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would concrete roofs help in hurricanes?

 
sudden 2017-09-10 11:08:11 

looking at this devastation from this hurricane and how we can improve our building stock across the region, i wonder, would concrete roofs be better for hurricane resistance?

 
bravos 2017-09-10 11:28:20 

In reply to sudden

It's all in the design and construction,not necessarily the material only..

Concrete roofs can be also a trap though...

 
sudden 2017-09-10 11:36:38 

In reply to bravos

explain, mate?

 
bravos 2017-09-10 11:55:38 

In reply to sudden

You have to consider other factors like compatibility with other possibilities such as earth quakes...

A regular concrete roof in an earthquake is a scary proposition..

In other words a ground up design factoring all components and considering all possibilities must be the key,not just the roof materials on top the ring-beam,ie a concrete roof would be much times heavier than conventional roofs and the pressure of a strong storm may make regular block walls cave in with the additional down force and torsion.

So basically what I'm saying is it's not just a question of concrete roofs but a question of design and construction effectively integrating all that as opposed to just a choice of materials to put on your four walls,and if that's the case the best option is a steel roof which fabricated and erected properly actually strengthens a house at the top with much less load,kinda like a fuselage..

 
sudden 2017-09-10 12:20:01 

In reply to bravos

by steel roof you are referring to the framing and not the cladding, correct? what cladding would you use that would resist peeling off from a hurricane?

the reason for the concrete roof is that in addition to weight and tie in with the structure, there is nothing to peel off like tiles or permaclad.

 
bravos 2017-09-10 12:38:19 

In reply to sudden

Yes I was referring to the structure...but the structure is the also the foundation of strength for the cladding..steel beams ,purlin and sheets normally do it,have seen such roofs remain whole while the walls crumbled below..

I like the idea of an all concrete house but it has to be a ground up design to be optimum.

 
pelon 2017-09-10 12:43:43 

In reply to sudden

Take a look at the roofs on homes that survive hurricanes - the rafters are are embedded differently than our newer homes. Bravos is right... it is all about the right materials and the right design. see pm (I've weathered every storm there)

 
mikesiva 2017-09-10 12:44:03 

In reply to sudden

A lot of roofs in Jamaica are concrete constructions, and they are good for hurricanes. Of course, windows have to be properly taken care of. Also, nearby trees should ideally be cut down.

Most of the houses I lived in had concrete roofs, and two of them were fine during hurricanes. Naturally, they also had to meet building standards.

The last time Kingston had an earthquake was in 1907. That's a risk worth taking.

 
birdseye 2017-09-10 12:46:10 

In reply to bravos

You can design structures to withstand most forces – all steel and wood and other building materials are manufactured to certain specifications with specific load bearing capacities – you the builder use the proper materials and design for the worst case scenario - then up the safety factor to say two and a half times the worst conditions you expect will happen – if you expect highest wind to be 140 mph – then you design to withstand 2.5 times 140 --- the reason people don’t do that is COST

 
sgtdjones 2017-09-10 13:11:17 

One must remember

A roof holds the four walls together ie the weight of the roof.

An engineer must do a weight distribution analysis before materials are sought.

There are buildings designed to withstand hurricane force winds.

As expected cost is a major problem.

One must not put a concrete roof on brick walls unless such is reinforced with rebars and concrete inside the bricks to prevent movement.

If putting a steel roof an engineer will look closely at the prevailing winds
especially at the windward sides.
Special anchors are made to keep the roof and wall from movement during
high winds.

Another method is to build the home on a concrete platform sitting on leaf springs such as the CN tower in Toronto.The upper reaches of the CN Tower are built to withstand turbulent winds with a wind resistance factor of up to 418 km/h (260 mph)

Walls must have anchors that hold steel cables that compress the concrete and give it its strength — can never be replaced.Without it, the walls would be thrown into tension under high winds and would collapse.

