Hurricane damage question

[Mamushka]

Fortunately we did not suffer any damage during Irma even though it went over us at a Cat 2. Our house was built in 2005 so I'm guessing that helped (meets current code, no large trees near the house, etc.). Also most people in our neighborhood did a very good job of moving everything that could become a projectile inside.

For those of you who did suffer damage was it mostly roof damage/flooding or did anyone have windows blown in/broken. We did not board up the windows and to be honest I'm wondering how much it really helps. If you lose the roof long before you lose the windows would it really save much?

I also am not thrilled with making my house a nearly inescapable fortress. My neighbor had every window and door protected by steel shutters for a full 7 days, he had to enter/leave his house through the garage. If he would have had a fire start in the garage or the kitchen (right next to the garage) they would have been done. That being said I would only do the hurricane cloth and would keep a box cutter handy.

So, before I drop $$$ on hurricane cloth shutters are the windows really worth protecting, or will the roof be long gone before the windows are in danger of going? Any and all experiences appreciated.

[dug]

I put everything loose in the shed or garage but didn't cover any windows.  There are a few large pines in the yard next door and all night we had branches and pine cones hitting the side of the house, which is also where the bedroom is located, so we didn't get as much sleep.  One branch hit one of the bedroom windows directly and I suspect if there were more wind it would have broken but instead it just ripped the screen (and woke us up very quickly.) 

Everything else was fine though so I debated the cost and effort to to buy plywood, store it, install and remove vs. the cost of possibly replacing one or two windows.  I'm thinking for the big bay windows and patio doors it might be worth it but for smaller standard windows maybe not.  Then again I'm in Jacksonville and we typically aren't directly in the path but if we were in Miami it might be different.   

[mcluvin]

My understanding is you don't want that wind getting inside the house.  Once that happens you've now got wind pushing up under the roof, and a much greater chance of losing it and everything else.  That hurricane cloth looks like a great idea.   

[wsrainc]

Disclaimer: I'm not a structural engineer, just an engineer.

Preventing windows from being breached is extremely important, be it by shutters, plywood, or any other method, to prevent catastrophic roof failure, such as trusses being ripped off, losing your sheathing, etc.

The purpose of shutters is to prevent the windows from being breached, and in turn, maintain the pressure differential between the interior of your structure and the outside atmosphere. The actual forces here are very complex, but in a simple sense, imagine a shoebox lying top down on the floor. If you blow it with a strong fan, forces tend to push it sideways. If you cut openings in the same box and use the fan again, the pressure can cause the box to flip over, since the pressure now has a significant upward force.

This is the same reason for hurricane straps on post-Andrew Florida building codes. To keep your roof on, you want to minimize the upward net force on the roof structure, which is done by keeping the structure sealed and strongly attached. Strap the trusses to the walls, use longer and more nails in the sheathing, etc.

I'm sure the shingles and underlayment add some degree of rigidity to the roof as well, but I can't say how much.

Edit: Here's a paper that discusses the effect of pressure differentials, and other factors, in roof failure. http://www.floridabuilding.org/fbc/Hurricane_Mitigation/gravel/2007_Baskaran_et_al_7.pdf

[Ron Donohue]

I am also not an engineer, but have been told that what WSRAINC posted is a major benefit.  If you want more detail, you could always reach out ti pinballcorpse, who is a structural engineer who focuses a lot of his efforts on investigating structural failures and determining the cause of those failures.  Since this discussion  is not in a pinball area of the Village, he may not see it.

From a financial perspective, when I bought hurricane shutters I had a wind mitigation inspection, and the addition of the shutters resulted in a substantial reduction in my wind storm insurance.  In essence, the shutters paid for themselves in reduced insurance over a five year period.  I know that the discount and rates vary widely by location within the state, but that was my experience here in Palm Beach County.  I also note that we have, over time, added hurricane windows in spots and a hurricane rated front door with glass, allowing light into the house and greatly reducing the "cave" feel that many find troubling.

Ron

[Mamushka]

Disclaimer: I'm not a structural engineer, just an engineer.

