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This may seem like a no-brainer but I just wanted to confirm my thought process. I'm finishing our basement and reached the point where I need to install the baseboards. While the slab is relatively level (±3/8" across the whole foundation), I am curious if it is more important to have the baseboards level or to have them follow the variances in the slab (resulting in trim that is the same height overall)?

My assumption is to have them level at the top and cut any variance in the slope of the slab off the bottom to allow for my carpet to still be tucked underneath, but figure I would get the opinion of the masses.

Thanks in advance for any input you may have.

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    A matter of personal opinion. Depends a lot on the particular scenario.
    – Hot Licks
    Dec 10, 2020 at 16:45

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When putting a narrow item on a wall hang it level. When putting a wide/long item on the wall hang it parallel to the floor or ceiling, whichever is nearer. The eye can see a picture frame askew because it just doesn't "look right." But something long like a 10 foot long dry erase board, a wide painting.. or trim work like baseboard or crown molding.. will be judged by its parallelism with the adjacent floor or ceiling. Nobody can tell whether the floor or the ceiling is actually level; we all just assume that it is.

Likewise, don't adjust the width of a baseboard so that the lower edge can track the floor and the upper edge remains level. The resulting wedge-shape baseboard will stick out like a sore thumb. Choose some spacer stock (scraps of 1/2" drywall, scraps of the baseboard itself, etc), support the section of baseboard on several spacers to keep consistent distance off the floor, and nail it in place.

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    That is better wording than mine and absolutely correct.
    – DMoore
    Dec 10, 2020 at 6:50
  • Thank you for your answer. I am glad I asked and will heed your advice when installing.
    – Jason Reed
    Dec 10, 2020 at 15:27
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They don't have to be level, they have to look straight. This can actually get quite complicated when doing tile or vinyl planking (especially those with no underlayment).

If you have "rooms" and the basement broken up a bit this shouldn't be a big issue. Try to get trim in one piece for each wall - if it isn't then set each wall and take a look before nailing. You want the top to be straight and not pressing the trim on the floor to make it angled. Not only will this look bad but it wont meet corners right.

There are time where you will just live with a pretty big gap on the bottom on certain runs - can be a good 1/4". Then you can decide on if it looks ok or if you need to put down quarter round or something comparable.

If you think you are going to rip the boards at a slight angle or even plane them... well I am sure it is doable but you are in for a logistics nightmare and tons of work for possibly something that looks worse.

I for one just leave the gaps - as-is - on the bottoms. I see it, yes I see the gap but no one else ever notices and it looks cleaner than quarter round or shaving. That is unless you are lying on the floor look at the gaps.

If you lay it out and the gap is not acceptable a work-around would be a nice decorative rectangle trim cap in the middle and start over from there. But with carpet you have a ton of play - way way more than 3/8". So you should be able to start low on the higher end and go straight across.

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  • This is much better than the accepted answer. There are so many reasons not to follow a non-level floor. Most importantly you want trim to be square with the wall corners so that it doesn't look visibly non-square or require extraordinary measures to align the mitered edges around corners.
    – R.. GitHub STOP HELPING ICE
    Dec 11, 2020 at 19:35
  • One trick, if the gap is unacceptable because aligning to the highest point makes the trim too high everywhere else, is to shave it down at the highest points so the overall level can be lower.
    – R.. GitHub STOP HELPING ICE
    Dec 11, 2020 at 19:37
  • @R..GitHubSTOPHELPINGICE - in extremes if your shaving and don't want to spend 20 hours getting the corners to look right a simple corner trim block makes things simpler. That isn't really for a 3/8" slope across basement. I have dealt with basements sloping almost 2" from one end to another.
    – DMoore
    Dec 11, 2020 at 19:42

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