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carson618 · Mar 3, 2009, 01:07 PM

I'm interested in GAF Grand Canyon Shingles that weigh 450lbs per Sq. My roof truss's are 24 inchs on center with a roof decking of half inch plywood. I can see some dips between the trusses with the old roof now. The roofers I've had out said the roof will hold and the dimension of the shingles will disguise the dips. Is this True?

ballengerb1 · Mar 3, 2009, 02:59 PM

I'd get 2 more roofing bids. If you already have dips you already have a problem. See what the next 2 guys have to say and then pick the best bid.

21boat · Mar 3, 2009, 03:12 PM

I've never seen a shingle in my life that will hide dips between trusses. That's a physically impossibility unless you add between the dips and then the shingles. The reason you have dip to begin with is the roof sheeting should have been 5/8" thick not 1/2" What ever roofer said that apparently doesn't know the word telegraphing

This like saying if I resurface your driveway and it has dip 24' dips in it the new asphalt at the "same" thickness will hide the dips.

As soon as you get a roofer out there that tells you 24 oc rafters needs 5/8" sheeting for proper structural roof then he's a roofer 1/2 is not code here and for good reasons Look at your roof and it will get worse in time.

They way they keep taking an enth off studs and ply eventually we will need 3/4s to sheet roofs in.

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carson618 · Mar 3, 2009, 04:03 PM

What are my options? A lighter weight shingle, Re deck the entire roof, What if I go w/ the grand canyon under the circumstances, what problems will I run into in the future?

21boat · Mar 3, 2009, 04:32 PM

To fix it right re deck the roof. I don't know if you want to do it yourself but we can walk you through that.

If you do sub it out pay attention to the roof clips that needs to be between each roof sheet and its placed between each roof rafter, centered.
http://www.tecotested.com/techtips/pdf/tt_edgeclips

What that does is keep the sheeting from touching each other so a roof buckle doesn't happen. At the same time it act as a tongue and grove from sheet to sheet so when a load is between each sheet in the middle of the rafter bay the other ply helps support the load and spread it.

If you don't have a ridge/peak vent add one to the peak. I usually like to do the whole peak and keep the ridge vent 1 foot from roof peak edge. It's a bit of over kill but it gives the whole peak a uniform look.

Another side note: since you need to upgrade to 5/8 sheeting now is the time to look at the insul in the bottom/cord rafters. If you want to upgrade the (R) value now is the time to do so. With the old roof sheeting off it's a cinch to add and not crawl around in that tight area. I always try to talk my costumers into this when I run into an under sheeted roof.

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carson618 · Mar 3, 2009, 04:50 PM

Can I just put 1/2" on top of the current decking? giving me a total of 1"

21boat · Mar 3, 2009, 05:25 PM

No You don't want to load up the roof with weight. Also if moisture gets trapped between the sheets and freezes it will be a BIG tear off.

DeLamination etc.

Tear off is some work. If you have a partial stand up a person underneath the roof can use a big board to bump it up like a big hammer while another person can use another board at an angle from a rafter to apply pressure so the sheeting will pop on sections.

Once you get on to it it will go all right.

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Stratmando · Mar 4, 2009, 06:23 PM

The shingles look like they could hide a little.
While the old roof is off, if it can be corrected,
Would give nice look:
Grand Canyon Shingle Page
Nice shingles.

ballengerb1 · Mar 4, 2009, 09:27 PM

Carson, I got to stick with my post #2, get 2 more bids. I think you will hear competent contractors recommending a complete tear off the shingles and the decking. If the existing plywood bows now it will bow more and more each year. That new shingle is rated for a lifetime warranty and it weight 20% more than the shingles that are up there now. Do you really want to put it down on top of ply that is already failing. I am afraid this would be penny wise, dollar foolish.