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ventilation for roof valleys

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.

Re: ventilation for roof valleys

Look into roof dormers.

Re: ventilation for roof valleys

Can you be more specific? When I think of roof dormers, I pictue a valley that ends some distance from the eaves of the main roof. My concern is that, with R-48 to R-60 insulation (i.e., 15" - 20" deep) and a 4 pitch roof, there are several "channels" (roof deck between two trusses - I'm not sure of the technical term) that terminate at the valley and do not extend all the way to the soffit, so the usual practice of installing baffles to preserve an air channel next to the roof does not provide a path for outside air to flow.

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