basement work, need advice

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Powermuffin
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basement work, need advice

Post by Powermuffin »

Hi all. We are working on our 1908 basement, which was originally a crawl space. At some point it was dug out to about 5 feet height and partial wall (I don't know what this is called) was built on both sides. Over the years joists have been butchered and the floors are suffering. The space is roughly 20 by 40. It has the original flagstone foundation, which my husband is currently repointing. We have had our structural engineer out and he sees no real structural issues. There are areas where the floors have sagged from the installation of a wood stove, brick surround all on a flagstone foundation in the sitting room. We have removed all of that and hope to straighten out the floors, and eventually dig out the basement a couple of feet and finish it off. The floors are pine or Doug fir, without a subfloor and they run under the walls. We want to keep them.

My husband is researching ways to handle reinforcing the floor joists and the center beam. The way that the joists were done is to overlap two 12' joists to make the 20' span. I think he is going to add a center post once the joists are fixed. How would you reinforce the floor joists?
Thanks,
Diane

phil
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Re: basement work, need advice

Post by phil »

if you dig deeper you need to make sure the slope and drainage can support it. if you have city drains that are lower you are ok. sump pumps can be a workaround.

near me they do it often. they hire a house lifter , they can lift your house right up high in one day. then they put big beams under the house to support it temporarily.. then they drive underneath with a bobcat and clear for a new foundation, then they pour the foundation and the floor and set the house back down on it's new foundation. after that the house is worth another 100K or 200K because the basement is high enough for legal suites.

in one case they moved all the houses and build commercial space below and then set three nice old housed back on top, you can't even really see from the street that there is this space below..

You might to want to go to that extreme it depends on the site and real estate value and if you value the old foundation that much.. You can hire an engineer to look and make recommendations. you will needto do that if you are doing stuff to code. You can sister joist, just double them up , you can add cross bracing like this :
http://c8.alamy.com/comp/B3FRN5/cross-b ... B3FRN5.jpg

that spreads the load and might make the floor more rigid and stronger without huge expense.
Last edited by phil on Tue Nov 07, 2017 10:50 pm, edited 1 time in total.

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Gothichome
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Re: basement work, need advice

Post by Gothichome »

Dianne, if I have read this correctly, the twent foot span is is sitting on a beam in the middle of the span. At what point in this twenty foot span has sagged due to excessive floor weight?
Once notched (butchered) the joist is only as strong as the narrowest part when mounted between load bearing walls, beam, post ect.
Or has the beam sagged or bowed, there is a different fix for each.
The long term fix though may mess up your plans for a taller basement though.

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Powermuffin
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Re: basement work, need advice

Post by Powermuffin »

Thanks Phil and Gothihome. Beam isn't sagging, the foundation is sagging where the wood stove was. We have to fix that even though it isn't moving currently.

My husband thought that the old floor joists might need to be replaced. So his options would be to do that or sister them. Seems to me that sistering the joists would make the floors more stable. Fixing the foundation will be tackled as part of digging out the basement.

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Re: basement work, need advice

Post by phil »

is the floor sagged or did it spring back up once the stove was removed?
if it is sagged and you jack it back up to flatten the floor you might havs some cracked plaster or drywall.. maybe there is a wall above that you are also lifting.

My house has posts down the center of the basement and beams on top of those posts, they break up the span. then there is a wall above that on the second floor that is a bearing wall. It in turn is basicly holding up the attic. In my case all that is still square... but if it were sagged and I jacked it I'd be not only moving the floor but the bearing wall as well and that might crack stuff.

when people straighten things like that they often do it slowly over time, this lets things normalize and reduces the damage. If you are in effect straightening the house because it sagged in the middle you might start that now and allow time maybe raising it 1/8" per month or something like that.

On the other hand if it sagged from weight and sprang back to straight once the weight was removed that might make the floors kind of springy.. but you might not have to straighten the house much and that would be easier. if that's the case maybe it isn;t putting much or any weight on the center right now.. and you need to stabilize that center point then maybe it will be ok?

a useful cheap tool for comparing stuff is a water level.. just buy 50 feet of clear plastic hose about 1/8" diameter. fill the hose with water and lift the two ends don't plug the ends. The water will always level itself to the same height at either end. Then you can pick a point that won't move. that could be a big rock outside or the top of your back steps or whatever.. then you can make references to that benchmark.. in other words you can use the hose to check what the difference in height is between any given point and your benchmark. in this way you can write down the difference between any point in the house and the benchmark.. then if you start jacking and moving stuff you always have a reference point so you know how much things moved..

lots of houses have a little sag or unevenness often this isnt; a structural problem, in many cases a house took 100 years to get lop sided and it isn't going anywhere.. so in your case you might try to make things better, but not try to go to the extent of making everything too perfect.. if you start jacking things up an inch in one spot you might notice cracks forming all over the place where you didn't even realize you were applying stress. some degree of out of level or out of square may be tolerable at this stage.

ever have floods? maybe the center foundation sunk not because of the stove but because the soil below the center is not dug down to hardpan and at some point a flood allowed it to get mushy there and sink a little?

I think a lot of our old houses weren't dug in super deep because the digging tool was a shovel, but today they can easily go deeper because now we use a backhoe.

put it this way. you are having an anniversary party, so you have all your inlaws and kids over , maybe 50 people in and around the house. then someone starts clinking their glass to make an announcement so everyone walks into your living room at once.. now you might have 50 people in the room standing shoulder to shoulder. ,, that might be 8000 lbs of people. indeed an unusual situation but not that unrealistic.. houses need to be able to withstand these situations and they usually are , so I question why a stove that might weigh a thousand pounds if that would cause the foundation to shift.. maybe it did over time.. I don't know..

Phil

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Re: basement work, need advice

Post by Powermuffin »

Thanks again Phil. The area where the wood stove was, drops 3" in 3'!! Yes, we recognize that we will have to go very, very slowly and the floor will not be level when finished, but better than it is now. We are mostly interested in supporting the old floors as best we can so that we minimize future damage, leveling as much as possible and then making the basement more usable.

Thanks for your input!
Diane

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Re: basement work, need advice

Post by phil »

that sounds like a pretty severe dip in the floor ;-) more than I imagined.
I had a neighbor that tried to just use floor leveling compound, poured it like an inch thick. What a mess ;-)

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Re: basement work, need advice

Post by Seabornman »

Sistering the floor joists is a lot better than replacing from personal experience. The biggest issue is logistics: finding a way to get a long 2x where you need to, knocking out things that get in your way, and jacking them into place until you can nail or screw them. A framing nail gun is very handy for this kind of work (and very satisfying!). You may not need to sister all the way to the support point depending on the situation. Good luck!

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Re: basement work, need advice

Post by 1918ColonialRevival »

Agree that sistering is better than replacing, but if there is no significant sag or rot on the joists, then I don't see a need to sister them.

A picture would really help visualize what's going on and might solicit better recommendations from the group.

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Powermuffin
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Re: basement work, need advice

Post by Powermuffin »

I will take a picture and post it. Thanks all!
Diane

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