Half-round or K-style gutters?

The capacity difference is the real one

K-style gutters have a flat back and bottom and a profiled face that resembles crown molding. Half-round gutters are a pipe cut lengthwise.

That shape difference does one thing that matters: K-style carries more than twice the water of a half-round gutter of the same width. This Old House Magazine is the source, quoted on two separate This Old House guides.

So a 6-inch half-round is not a capacity upgrade over a 5-inch K-style, despite being wider. If your roof sheds a lot of water, K-style is the answer and the rest of this page is about what you give up to choose otherwise. Our sizing page has the figure that makes this concrete: one inch of rain on an average roof is 1,900 gallons.

What each style costs per foot

Bob Vila is the only one of our sources that prices gutters by style rather than by material:

This is where the usual framing starts to wobble. Every source here says half-round costs more than K-style. This Old House's half-round guide says so outright, their gutter types guide says half-round often costs more because it needs specialized materials and more experienced contractors, and their installation guide says the same.

But the only published per-foot figures we can find put the two bands almost on top of each other: $3 to $25 against $4 to $25. One dollar at the bottom, identical at the top.

Our reading, marked as ours. The price difference is real but it is not in the gutter. This Old House's half-round guide gives the actual reason: half-round gutters cannot sit flat against the fascia board, so they need more brackets and accessories, and most homeowners cannot fit them, which removes the cheap end of the market. What you are paying for is the installation, not the metal. That is why a per-foot material band does not show the gap, and neither source makes that distinction.

Lifespan, where half-round has a real case

This Old House's half-round guide is the only source we have that publishes lifespans for this style:

They attribute the durability to the shape itself: a smooth, crease-free interior resists corrosion and leaking, which is a sensible mechanism and the one genuine performance argument for half-round.

A flag on that 100 years. This Old House publishes three different copper lifespans across its own gutter pages. The installation guide says 50 years or more, citing InterNACHI. The copper guide says 50 years or more and separately notes that some gutter companies estimate 80 to 100. This half-round guide simply states 100. We would plan on 50, for the reasons set out on our copper page, and treat 100 as a figure that has lost its qualifier somewhere between pages.

Which collects more debris

An honest point against K-style, from This Old House's gutter types guide: the angled interior of a K-style gutter collects debris more easily and needs more frequent cleaning. Half-round, with fewer interior angles, drains more easily and is less prone to buildup.

Our arithmetic, marked as ours. Our cleaning page puts a typical clean at around $300 and the usual schedule at twice a year. If half-round genuinely saved you one visit a year, that is $300 against a style premium that lands mostly in the installation. Neither source quantifies the cleaning difference, so we are not going to pretend this is a calculation, only that it is the shape of the trade.

Box gutters, the third option nobody asks about

Box gutters are built into the roof structure rather than hung off it. Both This Old House guides say the same things about them: greater water capacity than K-style, a hidden appearance, and more complex and expensive installation, repair and maintenance. They are mainly a commercial choice, used on homes with complex rooflines or high drainage needs.

If your house already has them, the repair economics are different from everything else on this site: our repair page notes that styles requiring construction to access, box gutters among them, can double the repair cost.

How to choose

1. Heavy rain, large or steep roof. K-style, and consider 6-inch. The capacity figure settles it.

2. Historic or rounded architecture. Half-round, and size up, because you are starting from less than half the capacity per inch of width. That shape difference also decides whether you can hang them yourself: our do-it-yourself page covers why half-round is a professional job.

3. Planning to own it for forty years. Half-round in copper or zinc is the longest-lived combination any of our sources publishes, and also the dearest. Our copper page works out whether that lifespan pays.

4. Most houses. K-style in aluminum. This Old House's own answer to which gutter type is right is that K-style offers the reliable balance for most homes, and our cost per linear foot page shows what that should cost.