Building an addition and adding a perpendicular roofline to an existing roof with a California framing. The new gable roof will be perpendicular to the existing gable roof. I would like to keep as much as possible of the existing shingles.

  • Do the shingles under the California framing (on the existing roof) have to be removed?
  • If yes, what is the recommended clearance between the cut of the existing shingles and the new bottom plate of the California framing siting on the existing sheathing?
  • What is the best way to build the transition between the new California roof addition and the existing roof at the valley?

1 Answer 1


The roofing under the California framing (also called an overframe) does not need to be removed but it would be better to get rid of it.

I might be misunderstanding question # 2- so this is what I think you are asking- You want to cut out a section of the existing roofing so that your California framing sits onto the existing roof sheeting rather than on the shingles and you want to know how much of the old roofing to remove. This will depend on your roof pitch. I am going to assume your existing and new roof are pitched the same. The California framing would usually require 2 bottom plates under the compound angle cut rafters because the level cut (the horizontal) cut on those rafters would be quite long. Actually that cut gets shorter as your roof pitch gets steeper. The way to determine this length is to draw your roof pitch plumb cut (the vertical cut) on a rafter and then draw a 90º line perpendicular to the plumb cut line.

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As for question # 3 the transition between the new roof and the old will be done with the framing you do. Your sheeting (plywood cover) will finish right into the existing roof sheeting. You (or your roofer) will need to remove shingles (whether asphalt shingle or wood shingles it is the same either way) so the valley can be properly tied in. Valleys are a critical component of the roof that must be done correctly due to the deliberate concentration of water that will be there. Usually a valley flashing is installed and both sides of the roofing at the valley terminate over that. If your roofing is asphalt shingles then I have also seen those weaved in the valleys where you work both sides of the valley at the same time and overlap one side on one row and the other side on the next row. Personally, I prefer a valley flashing (often called w flashing or w metal).

  • Thank you for your great answer! You got my second question perfectly right. What I am wondering about is how difficult it is to place the new flashing underneath the existing roofing shingles. I am worried to damage them or break them. The existing roof is about 14 years (2008). How difficult is it to work with the existing roof to tie it well to the flashing on the open valley?
    – Max
    Aug 27, 2022 at 3:33
  • The existing and new roof are both 4:12 pitch.
    – Max
    Aug 27, 2022 at 3:35
  • Is it wood shingles or asphalt shingles (sometimes called composition shingles or comp roof)? Either way I would not trust any way other than removing existing roof shingles so the valley metal can be set and then doing a proper tie in to the existing roof. You cannot slip the valley metal under the existing shingles and expect it to work properly. There will be nails in the shingles under the row above and getting it watertight would be miraculous. This is not a DIY job and should have a professional licensed and insured roof guy doing the roofing work.
    – Kyle
    Aug 27, 2022 at 3:44
  • Thanks @kyle. They are asphalt shingles. When you say removing existing roof shingles? Does that mean re-roofing the entire roof?
    – Max
    Aug 27, 2022 at 4:47
  • No- just enough to do the valley and a good tie in. It does depend on the age of your roof and whether or not it can be tied into properly.
    – Kyle
    Aug 27, 2022 at 5:19

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