Do I HAVE to remove sheathing?


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Old 09-07-07, 01:12 PM
J
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Do I HAVE to remove sheathing?

I'm working on a lower portion of my dutch colonial's roof right now, removing 2 layers of asphalt and the original cedar shakes from 75 years ago.

The upper portion is in seriously lousy condition, too. But I'm not too crazy about going way up there, on a steep angle, and having to rip off those cedar shakes as well as the crumbling asphalt.

From inside the attic, those shakes are in prime condition. From outside, they're probably not so great, which is why they were covered with asphalt.

But the general rule of thumb is, "After 2 layers of asphalt, you've got to replace the sheathing."

But why? Especially when its in good condition?

J
 
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Old 09-07-07, 01:58 PM
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If you can see the cedar shakes from the attic you have no sheathing. Most shakes are installed on slats spaced about 6 inches apart with no sheathing. I have seen many roofs installed with sheathing installed over the slats. I would never install asphalt over shakes.
 
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Old 09-09-07, 02:44 PM
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Why? The main reason is weight.

Your average asphalt/fiberglass shingles weigh between 225 and 250 lbs per 100 sq ft. So if you put one more layer on, for a total of 3 layers of alsphalt shingles, you could conceivably have 750 lbs of roofing which is a LOT of weight. You can't just continue to add weight to a roof, so most jurisdictions have set an arbitrary limit that is both reasonable and practical.

On many older homes the roofs were "sheathed" with 1x8's that are spaced approximately 2" apart. You will be able to see that from inside the attic. When you tear off, most roofers usually just install some OSB over the top of the 1x8's. Others will fill in the gaps with 1x2's or something.
 
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Old 09-13-07, 01:20 PM
J
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To clarify, the cedar shakes are fixed to slats. On the lower sections of the roof, I removed the shingles and the shakes, and affixed plywood sheathing.

I was wondering why I cannot tear off the two layers of asphalt and nail on a fresh layer of shingles over the shakes?

J
 
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Old 09-13-07, 04:42 PM
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Because shake shingles are not FLAT. An asphalt shingle may lay flat on your shakes but that is only because it is sitting on the high points of 2 or more rows of wood shingles. When you go to fasten the asphalt shingles you will have trouble with the roofing nails piercing the shingle when they are hammered into the voids. Even if the nail does not pierce the shingle, it will certainly distort the shingle if it is nailed down into one of those voids. If you decide to nail only on the high points of the shake shingles you will most certainly void your warranty because shingles must be nailed in the designated area, according to the manufacturer's instructions.

I've seen it done before and it doesn't result in a very flat looking roof. If the shingles don't lay flat it can possibly prevent them from sealing down properly.
 
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Old 09-14-07, 12:14 PM
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Well, the previous owners must've got around all this by laying roll roofing down first. Then they nailed a layer of asphalt, followed probably 20 years later by another layer of shingles.

All told, the roof must weigh several tons more than one might expect!

Still, it looks pretty uniform and flat. Only problem is, its ancient and I don't have the strength or money to invest in a commpletely new one.

Just thought I might remove the old asphalt and put a fresh one without disturbing the shakes.

Or is there a risk that the shakes are so old and dry, and full of nail holes, that they wouldn't be able to hold the shingles in a storm?

J
 
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Old 09-14-07, 04:50 PM
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You can certainly do it the way you like, it's your house. Michaelshortt pretty much summed it up when he said, "I would never install asphalt over shakes." I've tried to give you plenty of reasons not to do it, so I really don't have anything else to add. Good luck with the roof, and don't fall off. Dusty shake shingles can be quite slippery.
 
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Old 09-14-07, 05:18 PM
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Somehow I would do it the right way. I would not buy a house with a roof the way you are going to do it, unless of course you brought the price way down. You have been given great advice, good luck.
 
 

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