Me also (Mechanical) 

What I really am wondering is if the windows are truly the weak link, common sense says yes but as you know that is not always the truth. If you typically lose roof sheathing before the windows fail I'm not sure there is enough benefit vs cost to protect the windows. That is why I was wondering the amount of roof to window damage that actually took place.

[Mamushka]

I know that the discount and rates vary widely by location within the state, but that was my experience here in Palm Beach County. 

That makes sense, I'll check to see if it would indeed lower my rates. I would think due to location I would not get nearly the reduction you would but it does not hurt to ask. One thing I noticed, since we are not on the coast the surface wind speed was much lower that the storm wind speed (wind shear?). The west side of the eye went over my house as a Cat 2 and the news was reporting surface wind speeds of ~45MPH with gust up to 70 even though the storm was at 110MPH. 

[NormaJ]

Hi all,

I just wanted to chime in and say my husband and I got tired of putting shutters on the house, so we invested big and went with Cat 5-rated hurricane windows (New South) all around the house this spring. We probably got gusts that were around a Cat 2, but they were completely sound, and I am pretty sure they would have survived anything. They cost a fortune, but we thought about the cost of not doing it. I also liked the additional soundproofing.

Being able to see what was happening outside was really important to us. And not having to take down the shutters after the storm was a blessing. We were the only ones on the block who could see everything as it was going down.

After the storm, the temperature indoors stayed pretty consistent for days, even though it got very humid and was still difficult to sleep through.

[pinballcorpse]

If you are reading this, I am thankful you are ok.

Yes, as Ron stated, I am a Professional Engineer in Florida practicing structural engineering who examines structural failures.

The short answer is: It is prudent to protect the windows.

You can stop reading here if you'd like.

Aside from projectiles coming in and potentially impaling occupants and the interior, it keeps wind pressures out of the home.  Winds develop downward pressure, uplift pressure and lateral pressure (side to side, ie push and suction). Once inside the house, wind will try to blow the house up like a balloon. (The windows act as drains if you will once the wind is inside; and more wind will get in than can get out. Think of pouring a lot of water suddenly into a sink, the water backs up before it all drains out). Winds can also slide an entire roof off the house-that is why straps also have to resist lateral forces, not just uplift.   

The important thing about wind is this: The pressures vary as the SQUARE of wind speed, not linearly. Therefore, as an example, the pressures at 100 mph are 4 times higher than winds at 50 mph, not 2 times.  And to make it more complicated, the height of the structure above ground plays a significant role. 

Regarding egress issues and shutters, there are accordion shutters that have handles on the INSIDE as well.  That will allow for escape.  Boarding up, or placing panels on the entire house can pose a safety threat if you stay in the home, but it is a balance of risks to address immediate threats. (Winds/tornadoes vs fire or other need to escape. It is a tough call, because neither danger is "better", but you have to make decisions to protect you and your family).  Therefore keep an axe or other tools available to break out if necessary. 

The 2005 Florida Building Code (FBC) had many changes to improve designs for wind events.  One of the revisions after Wilma was to require backer boards on all roof ridges since the ridge tiles were typically only held in place with mortar (which is weak in tension).  It was clear to see all of the homes with ridge tiles stripped off (highest wind pressures develop at corners, ridges and edges regardless of wind speed). The cost for repairs was astronomical.  Now Code requires mechanical fasteners for tiles on ridges.  Reroof projects also require re-nailing of the sheathing with longer nails, and more frequent spacing. (The nailing is one of the questions asked on the mitigation forms for homeowners insurance)

The FBC has been updated in 2007, 2010, 2014 and another revision is coming (even before we knew of Irma).     

Honestly, there is so much more to talk about structurally (we have not even discussed forces from wave action), but I do not have a lot of time to post everything that could be discussed here as I am swamped looking at buildings, and writing reports, but I felt a need to help out those in the community who might be reading this.

FYI:  wsrainc brings up good points.

Sincerely,

-Jeff

[dug]

Great information here.  I didn't realize the issues related to wind inside the house so I might have to reevaluate. 

The previous owner did replace all of the windows in the house though and I was wondering if there was any sort of industry standard to help identify how they are rated?

