Replace entire roof deck?

[MacAttack]

I'll try to keep this short - when my 3-piece house was built, the roof underlayment was paper with a few reinforcing fibers, and black spray paint (asphalt, but a really thin coat). My house developed leaks about the third year. Last year (year 7) I replaced about 5 squares of roofing, along both marriage lines. At that time, I replaced the adjacent roof deck sheets with one sheet spanning the gap. I also used Tyvek underlayment, and sealed the roof deck sheet seams with waterproof roof tape. But: I still have leaks. They run down the ceiling (which has plastic above the sheetrock) and pool above the windows, where they eventually leak out.Here is my question -
I think I need to strip off the old roof, at least on the lower sections. I think the underlayment is leaking - I found lots of evidence of tearing, so I think it's pretty worthless.. While I am there, I plan to replace the roof deck with plywood. I'm 220#, and after walking around a bit, I notice that the roof deck starts to get small permanent waves (I'm stepping between the rafters). The rafters are 2x2 on 24" centers, and the deck is OSB. The plywood I spanned the marriage lines with is much better.
I think I can pick away at this, doing one half each summer. My questions are -
Am I on the right track? Should I do the roof deck all the way up (removing my old work and re-doing it)?
I'm planning on using tyvek underlayment, since it seems to breathe but is strong and waterproof. Does this sound like a good way to go?

Thanks!!! Mac

[Jim from Canada]

First, when you are on the roof, step on the rafters, not between them, it will support your weight better.
If you are re sheathing the roof with plywood, do the whole thing and then cover it in ice/water shield. Preferably Grace brand if you can get it. Once that is on the roof is waterproof and anything else to cover it is to protect it from UV and is eye candy. I did mine in a 30 yr shingle. The Grace ice/water shield will seal around every nail. In fact you can put a nail in it, remove it, and it will seal the hole.

[JD]

Grace Ice & Water Shield and similar products offer excellent protection against leaks. Definitely recommended for mobile homes, especially ones with no overhang and/or low pitch. But any roof underlayment is your second line of defense. If your roofing leaks, you have a problem and it needs repair. I would not use Tyvek as an underlayement. I would only use roof felt or the rubberized roof underlayment.

Those permanent waves you mentioned may be caused by a high moisture content in the OSB sheathing and as Jim said, walking between trusses. As your roof leaks evaporate to vapor, the moisture can spread out quite a bit. I would recommend replacing the sheathing 1-2 sheets at a time to maintain the roof's strength while you are working.

JD

[MacAttack]

Thanks guys! I tried to step on the rafters, but...
I'm going to proceed as you guys suggested. I plan to live in this place another 40 years at least, and I'll have one solid roof! I was astounded at the difference between the plywood I added to span the marriage line and the OSB it replaced - the plywood is far stiffer.

And the waterproofing... you bet! We live in the forest and part of the house is in continual shade.

Thanks again! Cheers, Mac

[Jim from Canada]

If you want 40 yrs out of it plywood is the way to go. I would recommend 5/8 T&G.
my facebook photos of my roof job are here,

http://www.facebook.com/photo.php?pid=3 ... =540237889