I've installed soffit vents and baffles to allow airflow along the inside of the roof, but my roof has several valleys where the trusses (and channels between them) do not reach the soffits. With a fairly low-pitch roof (4-5 pitch) this means that the roof on both sides of the valley has no ventilation, and I get ice dams.

My question: what is best practice to provide ventilation to those areas? What are my alternatives? ( I've thought about attaching sttyrofoam baffles crosswise to create some dead air space next to the roof, but I suspect there's a better way.)

Thanks in advance for your ideas . . . I'm stumped.