Consult a qualified Engineer a prerequiste

 
pelon 2017-09-10 13:25:43 

In reply to sgtdjones

Consult a qualified Engineer a prerequisite
correct, exactly what I said in a pm, I also showed him the way we did it for years and years....

 
bravos 2017-09-10 14:55:07 

In reply to birdseye

Yep..

 
bravos 2017-09-10 14:55:14 

In reply to pelon

cool

 
sgtdjones 2017-09-10 15:27:33 

In reply to bravos

The building built by the Chinese will not survive any earthquake over 7.0

and any cat 3 hurricane.

They will end up in Venezuela.

Make sure your home is above the sea level by 200 ft, should the sea bed collapse with all the natural gas and oil extracted, it will be a horrendous tragedy .

The tsunami will be 60 ft high.

 
Norm 2017-09-10 15:54:06 

The primary concern for the roof from wind loads would be uplift. Therefore, concrete would be better than other materials, because of its weight. The concrete roof must be reinforced with steel and properly anchored to its supports (walls) tho.

On the other hand, the weight of the roof increases earthquake loads on the walls and foundation. So, beef up the roof just enough for the expected wind loads only.

Also, concrete assemblies (roofs, floors or walls) should not be supported by wood.

Wooden roofs could be fine too but the nailing, anchoring and overhangs need to comply with an adequate building code.

Some new building codes address these issues very effectively and economically. So, build or modify per a code such as the International Building Code. Consult a good civil engineer too.

 
Chrissy 2017-09-10 16:17:05 

In reply to sudden

Mona Heights and Portmore never lost a roof during Gilbert for that reason - but the houses are hot as hell.

 
sudden 2017-09-10 17:02:17 

In reply to Chrissy

Yeah that is an issue. I see where people have discreet vents near the roof line to release the internal hot air as it rises.

Interesting posts so far

 
Norm 2017-09-10 18:15:52 

In reply to sudden

A question that would naturally follow from the original question would be the disadvantages of using a concrete roof for a home.

Some were mentioned before. Weight increases earthquake loads and hot air buildup below the roof. Add to that increased overturning potential, cost, roof leaking and roof drainage and aesthetics. "Cost" and "aesthetics" are non-technical issues but the others could all be addressed relatively easily and reliably through proper design.

A good solution to the heat and aesthetic problems is to build a roof garden on the roof. Concrete roofs are usually flat and used for recreation. Of course, you would need a parapet on the perimeter of the roof. The roof garden may consist of plants in pots or boxes, or in a permanent soil layer on the roof. In hurricane country, the removable plants might be better.

 
Dan_De_Lyan 2017-09-10 18:35:08 

In reply to Norm

any roof has a structural integrity on its own....so does any wall.

The issue is the connection point of the roof and the wall is usually the culprit.

Peeps don't conduct the Failure Mode and Effect Analysis (FMEA).

That would identify the failure and prevent an over-design of the roof. But target the connection method.

 
camos 2017-09-10 18:35:24 

In reply to Chrissy

they are hot because the roofs are low,12 feet would help but send up cost and these are lower income houses.

 
camos 2017-09-10 18:37:22 

In reply to Dan_De_Lyan

I notice the steeper roofs better withstand wind force than the flatter ones.

 
black 2017-09-10 18:41:36 

In reply to Norm

A good solution to the heat and aesthetic problems is to build a roof garden on the roof. Concrete roofs are usually flat and used for recreation. Of course, you would need a parapet on the perimeter of the roof. The roof garden may consist of plants in pots or boxes, or in a permanent soil layer on the roof. In hurricane country, the removable plants might be better.


Damn Norm, these guys are trying to figure out how to build a better roof, you are trying to plant a garden. lol

 
camos 2017-09-10 18:48:16 

In reply to Norm

A good solution to the heat and aesthetic problems is to build a roof garden on the roof. Concrete roofs are usually flat and used for recreation. Of course, you would need a parapet on the perimeter of the roof. The roof garden may consist of plants in pots or boxes, or in a permanent soil layer on the roof. In hurricane country, the removable plants might be better

some of that is taking place in commercial and multifamily buildings but the movement is driven by environmental concerns.

 
Norm 2017-09-10 18:50:20 

In reply to black

these guys are trying to figure out how to build a better roof you are trying to plant a garden.

