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  #1  
Old 8/4/12, 11:15 AM
Humberto Carvajal's Avatar
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Default Cement tiles too heavy for roof?

Was doing a Wind Mitigation inspection, we typically are asked to do here in Florida the other day. When I went on the roof, I noticed the roof was "wavy" is the best way to describe it. Gable roof and both sides were wavy. The waves were perpendicular to the trusses. When I came down, I went into the attic to look around and what I saw were several trusses leaning, split, bowing, plywood was uneven where they butted up to each other.

I wanted to share these few pictures. They really don't do it justice as you would need to be there to see it better. The roof was put on in March of 2011. The buyer had recently had a friend of a relative do a "general" inspection. i was called out because that inspector wasn't able to do a Wind Mitigation.

Not being an engineer, I advised the buyer to contact one and get their professional opinion on the situation and probable cause. Anyone here run into this before?


Bert
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cement-tiles-too-heavy-roof-img_6062.jpg   cement-tiles-too-heavy-roof-img_6071.jpg   cement-tiles-too-heavy-roof-img_6070.jpg   cement-tiles-too-heavy-roof-img_6064.jpg  





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  #2  
Old 8/4/12, 11:53 AM
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Default Re: Cement tiles too heavy for roof?

I'd say that was probably a good call. Picture #1 is really a non-issue, but #2 & #3 look like a "stressed" truss. Pic #4 was probably not caused by the weight, but should be addressed none the less.



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Last edited by jpope; 8/4/12 at 12:32 PM..
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Old 8/4/12, 12:14 PM
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Default Re: Cement tiles too heavy for roof?

Yes, several trusses appeared as the pictures in 2 and 3. The truss span is 24" OC and the home built in 79. There were clay or cement tiles on it before as this particular city, does not allow shingle tiled roofs ( City of Coral Gables, FL ). Another possibility that came to mind was maybe the damage was caused previously and the repairs just never took place when they re-roofed. In any event, I felt better advising him to seek a professional opinion. This was a short sale property owned by an investor. The buyer thanked me for pointing this out. Possibly saved him some money and who knows what other problems in the future.


Bert





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Old 8/4/12, 7:05 PM
Robert Ernst Robert Ernst is offline
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Default Re: Cement tiles too heavy for roof?

I have seem some tile roofs sag a little . But I have seen pictures similar to what your showing here on a house that was re-roofed with tile. The local building officials were notified and they told the people to move out. Concrete roofs can weigh 10 times what an asphalt roof does.



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  #5  
Old 8/4/12, 8:25 PM
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Default Re: Cement tiles too heavy for roof?

my take:
Photo 1. Looks like the truss was damaged before or during installation. The lateral displacement of the gangnail was not caused by weight from above, but more likely from impact from the side. I'm guessing this was the topmost truss in a bundle lying flat on the ground and they bumped the butt joint with a load of trusses as they were setting trusses with a crane.

Photos 2&3: Look like a truss bowed to the side rather than sagging from weight. It's hard to tell from the photo.

Photo 4: if a split were to be caused by excessive weight for which the trusses were not designed, the splits would most likely occur at the midpoint between support points instead of at the peak where trusses are prevented from slipping against each other by a gangnail and are well supported by opposing each other. I'd guess this was split when the truss was assembled or damaged by bumping during the truss setting process.

It looks to me like either the crane operator or the truss-setting crew were not very good.

This is just in general. The problem may be excessive weight due to a change in roofing material. Drawing conclusions from photos alone can be tricky.

In looking for overloading of trusses by a change in roof-covering material, I'd be looking for general bowing of the bottom chords and compression cracking of drywall at the outside walls upon which trusses bear. This would be vertical and horizontal cracking, mostly at drywall seams, as opposed to diagonal cracking typically caused by soil movement.

Did homes near this one have lighter roof-covering materials?




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Last edited by kshepard; 8/4/12 at 8:41 PM..
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Old 8/4/12, 9:10 PM
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Default Re: Cement tiles too heavy for roof?

No Kenton. All homes in this area are either flat tiles or barrel tile type. No shingles allowed. I did not see any cracks on the drywall surfaces. What caught my attention was the waviness of the roof when looking from the top. That's what prompted me to take a closer look at the trusses inside the attic.





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Old 8/4/12, 9:23 PM
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Default Re: Cement tiles too heavy for roof?

I know it's a bit difficult to tell from this first picture but the ridge tiles were actually wavy on this roof. In the second picture of the roof to wall connection, it almost seems the strap is buckled. It may not be anything more than what you've already explained Kenton, but I felt it would be better to have the buyer consult someone more knowledgable and qualified to make that call.

