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Old 02-22-2012, 12:50 PM   #1
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Floor Joist


This 1905 house has real 2x8 floor joists. But they seem a little too soft for laying laminate flooring on top of the original hardwood. That floor is married to an addition that was added 20 years ago. I would like your opinion on taking OSB board, cutting it 8" and then marrying it to one or both sides of the original beams with screw and glue. I am thinking this will stiffen up the floor enough to handle the flooring. If I am missing any other issues here, please help decrease my ignorance. Thanks.

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Old 02-22-2012, 03:09 PM   #2
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When you say soft, do you mean the joists are rotten, as in you can push a nail into them by hand pressure? Or do you mean the joists are not stiff enough, as in they bounce when you step on them? Or do you mean the boards are not strong enough, as in they feel like they are going to break when you walk on them?

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Old 02-22-2012, 05:50 PM   #3
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' springy ' floor joists ? we did that in another house but used 3/4" ply, NOT osb,,, osb won't have much tension or flexural strength for this use,,, tack to existing joists then thru bolt thereby increasing total thickness to original 1 1/2" + 3/4" + 3/4" or 3" total,,, we typically use 2x8s for strengthening condo floors over crawl spaces & never have had any trouble,,, daniel can give you the bolt pattern,,, you're welcome
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Old 02-22-2012, 05:56 PM   #4
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The wood is in very good condition, especially considering it sat inches off the ground for 85 years of its life. It measures 2" wide, not 1 1/2 by the full 8". But I was told that there was too much bounce to install the laminate. So I am just looking to stiffen it up. As mentioned, there is also original hardwood on top married to 3/4 in plywood in the addition. I had considered plywood, but the OSB seemed to me that it would be even less likely to give. BTW, it is a 14 foot span. Thanks for the replies
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Old 02-22-2012, 06:05 PM   #5
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2x8 for a 14' span is too light a joist for me but i'll bow to daniel's expertise + he's got a pro license
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Old 02-22-2012, 07:38 PM   #6
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A true 2x8 joist, 16 inches on center, with a 14 foot span, has an L/D ratio of approximately 370, assuming 1.5 million psi modulus of elasticity (possible for old timber), 10 psf dead load, and 40 psf live load. This should be stiff enough for laminate. You did not say what type of laminate you are putting in, but I would double check with the supplier and ask them EXACTLY why they believe the floor is not stiff enough for their product.

Course, you did not say your joists were 16 inches on center, maybe they are further apart, which would mean they are less stiff.
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Old 02-22-2012, 07:51 PM   #7
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Try adding 8" steel studs in, they are dimensioned to true 8" and you can span 16' easily with a 16ga stud used as a joist. Added to what you already have will stiffen things up nicely.
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Old 02-27-2012, 01:03 AM   #8
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Yes they are good construction and on 16in centers and made of oak. I just have a general contractor in the house that feels the floor is too bouncy for laminante. But your point of what kind of laminate I choose may be more pertinent to the discussion even if I do marry on osb scabs. I was also going to install the standard crossmembers to help stiffen them as well. I just hate taking up perfectly good carpet to find that my floors somehow won't accept the laminate. So I am out here looking for good backup information and I think I have found it in this forum. Thanks
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Old 02-27-2012, 01:14 AM   #9
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Those cross pieces do nothing to stiffen a floor. There to stop the floor joist from twisting. If that have not twisted by now there not going to.
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Old 02-27-2012, 12:36 PM   #10
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I'm no expert nor Engineer. just an old hillbilly, do it myself kind of guy. I don't see anywhere what the span of these 2x8's is? how long/wide the house is? you say, your joists have been inches from the ground since 1905. I'm assuming you have little working space below the house? maybe you just need a beam under joists to stiffen them? a 2x8" or even 2x6" box beam may be sufficient yo stiffen joists enough for laminate flooring? Daniel. may agree? a beam down the center will cut span by 1/2 the span it currently is.

start, by lag bolting a 2x6 to the center of another 2x6+ a 2x6 on each edge of flat 2x6 that will be the top of beam. find center of house, chalk a line down center from end to end, you can shift chalk line either way 2 5/16, to correspond with edge of 2x6. start lag bolting flat 2x6 onto each joist on chalk line 2 lag bolts in each joist, one on either side of the one in center. when get to the end, another 2x6 lag bolted to each side and on the bottom. use washers large enough to prevent heads of bolts from working into the wood! it might take some jacking to get beam up tight to joists?

once beam is placed, you'll need pillars for beam to rest on, blocking of some sort setting on good undisturbed footing. you'll want the beam straight as possible, a simple laser pointer can help with this, maybe $6.00? tack a 2x block under beam on one end, tape/strap laser pointer on bottom of block. if you can get laser light at same distance from bottom of other end, as well as under entire2x6 box beam? house will be level and floor straight. an 1/8-1/4 either way ain't the end of the world over length of house. can use shims between beam and pillars if needed?

this should adequately stiffen your joists enough to apply laminate flooring, without having to stand on pieces to lock them in. build pillars every 6-8 feet under beam.
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Old 02-27-2012, 12:49 PM   #11
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I believe the OPS stated the joists were 14 feet long, true 2x8 construction, 16 inches on center. As previously noted, the OSB does not stiffen the floor, nor does addition of cross bracing. However, as I previously noted, the stiffness of your floor joists as determined by L/D ratio (the industry standard way to measure stiffness) is quite adequate for laminate, unless you have an unusual definition of the word laminate (i.e. the floor is not stiff enough for 24 inch square porcelain floor tile, it is not stiff enough for natural stone tile). I do not understand what the basis for your contractor stating the floor was not stiff enough for laminate, I would go back to him and ask EXACTLY why he believes the floor is not stiff enough for laminate, and what he proposes to do about it. If his basis is some intuitive feeling based on how it feels under foot, you may want to ask him to perform standard D/L calculations and compare the value against manufacturer recommended minimum for the particular laminate you have in mind.
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Old 02-27-2012, 05:42 PM   #12
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I'll say it again... 8" steel studs, they're cheaper than you think and would work perfectly in this situation. I use them EVERYDAY for the decks I built and they beat the pants off wood for durability and strength.
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Old 02-27-2012, 10:50 PM   #13
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Floor Joist


Thanks for all the great information. I am starting to think I need a second opinion from someone who lays laminate. I think my guy just does not want to lay it. I do know that my sister had hers laid in her whole one story Gunison house and there was only one place where the boards creaked against each other when you step on it. A little furniture glue took care of it (for now).
BTW, the joists were in a crawl space, but now stand 9 1/2 feet above my cement garage floor. I still puzzle why the contractor dug out the floor so deep. So working on the joists is rather high, but accessible. So I think the fact that the joists rest on beams that are only supported on four corners might contribute to the bounce factor. But if it were not enough support, you'd think the drywall would crack over this decade.Thanks again all. I am sure I will be back with some more ignorant questions on new subjects down the road.

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