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I recently bought a new home. Also on the property is an accessory building which I am using as an office. The building is finished on the inside and has a cheap parquet floor. I'm not sure what's underneath, but the building is on blocks, not a slab. I infer from this that the construction is just beams on the blocks with joists running across them, covered by 3/4" plywood subflooring and the parquet on top.

The floor is pretty unlevel in places. It seems to have a crown in the middle-ish of the room. It also feels really soft in places.

If this were a full-sized pier & beam construction, it would have a crawlspace, and addressing these problems would be pretty straightforward. However, this building has no crawlspace at all. I'd be lucky to even be able to see anything under the outside edge.

How do I try to address these issues when I can't get underneath?

edit: pulling up the floor, or at least parts of it, is an option. But if I do that, then how do I work on the floor from above?

  • If you are planning on removing the parquet, you can always lift the subfloor as well to get underneath. – diceless Nov 11 '14 at 21:31
  • Well, sure - I can lift the floor, but then what? How do you fix a messed up floor from above? – Ben Collins Nov 11 '14 at 21:32
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    Same way as from below, just you don't have to do the work on your back. With the sub floor up, you will get an idea of what is wrong and tackle the work standing up. – diceless Nov 11 '14 at 21:37
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    Alternatively, jack the whole building up, fix it, and either set it down again or set piers under it at a somewhat more elevated position. Or go hog-wild and put a basement under it ;-) – Ecnerwal Nov 12 '14 at 0:34
  • Thinking outside the box: For the room in my house which is most tilted, my long-term plan involves built-in furniture levelled to compensate for the floor. (It isn't worth trying to jack up the house and bring it level again; too much has been done with it in its current shape, and nothing this old is ever square or level anyway.) – keshlam Nov 12 '14 at 1:07
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Before I suggest how to investigate your problem, my guess is that one (or more) of the concrete blocks with a post/pier that is supporting a joist or beam has settled. The solution to this can range from removing the flooring in a small section and resetting the block, to realizing that all of the blocks are out of whack and maybe the ground the building is set on was not properly prepared for supporting a building. You can find a couple of great guides to building large 'accessory buildings' (sheds, studios, etc) on Fine Homebuilding, Family Handyman, etc, but the process generally starts with making sure the ground underneath has proper structure and adequate drainage (e.g. gravel/baserock tamped down, filter fabric, etc). Depending on the age of the building this might also be normal (I wouldn't expect a building sitting on small concrete blocks (instead of a solid concrete foundation) to last 20-30 years and have a flat floor).

For tackling your specific question, the general idea would be to try to remove a small section of the parquet floor and subfloor where there is a problem (soft spots or out of level floor) without cutting through the joists or beams, in order to better assess the situation. Once you have that section removed, you should be able to see the exact construction and state of the supporting members (joists/beams/concrete blocks) which should help to identify the cause of the problem.

To identify where the beams/joists are so that you don't cut into them, you could use a mirror and flashlight on the outside of the building, and take approximate measurements.

Another approach would be to just cut right into the soft / out of level area, as you will likely need to repair replace that anyway.

If you removed the parquet floor first, it should be really easy to see where the joists are by looking at the nailing pattern in the subfloor. Subfloors are nailed to the joists (typically a builder will put the subfloor down on top of the joist, snap a chalk line on the subfloor that is at the center of joists, and then nail along that chalk line). So you could cut a section of the subfloor out in between the joists and check out the problem.

Since you asked how you would work on a floor from above, all of these suggestions about cutting into the floor would need to be done from above the floor, i.e. using a circular saw, hole saw and reciprocating saw, oscillating saw, etc. Once the floor is off and you see what the problem is, you would fix it and build the floor back up. For example, maybe you would decide to just add shims under the joists, or maybe you would put in a new concrete block and post and a new joist or blocking, and then install new subfloor, then finish flooring. I hope that helps, please let me know if anything is unclear.

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You can rip up the subfloor and replace it all, or you can use a leveling compound (Similar to concrete) to get your floor much more level.

Neither option requires getting under the structure, but both will involve floor destruction.

Leveling Compound

  • Is this rigid like concrete? What happens if the floor structure flexes; does it crack? – Ben Collins Nov 12 '14 at 1:09
  • On top of a floor you describe as "really soft in places" it will most certainly crack. – Ecnerwal Nov 12 '14 at 1:15

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