Replace Roof Sheathing and Truss Question

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MandMLawson
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Joined: Fri Apr 28, 2017 3:10 pm

Mon Aug 28, 2017 9:16 am

We have a mid 80s manufactured home. I am in the process of replacing the shingles. I have some concerns about the integrity of the sheathing and trusses because there is some waviness in the shingles. I took a picture to show, but it doesn't come out clearly in a picture. The house has two layers of shingles and not much in the way of venting. No gable vents, no turbine vents, just two low profile vents. There is a gap at the top where it may, at one time, had a ridge vent, but I don't see any signs that it did. Even if it did, it was covered by two layers of shingles so it wasn't venting anything.

I tore some shingles off to get an idea what lies beneath. Although the sheathing looks clean and dry, it definitely has a bit of sag to it. I pulled one up that was around a skylight I am removing to see how things look underneath. I placed a level on one of the trusses and you can see a sag below.
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On the bottom of the sheathing I noticed some mold. Nothing I would say that is terrible, but there none the less.
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With this in mind, can someone provide some advice on the following questions.

1) should I replace all the sheathing?

2) if yes, should I upgrade it from 7/16 to 1/2? I figured this would help with future sagging.

3) Should I do anything to deal with the sagging or just shim to give the sheathing something to lay on?

Thanks


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Greg
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Mon Aug 28, 2017 11:45 am

It looks to me like the trusses are probably fine, I would think the wave is from the sheathing. Since I don't know your location I can't say if snow load could be an issue or not.
It looks like there may be a moisture issue somewhere, either from roof leaks or condensation from under the sheathing.
I think I would replace the sheathing, but keep in mind that roof weight is ALWAYS an issue. You may want to consider a steel roof.

Greg
"If I can't fix it, I can screw it up so bad no one else can either."

MandMLawson
Posts: 8
Joined: Fri Apr 28, 2017 3:10 pm

Tue Aug 29, 2017 3:36 pm

I can tell by the size of the trusses that weight is a serious consideration. The house was built in 1993 (I was off from what I stated before). The sheathing is 7/16 and it had two layers of shingles on it.

That said, do you think it would be safe (trusses able to handle) upping to 23/32 with just one layer of shingles? Each sheet will weigh about 28 more pounds, but I have to think that 4 x 8 of shingles weighs more than that, so dropping to just one layer should more than compensate for the added wood weight.

7/16 @ about 34 pounds
23/32 @ about 62 pounds

Is my reasoning sound?

I did consider steel, but I've never done it and we are planning to replace the roof this labor day weekend and I don't have time to shift gears to calculate steel needs.

Thanks

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Greg
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Tue Aug 29, 2017 5:15 pm

Some where in the home, often by the breaker box there is a sticker with the ratings for the home. this will show the wind rating, insulation values and roof rating. Most homes not in the snow areas have a 20lb/sq. ft. rating so you could use that as a guide. figure a 4x8 sheet is 32 sq ft so you would be just over a pound, then add in shingles & paper. the rest would cover snow load if it applies to you.

Greg
"If I can't fix it, I can screw it up so bad no one else can either."

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Jim from Canada
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Joined: Mon Mar 05, 2007 10:39 am
Location: Seaforth, ON

Wed Aug 30, 2017 10:09 am

When I did my re roof I did some upgrades at the same time.

First, my trusses were 24" OC and the sheathing was also 1/2" with H clips and I also had venting issues as you do.

I had the work done, I did not DIY this job.

I had them strip the roof to the trusses.
Then I had them add a 2 x 4, on edge, to the top of every truss using PL premium construction adhesive and screws.
I then had them put the sheathing on which is now 5/8" T&G plywood. I also had them cover over the area where there was a sky light I had them remove. One of them cheap plastic single pane bubble ones that was really yellowed.
Then it was covered, 100%, with Grace brand ice and water shield.
Then covered with a 25 year shingle rated for a lower slope, which I have.
It rained the night before they shingled and I did not have any leaks with the Grace installed, except the area where there was a hole for the chimney, which would only be logical.
With the added air space provided by the 2 x 4's I added to the trusses I was now able to put in a ridge vent and soffit vents.
The fascia is made up of 2 x 6 dimensional lumber, then covered with aluminium. It is nice and straight and solid.

It has made an amazing difference in how hot the ceilings get in the summer inside the home.

There may even be an old thread in this forum that shows photos of the operation. If they were uploaded with links from Photobucket they are likely gone as I cancelled my account with them when they did the money grab for 3rd party hosting.
Remember, minimum code requirement is just that....MINIMUM

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