Roof deflection

Clay E White · 09-26-2007, 11:58 AM

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**Jerry Peck** · 09-26-2007, 12:10 PM

I would suspect, because it looks to be more than just 'between trusses', that it was framing/trusses/rafters which were not installed in proper alignment.

I doubt there is a suitable repair which would not cause more damage than you would think.

I also doubt that there is a structural issue there.

HOWEVER, you *will* have water trying to run laterally across the shingles, and shingles are not designed nor intended for that, which means that is a roof leak waiting to happen.

How to address the 'roof leak' problem? About the only way would be to remove a sufficiently large area of shingles, install a couple of extra layers of felt, or that new peel and stick stuff then the felt underlayment, then lay new shingles in the area that was removed.

Of course, once the shingles have been removed and the underlayment removed, why not (at that time) shim the roof sheathing up flat and even, re-nail everything, then lay new shingles in that area.

Both are about the same amount of work, both will result in eliminating the leak, one will make it look 'right' and the other will only result in it being reported again when the buyer sells. Of course, the repair and shimming might result in that too, if not done 'properly', with permits, etc.

**Jerry Peck** · 09-26-2007, 12:27 PM

Originally Posted by Clay E White

Just so I understand you correctly, you would not recommend an engineer look at the deflection, just roof repairs to prevent water from traveling under the shingles.

That's my take on it after having seen hundreds or thousands like it.

Only you know what the structure looked like inside the attic though.

**Jerry Peck** · 09-26-2007, 12:39 PM

Originally Posted by Clay E White

I mispoke a bit.....there is NO attic at this area of the house. Its a vaulted ceiling.

"Vaulted ceiling" meaning what?

a) Rafters extended down and out over the open area below, with roof on top and ceiling on bottom (in which case, did the ceiling have a similarly located dip) *Could* be 'structural', but I'm still guessing it's 'installation misalignment'.

b) Scissors trusses with limited space in them? As above, did the ceiling have a dip in that area? *Most likely* 'installation misalignment', remote chance it would be 'structural'.

**Jerry Peck** · 09-26-2007, 03:31 PM

I wouldn't call for an engineer, if I was concerned, I would state something to the effect of 'while the roofing has been removed in that large area [hinting that it will take a large area], any concerns regarding the structure can be seen by removing an area of roof sheathing, check the structure, then re-install the roof sheathing and complete the repair' ... that's what the structural engineer would have to do to even see what might be wrong, if anything, in that area - they don't have x-ray vision either.

**Rick Hurst** · 09-26-2007, 04:27 PM

Do you think this deflection is a problem. Makes a great roof gutter.

Seriously, this house has had a fire and the roof trusses had been replaced by Joe Homeowner.

Richard Rushing · 09-26-2007, 04:38 PM

I agree that a structural engineer would be an over-kill. I would recommend repairs by a framing contractor.

That peel and stick stuff is pretty good and would certainly assist with additional waterproofing and then re-covering. Since these are vaulted ceilings, that's probably the best way to approach it in lieu of trying to come up from the inside.

rr

**Bob Knauff** · 09-27-2007, 04:56 PM

I have been seeing (or at least noticing) more and more of this type of deflection in roof lines lately, mostly in newer construction. I have become convinced through research and interviews with contractors and repair type folk that some of the deflection is due to improper installation practices by the installers of the roof sheathing. During my research (I'm too lazy to find the exact source again right now but believe it was the APA) I came across instructions concerning proper installation techniques for roof sheathing using plywood and OSB. It is always recommend that the installer stand on the sheathing directly at the rafter to promote good sheathing to rafter contact as it's being fastened but if the sheathing is a thinner type, it was made quite clear that if the installer stood to either side of the rafter while nailing, the sheathing may sag and create a dip in the surface plane of the roof after being nailed in place. The problem will most likely not be noticeable to the crew on the roof at the time but from a distance or at an oblique angle, particularly as the sun glances across the roof plane after shingling, it is very noticeable. Of course this problem has no structural consequence but the building aesthetics greatly suffer.

**Rick Hurst** · 09-27-2007, 07:33 PM

Welcome back to the board Bob.

Your comment does make sense to me. I watched some guys decking a second story home down the street the other day. They would actually lay down a section of the OSB and nail the upper corner just to hold it in place. Then lay down another piece, nail it the same way and then go back to the prior piece while laying on it and nail the bottom edge. When I saw this I thought he's nailing it with his weight on it so he creating the deflection with the install. Make sense?

rick

**Jerry Peck** · 09-27-2007, 07:35 PM

(highlighting with bold is mine)

Originally Posted by Bob Knauff

I have become convinced through research and interviews with contractors and repair type folk that some of the deflection is due to improper installation practices by the installers of the roof sheathing.

