Ice Jambs

Keith from Michigan asks: Good Morning, I have a roof over my two bedrooms that always get ice jambs. I have to shovel and hammer ice off all winter. I’m going to reroof this area next month. I’m tearing off old shingles and leaving the old planks. I would like to get rid of ice jambs as much as possible. A friend said to place vertical battens over the planks and apply 1/2 inch plywood with the ice shield stuff and then asphalt shingles. I also plan on removing board facia and soffit with aluminum. Soffit will be vented. Also placing a roof to wall vent to help with venting. My question is having that air gap between the old planks and the new plywood cause a condensation problem between the two? Should I just place plywood on top of existing planks instead of? The roof has probably a 3:1 or 4:1 pitch. Thank You for your time! Getting to old to keep going roof for ice jambs.

• Ventilation: Since you're adding a vented soffit and a roof-to-wall vent, ensure a straightforward, continuous airflow path from the soffit to the ridge or upper vent. Installing baffles in every rafter bay is critical to keep that airflow from getting blocked by insulation.
• Insulation & Air Sealing: The root cause of ice dams is usually heat leaking into the attic, warming the underside of the roof, and melting snow unevenly. Before reroofing, seal attic penetrations (plumbing vents, wires, top plates) and ensure adequate insulation.
• Ice and Water Shield: Install ice and water shield membrane at least 2 feet inside the heated wall line per code—this is your backup defense. 
• Roof Decking: Unless you're converting to a cold roof with a vented over-deck system (which involves more complexity), install the new plywood directly over the planks and focus on ventilation and sealing the attic below.