A closer, clearer pic would help, but based on this it kinda looks like a sedum. Did you try to manually remove it? Sedum will pull up very easily.

yes.. need a closer pic ... for an ID...

round up will take care of it ... but you will have to read the label..and mix your own batch ... some of the premix stuff.. might not be strong enough to outright kill a waxy plant ... and multiple spraying may be required ...

being a plant guy.. not a roof guy.. i wonder about leaving the dead roots to rot in the roofing material ... sounds like that might be a path for future water problems ... leaving compost in the material ...
so.. killing it might not solve your problem.. especially if its been there for years ...

is there a roofing forum ... lol.. wouldnt surprise me ...

ken

Sedum, very likely our native Sedum acre if it self seeded up there. They manage on very little water and are a key component in green rooves but they have a special waterproof substrate. You can just peel it up and remove any accumulated soil with a dustpan and brush. It is very shallow rooted. There is absolutely no need to spray poison on your porch.

And perhaps you can find it a home elsewhere in your garden.

I think it could be removed as a sheet as well. Mat forming plants like that establish in the medium provided by bits of soil and decomposing litter and they'll often hold a bit of moisture under the mats where the roots are, making it easily dislodged. If it is sedum, and it very well could be, it's paricularly easy to 'lift' like that. We have a lot of groundcover sedums I use in lieu of mulch and we used to regularly lift sheets of it up to give to a groundskeeper, who if he kept it moist for the short distance he had to go to get it back to his establishment, and had disturbed, bare soil ready, could just lay it down like carpet, water it in and let it do what it does naturally.