[pinballcorpse]

Great information here.  I didn't realize the issues related to wind inside the house so I might have to reevaluate. 

The previous owner did replace all of the windows in the house though and I was wondering if there was any sort of industry standard to help identify how they are rated?

Look for a sticker on the frame. If there is a sticker, it might have an NOA (notice of acceptance), or a product approval number and/or a chart with wind pressure capacities.   

[Mamushka]

First, thank you for taking the time to post.

If you are reading this, I am thankful you are ok.

Yes, as Ron stated, I am a Professional Engineer in Florida practicing structural engineering who examines structural failures.

The short answer is: It is prudent to protect the windows.

Awesome, I really was not interested in taking advice from a website trying to sell me hurricane shutters, I appreciate getting a opinion from someone not trying to sell me something that is experienced in the topic at hand.

Regarding egress issues and shutters, there are accordion shutters that have handles on the INSIDE as well.  That will allow for escape.  Boarding up, or placing panels on the entire house can pose a safety threat if you stay in the home, but it is a balance of risks to address immediate threats. (Winds/tornadoes vs fire or other need to escape. It is a tough call, because neither danger is "better", but you have to make decisions to protect you and your family).  Therefore keep an axe or other tools available to break out if necessary. 

Like many I live with a HOA that would not permit permanent shutters (would be my first choice)  We had several structures catch fire locally, (a school, a cops house in the next neighborhood, etc.) when the power came on so the treat of fire is not a silly "what if" scenario here. I'm not suggesting you implied that, just letting people know that fire is a real possibility during events like this.

Honestly, there is so much more to talk about structurally (we have not even discussed forces from wave action), but I do not have a lot of time to post everything that could be discussed here as I am swamped looking at buildings, and writing reports, but I felt a need to help out those in the community who might be reading this.

Would love to revisit this topic when things get back to normal, once again, thanks for taking the time to post.

[pinballcorpse]

First, thank you for taking the time to post.
Awesome, I really was not interested in taking advice from a website trying to sell me hurricane shutters, I appreciate getting a opinion from someone not trying to sell me something that is experienced in the topic at hand.Like many I live with a HOA that would not permit permanent shutters (would be my first choice)  We had several structures catch fire locally, (a school, a cops house in the next neighborhood, etc.) when the power came on so the treat of fire is not a silly "what if" scenario here. I'm not suggesting you implied that, just letting people know that fire is a real possibility during events like this.Would love to revisit this topic when things get back to normal, once again, thanks for taking the time to post.

Glad to help.  Anytime. (Prefer talking pinball, but we know that )

So, I am curious, you are saying your HOA will not allow accordion shutters, because they are "permanent"?  What do they allow?   

And yes, to reiterate, the potential for fire is real and scares me, and is a real threat, hence the recommendation for keeping an ax or tools in the room to get out. Code enforcement requires shutters to be removed within a short period of time after the storm due to egress/safety issues.   

Non-engineering recommendation: I also recommend staying fully dressed with shoes ON and flashlights kept on your person if there is not other light present.  Boarded up houses get DARK without power and if something goes wrong, or there is broken glass on the floor (Die Hard anyone?) fumbling around in the dark is not going to be fun. In fact, there is nothing "fun" about storms and protecting yourself and your family during the event.   

(BTW I also have a ME degree. My PE license is from passing the Civil/Structural PE exam, since that is the area I practice  )

[Mamushka]

So, I am curious, you are saying your HOA will not allow accordion shutters, because they are "permanent"?  What do they allow?   

I think I misunderstood what you were saying, I thought you were talking about functional colonial style shutters like these: https://www.assuredstormwindow.com/wp-content/uploads/2016/03/Colonial-Shutters.jpg
None of the houses in my neighborhood have shutters so I am assuming (based on other neighbors experiences) a request would be turned down. Guess I could ask.

(BTW I also have a ME degree. My PE license is from passing the Civil/Structural PE exam, since that is the area I practice  )

Funny where we end up, BSME and I'm in Nuclear Quality Assurance. Never remotely dreamed I'd be here At least it has stayed interesting for the last 10 years