Bob,” an old timer who seemed to know his bricks from his beams. Bob was recommended to me by a friend in the construction business who talked about him as someone who “knew how to get things done in Brooklyn.” We had chatted on the phone so he had a good idea of what we were after.
Bob was a wealth of information – both practical and historical. Although typical homes in Park Slope allow for a load of about 40 lbs/sqft, Bob said that sometime around 1950 they realized they didn’t need quite that load and resized things down a bit to 35 lbs/sqft. Since our building is from 1920 we should theoretically be able to handle more weight than some newer construction, but I guess we would also have to factor in the age of the beams. One thing we didn’t think of was that the ceilings of our apartment have to be factored into the load calculation, as they hang off the roof beams. Also included in that number should be the roofing material, of which there may have been three or four layers applied throughout the years.
I was beginning to think my green roof modules were doomed! At roughly 15-20lbs/sqft when saturated – could these work on our existing roof? Bob had a lot more questions, for instance - Where are the load-bearing walls? What size are the beams and how far apart are they?
His thought was that our type of building, a 29ft x 60ft building with a central staircase, would typically need to be supported by two load-bearing walls in order for the single wood beam to span the 29 ft across without sagging. A quick trip to the basement confirmed that our building had load bearing columns each about 10ft offset from the side walls of the building. See the image below for the 1936 basement plan with my annotations – my trip to the DOB was worth it after all!
Essentially what this means is that we could cut through the roof and build up from that load bearing wall to create a low wall, or parapet, in the middle of the roof. We could then frame the deck off that wall and the side brick parapet. Obviously the next steps are contingent on the investigation of the beams, but Bob’s feeling was that the green roof modules would be okay! Let’s hope those old builders in the `20s overcompensated on their structural load calculations.
Without original building plans, we will have to do some investigating into the beam size and spacing. So . . . we’re looking forward to cutting a hole in the ceiling! We always wanted to see if we could ever raise our ceilings higher – now here’s the chance. We’ll let you know how that goes . . .
We were also a little surprised to learn that architect, engineer, and permitting fees could be close to $5000 for even something this simple. In most cases, design and permitting fees should be between 10 and 20 percent of the total construction cost. So these projected fees definitely have us concerned, as they could be more than we’ve planned for. In any case, we’ll feel better about having it permitted, both for our own peace-of-mind and ease of resale somewhere down the line.
While this meeting was productive in moving the process forward, we still felt left with more questions than answers. Until we do our own investigations (i.e. the pending hole in the ceiling) we won’t really know anything. We also left feeling that we wanted a general cost comparison between using and not using steel on the roof. All you structural engineers out there - feel free to weigh in right about now!
Although we don’t want to get into specifics on finances, we understand it may be difficult to budget for these types of projects, so we will answer your budget questions by email. Also, we know how hard it is to find good people, so . . . we would be happy to share additional info about our structural engineer and other friends. Drop us an email at greenroofguy@gmail.com.