wind mitigation

Wind Mitigation

Wind Mitigation

Wind mitigation techniques

Wind mitigation is the implementation of certain building techniques in order to limit damage caused by intense wind.

A Few Facts About Windstorms and Wind Insurance

  • In 2006, Citizens Insurance, one of the largest property insurers in Florida, requested a 45% rate increase for wind insurance. Other insurers took similar actions.
  • In Florida, the portion of a homeowner’s premium covering wind damage can be up to 70% of the total, depending on location.
  • Wind mitigation benefits homeowners, private insurers, and all levels of government.

Incentives for Wind Mitigation

  • In some states, homeowners can benefit from reduced insurance premiums. The Gulf Coast states, which are most prone to windstorm damage from hurricanes, have each considered mandating incentives to mitigate damage due to wind. Mississippi and Texas currently do not have such legislation, although Florida has been successful. Following Hurricane Andrew, Florida passed a law requiring insurance companies to offer their customers discounts and credits for existing building features and home improvements that reduce damage and loss from wind. In order to qualify for this discount, homes must undergo a certified home wind inspection. However, many Floridians do not know of this law.
  • Those with windstorm insurance can avoid a costly deductible. Deductibles for homes in hurricane-prone areas can exceed $20,000, meaning that mild to moderate wind damage might not be covered by insurance at all. If proper wind mitigation techniques have been used, these expenses can be avoided altogether.
  • Wind mitigation helps protect the home from damage. Even if a home is insured, it is always costly when a house is damaged, both for the homeowner and the insurer. Repairs can take months, especially during material shortages that follow massive destruction to entire communities, as was the case after Hurricane Katrina struck Louisiana.
  • Lenders in Florida require homeowners to carry windstorm insurance in order to be approved for a mortgage. Insurers may not provide windstorm insurance to homes that are vulnerable to wind damage.

Checklist for Wind Mitigation Techniques:

  • garage doors:  These commonly fail during windstorms due to:
    • inadequate door-track strength and mounting systems; and
    • flimsy metal panels.

The following features can protect a garage door from wind damage:

    • no windows;
      • track brackets that are securely attached to the wall; and
  • horizontal and/or vertical reinforcementAreas of high and low pressure can cause roof failure on all panels.
  • opening protection:  Glass doors and windows should be replaced with impact-resistant glass. They should be structurally attached to the building in order to prevent the entire window from popping out of its frame. Sliding glass doors are especially vulnerable to flying debris due to their large expanse. Once an opening is created during a windstorm, the pressure within the house can rise high enough to cause the roof to fail in areas of low pressure. The picture to the right demonstrates how these areas of low pressure can form.
  • roof covering: There are many kinds of roof covering materials, and some resist wind damage better than others. The most common roof covering materials in Florida are composition shingles and tiles. A key factor in roof covering performance is the method of attachment of the roof covering material to the roof deck. Nails, not staples, should be used to fasten these materials.
  • roof shape:  “Roof shape” refers to the geometry of the roof, rather than the type of roof covering. The end-walls of gable roofs extend vertically to the sloping roof line. These gable end-walls, if not properly built or braced, have been known to fail outward due to the negative suctions on the wall. Additionally, field testing has shown that hip roofs receive up to 40% less pressure from wind than gable roofs.
  • roof deck attachment:  According to insurance claim data, a house becomes a major loss once the roof deck fails, even partially. The most common roof deck types are plywood and OSB. The most important feature of the roof deck by far is the attachment to the framing compared to the deck’s thickness. The following building techniques can help prevent wind damage:
    • roof coverings using shingles that meet the FBC requirements;
    • roof decks that have been installed with large nails and close spacing;
    • hurricane clips/straps that hold the roof structure to the walls; and
    • protection of windows and glass doors with impact-resistant glazing or other protection systems.
  • roof-to-wall connections:  This connection is a critical safeguard that keeps the roof attached to the building and acts to transfer the uplift loads into the vertical walls. This connection is crucial to the performance of the building due to the large negative pressures acting on the roof. Proper installation is essential to connector performance.
  • secondary water resistance: This is a layer of protection that shields the home in the event that the roof covering fails. It will reduce leakage if the shingles are blown off. A secondary water barrier is relatively rare in homes. The two most common types are:
    • self-adhering modified bitumen underlayment, which is applied to the exterior of all joints; and
  • foam seal, which is sprayed onto the underside of the decking.
In summary, wind mitigation is a strategy designed to limit the amount of wind damage inflicted on a structure. Various incentives are in place to motivate homeowners to implement these enhancements, and qualified inspectors can determine which improvements are necessary.
Home inspection

