When is a roof leak a repair and when does the roof need replacing?

The deciding factor is not the leak, it is the condition of the roof around it. If the shingles still flex enough to be lifted without snapping, the granule cover is intact across the field and the decking is sound, a leak is a repair. If shingles break when lifted, the field is worn smooth, fasteners no longer hold or several unrelated faults appear in the same season, the roof is at the end of its service life.

Is it worth replacing just one slope of a roof?

Sometimes, particularly where a lower roof over an addition or porch is a different age and assembly from the main roof. On a single continuous roof it is often a poor deal: the tie in creates a new joint, the colours will not match and will diverge further as the new work weathers, and the older section will need access again sooner.

Does Missouri license roofing contractors?

No. There is no state roofing licence in Missouri and bills to create one have failed. What exists is municipal registration where a municipality requires it, general liability insurance and workers compensation cover, all of which a homeowner can ask to see.

Repair the Leak or Replace the Roof

Start from the default

The default is repair. A pipe boot, a length of step flashing, a valley, a set of popped fasteners are discrete faults, and a roof with a discrete fault is a roof that is otherwise doing its job. Replacing a functioning roof because one component on it has failed is expensive and unnecessary, and a contractor whose first answer to every leak is a new roof is telling you about their business model rather than about your house.

What moves the answer away from repair is not the leak. It is the condition of everything around the leak.

The five things that actually decide it

Can a shingle be lifted: Almost every repair on a shingle roof requires lifting the courses above the fault without breaking them. Asphalt stiffens as it loses its volatile oils. When shingles snap instead of flexing, each repair creates new faults, and the roof has effectively become unrepairable regardless of how it looks from the street.
Granule loss: The granules are the shingle's sunscreen. When the surface is worn smooth in the field, not just in traffic paths and under downspout discharge, and the gutters have been filling with granules for years, the mat underneath is being cooked directly and the clock is running fast.
The state of the deck: Soft, delaminated or rotted decking under the leak is a repair issue. Fasteners that no longer hold anywhere on a plane is a replacement issue, because new nails driven into the same tired boards will not hold either.
How many faults, and how spread out: One failure is a fault. Three failures in three different places on the same roof, in the same season, is a pattern, and a pattern is information about the whole assembly rather than about any one component.
How long you intend to keep the house: A legitimate part of the decision and one that a contractor should ask about rather than assume. A repair that buys three or four seasons is a good answer for some households and a poor one for others.

Looking down from the ridge of a completed Keys Roofing job: a new grey and charcoal architectural shingle roof with a ridge vent fills the right and lower part of the frame, and the adjoining older section at the upper left still carries its weathered brown shingles with debris visible in its gutter. Below is a winter back yard with timber fences, a bare tree, a white recreational vehicle in the alley and neighbouring houses beyond. — **Plate seven // the colour break** A new plane laid against an older one on the same property. This is what a partial replacement looks like from above: the two surfaces will not match, and they will diverge further as the new one weathers. Worth knowing before agreeing to replace half a roof.

Partial replacement, and why it is often a trap

Replacing one slope or one section is sometimes exactly right, particularly where a lower roof over an addition or a porch is a different age and a different assembly from the main roof. It is often wrong on a single continuous roof, for three reasons. The new work has to be tied into the old at a ridge or a valley, and that tie is a new joint that did not exist before. The colours will not match, and cannot, because shingle blends change and existing shingles have weathered. And the old section will reach the end of its life first, which means paying for access twice.

The line worth holding

A leak is a reason to look at the whole roof. It is not, by itself, a reason to replace it.

What a replacement actually involves here

A full tear off, down to the deck, so that the condition of the boards can be seen and any soft or rotted sections replaced. Laying new material over old shingles hides exactly the information you are paying to find out. Then underlayment, ice and water membrane at the eaves and in the valleys, new flashings rather than reused ones, new pipe boots, new drip edge, and a ventilation arrangement that actually has intake as well as exhaust.

On permits, the baseline in unincorporated St. Louis County is that a like for like asphalt replacement on a slope of 4:12 or steeper does not need one, while a shallower slope, a change of material, or replacing more than a quarter of the decking does. Municipalities inside the county set their own rules, and Ballwin and Kirkwood run their own contractor licensing, so the municipal rule governs where you live. In St. Charles County, confirm the current requirement with the county's building division directly before work starts, because published guidance there is not currently reliable and it is not worth guessing on your behalf.

One thing Missouri does not have

There is no state roofing licence in Missouri. Bills to create one have been filed repeatedly and have failed, so a contractor claiming to be state licensed for roofing is describing something that does not exist. What is real is municipal registration where the municipality requires it, general liability insurance, and workers compensation cover, all of which you can ask to see.

How Keys answers this question

By opening something up and looking. A shingle gets lifted to see whether it flexes or snaps. The gutters get checked for granules. The deck gets examined from the attic if there is access and from above if there is not. Then you get told which of the two conversations you are in, with photographs of your own roof, and if it is the repair conversation you get a repair scope rather than a sales pitch. Keys installs Atlas and Malarkey shingles and does roofing, gutters and downspouts only.

The other answer