Bert
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cement-tiles-too-heavy-roof-img_6009.jpg   cement-tiles-too-heavy-roof-img_6068.jpg  





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Old 8/4/12, 10:10 PM
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Default Re: Cement tiles too heavy for roof?

Quote:
Originally Posted by hcarvajal View Post
I know it's a bit difficult to tell from this first picture but the ridge tiles were actually wavy on this roof. In the second picture of the roof to wall connection, it almost seems the strap is buckled. It may not be anything more than what you've already explained Kenton, but I felt it would be better to have the buyer consult someone more knowledgable and qualified to make that call.

Bert
I understand Humberto, and quite right. It's best to pass on the liability if you aren't sure what you're looking at, and there's no shame or risk with the agent in doing it unless it's an obvious call, which this doesn't seem to be.

The waviness can be caused by either sagging of the trusses or tiles that are not installed in a straight line, and this looks like poor installation to me. The wavy strap at the outside wall in the 2nd photo is just that; a thin strap that bends where the nails are installed.

No worries, you did right to recommend evaluation by a specialist. None of us knows it all (despite some of us who claim we do!) and it takes time to build skills. This is a business in which nobody ever knows it all.




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  #9  
Old 8/5/12, 10:47 AM
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Default Re: Cement tiles too heavy for roof?

Quote:
Originally Posted by kshepard View Post
Photos 2&3: Look like a truss bowed to the side rather than sagging from weight. It's hard to tell from the photo.
Which is a classic indication of an overloaded truss. Trusses (an engineered system), don't "sag." When a truss is overloaded it will "twist" until the point of failure.

Quote:
Originally Posted by kshepard View Post
Photo 4: if a split were to be caused by excessive weight for which the trusses were not designed, the splits would most likely occur at the midpoint between support points instead of at the peak where trusses are prevented from slipping against each other by a gangnail and are well supported by opposing each other.
You're confusing "trusses" with "conventional framing."

The internal members of a truss (diagonals) are not "supports." They are active members of the engineered system and will be in compression or tension at any given moment, depending on the imposed load.



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Old 8/5/12, 6:40 PM
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Default Re: Cement tiles too heavy for roof?

And judging from those assumed 24 oz. hammer blows, the truss was split hammering it into position when the temporary lateral bracing was holding it from going where they wanted it.
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Kenton, I agree with Jeff on this one.

And don't know about everyone else, but wouldn't some insulation help in that part of the Country?
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Old 8/5/12, 8:35 PM
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Default Re: Cement tiles too heavy for roof?

There was insulation Marcel. Cellulose, but definitely could have used some more, there definitely wasn't enough as it was thinning in many places.

Bert





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  #12  
Old 8/6/12, 4:52 PM
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Default Re: Cement tiles too heavy for roof?

I did a inspect on a cement tile roof a couple of months ago and had structural stress problems I called for a sructural engineer and it ended up costing about 8K to repair seller was shocked and a little depressed as they had not had a inspection when purchasing.



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Old 8/6/12, 4:59 PM
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Default Re: Cement tiles too heavy for roof?

How thick was that plywood? You have some serious issues there. My first question would be is where is the permit for that roof. If that was shingle there should have been an engineering analysis to switch it over to tiles. I am guessing not permit.
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  #14  
Old 8/7/12, 10:53 AM
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Default Re: Cement tiles too heavy for roof?

The roof was installed just last year and was permitted. I have that information. I was told that the City of Coral Gables doesn't allow Shingled roofs but, this home was annexed into Coral Gables from West Miami I believe. So it is very possible it had a shingle roof prior to this. But, it was permitted and finaled by Coral Gables.

Bert





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  #15  
Old 8/7/12, 11:02 AM
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Default Re: Cement tiles too heavy for roof?

Quote:
Originally Posted by hcarvajal View Post
Was doing a Wind Mitigation inspection, we typically are asked to do here in Florida the other day. When I went on the roof, I noticed the roof was "wavy" is the best way to describe it. Gable roof and both sides were wavy. The waves were perpendicular to the trusses. When I came down, I went into the attic to look around and what I saw were several trusses leaning, split, bowing, plywood was uneven where they butted up to each other.

I wanted to share these few pictures. They really don't do it justice as you would need to be there to see it better. The roof was put on in March of 2011. The buyer had recently had a friend of a relative do a "general" inspection. i was called out because that inspector wasn't able to do a Wind Mitigation.

Not being an engineer, I advised the buyer to contact one and get their professional opinion on the situation and probable cause. Anyone here run into this before?


Bert
I would guess, picture 1 and 4 were from a poorly done repair. You can see the hammer marks on the wood in picture number 4.
The other two could have been caused by excessive heat or the extra weight. What size plywood was used?



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