Wind Resistance of a Structure
With my many years of home construction background and building homes, I, along with many other home builders and remodelers, know the value of building a strong structure. Here in the southeast Houston Texas metro area we have a good amount of strong winds and with Houston being so close to the coast, we are even more vulnerable to hurricanes.
There are two forces a homeowner or anyone living in wind-prone areas of the USA should be aware and informed about. The first being “uplift force” and the other is “racking force” created from shear wind blowing directly at the home or structure.
The US Department of Agriculture
The Forest Products Laboratory (FPL) is the national research laboratory of the United States Forest Service. The FPL is part of USDA) US Department of Agriculture) and they conduct extensive testing and research on timber and building studies. They have published a study where plywood (or OSB) was added to the outside walls of the studs of a structure. The FPL (Forest Products Laboratory) study noted that they documented at least a 300% gain in stiffness and success in stopping any racking force from excessive wind force.
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration (NOAA) is a science-based federal agency within the Department of Commerce with regulatory, operational, and information service responsibilities and having a presence in every state of the country and territories. The NOAA has also conducted a study on ground level based shear wind or wind shear and noted the forces and pressure. When the NOAA was asked, “what is wind shear”?, they answered, “a change in horizontal wind speed and/or direction with height. Also known as a microburst, wind shears are a short-lived, ground-based, small-scale event and associated with thunderstorms”. Yep, that would be one aspect of weather experienced here in Texas!
Racking Force due to Wind Shear
The reason we are discussing Racking Force to a home due to Shear Wind in this siding post is because it is an important concern many homeowners should be aware of and considering when evaluating their home for high winds.
Right around the year 1999 here in Houston Texas many homeowners were being pitched and marketed to move away from vinyl siding and installing, in its place, fiber cement siding. The installation of this fiber cement (like HardiePlank) siding product often meant removing the old wood siding, stripping off the OSB or plywood sheathing down to the studs and installing the new fiber cement product. In the photo below, you can clearly see how builders across the country will often build diagonal, “let-in”, bracing (per the green arrows in the photo) into a home to help combat the racking force caused by shear wind.
Single Wall Construction – Non Wind Areas
Single wall construction is the method of installing the siding directly to the studs without any sheathing like OSB or plywood being attached first. Single wall construction with fiber cement siding is perfectly fine for non-wind/non-coastal areas of the country (as can be seen displayed in the photo below). However; for high wind areas, more than diagonal “let-in” bracing is needed as per Texas Department of Insurance TDI TDI Wind department hence, double wall construction with OSB or plywood sheathing is required to be installed before siding for added strength.
Double Wall Construction & Let-In Bracing
– Wind Prone Areas
The best practice of using the diagonal bracing will help stop any home from racking (tilting) when strong winds are blowing against the home. Builders will often install OSB or plywood over the outside of the walls by nailing them to the exposed studs as can be seen on the left side of the diagram below (labeled “Wind Areas/ Houston Double Wall Construction”). Once the OSB or plywood is installed, the builders will then install the siding over this plywood layer. By having this base layer, consisting of some type of OSB plywood, a product like LP Oriented Strand Board (OSB) or sheathing, attached to the the studs of any outside wall, will give the home increased strength and shear wind resistance to combat racking force. This method is called “double wall construction“.
Fiber Cement Hardie is Not Alone for Single Wall Construction
Coming from my many years of experience from using and my knowledge of fiber cement, I have found the product to have very little material structural strength and it can break quite easily. The product offers little structural support (if any) to the outside of a home and it can, in fact, be a liability. Don’t believe me, but try taking a hammer and moderately hitting the Fiber Cement siding to demonstrate for yourself how easily it breaks and crumbles to the ground.
I was in shock back in 1999, in Houston Texas ,as I observed (even participated in) siding contractors removing lap wood siding and T-111 vertical siding, later realizing this ultimately affected the structural value which had been an asset to the home. This product was then replaced with the installation of fiber cement without installing any OSB or plywood under it offering nearly no structural value to the home and taking away the stability it was providing.
The image on the right is of a home I had received a call on which was a “call back” from a homeowner on an installation by another siding contractor. The contractor had removed the old wood siding and had not install any OSB or plywood under the newly installed Fiber Cement.
As you can see, the result was that the home moved causing cracking of the fiber cement product and allowing water intrusion along with other problems for the homeowner.
This Houston TX homeowner will continue to have movement problems until all of the fiber cement siding has been removed and some sort of structural grade of sheathing is installed like OSB or plywood to help prevent the movement.
Keep in mind that this homeowner paid over 14k for a siding job that was done incorrectly and the contractor did not do them any favors. In Texas, homeowners often experience movement in their homes, this is yet another reason to install OSB or plywood sheathing prior to the fiber cement siding. Using this method of installing double wall construction will add more stability to Houston TX homes.
How to Install for Double Wall Construction
The diagram on the right displays how to correctly install the layers (sheathing like OSB or plywood – double wall construction) prior to installing the fiber cement siding. This process of installation will help increase any home’s structural value for both shear force, racking force wind and any settling movement by providing increased strength to the exterior walls of the home.
Keep in mind the importance of this layer and understand id is a much better re-siding approach for homeowners especially when removing old structural grade siding and installing fiber cement siding in its place to provide stability.
LP SmartSide Siding Best for Single Wall Construction
Double wall construction is the best way to build strength onto any outside wall for homes in coastal areas that are being sided with fiber cement siding products. Another options is LP SmartSide which is wood based and is a product that provides lot of, what wood works calls, structural value, something the fiber cement siding product does not provide.
One might want to keep in mind, that by not choosing to side your home with single wall construction, a propelled airborne object could quite easily penetrate right through the fiber cement siding, the insulation and sheet-rock, entering your home living space.
When building a home (or if you are re-siding your home and it has no OSB or plywood under the siding and was constructed using single wall construction), I recommend using the LP SmartSide Siding due to its proven brute strength. When you make this choice, you will rest assured that the SmartSide siding product is a great asset adding integrity to your home’s exterior walls helping to keep those that you love safer inside your home.
Additionally, with the SmartSide siding product, it is NOT necessary to install OSB or plywood sheathing under the the LP SmartSide product, it is NOT needed! Racking force from shear wind becomes much less of an issue due to the increased strength of the exterior walls with the LP SmartSide Siding which actually takes the place of OSB (or plywood) providing great structural value and it looks great too.
The must-see video below explains clearly what this means for your home. Fiber cement siding, is a great siding option. And please insist, if you are having the fiber cement product installed, that your siding contractor install double wall construction with OSB or plywood first for the what Wikipedia calls structural integrity of the building.
The moral of the story is:
Fiber Cement Siding Installed on Single Wall Construction = a Liability.
LP SmartSide Siding Installed on Single Wall Construction = an Asset.
Featured Video: Demonstration of LP SmartSide vs Fiber Cement Durability
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