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Old 09-03-2007, 08:44 PM   #1
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Concrete deck -- rotting floor joists


I bought a 1951 concrete block construction home, probably built by the original owner. The house itself is pretty solid but there's a 12' x 25' deck out the back that's a bit of a mess.

The walls underneath are built from concete block. The floor is poured concrete with rebar reinforcement. Over this, a previous owner had put in a wood deck floor over the concrete. Part of the deck is covered -- which is attached to the roof of the house.

Underneath is pretty much a crawlspace. There are 2" x 6" floor joists and a 4" x 8' support beam to cut the span. There is pretty severe termite and water damage to about 8 of the joists and the support beam, which broke in half. It seems that water has been trapped between the wood and concrete floors, resulting in cracks and some bowing in the concrete. The wood floor above seems OK -- for now. The truth is, you wouldn't recognize that there is a problem until you looked underneath.

To tear the whole thing down at this point would be a major undertaking which would include re-roofing the house. In the meantime, my plan is to replace the damaged joists and beams. However, there's not enough room in the crawlspace to manuever full lengths of lumber, so I thought I would join 2 8' lengths for the joists (overlapping about 4 feet) with 3-4 carriage bolts. I would also replace the broken part of beam in a similar fashion and reinforce with cinder blocks and lolleys underneath.

I'd appreciate anyone's advice, particularly if they feel I'm doing something dreadfully wrong.

Thanks!

John

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Old 09-03-2007, 09:56 PM   #2
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Concrete deck -- rotting floor joists


Hey John,

Could you post some photos? It would help us.

Eddy

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Old 09-03-2007, 11:21 PM   #3
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Concrete deck -- rotting floor joists


Thanks, Eddy for the quick reply!

I posted some photos here:
http://www.flickr.com/gp/12640579@N04/zt2fK1

There's also a layer of 3/4" tongue and groove paneling and tarpaper above the joists that you can see in the photos. This is also rotted away in the problem area.

The photos are about a year old and I've since cleared away the rotted wood and had the area treated for termites. I'll take some new pictures of what I've done so far next weekend.

Thanks again!

John
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Old 09-04-2007, 12:04 AM   #4
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Concrete deck -- rotting floor joists


How thick is the concrete platform? Are there any signs of failure in the concrete? Cracks? Large separations? Depending on how this was constructed you might not need as much support as was there. The wood might just have been a framework for the concrete to set on and not structurally needed after it cured. It doesn't look like it's been doing any supporting for a while. You would need to have someone look at it who would know what's needed. There might be plans on the construction methodology at the Building Dept.
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Old 09-04-2007, 09:43 PM   #5
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Concrete deck -- rotting floor joists


Thanks, Ron.

The concrete platform is 4" thick and reinforced with rebar (a piece of rebar is visible on one of the ends). There are large cracks and some bowing but no separation or chunks of missing concrete. I imagine it will just get worse over time, though.

I had a general contractor look at it a while back but he wanted to confer with an engineer -- and I haven't heard back. Rather than wait it out through another winter (which my wife won't like too much), I thought I'd try to shore it up myself. I'm not sure if the joists are doing all that much to support the concrete, but I figure it could only help.

John
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Old 09-04-2007, 10:52 PM   #6
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Concrete deck -- rotting floor joists


I am scared... Very scared... 2x6 is VERY undersized for a concrete floor even at 6' span. (unless maybe they are on 6" centers... even then I would be a little worried.)

Personally I would tear the whole thing out and either build a deck or have a concrete pad poured and have some nice steps build down to the pad.

I think decks and concrete should not mix the amount of extra framing and engineering required is just not worth it.
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Old 09-05-2007, 09:01 AM   #7
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Concrete deck -- rotting floor joists


This sounds like you need steel under there, not wood. The steel should probably be supported by concrete poles set in a footing. In order to get even contact I would think you would need to jack up the bowed concrete. This doesn't sound like a do it your self job to me.
You will need to get a structural engineer in there to get an educated opinion. Mines free and worth every penny.
Ron

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