I've already asked about how to level concrete, but now I'm contemplating going after my main living level. I'm going to replace the carpet with laminate, and thus, any imperfections will likely be much more visible (and I don't want any imperfections period!). I also know there are a few areas I'm going to have to work on, as they have 1/4" dips over 2' areas.
I'm wondering if anyone has any sage advise that could save me some time. If there's any really good tools that I might need, if there's a preferred way to measure levelness, or if there's any practices I should avoid.
Had a similar problem (generally a larger slope but some dips) on the second floor in a large room where I wanted to use a finished oak. I ripped up the carpet, to find press wood, ripped that up to find plywood. Used a laser level coupled with a long carpenters level to determine they size of straps to place on joists. Not at all an easy job and I was concerned about the accuracy at the time but it did turn out fine.
Is the unevenness caused by different thicknesses of plywood or the odd 2x10 being slightly crowned, or a more structural problem? If the former, then you can probably get away with planing and shimming. The latter would obviously be problematic, and if you don't intend to fix it you will have to live with it and shim as best you can. I had both when I did my family room a while back. For the minor stuff I planed the edges and used layers of 30# roofing felt. In some spots I was up to about 3 or 4 layers (and the whole floor had a layer of 15# on top of that - you may be using the spongy stuff normally recommended for laminate). Actually, I underdid it in some areas, could have done with another couple of layers. My learning from this is that you should not skimp on this preparation. Start by doing a detailed survey of the whole room with your straight edge (use a 4 or 6 foot level) and spray paint or chalk to note your high and low spots. Remember that you need to graduate your adjustments, so plane high spots smoothly and add felt for the lows. If you need several layers of felt, make them smaller as you get higher (bit like a contour map). Get your straight edge and don't stop until you have good smooth level (keep in mind it will compress). My experience has been with hardwood, nailed down. But I would imagine you need the same level of prep for laminate - to avoid some spots sitting up and moving when you walk on them. For hardwood I've found that humps running parallel to the run of the boards is more problematic (causes the gaps between the boards to differ) but with laminate I would imagine the humps perpendicular to the hump are more of a problem (because you're not nailing down to conform to the hump). If you have some small but extreme dips you can use thinset to build them up, but I used some leftover 12x12 self-adhesive linoleum tiles in a couple of areas.
The laminate with it's underlayment can go over small level heights just fine.
I had a much more severe problem due to the age of my house. Any long straightedge should give you a good indication of how flat the surface is, level has little to do with how the laminate will go down.
As far being level, the carpenters level was easier to deal with than the laser level for distances on the order of the length of the level.
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