Margin of error on level with Ledger Board

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Old 07-26-18, 10:27 PM
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Margin of error on level with Ledger Board

I'm building a 29' wide (along the house) by 18 ft deep and 14ft deep (away from the house and wraps around a part of the house that kicks out) deck, and spent a lot of time reading as much as possible. I had the help of my father and fiancee while hanging the ledger board, and had 2 different levels on my ledger board. Each of us confirmed that it looked completely level before sinking all of the 5" LedgerLok screws. When it came time to hand the 2nd ledger board around the corner, I decided it may be worthwhile to pick up a laser level, plus I happened to see that Amazon had a Prime Day deal and I'd been looking for an excuse to get one. After leveling the laser level with the corner where it would nearly meet the next ledger board, I noticed that the first ledger board (the one I already hung, since I haven't yet hung the 2nd one) seems to be off level by just under 1/4" over 14 ft. I think this is likely within a margin of error and won't create any problems, especially since it slopes away from the center/corner of the house and towards the edge where water can drain away from the house. But I was a bit alarmed to see that either our levels were out of alignment, my laser level is out of alignment, or none of the 3 of us were very good at reading the level. I'm looking for some reassurance that 1/4:" at the far side of a 14 ft ledger board won't present an issue. And then looking for some guidance that I just need to line the adjoining side of the next ledger board to the same height as my current one, and all should be fine.

If I've done a poor job describing any of this, please let me know. I'm hoping to hang the 2nd ledger board tomorrow or the following day, but don't want to back myself into a corner.
 
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Old 07-27-18, 03:17 AM
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This is the type of situation I hate, finding an error that probably is somewhat invisible to the whole of the the project but nagging that you know it is not correct.

If me I would take the time and make it right but that's because I am a perfectionist and hate the concept of DIY projects being half ass!
 
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Old 07-27-18, 05:35 AM
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You didn't say what kind of laser level you got. Some of the cheaper ones are not very accurate. A good laser level costs a small fortune and is accurate to 1/8" in 50 or 100 feet. Cheap ones might be 1/4" in 30' or worse. Your manual will say what kind of tolerance it has... and you should always verify that with the tool. And the same could be said for your other levels... what size were you using?

I have found that many people "think" they have something level when really they don't. There is margin for error in the level (if you flip it 180 degrees and it reads differently you might as well throw it away) and in the way your eye perceives the bubble in the vial. A short level is not as accurate as a long one... and if your board is not straight as an arrow you will get a different reading depending on where you set the level.

That being said, this is not a huge show stopping deal, if you feel that 1/4" is within your tolerances. If your laser is accurate, I would go with what it says.

You could check it by setting one of your joists up... set the level about 15 feet away... mark the line on each end of the joist. Then move the level to the OTHER side of the joist... 15 feet away. Mark the joist ends.

Then measure up from each end. The marks may not be equal... but the question is are the two lines parallel? If they are not, you just parallel found the margin of error in your level.

You can do the same thing with plumb in a doorway... set your laser up to follow the same line on the floor 10 feet on either side of the doorway... mark the top and compare any difference.




​​​​​​.
 
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Old 07-27-18, 06:30 AM
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Thank you both for the quick responses. I purchased a Dewalt DW088K, which is stated to have a margin of error of 1/8" at 30ft. Not sure if that can be extrapolated to shorter distances in a linear fashion, IE: 15ft accuracy is 1/16" or less. Admittedly, I haven't tested the laser level's calibration to confirm that it's accurate. I'll have to find an area that allows me to follow the manual's instructions on field calibration for scan direction (https://servicenet.dewalt.com/docume...432.1531883988), which indicates a fixed position using the laser level's mounting bracket at least 30 ft away from a wall. I'm not sure I have any spots inside my house that have a 30 ft span, and if I do it outside, I'd have to use a tripod instead of the built in mounting bracket. I'd think the tripod would likely be fine except that it introduces a potential other variable that could cause variation.

Also, in measuring the initial level, we used a 4 ft level as well as a torpedo level. We moved the 4 ft level around to multiple locations on the board and confirmed that it showed as level regardless of where we put it. It's possible that in driving some of the screws they pulled the board out of level, but I don't believe it would have been by 1/4". I would guess that at most have 1/8" or less of an impact over 14ft.

The 1/4" does bother me because I'm a perfectionist as well, but I'm not sure how best to fix. We confirmed it was level after driving a ledgerlok on each end by moving the 4ft level to multiple areas, and having multiple people confirm the bubble was dead center. It's possible the level itself is out of alignment, which I intend to check. But once we confirmed that it was level, we drove 27 or so LedgerLok screws, so completely undoing it will mean 27 holes in the ledger board and side of the house.

If I need to fix this, what are the recommendations on how to do so with minimal long term impact on the stability and structural integrity? As I see it, my options are:

1) Back out all of the LedgerLoks from the house, but leave them in the ledger board. Reposition the ledger board along the house and then re-drive the screws. The risk here is that some of the screws grab into their previous holes, or don't create as strong of an attachment because their new hole overlaps with a portion of the previous hole.
2) Back out all of the LedgerLoks from both the house and the board. Alternate the LedgerLok screw positioning (IE: where it was previously high on the board, go low, and alternate in a W pattern from there) so I'm creating new holes in the ledger board. Do I need to be concerned with filling the previous holes in the ledger board with some sort of sealant? Will this compromise the long-term integrity of the ledger board? Do I need to seal the previous screw holes along the side of the house?
3) Get an entirely new ledger board, and start over. Then my only consideration is whether to do anything with the holes along the house and potentially filling those in. I would presumably want to switch the LedgerLok spacing so it doesn't overlap with any of the previous holes in the house.
 
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Old 07-27-18, 06:41 AM
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Originally Posted by XSleeper View Post

You could check it by setting one of your joists up... set the level about 15 feet away... mark the line on each end of the joist. Then move the level to the OTHER side of the joist... 15 feet away. Mark the joist ends.

Then measure up from each end. The marks may not be equal... but the question is are the two lines parallel? If they are not, you just parallel found the margin of error in your level.

You can do the same thing with plumb in a doorway... set your laser up to follow the same line on the floor 10 feet on either side of the doorway... mark the top and compare any difference.
​​​​
Thanks for this suggestion, it's an easier way to calibrate than what the manual suggests. I wasn't quite following what you meant with checking plumb, but I haven't used that feature on the laser yet.
 
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Old 07-27-18, 07:13 AM
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I would be more concerned about the quality of the ledger boards than the quality of the levels. If the level is placed on a crowned section of the ledger board, the reading will not be accurate. Stretch a string tightly from on end of the ledger to the other end along the top edge to verify how much crown is in the ledger.
 
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Old 07-27-18, 09:58 AM
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I agree with Wirepuller about introducing error if your ledger isn't absolutely straight.

For leveling over a distance, a water level is cheap and accurate.
 
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Old 07-27-18, 10:33 AM
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Thanks. I'll definitely take a look at the crown of the ledger using a string from end to end. And I'll pick up the materials for a water level while I'm out getting some more joist tape today.
 
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Old 07-27-18, 11:11 AM
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And unless you are putting up something that's 8" long, a torpedo level is pretty inaccurate for anything long. The longer the level the better. A good 78" level is the the thing to have for most framing. Next time you are tool shopping I would highly recommend it. (Don't expect you to have an adjustable plate level).
 
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Old 07-27-18, 12:45 PM
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pick up the materials for a water level

Once I got my laser level I threw away my water level.

There may be some tol in the laser, there is more in the water level.

It's how you read the water as it curves up the side of the tube, I hated that tool!
 
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