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I've generally mitered joints and very rarely coped them in trim or molding, and have been able to achieve an appearance I was satisfied with.

But "traditionally," coped joints seem to have been the norm. Even in my 1970's house there are plenty of examples of coped joints in baseboard (skirting board) and some were done in the 90s. So even in the era of power miter boxes the people who did that work felt coping was a better choice. But personally I'm not sure what the rationale for that actually is.

(Coping clearly could be useful in a retrofit situation, matching up a new piece against something existing without disturbing what is already there. But I'm thinking more of a situation where you are joining two new components.)

Also, just for the sake of argument, assume that the skill of the woodworking / carpenter is good enough to create a good joint either way. I'm interested more in the inherent advantages of either approach.

Just for clarity, its a joint of this general type I'm thinking of:

enter image description here

(Image source)

but it need not be a perfect 90.

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  • You've done some sleuthing online, has the advantage of coped joints not been explicitly stated in at least some of the guides to doing it? Because the rationale does generally go hand in hand with the description of the methodology.
    – Graphus
    Jan 9, 2021 at 13:44
  • Hi @Graphus. Over the years I've come back to this topic a few different times. Each time I look into it the impression I get is that people believe / claim that you get tighter joints with coping. But for whatever reason this has seemed 'hollow'; maybe because its not really explained in detail why that is. And in principle I can't see why a mitered joint if executed well couldn't be just as tight. I have not read / seen a satisfactory explanation of that. I'm not actually doubting the advice, I would just like to get a much more detailed explanation of the reason.
    – StayOnTarget
    Jan 9, 2021 at 17:19
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    One problem with mitering the corners is that the corners are not always exactly 90 degrees, especially in older homes, so it is easy to end up with a bad joint finish.
    – Ashlar ♦
    Jan 10, 2021 at 1:28
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    Yes a cope is always more forgiving. Re. the thing about tightness, you're talking about initial tightness. It is, as you say, fairly straightforward to do a 90° mitre that's perfectly tight. But that's only at time of installation..... simple mitres in solid wood are notorious for opening up over time, where coped joints do not or at least to a much lesser extent [Both of these are chief advantages of a coped joint over a mitre that as I say should be explicitly stated in some or many of the online sources.]
    – Graphus
    Jan 10, 2021 at 10:25
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    Consider what happens when a miter joint opens up. From anywhere on a 45 degree line from the corner you can see all the way to the wall, and the gap is obviously deep. Even in principle you can only see all the way down a gap in a coped joint with your head right at the wall looking down the molding. Additionally, if the molding has curves (and it almost always does) these serve to further block your vision into the gap, especially with ornate moldings such as crown molding.
    – WhatRoughBeast
    Jan 17, 2021 at 3:21

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The obvious positive answer with mitered joints is 'speed'. You set the miter to the correct angle (generally 45 degrees for most corners, and cut. And in theory you put them both in the corner and you have a nice joint.

I say in theory, because I always have issues with my mitered joins being 'close' and thankfully mostly 'close enough'. But many homes the walls are not straight nor corners a perfect 90 degrees etc. This is where coping will shine.

Coping will take some more time, but the joint can always be perfect (with a little patience) because you are cutting it to fit for the actual site, not the 'ideal' site. in a corner you have 3 flat(ish) surfaces intersecting ideally at 90 degrees, but surprisingly often there are anomalies. Coping allows you to account for each individually, so you will have a beautiful joint that would take quite a bit of shifting of the walls or ceiling (or floor) to actually mess with the joint.

So the older the house or shoddier the original construction, the more likely coping will make the finishing touches shine. You can even cope the long sides of the trim when you have undulating floors or ceilings, to get a tighter fit.

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