Metal 5-rib replacing shingle

[Steve-WA]

I have 2 roofs shingle roofs to replace this summer: one singlewide that has 23 year old shingles that haven't failed yet, and one doublewide that had the roof poorly installed 6 years ago. Gonna replace with 5-rib metal panels, flashing at the ends and ridge vent. I am a landlord, know a little about a lot, but a lot about very little. I want to do this myself, but I have some questions:

1. What about the attic vents - can I remove the plastic caps and lay the metal panels right over the holes, expecting the new ridge vent to give enough ventilation?

2. Can I install the metal right over the single layer of existing shingles, or does the existing roof need to be stripped down to the sheathing?

3. Can the metal be screwed right to the sheathing (or sheathing through the shingles) or do purlins/furring strips need to be laid?

TIA

[JD]

1. It is hard to say for sure not knowing the the quantity or size (cfm) of the existing vents, but ridge vents used in conjunction with the proper amount of eave vents should be enough for your roof. For the ridge vents to work properly, there will need to be an open area in the roof decking right under the ridge vents. This can be hard to do with mobile homes with some products because of the center marriage beam. The wide metal vented ridge caps may work out better.

2. I have seen metal panel roofs installed right over existing shingles and I see professional roofing companies advertize that they save you money by not removing the shingles.

3. i have only seen these roofs installed with the 1x4 or better purlins and foam insulation laid in between. All of this is installed over roofing underlayment. You might be inviting condensation problems installing direct to the roof.

JMO. I do not install these types of roofs.