I have a 1960 ranch home and will be having my roof replaced in the near future. I currently have old space decking and the roofing company said that they need to put sheathing down. Is this something that can be put down over the space decking or should the old decking be taken off first?

  • Are there gaps between the 1x6 boards or are the boards closely fitting? – Jim Stewart Dec 10 '18 at 18:03
  • there is about an ~1/4 inch gap – Mar09 Dec 10 '18 at 18:19
  • Be aware that gaps of that size are common on roofs new and old, and don't necessarily warrant a sheathing overlay. Shingles will not fail because of them. As evidence, take the natural gap that occurs when one shingle laps onto another. It's not an issue. You might get a second opinion. – isherwood Dec 11 '18 at 16:45

So your existing roofing is either wood shingles, wood shakes or tile ( clay, concrete, etc.) These types of roofs can span across gaps in the roof sheathing.

Your new roof is going to be composition shingles that need solid sheathing.

Yes, it is quite common to add solid sheathing over the top of the spaced sheathing. The added weight will be off-set by removing the heavier existing tile roofing and the heavier wood shingles and shakes (when they are soaked with water).

Here are some precautions: 1) make sure the new roof sheathing is a minimum of 1/2” thick. Roofing manufacturers require a minimum of 1/2” for “holding power and withdrawal”...blow off. 2) Increase the height of your perimeter flashing by at least 1/2” to compensate for the additional height due to the thickness of the roof sheathing. (You want the same lap over the siding.)

  • Thanks you. the existing shingles are not wood or tile, they are composition shingles that are worn and damaged. – Mar09 Dec 10 '18 at 17:47
  • Sam is stating what is normal for spaced decking. But it is normal to put new decking over the old if it is in good shape, not rotted. So his answer is still good it is normal.+ – Ed Beal Dec 10 '18 at 18:27

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