would concrete roofs help in hurricanes?

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link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 7:13:11 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 7:20:43 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 7:22:45 PM 
In reply to camos
the movement is driven by environmental concerns.

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

link Dan_De_Lyan Joined: Jun 3, 2008
Posts: 7407
9/10/17 7:35:45 PM 
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.

link black Joined: Feb 28, 2004
Posts: 26845
9/10/17 7:42:16 PM 
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?

link Dan_De_Lyan Joined: Jun 3, 2008
Posts: 7407
9/10/17 7:48:09 PM 
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.

link camos Joined: May 6, 2003
Posts: 45295
9/10/17 7:50:15 PM 
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?

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 7:56:57 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 8:04:19 PM 
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!

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 8:07:28 PM 
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.

link Dan_De_Lyan Joined: Jun 3, 2008
Posts: 7407
9/10/17 8:11:18 PM 
In reply to Norm

like dubai...kudos to the leaders there

link sudden Joined: Nov 27, 2006
Posts: 33483
9/10/17 8:15:14 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 8:29:13 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 8:39:12 PM 
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.

link sudden Joined: Nov 27, 2006
Posts: 33483
9/10/17 8:59:26 PM 
Interesting. Floridians calling Caribbean structures inferior Link Text

link Headley Joined: Dec 2, 2007
Posts: 6967
9/10/17 9:46:38 PM 
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

link Ewart Joined: Mar 5, 2005
Posts: 8943
9/10/17 9:56:20 PM 
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.


//

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 10:24:18 PM 
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!

link Headley Joined: Dec 2, 2007
Posts: 6967
9/10/17 10:27:41 PM 
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

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 10:36:12 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/11/17 4:14:11 AM 
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

link Norm Joined: Nov 28, 2002
Posts: 22546
9/11/17 4:16:14 AM 
Looked up the OECS Building Code. Pretty rudimentary. Looks like most of the Caribbean has moved, or is moving, to the International Building Code.

link mikesiva Joined: Jan 12, 2007
Posts: 29167
9/11/17 5:41:26 AM 
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?

link Headley Joined: Dec 2, 2007
Posts: 6967
9/12/17 8:45:09 AM 
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.

link Runs Joined: Jan 4, 2003
Posts: 46030
9/12/17 9:49:09 AM 
avatar image
In reply to Norm

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

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