would concrete roofs help in hurricanes?

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link sudden Joined: Nov 27, 2006
Posts: 33483
9/10/17 11:08:11 AM 
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?

link bravos Joined: Oct 14, 2009
Posts: 33425
9/10/17 11:28:20 AM 
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...

link sudden Joined: Nov 27, 2006
Posts: 33483
9/10/17 11:36:38 AM 
In reply to bravos

explain, mate?

link bravos Joined: Oct 14, 2009
Posts: 33425
9/10/17 11:55:38 AM 
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..

link sudden Joined: Nov 27, 2006
Posts: 33483
9/10/17 12:20:01 PM 
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.

link bravos Joined: Oct 14, 2009
Posts: 33425
9/10/17 12:38:19 PM 
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.

link pelon Joined: Mar 22, 2008
Posts: 6268
9/10/17 12:43:43 PM 
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)

link mikesiva Joined: Jan 12, 2007
Posts: 29167
9/10/17 12:44:03 PM 
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.

link birdseye Joined: Mar 24, 2004
Posts: 32635
9/10/17 12:46:10 PM 
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

link sgtdjones Joined: Feb 16, 2017
Posts: 2691
9/10/17 1:11:17 PM 
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

link pelon Joined: Mar 22, 2008
Posts: 6268
9/10/17 1:25:43 PM 
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....

link bravos Joined: Oct 14, 2009
Posts: 33425
9/10/17 2:55:07 PM 
In reply to birdseye

Yep..

link bravos Joined: Oct 14, 2009
Posts: 33425
9/10/17 2:55:14 PM 
In reply to pelon

cool

link sgtdjones Joined: Feb 16, 2017
Posts: 2691
9/10/17 3:27:33 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 3:54:06 PM 
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.

link Chrissy Joined: Nov 14, 2002
Posts: 145319
9/10/17 4:17:05 PM 
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In reply to sudden

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

link sudden Joined: Nov 27, 2006
Posts: 33483
9/10/17 5:02:17 PM 
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

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 6:15:52 PM 
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.

link Dan_De_Lyan Joined: Jun 3, 2008
Posts: 7407
9/10/17 6:35:08 PM 
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.

link camos Joined: May 6, 2003
Posts: 45295
9/10/17 6:35:24 PM 
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.

link camos Joined: May 6, 2003
Posts: 45295
9/10/17 6:37:22 PM 
In reply to Dan_De_Lyan

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

link black Joined: Feb 28, 2004
Posts: 26845
9/10/17 6:41:36 PM 
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

link camos Joined: May 6, 2003
Posts: 45295
9/10/17 6:48:16 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 6:50:20 PM 
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.

link Norm Joined: Nov 28, 2002
Posts: 22546
9/10/17 7:05:25 PM 
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.

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