Man, the subject has evolved beyond mere mechanics. We are approaching Garden of Eden considerations here. smile

Seriously tho, roof gardens are becoming a requirement, as building technology integrates energy consumption into design considerations. If you will build a concrete roof, you will save a lot of money on cooling (or heating) costs by building a roof garden. Addressing the related structural issues is straightforward.

 
Norm 2017-09-10 19:05:25 

In reply to Dan_De_Lyan

any roof has a structural integrity on its own....so does any wall.

Not necessarily true, especially for concrete roofs (and floors), which should be slightly convex upward to have any structural integrity. Walls could be flat.

The issue is the connection point of the roof and the wall is usually the culprit.

Yes, but that connection needs to consider uplift (and lateral) forces, in addition to the traditional downward gravity loads. The uplift forces are often ignored by do-it-yourself efforts.

Peeps don't conduct the Failure Mode and Effect Analysis (FMEA).

You are not required by the building code to perform a project-specific analysis for simple homes, but you could if you wanted to. Why do that, however, when the code prescriptive design is adequate?

As it is, engineering costs based on code prescriptive methods are high. A project-specific analysis would be even higher, even with the very high quality structural analysis software currently available.

 
Norm 2017-09-10 19:13:11 

In reply to camos

they are hot because the roofs are low,12 feet would help but send up cost and these are lower income houses.

The cost increase for a concrete roof is significant. It would (about) double the cost of a single story home. Raising the roof would help with the internal heat, in addition to proper air circulation through venting.

The number of lower income homes would probably be halved if they included concrete roofs.

 
Norm 2017-09-10 19:20:43 

In reply to camos

I notice the steeper roofs better withstand wind force than the flatter ones.

Wind forces are essentially horizontal. You should therefore keep the building profile as small as possible to reduce wind forces on a building, and as low as possible to minimize overturning forces. (Same problem with a cricket sight screen too.)

Steep roofs are useful for reducing snow loads only. They absorb less sunlight than flat roofs and also allow the internal hot air to rise and keep your building cool, longer than a flat roof.

 
Norm 2017-09-10 19:22:45 

In reply to camos

the movement is driven by environmental concerns.

True, and economic now, as operational costs are being figured into investment decisions.

 
Dan_De_Lyan 2017-09-10 19:35:45 

In reply to Norm

Any structure that gains a code status has gone thru engineering design and analysis.

My use of the word integrity encompasses proper design for its shape...flat or steep.

Flat means it has dept with trangulation within. A flat roof factory.

 
black 2017-09-10 19:42:16 

In reply to Norm

Wind forces are essentially horizontal. You should therefore keep the building profile as small as possible to reduce wind forces on a building, and as low as possible to minimize overturning forces. (Same problem with a cricket sight screen too.


It's all about structural integrity. What about skyscrapers?

 
Dan_De_Lyan 2017-09-10 19:48:09 

In reply to Norm

If i am doing custom desigh, analysis is done as a requirement prove to the govering bodies habitability. If a design is picking components from a code book. Then the design can be cost effective and be expedited. Not everyone wants run of the mill pre designed comp.

 
camos 2017-09-10 19:50:15 

In reply to Norm

Wind forces are essentially horizontal.


didn't they say in mechanics that the horizontal force to an object is the cosine of the angle formed, or it is reduced by the cosine of that angle?

 
Norm 2017-09-10 19:56:57 

In reply to Dan_De_Lyan

... integrity encompasses proper design for its shape...flat or steep.

Two important differences between concrete and the other common building materials are that concrete is considered brittle and its connections to other concrete components are often internal (via rebar connection).

For a simple home, you would connect the walls to the floors or roof using the rebars embedded in the concrete, which would be adequate for hurricanes. Thus, these connection points are usually not a concern for concrete-to-concrete connections.

You absolutely need to make sure you provide just the right amount of rebar and camber for a concrete roof or floor to prevent catastrophic collapse. During construction you must provide strong and accurate formwork. Concrete roof or floor design and construction are not for amateurs.

 
Norm 2017-09-10 20:04:19 

In reply to black

What about skyscrapers?

