What a tarp is actually for
A roof tarp is meant to redirect water away from a damaged section until a real repair can happen, not to seal the roof permanently. Most homeowners' insurance policies expect this kind of reasonable, temporary step to prevent further damage while a claim or repair is pending.[1]
How a professional tarp job differs from a quick DIY one
A contractor-grade tarp job typically anchors the tarp under the shingle courses above the damaged area, rather than just weighing down the edges with boards or bricks, and uses furring strips or battens to keep wind from getting underneath and tearing it loose. A tarp only nailed or taped flat to the surface is far more likely to fail in the next round of wind.
How long a tarp should realistically last
A properly installed tarp can hold up for weeks in normal conditions, but UV exposure degrades most tarp material over time, and any storm strong enough to have caused the original damage can also be strong enough to work a tarp loose. Treat it as a bridge to a scheduled repair, not a long-term solution.
What a tarp doesn't do
A tarp doesn't stop water that's already found its way into insulation or framing from continuing to cause damage there, and it doesn't address the cause: a failed flashing, a missing shingle section, or storm damage still needs an actual repair underneath it once conditions allow.
It also isn't a substitute for documenting the damage. Photograph the affected area before the tarp goes on, since that's the version of the damage an insurer or a roofer's estimate will reference later.
Material and thickness make a difference
A heavier-mil poly tarp, or one specifically rated for roofing use, resists tearing and UV breakdown longer than a lightweight general-purpose tarp from a hardware store shelf. If you're buying one yourself for a short-term fix, the weight rating printed on the packaging is worth checking before price, since a thin tarp rarely survives a second storm.
Safety comes before speed
A wet roof, a steep pitch, or a roof still under active wind and rain are all reasons to wait rather than attempt a tarp yourself, even when the water damage inside feels urgent. The contained damage from a delayed tarp is almost always more fixable than an injury from a fall, and bucket-and-towel containment inside buys more time than it seems like it would.