Insulate attic before/after new roof.

I recently bought a bank-owned, 3 BR, 1 bath semi-detached home that I am going to be renting out. In my area, a "semi-detached home" means there are two homes side by side, which share a common wall in the middle, but each home has a separate owner. I own my side and someone else owns the attached property next door.
The home has an unfinished walk-up third floor attic. The previous owner had framed out the attic to create walls and a walk-in closet, but didn't do any sheetrock, etc. The existing roof is asphalt shingle in poor condition over a prior cedar shake roof. The roof doesn't leak, but my guess is that it will need a new roof within a year or so.
A new roof will cost around $8,500 and it will involve a complete tear-off of the asphalt shingles and cedar shakes, all new plywood decking, and then the new asphalt shingle roof over the new plywood. I could either have the new roof done now, or wait until later. My attached neighbor's roof is also asphalt shingle over an old cedar shake roof and is in similar condition. He does not want to have his roof done unless and until it starts to leak. Ordinarily, I would just have my roof done now, but because the two homes are attached, it would be better to do both roofs at the same time.
My question is about what the differences would be in terms of finishing off the attic before or after I have a new roof put on.
If I have a new roof put on before finishing the attic, I would then have the attic finished and would have insulation put in between the attic rafters with proper venting etc. That would be easy to figure out.
But, if I decide to wait on the roof, and have the attic finished first, I think I have two options:
1) finish the attic now, but do not do the insulation in the rafters for now; then when the new roof is done in a year or so, have the insulation put in from the top after the roof tear-off and before the new plywood decking goes down; or,
2) finish the attic now, and do the insulation now; and then have the new roof done later.
I am thinking that if I do the insulation now, when the tear-off is done for the new roof later on, the debris will end up in the insulation and will be a huge mess.
So, I guess my question is, "If I decide to do the roof later, and I finish the attic now, do I go ahead and do the insulation now or wait on the insulation until the new roof is done later on?"
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Definitely wait until the roof is done before doing the insulation. You are right that there will be significant debris from the removal of the cedar shakes. Having had a complete tear-off of an old asphalt shingle roof over cedar shakes on two houses, I can personally attest to the fact that loads of debris falls through the skipped sheathing.
One day when the roofers where doing the tearoff for our current house, one of them rang the doorbell. My wife came to the door and the guy sheepishly said, "Uh, I dropped my shovel through the roof, can I please go in your attic to retrieve it?" So you may end up with more than just the old roof pieces weighting down any insulation that you put up before hand. ;-)
Ken
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On Mon, 23 Mar 2009 09:32:26 -0700 (PDT), snipped-for-privacy@yahoo.com wrote:

I'd say don't even finish the attic before the roof is done. And if you do your side before the other side, depending on th style of the building, a false wall on the top, looking like the fire-wall extends through the roof, CAN be an attractive way to separate the 2 roof styles. You would "step flash" both sides to keep water from getting under the shingles at the dividing line - they would re-flash their side when they do their roof. The wall would be capped with a metal flashing "cap"
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snipped-for-privacy@snyder.on.ca wrote: >

I think that may end up being the plan -- get the roof done now, and then finish the attic.
What you described regarding the transition between the two attached houses is basically what two different roofers explained to me when giving me estimates on this job. Both also pointed examples of how the same thing had been done on similar twin houses across the street from mine, so I could see how the end product would look.
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Len56 wrote:

We had a new roof put on and I made arrangements with the roofers to pause after the old roof came off to allow us access for laying fiberglass batts.
Didn't work.
Too much climbing, ducking, pushing, twisting, cursing, and other inconvenient movements. Batts are not made to thread through rafters then rotate into position. So, we blew it off.
About eight years later, we dug the fiberglass out of the garage where it was stored and installed it in the normal fashion.
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How did they put shingles over cedar? It cant be done.
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I've seen fiberglass shingles not only over cedar, but over slate roofs as well!
When it comes to saving a buck, people will do anything, and butchers will do anything for a buck.
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ransley wrote:

Au contraire, it's quite common to put asphalt shingles over cedar shakes.
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The cedar roofs I have seen are not flat, the cedar curls and is warped, I cant see how it would be water tight. Recently I heard of some hack putting white foam over Slate!
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Nails.
JK
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On Mon, 23 Mar 2009 19:07:17 -0700 (PDT), ransley

It's been done for decades. Many farm houses around here have had 3 layers of shingles over cedar. Not a nice job tearing THAT off!!
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Len56 wrote:

When I had my similar roof replaced, I covered all the insulation in the attic with 4 mil plastic before the job began. There was a lot of crud on that plastic after they finished. I picked up the big pieces, then rolled up the plastic and removed it. The insulation would have been really messed up without the plastic.
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wrote:

But I'll bet your insulationwas on the "attic floor" between the joists,not between the rafters. He's talking a "finished" attic.
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