How to install gutters on a one-story house

What size gutters do you need?

Work it out from the roof area draining to each downspout and the hardest 5 minutes of rain your area gets, before you buy anything. On the house below, that means 5 inch gutters with a downspout at each end. Gutter size is a flow problem. The water arriving at the gutter depends on three things: the roof area draining to it, the pitch, and how hard it rains in the worst few minutes of a storm. The method that sheet metal contractors use comes from SMACNA's Architectural Sheet Metal Manual, and Berger Building Products reprints its tables in a free technical appendix. Here it is on a real roof.

The house: a 52 by 30 ft roof in plan, gable, 6/12 pitch. Each 52 ft eave drains half the roof, 52 x 15 = 780 sq ft of plan area. SMACNA does not use the sloped area of the roof, which would oversize everything; it multiplies the plan area by a pitch factor from its Table 1-1, and for 6 to 8 inches of rise per foot that factor is 1.10. Each eave therefore has a design area of 858 sq ft. Get your own roof dimensions from the roofing calculator and use the plan footprint, not the shingle area.

Next, the storm. SMACNA's Table 1-2 lists the 5-minute rainfall intensity that should be exceeded only once in 10 years: 6.8 inches per hour for Chicago, from records through 1978. NOAA's current Atlas 14 server gives 7.36 in/hr for the 10-year, 5-minute storm at O'Hare, and 10.2 in/hr for the 100-year storm. Use the NOAA number. It is newer, and it is higher.

How many downspouts do you need?

Enough downspout area for the roof each one drains, and never more than 50 ft of gutter per downspout. On a 52 ft eave that means one at each corner. The same table converts intensity into square feet of roof that one square inch of downspout can drain. Across the table the two numbers multiply to about 1,200, and the cities listed at 7.3 to 7.6 in/hr, Atlanta, Kansas City and Dallas among them, get a factor of 160 sq ft per square inch. That is the factor for 7.36 in/hr.

The usable area comes from SMACNA's Table 1-3, which lists a plain 2x3 rectangular downspout at 6.00 sq in and at 4.80 sq in for the inlet as actually formed, a quarter inch under nominal. I sized against the smaller number. For the 100-year row, cities at 10.2 and 10.3 in/hr get 120 in the table; I used 110, the value for 10.4 to 10.5 in/hr, to stay on the safe side.

There is a second reason for two downspouts. SMACNA calls 50 ft the practical maximum length of gutter served by one downspout, because of thermal expansion. A 52 ft eave is over that. Put a downspout at each corner and each one serves 26 ft.

Should you use 5 inch or 6 inch gutters?

Use 5 inch when each downspout serves 26 ft of this eave, and 6 inch if a single downspout has to drain all 52 ft. The numbers behind that come from a formula.

The appendix also prints the NIST formula for level rectangular gutters: width in feet equals 0.0106 x M^-4/7 x L^3/28 x (I x A)^5/14, where M is depth divided by width, L is the length of gutter feeding one outlet, I is intensity and A is the design area. SMACNA sizes K-style and other odd shapes by the rectangle that fits inside them, with a depth-to-width ratio of at least 0.75, so read the results as the width of that rectangle.

Two downspouts leave a 5 inch gutter with margin even in the 100-year storm. One downspout pushes the requirement past 5 inches, into 6 inch territory, and it also breaks the 50 ft rule. Englert says a 6 inch gutter carries about 40% more water than a 5 inch one. On this house the extra downspout costs $79.27 in parts and fixes both problems at once. Buy the downspout.

Pitch does not add capacity in this method. SMACNA treats any gutter sloped 1/16 inch per foot or less as level, and the usual residential slope is 1/40 inch per foot. The slope only makes the gutter empty.

Gutter materials list, with quantities and prices

Sectional aluminum, 5 inch K-style, white. The hangers are what some brands and stores call gutter brackets. Each eave gets six 10 ft lengths (60 ft, with 8 ft cut off), five slip joints, two end caps and two drops. Downspouts are 10 ft sections, one per corner, with two elbows to jog back to the wall and one at the bottom. Two more 10 ft sections, cut in half, become 5 ft extensions.

Two tubes of sealant for 18 seams is my estimate. In snow country, space hangers at 16 inches: 40 per run instead of 27, which adds 26 hangers and $56.94.

Tools: what you need, rent, or can skip

You need an extension ladder, a chalk line, a 4 ft level, a tape, a cordless drill with a hex driver, tin snips, a hacksaw or fine-tooth blade for the gutter, a caulk gun and a line level or string. A snap lock punch is not needed here. A pop rivet tool is optional if you prefer rivets to screws at the downspout joints.

Set the ladder right. OSHA's construction rule puts the foot of the ladder out about one quarter of its working length from the top support. Reaching a 10 ft eave takes about 10.3 ft of ladder and puts the foot about 2.6 ft from the wall. If you step off onto the roof, the rails have to stick up at least 3 ft above the edge. Two ladders and two people make handling a 26 ft section far easier than one person walking it along.

