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Could someone explain "deadweight" v. "live load" roof deck limits?From: jpwchi@yahoo.com
Category: Decks
Remote Name: 158.70.105.52
Date: 16 Jan 2004
Time: 10:04 AM
Comments I live in the top floor unit of a newly-constructed building with a private roofdeck. This summer, I want to put a rose garden in with eight 16" and six 20" planters. Before talking to the developer, I bought the roses (for spring delivery) and eight small teak planters (16"x16"x18", including 2" legs). Each teak planter will weigh roughly 80 lbs when full. I have held off buying the larger planters because I want to comply with any weight/safety restrictions. However, if I did get six 20" round planters, I estimate that the grand total of all deck furnishings (including all planters,light patio furniture and a grill) to roughly 2000 to 2200 lbs.
Although the L-shaped deck is 540 square feet overall, the planters would be placed along the perimeter of only two areas, which measure 15' x 8' and 5' x 8', respectively. According to the developer (who, incidentally, has been a really great guy) tells me that my deck is relatively "beefy." According to his engineer, the live load capacity is at least 100 lb/sq ft, and the deadweight limit is 22 lbs/sq ft. According to local code, the recommended snow load factor is "30% of the live load," i.e. 30 lb/sq ft. Also, if I understood my developer correctly, the wood beams are 16" (?) on center, but I couldn't tell you the size, grade or configuration of the beams.
Here's where I get lost. My developer told me that his enginner says that putting in even one of the smaller teak planters could be unsafe because the 80 lb. weight would be spread across a base of only 1.75 sq/ft. Thus, each teak planter would be FOUR TIMES the 22 lb/sq ft "deadweight limit."
I recognize that I'll probably have to ditch the plan for the 20" planters. However, even if I put the large rose bushes in lightweight 14" or 16" pots (thereby shaving off over 500 lbs.), these smaller pots, like the teak planters I've already purchased, would still flunk the "22 lb/sq ft. deadweight limit." In essence, my developer's engineer seems to be telling us "no big plants on the roof."
Could explain why the roof deck is safe for my living 200 lb frame, but not for a "deadweight" 80 lb planters?
If I have to scrap the whole plan and take a hit on the teak planters for safety reasons I will, but I just don't understand why.
Thanks.
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