Ah, another day of great progress on our safe house! The bottom part of the form for the roof overhang has been completed, and the bottom web of rebar on the roof is a little over half done. We needed some more lumber, and my contractor delivered it this afternoon – about eight hours after it was promised, but it is here. That means that David (the mason) and his son can continue working today!A friend and neighbor (Dick F.) visited yesterday afternoon. He happens to be a retired concrete contractor, with something like 1,000 years of experience in the trade (Dick is older than dirt). He used to run big crews who built large commercial buildings, rides at Magic Mountain, bridges, and the like. Suffice it to say that he knows his stuff when it comes to concrete. Well, he went out and inspected my safe house – and was largely satisfied with what he found. He gave me some very useful tips to help ensure the quality of the job, which I will certainly follow. But his approval of the workmanship to date is very comforting…
I learned something yesterday that completely removes the concern I expressed a couple of days ago, about the blocks on the west side being higher than the blocks on the east side. It turns out that I misunderstood David in a profound way – the blocks really are level after all. It's the form that's not level, and it is sloped in order to put a slope on the roof (to let rain water run off) while keeping the roof slab a constant thickness. That part is great, and makes perfect sense. What didn't make sense was the amount of slope: 2 inches in an (approximately) 18 foot run. This slope is actually called out on the plans as a minimum of 1/4 inch per foot of run, which works out to about 4 1/2 inches in the 18 foot run. When I pointed this out to David, there was a bit of consternation – but then he figured out that he'd simply make the slab thicker on the uphill side (by 2 1/2 inches) to adjust the slope. He believes this will cause no problem at all with the inspection.
Good morning, Simon...
ReplyDeleteWell, the additional weight works out to a 12% increase. Under normal conditions, I'm not worried about it at all -- the strength of the walls in compression is formidable; they could easily carry ten times the weight.
Where I am a little concerned is with the earthquake stress calculations, which are partly dependent on the strength of the walls in tension (this is provided by the rebar in the walls). Those also have a considerable margin of safety built in -- 50% at minimum -- but my concern is that the inspector will catch this, and require us to go through another plan check with the larger weight.
In discussing this with David, though, he just laughs this off. He says that inspectors never complain about extra materials (more rebar, thicker rebar, more concrete), as the problem they're always fighting is contractors trying to cut corners by using less material. He's planning to put all the waste rebar was have lying about up there, and he's positive that the inspector will like that.