How to install gutters, step by step

1. Check the fascia. Push an awl into the fascia every few feet along both eaves and at the corners. Replace soft wood before hanging anything; a hanger screw in rot pulls out under the first heavy snow.

   It passes when the awl does not sink in and a test screw bites and holds.

2. Mark the high point and snap the slope line. With a downspout at each end, the high point is the middle of the eave. Mark it about 1 inch below the roof edge, then measure 5/8 inch lower at each corner (1/4 inch per 10 ft over 26 ft) and snap a chalk line from the middle to each end.

   It passes when a level on the line reads a slight, even fall toward each corner, with no dips.

3. Assemble each run on the ground. Cut lengths with snips or a fine-tooth blade, join them with slip connectors, set end caps, and cut the outlet holes for the drops where the downspouts will fall. Seal every joint and cap with gutter sealant on the inside and let it skin over as the tube says.

   It passes when a bead is continuous along every seam, with no gaps you can see light through.

4. Hang the gutter. Clip hangers into the front lip every 24 inches (16 inches in snow country), lift the run with a helper, align the back edge to the chalk line, and drive each hanger screw into the fascia.

   It passes when a hose run at the high point sends all the water to the drops with no standing puddle longer than your hand.

5. Hang the downspouts. Fit two elbows from the drop back to the wall, a 10 ft section down, and an elbow at the bottom. Crimped ends always point downhill, into the next piece, so water never runs against a lap. Fasten with two bands per downspout and screw every joint.

   It passes when you can pull on the downspout and nothing moves, and water poured in the gutter exits only at the bottom elbow.

6. Send the water away. Attach a 5 ft extension at each bottom elbow and set a splash block at its end. The 2021 IRC, section R801.3, requires discharge at least 5 ft from the foundation where soils are expansive or collapsible, and R401.3 wants the ground to fall 6 inches in the first 10 ft everywhere.

   It passes when water from a hose test lands at least 5 ft out on ground that slopes away from the house.

Seamless vs sectional gutters

Seamless gutters are rolled from a coil of flat aluminum on site, cut to the eave length, so a 52 ft run has no joints between its ends. Sectional gutters come in 10 ft lengths from the store and join with connectors and sealant, five joints a run here. Every joint is a place sealant can fail, and that is the real case for seamless.

There is a catch on this house. SMACNA sets 50 ft between ends or expansion joints as the practical limit for thermal movement unless the system is designed for more. A single 52 ft seamless run is just over, so ask the installer how it will move, whether with an expansion joint in the middle or with the hangers left free to slide.

Gutter installation mistakes that cost money

Water standing in the middle of a run means the slope is reversed or flat. The fix is rehanging the section, with new hangers because the old screw holes are wallowed out: 14 hangers and a tube of sealant for a 26 ft section, $42.64, plus a day on the ladder.

One downspout on a 52 ft eave is the classic undersized install. The overflow shows up in the first hard storm, right over the entry. Adding the second downspout afterward costs $79.27 in parts: a drop, a 10 ft section, three elbows, two bands, half an extension and a splash block. Doing it on day one costs the same parts and no rework.

A downspout that dumps at the foundation wall is the expensive one, because the damage it causes lands in the basement. The extension and splash block cost $18.98 per downspout. Put them in before you put the ladder away.

Hangers too far apart let a gutter sag under ice and pull away. Going from 24 to 16 inch spacing on this house costs $56.94 in hangers when you do it at the start.

Should you install gutters yourself or hire it out?

On a one-story house with sound fascia, DIY saves $410.53 to $964.53 against HomeAdvisor's average and the top of its range, or $12.83 to $30.14 an hour for your weekend. Here is the math. Sheet metal workers, the occupation O*NET matches to gutter installers, earned a mean of $32.62 an hour nationally in May 2025 and $39.41 in Illinois. Loaded with benefits and payroll costs at the BLS ratio of 1.438 for private construction, an hour costs an employer $46.91 nationally and $56.67 in Illinois. A two-person crew is $93.82 an hour before overhead and profit at the national rate.

HomeAdvisor puts the national average for gutter replacement at $1,182, with most jobs between $629 and $1,736. That is a secondary source covering houses of all sizes, so treat it as a rough range. Against the $771.47 parts list, doing it yourself saves $410.53 at the average and $964.53 at the top of the range. If the job takes two people a weekend, 32 labor-hours by my estimate, you are paying yourself $12.83 to $30.14 an hour.

That math favors hiring more often than DIY guides admit. Do it yourself when the house is one story, the fascia is sound and you want sectional gutters anyway. Hire when you want seamless, when the eaves are two stories up, or when a quote comes in near the low end of the HomeAdvisor range, where the saving is too small to be worth the ladder time. Ask any quote for gutter size, downspout count and size, hanger spacing, and where each downspout discharges, then check them against the tables above.