Building Cavities Used as Supply or Return Ducts - One Source Real Estate Inspection your certified home inspector @ www.onesourceinspection.com

Building Cavities Used as Supply or Return Ducts

by Nick Gromicko and Ben Gromicko

Nearly all building codes restrict the use of cavity spaces as supply ducts. However, it has been common practice to use cavity spaces as return-air pathways. Building cavities used as return-air plenums is one of the leading causes of duct leakage in homes today. Inspectors can learn how air leakage from ductwork may cause home energy loss, increase utility bills, lower comfort levels, and make the HVAC system less efficient. 

 

Still commonly used is the panned floor joist. Using floor joists as return ducts by panning can cause leakage because negative pressure in the cavity will draw air from the outside into the cavity through the construction joints of the rim area at the end of the joist cavity.

The illustration above shows a floor joist cavity used as a return-air duct by nailing material, such as gypsum board, sheet metal, foil insulation or OSB, to the bottom of the floor joists. There are manufacturers that advertise “insulating” panning sheet products that aid in this practice; however, using panned floor joists as an HVAC air pathway is highly discouraged because air leakage will be very difficult, if not impossible, to prevent.

Some builders create pan joists by attaching a solid panning sheet material to the bottom of a floor joist to create a return-air pathway. Using panned joists is not the best practice because the return-air pathways cannot be air-sealed properly. 

Wall Cavities

Cavities (or interstitial spaces) within walls are also sometimes used as supply- or return-air pathways. These cavities often create a connection of inside air with outside air from an attic or crawlspace. It is very difficult to make such cavity spaces airtight. When cavity spaces are used as return-air pathways or supply-air ducts, a few issues will arise.

Because cavity spaces are leaky, building pressure imbalances across the building envelope will occur, driving air infiltration into the building. A cavity space used as a return-air pathway will pull pollutants into the building from unknown sources. Another issue with using cavity spaces as return-air pathways is fire safety. Building materials, such as wood products, do not meet the flame- and smoke-spread criteria as do approved duct materials. Using cavities as return or supply ducts is not a fire hazard in itself, but it will encourage a fire to spread throughout the building. In humid climates, a cavity space used as a return-air pathway will pull humid air into the cavity space, possibly encouraging mold growth or the deterioration of building materials.

Other common framing cavities used as return-air pathways or plenums are air-handler platforms, open-floor truss cavities, and dropped ceilings. Open-floor trusses used as return-air plenums can draw air from any place connected to that floor. Air-handler platforms used as return-air plenums can draw air from vented attics and crawlspaces through other connected framing cavities. While none of these spaces makes an acceptable air pathway on its own, some building cavities, such as floor joists, can make acceptable duct chases to contain an insulated, air-sealed, metal, or flex supply or return duct.

How to Use Building Cavities as Duct Chases for Supply and Return Pathways

1. The builder must plan the duct layout at the design stage. Floor joist cavities, dropped-ceiling soffits, or other building cavities that will be used as duct chases should be indicated. Required duct sizes using ACCA Manual D (ACCA 2009) must be calculated. The cavity spaces must be free of obstructions and large enough to hold the duct plus insulation.

 Floor joist cavities can make acceptable duct chases for insulated, air-sealed metal, flex, or fiberboard ducts. See the illustration by the U.S. Department of Energy below.
2. Only approved duct materials, such as galvanized steel, aluminum, fiberglass duct board, and flexible duct, that meet local code smoke- and flame-spread criteria must be used. 
3. All supply- and return-duct connections should be sealed with mastic or approved tape.
4. Because ductwork in cavity spaces is likely to be inaccessible, the duct system for airtightness should be tested with a duct-blaster test before installing the drywall.

Duct Distribution Quality Installation

Building cavities used as supply or return ducts should be avoided because of the difficulty of properly air sealing and insulating them.

If building cavities are used, insulation should be installed without misalignments, compressions, gaps, or voids in all cavities used for ducts. If non-rigid insulation is used, a rigid air barrier or other supporting material should be installed to hold insulation in place. All seams, gaps and holes of the air barrier should be sealed with caulk or foam.

