Back on the roof

[john in la]

Thanks for the advise last weekend on the underlayment for my roof project.
For $350 more I have decided to go with 100 percent ice and water shield instead of 30 lb felt.

I was going to go with a steel roof; mostly because I already have new unuse steel roofing that I bought for another project. I have decided against that and I will be going back with asphalt shingles.

Now to my question.

I got up on the roof a couple times this past week to get a good look.
First thing I noticed was over half the roof feels soft to me.
Not soft enough I feel I will fall through but soft enough you can feel the give when you walk across it.
The house is 33 years old and has 7/16 OSB 24 inches on center.
Yes it meets code with H clips but just barely.
While re-decking the entire roof is biting off a little more than I wanted to chew labor wise I could opt to hire the job out rather than do it myself.
On the other hand re-decking the roof will allow me to pull the shingles nails and decking off all as one piece. I can also cut the decking into 2x4 or 4x4 pieces to make taking it off more manageable.

So at what point do you re-deck a roof.
If the boards look sound and hold nails but just give when walked on does that constitute a re-deck.
I have not taken any of the shingles off so I really do not know the true condition of the decking.

7/16 OSB $670
1/2 OSB $740 plus $70
1/2 3 ply pine plywood $780 plus $110
1/2 4 ply pine plywood $825 plus $155

I got into this project house right so I have some wiggle room but do not want to spend my entire budget on the roof going overboard as it needs other work done to it.

Shingles and 30 lb felt $1350.
Shingles with a upgrade to 100 percent ice and water shield and re-deck with 1/2 inch 3 ply plywood $2500
Really do not want to spend the extra $1150 but it looking like that will be the logical thing to do.

 

[Jim in N.M.]

John, Do it the correct way, There's nothing worse than a Leakey roof during a heavy rain . just my 2 cents Jim in New Mexico

 

[Stephen Newell]

Can't say without being there. If the roof is too soft the problem you would have is it wouldn't properly hold the nails for the shingles. It might hold nails now but what about in the next 20 years. Very likely with the age of the decking it is time to be replaced.

 

[Loosehandle]

I don't use OSB for anything, just my preference.

 

[dhermesc]

Is it soft - or have you gotten heavier?

Best place to look is from the bottom side of the roof. If you've had leaks and seeps the wood will be discolored and show the issues. If you find some then you decide if you are going to replace sections of the roof or pull it all up and resheet it.

Whatever you do - DO NOT PUT A SECOND LAYER OF SHEETING OVER THE OLD LAYER. This is many times worse than putting a second lay of shingles on. The original wood is rotted and you put a layer of plywood directly on top of this damp rotting wood - the new layer rots out too.

I helped my brother reshingle his house - it was built in the early 1980s and we were reshingling it in 1996. A some point the roof had been stripped and a second layer of plywood nailed down. It was horrible. We tried patching the bad spots and eventually 1/3 of the roof was resheeted and I remember the plywood patches were some weird size as the original sheeting was 11/16ths or something and the second lay was 3/8s. The roof we were taking off had leaked in several spots and the water got trapped between the two sheets and rotted out massive sections of the plywood.

Our patches were cut through both layers and the single sheet patch had to match the thickness of the doubled up sheets - that varied depending on how clean the roof was where the second sheets were nailed down. By the time we got done the attitude was - it just needs to last a couple years and this place is sold. It lasted well over 20 years so we must have gotten the new roof on with no leaks.

 

[Old Ford Mechanic]

7/16 OSB is ok on 16 inch rafter centers but, not so good on 24 inch centers. I would at least go back with 1/2 thickness and 5/8 would be even better. And also plywood instead of OSB.

 

[Mike M]

I prefer OSB verses plywood for concrete forms. I found it is porous and lets the air escape, so you get little to no air pockets after it cures.

 

[kcm.MN]

Growing up in hurricane country and having worked on my own doing home repair and roofing, I have a little bit of experience with what you experienced. First, that little bit of 'give' is due to there only being a single layer of 7/16" OSB. I prefer plywood, but that has become prohibitively expensive! If using OSB, I would have preferred 3/4". But 7/16" is there and it meets code.

