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jbnb
Proper substrate for replacing cedar shake with shingles

We've been in our home for 1 1/2 years. Approx 10 yrs ago, the cedar shake was replaced with shingles directly onto the horizontal 1x6 planks. Roof is now failing due to poor installation. Have gotten conflicting opinions as to the necessity of laying down plywood sheating, or installing directly to the 1x6 planks. One contractor says that is OK, if done right, and I trust they would do it right, but would love to get an unbiased opinion if plywood sheathing is necessary. Obviously, the cost difference is significant. Thank you!

A. Spruce
Re: Proper substrate for replacing cedar shake with shingles
jbnb wrote:

One contractor says that is OK, if done right, and I trust they would do it right,

I would rethink that trust, if I were you. Asphalt shingles can't be directly installed over skip sheathing used under wood shake roofs, you need full support for the paper, shingles, and solid nailing.

The correct method of installation would be to strip the roof bare, install plywood sheathing, with either plywood clips or a 1x material supporting plywood edges that fall between strips of 1x6 skip sheathing. You can use OSB rather than plywood, though IMHO, OSB is not a good product to use for anything, particularly where it is prone to moisture such as a roof. Installation instructions are printed on the back of every package of shingle or is available from the manufacturer's website. Ultimately, it is the manufacturer's recommend procedure that needs to be followed, as this will not only affect the durability of the roof, it will affect the warranty.

Timothy Miller
Re: Proper substrate for replacing cedar shake with shingles

Hi, ten year old shake roof is only about 40% its life. Perhaps you will consider a bid to repair it. With out a picture cannot tell you if it is failing or not. Do you know if the deck was felted then inter laced felt between every course of shingles. The shakes job is to protect the felt from sunlight as sunlight oxidizes the asphalt and it then desolves. Sure the shingles also look pretty, shed most of the water, and protect the felt from penetrations from hail etc..
With spaced planks or spaced decking most building codes require a solid underlayment installed if you choose asphalt shingles. You might consider instead if you remove the shakes to install steel granule coated shingles. These look like cement or clay shingles. They can be installed with spaced decking. They will last 50+ years you may save $$ on homeowners insurance. Whatever you replace the shakes with let you home insurance know as you will likely get a reduced cost for your insurance.

jbnb
Re: Proper substrate for replacing cedar shake with shingles

The shakes were removed about ten years ago. There has been asphalt shingles since, nailed to the planks. I believe this, along with other sub standard installation techniques, is why it is failing.

I am trying to ascertain that it is NOT advisable to run asphalt over planks, and it is seeming to be so.

jkirk
Re: Proper substrate for replacing cedar shake with shingles

with cedar your dealing with a solid product, the planks are used to provide air flow under the shingles so they can dry out better
.

asphalt needs solid plywood behind it because they are flexible and require a specific nailing pattern. by only nailing the asphalt shingles where they land on the strapping you run the risk of the nails not being in the correct spot on the shingle which makes them more likely to be damaged by wind and frost

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