According to the U.S. Department of Energy's ENERGY STAR program, if building cavities are used as supply and return ducts, then:

• Supply ducts in an unconditioned attic must have insulation equal to or greater than R-8.
• Supply ducts in an unconditioned attic must have insulation equal to or greater than R-6.
• All other supply ducts and all return ducts in unconditioned spaces must have insulation equal to or greater than R-6.
• Total rater-measured duct leakage must be equal to or less than 8 CFM25 per 100 square feet of conditioned area.
• Rater-measured duct leakage to the exterior must be equal to or less than 4 CFM25 per 100 square feet of conditioned floor area.
• Duct leakage shall be determined and documented by a rater using RESNET-approved testing protocol only after all components of the system have been installed (e.g., air handler and register grilles). Leakage limits shall be assessed on a per-system (rather than per-home) basis.
• For homes that have 1,200 square feet or less of conditioned floor area, measured duct leakage to the outdoors shall be equal to or less than 5 CFM25 per 100 square feet of conditioned floor area. Testing of duct leakage to the outside can be waived if all ducts and air-handler equipment are located within the home’s air and thermal barriers, and envelope leakage has been tested to be less than or equal to half of the Prescriptive Path infiltration limit for the Climate Zone where the home is to be built. Alternatively, testing of duct leakage to the outside can be waived if total duct leakage is equal to or less than 4 CFM25 per 100 square feet of conditioned floor area, or equal to or less than 5 CFM25 per 100 square feet of conditioned floor area for homes that have less than 1,200 square feet of conditioned floor area.

Duct Installation Tips

ENERGY STAR requires that all ducts in exterior walls must be within the air barrier as well as the thermal boundary. It is important for the framer and HVAC contractor to coordinate on the location of a return duct. This allows for proper spacing of the floor or roof structure for installation of the return. If installing supply ducts within the walls, verify that the duct is capable of outputting the necessary air flow. Typically, only double-wall assemblies will have enough depth to allow for proper insulation and duct size. If installing return ducts using the floor or ceiling structure, ENERGY STAR recommends sealing both the exterior and the interior of all return boxes to prevent air leakage.

2009 IECC

Section 403.2.3 Building cavities (Mandatory). Building framing cavities cannot be used as supply ducts. Section 403.2.1 Insulation (Prescriptive). Supply ducts in attics are insulated to a minimum of R-8. All other ducts in unconditioned spaces or outside the building envelope are insulated to at least R-6.

2009 IRC

Section M1601.1.1 Above-ground duct systems. Stud wall cavities and spaces between solid floor joists cannot be used as supply-air plenums.

2012 IECC

Section R403.2.3 Building cavities (Mandatory). Building framing cavities cannot be used as supply ducts or plenums. Section R403.2.1 Insulation (Prescriptive). Supply ducts in attics are insulated to a minimum of R-8. All other ducts in unconditioned spaces or outside the building envelope are insulated to at least R-6.

2012 IRC

Section M1601.1.1 Above-ground duct systems. Stud-wall cavities and spaces between solid floor joists cannot be used as supply-air plenums. Stud-wall cavities in building envelope exterior walls cannot be used as air plenums.

 

Here's a joist cavity being used as a supply duct.

Here's a joist cavity with a disconnected duct. It has dropped down from the floor.

 

Here's the interior of an insulated duct.

 

Here's the interior of a joist cavity being used as a supply duct.

Here's a joist cavity being used as the main return duct. This is also the location of the air filter.

This is a panned floor joist cavity being used as supply duct.

 

Drainpipes should not pass through ductwork. 

 

This ceiling register was part of a return duct that used the floor joist cavity above.

 

This is a panned floor joist cavity being used as a return duct.

 

Here are two joist cavities above the central I-beam being used as part of a main supply duct to the second floor.

Here's a floor joist cavity being used as a return duct.

 

Here's a floor joist cavity being used as a return duct. The rest of the duct was never installed and connected to the HVAC system.

Here's a floor joist cavity being used as a supply duct.

Summary

Minimizing air leakage from ductwork can help reduce home energy loss, lower utility bills, increase comfort levels, and make the HVAC system operate more efficiently. Recognized and acceptable duct materials should be used for all HVAC airways. Acceptable duct materials include galvanized steel, aluminum, fiberglass duct board, and flexible duct. The duct layout should be considered in the initial framing design stage. Building cavity space alone should not be used as a supply- or return-air pathway. For the cavity to serve as a supply- or return-air pathway, it must contain a sealed, insulated duct made of approved duct materials. A duct-blaster test can be used to detect duct leakage and to confirm proper air flow at each duct supply outlet.

