Replace Gutters: Project Walkthrough

1. Measure the roof, not the old gutter

Use how to measure a roof without getting on it to get eave length, roof footprint, and pitch from the ground or from a ladder at the eave line rather than walking the roof surface itself. Run the gutter and downspout calculator with that footprint, your roof's pitch, and a rainfall intensity figure for a real storm in your area — a steeper roof throws water into the gutter faster than a shallow one for the same footprint, and the calculator adjusts for that, which a straight footprint-only estimate does not.

The output is a recommended gutter capacity and a downspout count, and both are worth checking against what's currently installed rather than assumed to match it — a house that's had an addition, a re-roof to a steeper pitch, or simply sits in a region with heavier storm rainfall than it did when the original gutters went up can genuinely need a bigger system than what's coming down.

2. Pull the old gutters and see what's actually under them

Gutters hang from hangers screwed into the fascia board or into the rafter tails behind it, and pulling decades-old gutters is the first real look most homeowners get at that fascia's condition, since it's been hidden behind hardware and running water the whole time. Soft, discolored, or crumbling wood at the hanger screw locations is common wherever a gutter has been overflowing, sagging, or leaking at a seam for years — water finds the fascia before it finds anywhere else, and the gutter itself often hid the damage until the moment it came down.

3. Size and repair the fascia to match what the new gutter needs

Run the soffit and fascia calculator for the full eave and rake linear footage once you know how much fascia board actually needs replacing, not just patching — a hanger won't hold securely in wood that's soft enough to compress under a screwdriver, and a new gutter hung on compromised fascia is a repeat of the same failure on a shorter timeline. Match the new fascia board's width to what the new gutter's hangers actually need for solid purchase, which may be a different dimension than what the original builder used if the new gutter capacity from step 1 is larger than the old one.

4. Hang gutters and downspouts

With sound fascia in place, hang gutters at a slight consistent slope toward each downspout — commonly a small fraction of an inch of drop per 10 feet of run, enough to move water without being visible to the eye — and set hangers at the spacing the gutter and downspout calculator assumed, since a wider hanger spacing than what the sizing was based on lets a full gutter sag under its own water weight during a heavy storm.

5. Finish the edge with drip edge that tucks behind, not in front

Run the drip edge calculator for the eave and rake lengths, and confirm the drip edge installs under the roofing but over the gutter's back lip — drip edge that ends up sitting in front of the gutter, rather than directing water down into it, sends roof runoff behind the gutter and straight onto the fascia and wall, undoing much of what a fresh gutter and repaired fascia were just installed to prevent.

Why the old gutter's size is not evidence the new one should match it

A roof footprint of 1,200 square feet at a 6-in-12 pitch, run through the gutter and downspout calculator at a moderate rainfall intensity, commonly comes back sized for a standard 5-inch K-style gutter with two downspouts. The same footprint at a heavier regional storm-intensity figure, or with the pitch bumped up from a re-roof, can push that recommendation to a 6-inch gutter — a capacity increase of roughly 40 percent in cross-sectional area for the same roof footprint, purely from the rainfall and pitch inputs changing, with nothing about the house itself getting bigger.

That capacity increase matters immediately for the fascia repair in step 3: a 6-inch K-style gutter is deeper and its hangers sit differently than a 5-inch gutter's, which can mean the fascia board width needed to give those hangers solid, fully-supported purchase is larger than what a straight like-for-like fascia repair would have used. Deciding gutter size in step 1 before fascia repair in step 3 means buying the right width fascia board once, instead of repairing to match the old 5-inch gutter's hanger pattern and then discovering the new 6-inch gutter doesn't sit correctly on it.

What goes wrong when new gutters go up on the old fascia without checking it

Hang new gutters straight onto fascia that was never inspected, and the hangers may find solid wood in some spots and soft, compromised wood in others along the same run — screws driven into softened fascia hold for a while and then pull loose under the weight of the first heavy, ice-laden gutter of winter, and a gutter that's pulled away from the fascia at one section usually sags and backs up water at that low point even if every other hanger along the run is holding fine.

The reverse mistake is repairing or replacing fascia before the gutter sizing is settled — a contractor who repairs fascia to a standard width without knowing whether the new gutter is staying at 5 inches or moving up to 6 can end up with a board that doesn't give the eventual gutter's hangers full bearing, which is the same problem as skipping the fascia inspection, just arrived at from the other direction.