A Garage Inspection

A Garage Inspection

by Kenton Shepard

Above:  garage exterior

This is the exterior of a town-home I was asked to inspect. During the garage inspection, I ran into a neighbor who told me that the roof of another garage, identical to the one pictured above two buildings down, had collapsed the previous winter under a snow load.

So, I decided to keep my eyes wide open as I went through the garage.

Above:  trusses and truss connections
Some defects you have to search for, and some are pretty obvious. These first two defects were obvious from the doorway:
  • improper alterations; and
  • improper bearing points.

Trusses cannot be altered in any way without the approval of a structural engineer. When you see plywood gussets added at truss connections like these triangular gussets, then an alteration of some sort has obviously been made and you have to recommend evaluation by a structural engineer.  So, that condition went into the report

Trusses are designed to bear loads at very specific points. Typical roof trusses should not touch any interior walls and should bear only on the exterior walls. The two trusses at the left of the above photo are bearing on an offset portion of the garage wall.

A portion of the structural roof load was being transferred to the bottom chords of the trusses at a point at which they were not designed to support a load.

Above:  the connection
Then I walked over and looked more closely at the connections where the trusses attached to the wall and found these problems:
  • inadequate metal connector (hanger);
  • inadequate fasteners (deck screws); and
  • improper fastener installation (through drywall).

These trusses would have best been supported by bearing directly on wall framing. The next best solution would be an engineer-designed ledger or engineer-specified hardware. And that may have been how they were originally built, but by the time I inspected them, 24-foot roof trusses were supported by joist hangers designed to support 2×4 joists. The hangers were fastened with four gold deck screws each.

Gold deck screws are designed to resist withdrawal. Fasteners for metal connecters such as joist hangers are designed to resist shear.

Withdrawal force is like the force which would be generated if you grabbed the head of a fastener with pliers and tried to pull it straight out.

Shear force is what’s used if you take a pair of heavy-duty wire cutters and cut the fastener. Fasteners designed to resist withdrawal, such as deck screws, are weak in shear resistance.

So, there were drastically undersized metal connectors fastened by badly under-strength fasteners.

To make matters worse, the screws were fastened through drywall, which doesn’t support the shaft of the screw and degrades the connection even further.

Above:  gang nail integrity destroyed

And, once I looked really closely, I found more truss alterations. The gang nail had been pried loose and the spikes which form the actual mechanical connection were destroyed. In their place were a couple of bent-over nails. This condition represented a terrific loss of strength and this roof, too, was a candidate for catastrophic structural failure.
In summary,during a garage inspection look carefully at connections for problems which may lead to structural issues, as some are more urgent than others.  Be sure to call these out in your report.  Also, all electrical receptacles in garages must be GFCI-protected, without exception.

Drywall Identification And Using XFR Techniques

X-ray fluorescence (XRF) is an analytical method using emission spectroscopy to identify the presence of specific elements in most materials.  Every element has a unique emission signature, making it possible to quantify the presence of an element by the relative strength of the emission.  Instrumentation has evolved to the point where hand-held XRF can be used in the field for drywall identification. While X-ray fluorescence is a very accurate and reliable instrumentation-based method for quantitative analysis of chemical elements, it should not be used as the sole identifier of toxic or Chinese drywall.  To identify problem drywall, XRF is used to target the alkali earth element, strontium, as the primary identifier of problem drywall.  There is no doubt the XRF will determine the accurate level of strontium in the wall section being scanned.  However, there are several chemistry-related considerations that should force us to take a closer look at using only strontium content as the flag for identification of problem drywall.

