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Old 01-08-2010, 01:22 PM   #1
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Hello, I have a realtively cheap manufactured house that has some craptacular "engineered" floor joists. The rest of the house seems pretty solid, but if you're standing on the floor and another person walks past, you can feel the floor sag and then rebound. The floor joists flex.

I'm just at the beginning stage of addressing this, and am wondering what the best strategy for improvement would be:

1) gluing/screwing in 3/4" plywood along the sides of the joists?
2) putting a 2x12 between (and parallel to) the existing joists?
3) ???

To further complicate matters, the builders put the heating ducts through the joists without any further bracing. So, whatever I have to do to strengthen the floor, I guess I will have to remove that and have the heating ducts put on the underside of the joists?? (which would reduce headroom in the full, unfinished basement).

I have no idea where to start with this, so any help would be appreciated.

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Old 01-08-2010, 01:56 PM   #2
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Can you post a pic of the joists & showing how much they cut out for the ducts ?

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Old 01-08-2010, 02:11 PM   #3
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Yeah, I could do that tonight.
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Old 01-08-2010, 07:23 PM   #4
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Ayuh,.. A single brace, perpendicular the joists, mid-span would Do alot, with little materials....
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Old 01-08-2010, 08:12 PM   #5
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Okay, here are the craptacular floor joists:


If it's possible to help stiffen the floor without significantly obstructing headroom in the basement, that's what I would like to try to do. Am I screwed in that I have to do something like what Bondo is suggesting? A beam running perpendicular under the middle of the joist span would have to span about 40', which I guess would require steel columns running along the middle of the usable basement space. I was hoping there are better options. Oh well, I am just looking for options, either for DIY or to discuss with pros. Thanks again!

edit: the house is a rectangle, approx 40' by 26', with a beam running down the length in the middle, supported by steel columns, so there already is a row of steel columns going down the middle of the basement.

Last edited by Brak; 01-08-2010 at 08:16 PM.
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Old 01-08-2010, 08:20 PM   #6
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me personaly I really like those type of engineered floor trusses. If it's springy then possibly the span is to great for the size they were made. I would think adding 5/8 ply to a side would realize a considerable increase in stiffness. You could also add a 2x6 insted of ply running continuous nailed to the vertical members as a stiffener acting like an internal header of sorts
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Old 01-08-2010, 08:28 PM   #7
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I would track down the manufacturer of the open-web floor trusses and ask their opinion.
Around here, they would need to be re-certified once the interior webs were removed.
Also, as far as I know, if you add a stiffener to one side, you might need to do the orther side of the truss as well.
But adding a stiffener may not solve your problem since there is no way to continue the stiffener through the heat duct.
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Old 01-08-2010, 08:31 PM   #8
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you're right totaly missed they removed a section, good catch
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Old 01-08-2010, 08:43 PM   #9
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I guess for long-term, I have no problems with removing the cheapo fiberglass ducts and contracting sheet metal ducts to be added in by a pro, under the joists. I guess I should also add that I'm not too concerned with "code", as my county has no building codes, nor is it likely to anytime soon. Moreover, this is family land, and a house that I inherited, so I don't ever plan on selling it.

Last edited by Brak; 01-08-2010 at 08:46 PM.
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Old 01-08-2010, 09:20 PM   #10
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Appreciate that "code" is a 'minimum' standard.
Just going by the code book won't mean it is a good job.
Same situation here with 'code'. The district I live in has a National Building code (and a Provincial one, too) but no Inspector to enforce it, so lots of 'shoddy' work happensthat wouldn't be passed in the city.
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Old 01-09-2010, 08:30 AM   #11
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Quote:
Originally Posted by jlhaslip View Post
Appreciate that "code" is a 'minimum' standard.
Good point - I guess I just meant that I'm open to ideas that might be unorthodox. I'm the first to admit I don't know much about building/construction. I'm posting here to get some general ideas. While I'd like to do it myself, I'm certainly not opposed to hiring a pro. I'd just like to know where to start.

Nobody has commented on the 2x12 between the joists. Overkill?
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Old 01-09-2010, 08:44 AM   #12
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Quote:
A beam running perpendicular under the middle of the joist span would have to span about 40',
Ayuh,.... Is the whole house Springy,... If Not,... Just reinforce the area that Is....
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Old 01-09-2010, 09:45 AM   #13
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Those are preengineered truss joists, and they look pretty good to me. As for the diagonals that are missing where the duct goes through, that was likely by design. With the type of joist you have, it is possible to elminate diagonals and retain most of the strength of the joist.

Before you spend a dime on improvements, you need to determine the cause of the springiness. You need to measure the joists and the spacing before you can begin to analyze their strength and suitability for the use. Measurements would include the width of the joist, depth of the joist, and spacing.

You should contact the manufacturer of the joists to determine the structural properties of the joists. The joists may turn out to be sufficiently strong for the application, but the deflection may still be more than you want. The truss manufacturer will no doubt have some good ideas on how to stiffen the trusses.

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