A different beast for the engineer. This is where Dan-de-Lyan's project-specific analysis is essential, and required for buildings more than 35 stories above ground.

In a simple sense, they are assumed to behave like a tall and slender pole stuck in the ground, with varying "modes of failure". They may consist of either a rigid outer shell (like a pipe) that supports everything inside, or a rigid inner core (the elevator towers) that serves the same purpose.

This stuff involves serious science and engineering!

 
Norm 2017-09-10 20:07:28 

In reply to Dan_De_Lyan

Not everyone wants run of the mill pre designed comp.

True, and thankfully so!

Some of the most beautiful and creative structures, large and small, have been those that are beyond code prescriptive design.

 
Dan_De_Lyan 2017-09-10 20:11:18 

In reply to Norm

like dubai...kudos to the leaders there

 
sudden 2017-09-10 20:15:14 

In reply to Norm

Brilliant stuff Norm. Would you recommend concrete roofs in hurricane zones? I know a lot of Ja homes are built this way as stated by Chrissy et al.

 
Norm 2017-09-10 20:29:13 

In reply to camos

didn't they say in mechanics that the horizontal force to an object is the cosine of the angle formed, or it is reduced by the cosine of that angle?

The normal load on a sloping surface is the horizontal load reduced by the cosine of the angle between the sloping surface and the vertical.

 
Norm 2017-09-10 20:39:12 

In reply to sudden

Would you recommend concrete roofs in hurricane zones?

Yes, as the first choice. Otherwise, strictly comply with the current International Building Code (for concrete roofs too).

Bear in mind that this is an expensive option tho.

 
sudden 2017-09-10 20:59:26 

Interesting. Floridians calling Caribbean structures inferior Link Text

 
Headley 2017-09-10 21:46:38 

Concrete roofs and hurricane design are matters which folks in parts of Jamaica affected by Gilbert have considered and solved.

There is no need to re-invent the wheel. Although it does surprise me how slowly non-salacious knowledge is dispersed through the region.

Most new houses in eastern Jamaica have concrete roofs. To reduce the weight and cost of concrete, especially in the foundations, and to reduce heat the entire roof is not made of concrete. The house is divided into a number of rectangles and each of those rectangles has a smaller rectangular opening above at roof level (with a concrete border of 2-3 ft and a short (12 - 20 inches) upstand beam around the edge of the opening on which a wooden roof is constructed). A separate wooden hip roof is constructed over each opening. A typical 3 bedroom house may have about 4 - 5 such hip roofs sitting on concrete.

NB Hollow blocks (loosely called bricks in Tdad) are used mainly in Tdad and Guyana. They are not used north of Tdad, for earthquake related reasons except, as vent blocks. For further advice and drawings please PM me for an estimate. big grin big grin big grin

 
Ewart 2017-09-10 21:56:20 

In reply to mikesiva

The last time Kingston had an earthquake was in 1907....



Jamaica recorded an 8.0 magnitude earthquake on the Richter scale on March 1, 1957... I was living in Kingston and I remember it well.


//

 
Norm 2017-09-10 22:24:18 

In reply to Headley

The house is divided into a number of rectangles and each of those rectangles has a smaller rectangular opening above at roof level (with a concrete border of 2-3 ft and a short (12 - 20 inches) upstand beam around the edge of the opening on which a wooden roof is constructed).

Interesting. The wooden roof is moved away from the turbulent areas where the roof meets the outer walls.

For further advice and drawings please PM me for an estimate.

Don't forget to give sudden the cc.com discount!

 
Headley 2017-09-10 22:27:41 

In reply to Norm

Don't forget to give sudden the cc.com discount!


No way!

I would give Sudden the tourist 'discount'. big grin

 
Norm 2017-09-10 22:36:12 

In reply to sudden

Floridians calling Caribbean structures inferior

US buildings suffer immensely too from natural disasters - no matter what you do. The building codes attempt to account for the individual building as part of its surroundings by using 4 broad and somewhat vague categories of "exposures". That deficiency shows up all the time - and will do so again as Irma and company work their way through the US in the coming weeks.