Drywall Identification

What is Strontium?Strontium
Strontium is a relatively plentiful element on Earth. Strontium-containing minerals, such as strontianite (strontium carbonate) and celestite (strontium sulfate), may be found in various concentrations in natural gypsum deposits. Natural gypsum is used in the production of drywall.  Therefore, drywall will often have some strontium present at varying levels.
Strontium is commonly used in paints and coatings for a variety of purposes.  Here are a few examples:
  • Strontium frequently replaces lead as a paint drier.
  • Strontium is used in yellow, blue, red and white pigments.
  • Strontium aluminate is used in glow-in-the-dark coatings, wallpapers and adhesive stickers.
  • Strontium chromate, borate and metaborate are also used in anti-corrosion additives, flame retardants, and anti-microbial agents in paints and coatings.  Therefore, it is conceivable that XRF readings for strontium could vary from room to room and even from wall to wall due to differing layers of paint.
Is Strontium to Blame?
The EPA, the University of Florida, and other entities have published reports suggesting that strontium sulfide is a possible source of the corrosive sulfur gasses emanating from problem drywall.  The difficulty with this scenario is that the chemical reactions do not work neatly using strontium sulfide as the source of corrosive and toxic gasses.  Strontium sulfide is a stable compound that is insoluble in water.  The generation of hydrogen sulfide gas from strontium sulfide requires reaction with an acid. Since drywall maintains a neutral-to-alkaline pH, it is difficult to calculate how the acid reaction will occur with the mere presence of humidity in the air.
Additionally, testing results from hundreds of known problem drywall specimens accumulated by the Exterior Design Institute report that problem drywall is typically ten times more alkaline than non-problem drywall.  The alkaline pH makes the generation of hydrogen sulfide gas from strontium sulfide even less likely.  There is more empirical data that indicates that strontium sulfide is not the source of the corrosive gasses.  The additional data lies in the fact that a known percentage of drywall specimens with high levels of strontium do not produce corrosive gasses.  Further proof lies in the number of drywall specimens with low strontium levels, which do produce corrosive gasses, according to the Building Envelope Science Institute (BESI).
What this means is that strontium is probably not present in the chemical that is producing the corrosive gasses.  Although high strontium levels have been found in a majority of problem drywall, by itself, strontium cannot be a 100%-conclusive indicator of problem drywall.   The strontium is more likely a marker or “ride-along” component in most problem drywall.  In the earlier days of identifying problem drywall, there was a test for elemental sulfur because it was believed to be the cause of the corrosive gasses. We have since discovered that, although elemental sulfur is present in many problem drywall samples, it is not the cause of the gasses. As a result, the presence of elemental sulfur was determined not to be a 100%-reliable indicator of problem drywall. The same appears to be true of strontium.

Summary

The XRF method tests for strontium, which:
  1. is naturally present in the drywall core;
  2. is commonly present in wall paints; and
  3. is NOT the proven source of the corrosive gasses.

To use the XRF method as a stand-alone tool to positively identify problem drywall makes no more sense than to use an X-ray machine as a stand-alone instrument to diagnose cancer.  There is no basis in science or experience to support its use as a stand-alone method.  There is a basis in science and experience to support the use of XRF as a highly reliable screening method for drywall identification.

Conclusion

While the XRF method is both fast and non-destructive, it should only be used in concert with complementary problem drywall-testing protocols and trained drywall identification. It is clear that the real benefit of the XRF method is as a very efficient and highly reliable, non-destructive screening tool.

 *****************************************************
by Nick Gromicko, CMI® and Dennis Rose
Nick Gromicko is founder of the International Association of Certified Home Inspectors and the executive director of the International Association of Certified Indoor Air Consultants.
Dennis L. Rose is an industrial chemist and president of D. L. Rose and Associates, LLC, in Ocala, Florida.
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