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TOPIC: Roofing over existing roof

Metal roof over wood shakes

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Our 15 year old shake roof will soon need replacing. Living in the Pacific Northwest, we are thinking about going with a metal roof. Some advise that the shakes need to be pulled off, others say a metal roof can be installed over the shakes. They are not yet in very bad shape. We have cathedral ceilings and the pitch is 3/4. Thanks
Christa Bellefleur

4/3/2004
With proper installation, there are several products which can be installed over wood shakes. I would suggest requesting references of past jobs over shakes and going and looking at them. I also suggest discussing what special steps the contractor takes when installing over shakes, and then confirming those procedures with the manufacturer of the metal roof system. Overall, of course, there is nothing wrong with removing the old shakes either. It might be wise to ask the contractors who suggest removing them why they suggest that. Todd Miller
Todd Miller
Isaiah Industries, Inc.

4/3/2004
What are the problems of having a metal roof installed over a 16 years old wood shake roof. Specifically would the shake under the metal continue to deteriorate due to condensation/moisture and crumble, pulverize. What happen in this scenario?This would shorten the life (50 years plus for metal) of the roof. On the other side, keeping the wood shake would give better insulation and also save few thousand removal cost. The existing roof can take additional weight of the metal. Thank you.
Guest User

8/6/2004
First of all, it is critical that the manufacturer of the metal roof approve of this lay-over installation, and the installation methods being used. They will want to know whether the old shakes are over solid decking or spaced sheathing. I have had experienced with many many metal roofs over wood shakes, dating back over 20 years and I have never encountered one where I later regretted that the old shakes were not removed. There should be a quality underlayment placed over the shakes before the metal goes down. This isolates the shakes from moisture. Also, the old shakes perhaps "breathed" a bit more than the new system will. You will likely want to increase attic ventilation with the new roof. This may include increasing soffit intake vents as well as roof exhaust vents.
Guest User

8/6/2004
if wood shakes are tore off can metal shakes be installed on wood lath? or will it have to be decked?
Guest User

8/6/2004
All aluminum shakes must be over solid decking. Some of the steel shakes can go over battens but some require solid decking. However, new battens may need to be installed as your existing lathe probably does not have proper spacing. The manufacturers of these products will be able to answer your questions.
Guest User

8/6/2004