Following on from my last post on construction for hurricane protection I have a few more tips but this time for wall construction using concrete blocks (concrete masonry units - cmu).
This type of construction is very common in the Caribbean and southern Florida due to the higher hurricane resistance of this type of construction.
In order to ensure that your hurricane resistance is maximised first and foremost a qualified structural engineer should work with your contractor to confirm proper practice is adhered to. As a client however there are a few things you can look out for as major red flags. it is vital that your roof structure is properly connected to your walls. This is usually done using a capping beam and reinforcement in the block holes approximately every 4th block hole in non loadbearing walls and in each hole for walls carrying heavy loads. If this is not the case on your site ask a question of your contractor and/or your engineer.
Your wall reinforcement should continue all the way to the foundation and tie in correctly there as well. It is also good practice to include stirupps in the corners and wall intersections and to reinforce and pour all block holes in these areas. This will cause your corners to act like columns and bring greater stiffness and strength to your structure.
How To Build Your Home To Resist Extreme Wind Events
In my previous post I mentioned two major considerations in hurricane resistance. Today I will tackle the final piece of the puzzle.
The shape and type of roof is a third factor which affects how resistant a home is to extreme wind events. A few design characteristics make a roof more susceptible.
First of these is the slope. A flatter sloped roof increases suction on the roof as air passes over it in the same way an aircraft wing would. This uplift is capable of ripping the sheets or removing the entire roof. Roof pitch should therefore ideally be in the region of 15 to 20 degrees of slope.
Secondly, the amount of overhang at the edges (or eave) can also make a roof easier for the wind to lift. Overhangs should be limited to 12 to 18 inches to reduce the likelihood of this occurring.
While these tips should shed some light on what you ought to look for in a good design they are in no way exhaustive and should not prevent you from engaging an engineer to provide additional details to ensure that your structure is safe during hurricanes.
How build your home to resist extreme wind events
We’ve all see the post hurricane photos like the one above shot in Miami, Florida or Galveston, Texas or any of the islands of the Caribbean. Homes flattened by hurricane force winds. Sadly, many of the structures, especially those in lesser developed countries, really weren’t constructed to resist the winds that they should be able to. What makes it even more sad is that these buildings can be constructed to withstand most winds.
One place where buildings fail in high winds is the roof and this failure can occur in many ways.
1. Connection Failure
A connection failure is a failure of the fasteners which hold your roof together. Roofs of buildings in hurricane prone areas should be held together with hurricane straps at the appropriate areas, the roof eave and peak/ridge. You should insist that your builder install these at the appropriate areas.
The builder must also install fasteners to connect the roofing material to the structure of the roof. These fasteners should be structural screws or any fastener designed against pull-out.
2. Material failure
The materials used in a roof must be chosen to be compatible and strong enough to resist hurricane winds. In the Caribbean islands we are fortunate enough to have access to south american hardwood like purple/green-heart which is much stronger than southern pine. If Galvanised sheets are used these must be of the correct thickness to prevent the roof fasteners from just pulling right out.
3. Design… (to be cont’d)