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Mikeman 09-27-2011 08:43 AM

Sistering Joists and Adding a Beam
Hi everyone,

I have a 95 year old home in Ontario, Canada.

The main floor total span is 22 feet, and there is a beam (sound and sturdy) running down the (almost) middle of the span. The joists are 2x8 and 16'' OC and after accounting for the beam, the joists span 10' on one side and 12' on the other.

On the 12' side, there is a double 2x8 supporting a load bearing main floor wall (supports 2nd story floor).

In someone's infinite wisdom, the double 2x8 was cut to make room for a HVAC duct. One of the 2x8s is completely cut and the other is notched about 2''. This means I effectively have a 2x6 supporting a load bearing wall over a 12 foot span. As you can imagine, the main floor has sagged in this area.

I cannot be sure how much it sagged before I bought the house (a year ago), but there are two temporary lally columns under what is left of the joist, and the sag is about 3/4'' now.

I plan to:

1) jack the joists to remove as much of the sag as possible. I know getting 95 year old joists to bend back is a challenge.
2) sister the joist in question with 1 or maybe 2 - 1 3/4'' x 7 1/4'' LVLs
3) sister the 2 or 3 joists on either side of the problem one with 2x8 SPF dimensional lumber
4) add a built up or LVL beam under the joists about (about 6 joists in total so about a 7' span).
5) The LVL beam will be supported by two new lally columns at either end set onto 12 x 12 x 12 footings.

I should mention my basement is unfinished and I have no problems with the headroom issues the above configuration will create.

My questions are:
a) should I use the new beam as the support when jacking up the joists, or should I jack up the joists separately and install the beam afterwords?

b) does anyone see any problems with my plan? Please feel free to blast away...I am an accountant by trade, but relatively handy(relative to an average accountant, that is).

Thank-you in advance for any guidance.

gregzoll 09-27-2011 09:57 AM

You are going to have to support the span with jackposts, then get two new 2x8's on either side of the cut joists. Oonce they are in, you can bolt to hold.

Mikeman 09-29-2011 08:00 AM

Thanks for the reply.

I guess my question is still, should i use the new beam to support the joists when jacking it up, or should I install the beam only after the joists have been sistered?

Thanks again,

gregzoll 09-29-2011 08:28 AM

You place a 4x4 or 6x6 under the span and use Jack posts with 3/4" Ply-wood between them and the beam, along the span to lift everything up, but the cut joists. It will mean that you would have two spans on either side of the problem joists, only turn a little at a time. That means that it can take as long as two weeks to be ready to put in the new joists.

Knucklez 09-29-2011 08:21 PM

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will your jack posts require a footing? probably if they are considered load bearing. also must think about how to stop the jack post threads from losening over time. some people install these so the threads get burried in concrete, others install threads at top and damage the threads so they can never unwind.

turning the jack posts 1/4 turn per day... so it can take a long time.. but you're not in a rush so no matter.

also, it may not be possible to return to original level if the entire house has settled to new location. but your method sounds good so maybe you will have better luck than most.


gregzoll 09-29-2011 08:52 PM

Knuclez, if only temp to put in the new joists, they should just need some Oak blocking under it, until they get done.

Knucklez 09-30-2011 08:11 PM

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you're totally right, i thought it was permanent.

what i have seen under out riggers on big scope trucks is to have three 2x6 boards parallel & side by side each piece 12" long, over top three more 2x6 boards parallel - but 90 degrees to first layer, followed by one more layer stacked on top same dimensions but again 90 degrees (matching orientation of base layer). seemed good enough for several tonnes and cheap to assemble.


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