100 year old floor joist

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  #1  
Old 08-15-05, 08:25 PM
RickinDC
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100 year old floor joist

Good evening,
I'm considering buying a 100 year-old townhouse here in Washington, DC but am curious as what this community thinks about this problem:
Several of the floor joists between the basement and the first floor are termite-eaten/rotted to the point where they are like paper. As the house will be gutted, replacing them should be straightforward. However; the house is 12' wide, and the joists were built into the brick party walls when the house was constructed in 1905. A course of brick was laid, joists were set in place, and then the wall continued up, building around the joists. Which, by the way are true, dimensional 2x10s. The brick party walls appear to be two or three bricks thick, depending on which way they were put down. Getting the old rotten joists out will be no problem, but I'm interested in hearing how one might install new ones.

Thanks for your time,
Rick
 
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Old 08-15-05, 10:33 PM
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100 year old floor joist

If and when you get the new joists in, the floor over them will not act the same to the extent you will notice it.

Comparing full 2x10's with modern 2x10's will give you a big difference. Based on the reuced size, bending and flexural strength, there will be about 35% lower strength. You will have lower strength and more deflection. The floor may be strong enough for code, but the new section will be feel much softer unless something is done. This is all assuming that the new growth lumber you buy today is as dense as the old. - It still will better than the termite infested joists.

One thing you may run across if you get an inspector. - According to code, wood cannot be imbedded into a masonry wall. This is not the same as using a masonry pocket (clearance around wood) as a bearing for wood framing so don't let the inspector try to pull this one. - If you have the wood in contact with a "wet wall", you may need PT, unless the electrician was able to get away with normal wiring in the same wall.

Consider sistering joists for the center portion of the span in the opening between the masonry walls.

Just a question - how do you get a 12' 8" joint into pockets in two walls 12' apart? - A hammer to the wall to get wiggle room? Those brick are not too hard and can be patched.

Love those old townhouses and the whole city! Lived in Virginia Beach for 4 years and spent at least one weekend a month in DC.

Dick
 
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Old 08-15-05, 11:18 PM
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Hi Rick,

Based on your description, it seems the issue is how to slide the new joists into the existing slots vacated by the old rotten joists, such that they fit well and can fully support the load.

One idea I have seen used in a similar situation seemed to work well. In this case, a new joist was made that was long enough to span between the original space, but short enough to allow the joist to be installed by sliding it fully into the slot at one end, lifting it level and sliding it forward until both ends of the joist were supported within the original slots. At each end, two thick steel "braces" were inserted on each side of the joist into the slot until they were fully seated. The remaining length of the braces had five large pre-drilled holes, through which holes were drilled into the joist and large bolts where installed.

The results were very stable and strong joists, without the need to reconstruct portions of the foundation.
 
  #4  
Old 08-16-05, 07:32 PM
RickinDC
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Floor joists

Thanks for the suggestions. The existing joists are pretty solidly anchored into the wall. Or rather would be if they weren't paper thin from rot/insects. I'm wondering though if there is any room at all to manuever a new joist into the existing pockets.

rdn2113: Any idea of a manufacturer for those steel brackets you mentioned?

Thanks again,
Rick
 
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Old 08-16-05, 10:54 PM
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The braces were custom made by a local metal fab shop. If I remember right they were about 36" long and 1/2" thick - I also remember they were heavy. Part of the reason for the length and mass was to provide additional rigidity - which they did quite well. The cost I believe was about $100 per joist (4 braces each joist). Note that they did have to enlarge a few of the pockets to get a proper fit. I think they replaced about four joists total.

Concretemasonry's guidance regarding building code and imbedding is important and should be heeded even if you don't have it inspected. Later on down the road you may want to sell and it could become a sticky point with potential buyers.

The technique I've described above should be OK, since the overall length of the joist and the braces prevented the joist itself from being "imbedded". It resulted in a "pocket sill" as they called it. They coated the entire pocket with a concrete sealer called "Dry-Lok", then glued a segment of poly-based "sill sealer" (it comes in a roll and is used to seal between the foundation and the wood sill) on the "pocket sill" so the end of the joist would not actually touch the foundation. Also, they coated the braces with a rust inhibitor and the joist with a sealer before they installed it. Seemed pretty water tight and strong to me.

Hope this helps. Best wishes, Rick!


Rick (aka rdn2113)
 
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Old 03-05-14, 04:10 PM
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old joists are rotten how to insert joists into existing pockets

Any idea what is the best way to insert new joists into existing holes on cmu wall?
 
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Old 03-05-14, 04:42 PM
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Refer to Basements since this is a duplicate of that thread. CLosing this thread due to age.
 
 

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