Floor Joists. Do they still do it this way?

ntl1991December 13, 2010

My late 1940's 3-family (30'x34') has 2 8x10 beams (below the 1st floor) in the center of the house running the from the front of the house to the back, with about a 5' gap between them (the space between the beams is basically the front stairways and rear stairways on each floor, and continues all the way up to a 6' wide center dormer on the 3rd floor. The joists are all 2x8's, which are 12" on center. Under each wall (most run parallel to joists) are double joists and even triple joists in some places. The joists are notched out to "hang" on the beams, and then a 2x4 is nailed to each side of the beam to add additional support for the joists to rest on. Above the beams are bricks with mortar (I'm guessing this is a fire stop so it won't enter wall cavities?) This is also done along the two sides of the house, but the front and back just have these rim joists, as far as I can see.

Also, the walls around the front and back stairwells have double layers of what looks like 3/8" drywall. This is even applied to the ceiling (bottom of staircase above) of the stairway as you walk down the basement stairs. (Stairs are stacked)

I've never seen a house before where joists were 12" OC, also, I've never seen the whole brick and mortar thing. Is this commonplace, am I a lucky guy who has an overbuilt house, or is it necessary to hold up three floors of house?

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Yes, as you suspect the brick is fire- and vermin-proofing. Always a nice touch. Until the mechanical people trash it running pipes, ducts and wires.
The fact that they added the 2x4 ledger to the main girder to support the bottom edge of the notched joists is also a thoughtful move. The indications are that the builder took great pride in his work.
12" centers is always nice, with 2x8's probably reduces the bounciness considerably. It's at least 1/3 stiffer than a 16" OC spacing.

    Bookmark   December 13, 2010 at 12:13PM
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The standard on custom homes here is a minimum 2x10 @ 16" o.c. with a 3/4" ply decking. My last build was speced at 2x10 @ 12" o.c. with a 3/4" ply decking.

As Americans get fatter and fatter, what is luxury may become necessity.

Is your house ready for this load?

    Bookmark   December 13, 2010 at 2:56PM
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Thanks Casey. I've been reading about notching joists, and it seems like the same rules didn't apply back then. The notches in my floor joists are 3.5" tall, and it seems like many of the joists have a horizontal crack from the corner of the notch to maybe 4 or 5 inches into the joist. See attached pictures.

The fire-blocking is about 95% intact, but, it is true that the plumbers and electricians I've had in just chisel it out to run things through or up into the wall.

True. We are MUCH larger now than 60+ years ago when my house was built... Also, I think furniture has a lot to do with it too. No things like water beds, today's massive refrigerators, televisions, and all the furniture we pack into rooms.

It's changed just like the electrical loads... Two outlets in each bedroom with all bedrooms and a bathroom on the same fuse just doesn't cut it for the number and load of electrical consumers today...

    Bookmark   December 13, 2010 at 4:32PM
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What I want to know is , Worthy, how did you get my prom picture?

    Bookmark   December 13, 2010 at 4:40PM
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A real hottie, eh?
A friend grew up in a 19th century farmhouse built with solid fieldstone walls. The floor joists were 2x12s--not nominal.

Restored Scarborough, Ont. farmhouse.

    Bookmark   December 13, 2010 at 6:39PM
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Three water tanks?

    Bookmark   December 13, 2010 at 6:41PM
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Yes. It is a 3-family home, the large tank was the whole-house tank, but when I converted from the whole-house steam system to 3 individual hot water systems, I installed two other hot water heaters. The large tank, a 75 gallon is for the smallest apartment, 3rd floor, because it was on the 3rd floor gas line, and the two 40 gallons are for the 1st and 2nd after I had two more gas meters installed.

So, I have 3 washers, 3 dryers, 3 water heaters, and 3 furnaces. (Along with two oil tanks; 3rd floor boiler is gas)

Everything is separate. No more, "It's WAY to hot in here!" or "She left her clothes in the washing machine!"


    Bookmark   December 13, 2010 at 8:06PM
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Joist are no longer notched at the ends to create a bearing area on a ledger strip.

As you noted, it leads to stress concentration and often results in cracks at the top of the notch that run out into the joist.

The problem is that the neutral plane at the supported ends is NOT in the middle of the joist.

    Bookmark   December 15, 2010 at 9:21AM
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