The wind speed requirements are being refined all the time by the IBC (International Building Code), which is used over most of the US and Puerto Rico. I will have to look up the OECS Building Code.

 
Norm 2017-09-11 04:14:11 

In reply to Headley

I would give Sudden the tourist 'discount'.

Hahaha! Don't forget to slap the lawyer and Bajan discounts in his arse too. And no czechs either! smile smile

 
Norm 2017-09-11 04:16:14 

Looked up the OECS Building Code. Pretty rudimentary. Looks like most of the Caribbean has moved, or is moving, to the International Building Code.

 
mikesiva 2017-09-11 05:41:26 

In reply to sudden

Apples and oranges...the Floridians seem to be talking about houses in places like St Martin.

My aunt lived and worked in St Martin for years, both sides, and when she heard that Irma was barrelling down on that Dutch-French colony, she shook her head sadly. She then proceeded to tell me that the houses there are just as flimsy as the houses you find in Florida. Very few houses are made of concrete in St Martin.

She was similarly not impressed with the houses in Anguilla and their ability to resist hurricanes.

Clearly, not all Caribbean islands have the same traditions of building houses.

Interestingly, it seems that Antigua suffered very little damage from Irma. Can anyone speak to the construction of houses there?

 
Headley 2017-09-12 08:45:09 

This picture shows a very interesting feature. If you look at the one structure with no obvious damage you will notice that it has a hip roof.

Picture here

Correlation is not the same as causation, but as I mentioned above in this thread, hip roofs are recommended as being the best design to resist hurricane force winds. The steeper the angle the better.

 
Runs 2017-09-12 09:49:09 

In reply to Norm

Guyana seems very vulnerable and ill prepared for such natural disasters, what is your take on her cuz. cool

 
Norm 2017-09-12 14:30:33 

In reply to Runs

Guyana seems very vulnerable and ill prepared for such natural disasters

Hurricanes could hit Guyana, and it would be a complete disaster if that occurs. Most of the buildings are wooden and will not survive a hurricane. (Many would not survive even a tropical storm.) The storm surge will wipe whatever survives the wind.

The Guyana coast, for up to about 20 miles inland, is also very vulnerable to tsunamis. Currently the most likely cause would be the eruption of marine volcanoes near the Azores, which could occur anytime.

Buildings in Guyana are designed to survive the frequent flooding that accompanies the heavy rains (by being raised off the ground), but not hurricanes or earthquakes. A few of the large buildings, such as the Bank of Guyana (which has a steel frame and concrete walls) and Brickdam Cathedral should survive, but others like St George's Cathedral (made entirely of wood) would not.

 
Runs 2017-09-12 15:41:36 

In reply to Norm

Let's pray none of what you described ever happens. The government and citizens are not prepared and I shudder to even imagine the consequences. I have seen debates about it on social media hence my curiosity, some even said because we are close to the equator we are not in the hurricane belt. I am happy I can ask a qualified individual to get his expertise. Thanks. wink

 
Runs 2017-09-12 16:10:40 

Here is an ex WI cricketer opining. I am amazed at the hubris.

"Today I'm in support of all my premier League brothers. You are welcome to win as big as you like! So the Champions League gods can smile on us.
In other news hurricane experts from Guyana stop trying to show us what would happen. We are not close to the hurricane belt and we are very close to the equator which spells good news for us.
Best wishes goes out all those affected by Irma". lol

 
Norm 2017-09-12 18:35:52 

In reply to Runs
The remains of trees uprooted over large areas of the Essequibo Coast hundreds of years ago are still there. Also, Caracas was struck by a hurricane less than 100 years ago.

The ITCZ (Inter-tropical Convergence Zone) along the equator, which is supposed to keep hurricanes out of the approximately 10-degree belt centered on the equator, is not stable. Not to mention, Guyana's coast is just outside of it.

So, some folks will bury their heads in the sand about such matters. One hurricane or tropical storm is all it will take to set Guyana back about 500 years.

 
Runs 2017-09-12 19:29:28 

In reply to Norm

Amazing, thanks for the informative posts.
Taking back Guyana 500 years for a fresh restart may not be such a bad thing. lol