...

It is always recommend that the installer stand on the sheathing directly at the rafter to promote good sheathing to rafter contact as it's being fastened but if the sheathing is a thinner type, it was made quite clear that if the installer stood to either side of the rafter while nailing, the sheathing may sag and create a dip in the surface plane of the roof after being nailed in place.

Bob,

Improper installation practices are a definite contributing cause, but not the full cause.

The thinner (less than 5/8") sheathing is the main cause.

The rating on the sheathing for allowing a 24" span for 3/8" sheathing does not (for any span rating for any wood, including structural panels) make ANY consideration for "building aesthetics". The span rating is simply a structural rating of what it will withstand within the limits of its design, including safety factor.

Considering 'H' clips as "edge support" helps attain the design load rating, but, as we all know, does not help keep thinner roof sheathing 'in plane'.

The fact of using thinner roof sheathing panels is the main cause (by far) for roofs which sag or deflect 'out of plane'.

Getting back to installation problems, one big installation problem is with the span rating and cutting of the panels.

APA recommends no less than 1/2 a sheet be used ... that's no less than 2' x 8' or 4' x 4' ... and remember, like lumber, structural panels are rated for installation over two spans, three supports - MINIMUM.

Those small pieces, they are just a no-no, but it is down ALL THE TIME.

Now, though, we must get into the roofs in the photos which show an 'out of plane' area which is larger than the spacing of two trusses or two rafters ... that now becomes an installation issue, installation of the trusses or rafters, where they are not installed 'in plane' across the top of the top chords of trusses or where rafters are installed which are not 'flat In plane', i.e., the rafters have a crown to them.

If the supports are not 'in plane' how can the roof sheathing which is nailed to those supports be expected to be 'in plane' when they are installed?

With trusses, even being made in a truss 'factory' setting, 'identical' trusses are not "identical", some slightly longer, some slightly shorter, some slightly taller, some slightly less tall, set one of each side-by-side and the top chords will be 'out of plane' from the start.

From there, it's all downhill.

Kind of like what I was telling a window manufacturer two days ago, if they keep changing their engineering to match the installation instead of changing the installation to match the engineering, when it goes to court, their case will be like a soap box derby racer ... it will go downhill FAST.

**Bob Knauff** · 09-27-2007, 07:56 PM

Thanks Rick. I've been exceedingly busy and have only so many hours in a day so haven't had time to visit Brians domain in some time. Glad to see you regular guys are still so active! I'm not sure I like Brians new (to me) format but then I always was resistant to change...

The roof deflection problem is addressed in a publication that can be read at: http://www.gp.com/BUILD/DocumentView...elementid=3194

It also says, in part, bowed trusses should be braced straight and shims or planing should be done to achieve a flat surface on which to attach roof sheathing. I don't know about you guys but if I saw a contractor install shims or plane a truss to achieve level in order to achieve a nice smooth roof afterwards, I believe I'd drop dead right on the spot out of shear shock!

See ya.

**Frank Bombardiere** · 10-01-2007, 06:51 PM

If that is a cathedral ceiling, I have rarely ever seen one that did not have some deflection. My guess is the jack rafters and hip structure are holding up fine and the long rafters of the cathedral ceiling have deflected like they are prone to do because of the span. Probably not a major problem other than the way it looks.

**Rolland Pruner** · 10-02-2007, 11:01 AM

Jerry:

I would report findings as sag in roof and have builder evaluate and adise on and if repair is needed, this would take you off the hook.
We cannot advise on something we cannot see.

Rolland pruner

**Frank Bombardiere** · 10-02-2007, 06:20 PM

I agree we cannot inspect what we cannot see, however, if we sluff everything we see off onto someone else, what good are we? I have seen enough of these in over 2200 inspections to have an opinion and after all that is what we are doing is giving our opinion about what we see.

The reason I said PROBABLY not a major problem is the fact that I am not the one that inspected it and do not know all the facts. I do not hesitate to defer to specialists if I do not feel comfortable about something, but I feel it gives us a bad name to try to put everything off onto someone else and escape any responsability.

I think many home owners or buyers can see that there is a sag or a crack somewhere etc, that is why they hired us for our expert opinions. If we defer everything we see then they would be better off to do the inspection themselves and hire the appropriate trades for further evaluation of everything they see as questionable.

You may not be that kind of inspector and I am not saying you are. It just sounds like it when you say " then it takes you off the hook" To be a good inspector and respected around your area, you need a strong back and fortitude to give your honest opinion. I actually hate to defer for further evaluation, although I do at times. It does take some time to feel comfortable about things we see, the more inspections you do the more confident you are in your opinions. Sorry about the rant, I just get a little irritated about inspectors wanting to put things off so as not to have any responsibility.