JayN wrote:
I live in a condo (end unit townhouse). There is a slanted wood trim
near the roof on the side of the building. There is a gap behind the
wood trim and wasps (yellowjackets) have been flying into the gap
behind the wood trim and building nests there. Although I wasn't
aware of this at first, my impression is that they have been nesting
there every year. I've been here almost 4 years.

If they haven't gotten inside the building or bothered anyone, are
they best left alone, or does leaving them alone typically lead to
them causing damage?

Seems to me the only permanent solution would involve screening off
the gap, but the wasps would need to be exterminated first, and one
would have to be very certain they are all dead before screening off
the gap. Should I insist this be done, or are they best simply left
alone?

Thanks,

Jay

Paper wasps, I leave alone, but yellow jackets, I kill. Nasty little
buggers and you never know when one will sting you. One sent me to
doctor with swollen hand from single sting on a finger.

Sealing the opening before or after you spray the nest will get rid of
them as the trapped ones will die off. I've had a lot of problems with
yellow jackets nesting in house through smallest crevices and have had
to seal off outside house lights as they were getting under the fixture
and getting in the wall through the conduit opening. One on front
porch, I sealed openings and could hear buzzing in wall which eventually
stopped.

For spray, get one of those wasp and hornet sprays that reach 25 feet.
If you get in nest opening you will kill nest. When they nest in lawn,
I'll dump a gallon of pesticide solution in opening.