Second, you're closer to the coast than I was. I was on the north side of Houston. While we had a decent buffer from the blunt of hurricanes, I've seen enough video to know that if wind has ANYTHING to grab hold of on your house or outbuildings, the roof and even the building can go bye-bye. So this one is on you, John. Only you can say if you want to invest more money to beef up your roof.

All that said, your roof is your primary defense at keeping Mother Nature out of your home and making that home your shelter from the storm. So again, you need to decide if you want to beef it up or let it be.

...Just wanted to re-state what you already know. It's a tough decision, for sure!

 

[BradCNY]

More to think about, if your trusses are on 24 in centers your roof will sag between. If you put metal on your roof, the purlins would span over the sags and roof would be flatter.

 

[bobfeather]

can't make your decision, but in 79 when we built our house put 5/8 tongue and groove plywood on roof and floors never an issue since not sure how long you plan to live there, or plan to live , so no advice , if leaving soon, do it cheap, if planning long term , spend the $$$
bob

 

[sms]

Years ago I read an article on hurricane failures. Most damage was attributed to fasteners. My opinion is that the sheathing is getting soft and I would be worried about nails holding. I like plywood and is about all I have used in 25 years. As others have said if you plan on keeping it I would do it right. You asked. Lol

 

[MarkB_MI]

7/16 OSB is marginal, and after thirty years will be pretty weak. New sheathing is pretty much mandatory; if you don't replace it, the roofing nails won't hold well and a good wind will rip off shingles.

As long as the old sheathing isn't rotten, adding a second layer of 7/16 OSB over the first will give a pretty solid roof. Stagger the joints so the new sheets span the gaps between the old sheets. I put 7/16 OSB over some old 7/16 plywood and that roof is in great shape ten years later. In that neighborhood all the roofs were built the same, and everyone who didn't re-sheath their roofs when they replaced their shingles had to come back a few years later and redo everything.

If you're tearing off of the old sheathing, I wouldn't use 7/16. 1/2 OSB or plywood is solid to walk on and holds nails well. My post-frame shop has 5/8 OSB and that roof is really solid. (It was supposed to be 1/2 OSB, but I think the lumberyard ran short of half inch and substituted the 5/8).

 

[Geo-TH,In]

30 years ago I used 5/8 5 ply plywood. The felt got rained on and half the plywood sheets came unglued. That's the last time I used plywood.
After that I've used 1/2 osb.
Remember I sometimes have a snow load.

Which decking material would be better if you decided to go with metal after the next hurricane?

 

[Absent Minded Farmer]

What's the SF?

Mike

 

[Hoenes]

We're adding on to my son's garage. Using 1/2 OSB. I've had bad luck with fir plywood delaminating, if not covered in time. OSB is more resilient to rain. Also 19.3 centers on the trusses. Stiffer. Yes, 19.3 is a thing, it's the diamond stamps on your Stanley tape. One more truss in 8 foot than 24 inch centers.

 

[showcrop]

At 36 years that OSB owes you nothing, especially at 24inches. Do it now, don't be regretting it after sending the $ on the shingles.

 

[Texasmark]

I had my roof redone about 3 years ago with 30 year asphalt-glass shingles. I built the house in 1979 and had access to 100 sheets of 1/2 3 ply, CD plywood which I used for roofing, siding and floor underlayment. Same truss spacing as yours with H clips. I had one small bad spot where water had gotten in that I replaced.

Otherwise took 2 layers of shingles off and on with the new. I could walk on the roof and find several places that would deflect when I walked on the center (between trusses at the center of the 4x8 sheet,but having a concentrated load of my 235# at the time and having rain or snow + shingle weight distributed across the same span is apples and oranges.

 

[sotxbill]

get the foil lined osb to dramtically reduce the heat load on the house. You will see a huge difference in the summer!!!!!!!!!!!!!!!

 

[dpendzic]

use an APA rated sheeting for 24 inch or smaller--the thickness of it doesn't tell the whole story--also the allowable deflection for a roof is L/180 where a floor it is L/360