Guidelines for blocking to run hardwood floor parallel to joists?

HoneyDoodApril 19, 2011

Hello All,

This is odd. I am posting this question for the 3rd time now, and it keeps disappearing. No email, nothing. So I'm going to assume there is a problem with the forum and re-post.

Forgive me if this question has already been asked and answered. I can't seem to find what I'm looking for although I don't doubt it's somewhere here.

I'm about to close on a 23 year old home with hardwood flooring. They installed it "correctly", being perpendicular to the joists, but it's parallel to the windows, and is laid with the short walls in the rooms.

This is on the first floor, the sub is plywood, and the house has an unfinished basement. So my plan is to block the joists and replace the tired, ugly flooring with something new run perpendicular to the windows, but parallel to the 2x10 joists.

There is a steel I going through the middle of the house. The span is about 14 feet from foundation to I. How many rows of blocks should I install, and where? I keep finding info on how to block (which is not exactly rocket science), but nobody seems to talk about how many rows need to go in. One in the middle? Two divided evenly? Three? Is sistering necessary? (hope not, lots of plumbing and wiring in the way)

Thanks in advance!

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You don't need sistering. The blocking is to help prevent sag of the flooring between the joists, obviously.

There is no rule of thumb concerning this. I would space them about 24" on center.

I assume you are removing the existing floor. After you have it up and gone, check with a straight edge between the joists to see how much sag you actually have.

I've had posts disappear also...strange.

    Bookmark   April 19, 2011 at 11:39AM
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Solid joists as opposed to engineered joists are often inconsistent in their levelness due to crowning. It is possible you may end up with an undulating floor because of this even if you have strengthen the subfloor between with blocks.
Once the subfloor has been exposed check with a straight edge to determine whether it will be flat enough for you. Bear in mind if it is a prefinished floor you are installing each surface will reflect as if it were a small mirror and accentuate the rolling nature of the subfloor.

    Bookmark   April 19, 2011 at 2:28PM
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