From Building Cavities Used as Supply or Return Ducts - InterNACHI http://www.nachi.org/building-cavities-supply-return-ducts.htm#ixzz30PKc8vRS

Non-Conforming Bedrooms

by Nick Gromicko

 

 

A room must conform to specific requirements in order for it to be considered a bedroom or sleeping room. The reason for this law is that the inhabitant must be able to quickly escape in case of fire or another emergency.

 

Why would a homeowner use a non-conforming room as a bedroom?  Some of the reasons include:

• to earn money from it as a rental. While they run the risk of being discovered by the city, landlords will profit by renting out rooms that are not legally bedrooms;
• to increase the value of the home. All other considerations being equal, a four-bedroom house will usually sell for more than a three-bedroom house; and
• lack of knowledge of code requirements. To the untrained eye, there is little obvious difference between a conforming bedroom and non-conforming bedroom. When an emergency happens, however, the difference will be more apparent. If you have any questions about safety requirements, ask your InterNACHI inspector during your next scheduled inspection.

Homeowners run serious risks when they use a non-conforming room as a bedroom. An embittered tenant, for instance, may bring their landlord to court, especially if the tenant was forced out when the faux bedroom was exposed. The landlord, upon being exposed, might choose to adjust the bedroom to make it code-compliant, but this can cost thousands of dollars. Landlords can also be sued if they sell the home after having advertised it as having more bedrooms than it actually has. And the owner might pay more than they should be paying in property tax if they incorrectly list a non-conforming bedroom as a bedroom. Perhaps the greatest risk posed by rooms that unlawfully serve as bedrooms stems from the reason these laws exist in the first place:  rooms lacking egress can be deadly in case of an emergency. For instance, on January 5, 2002, four family members sleeping in the basement of a Gaithersburg, Maryland, townhome were killed by a blaze when they had no easy escape.

The following requirements are taken from the 2006 International Residential Code (IRC), and they can be used as a general guide, but bear in mind that the local municipality determines the legal definition of a bedroom. Such local regulations can vary widely among municipalities, and what qualifies as a bedroom in one city might be more properly called a den in a nearby city. In some municipalities, the room must be above grade, be equipped with an AFCI or smoke alarm to be considered a conforming bedroom, for instance. Ceiling height and natural lighting might also be factors. The issue can be extremely complex, so it’s best to learn the code requirements for your area. Nevertheless, the IRC can be useful, and it reads as follows:

• EMERGENCY ESCAPE AND RESCUE REQUIRED SECTION: R 310.1 Basements and every sleeping room shall have at least one operable emergency and rescue opening. Such opening shall open directly into a public street, public alley, yard or court. Where basements contain one or more sleeping rooms, emergency egress and rescue openings shall be required in each sleeping room, but shall not be required in adjoining areas of the basement. Where emergency escape and rescue openings are provided, they shall have a sill height of not more than 44 inches (1,118mm) above the floor. Where a door opening having a threshold below the adjacent ground elevation serves as an emergency escape and rescue opening and is provided with a bulkhead enclosure, the bulkhead enclosure shall comply with SECTION R310.3. The net clear opening dimensions required by this section shall be obtained by the normal operation of the emergency escape and rescue opening from the inside. Emergency escape and rescue openings with a finished sill height below the adjacent ground elevation shall be provided with a window well, in accordance with SECTION R310.2.  
  • MINIMUM OPENING AREA: SECTION: R 310.1.1 All emergency escape and rescue openings shall have a minimum net clear opening of 5.7 square feet (0.530 m2). Exception: Grade floor openings shall have a minimum net clear opening of 5 square feet (0.465 m2).
  • MINIMUM OPENING HEIGHT: R 310.1.2 The minimum net clear opening height shall be 24 inches (610mm).
  • MINIMUM OPENING WIDTH: R 310.1.3 The minimum net clear opening width shall be 20 inches (508mm).
  • OPERATIONAL CONSTRAINTS: R 310.1.4 Emergency escape and rescue openings shall be operational from the inside of the room without the use of keys or tools or special knowledge.
    
• WINDOW WELLS: SECTION: R310.2 The minimum horizontal area of the window well shall be 9 square feet (0.9 m2), with a minimum horizontal projection and width of 36 inches (914mm). The area of the window well shall allow the emergency escape and rescue opening to be fully opened. Exception: The ladder or steps required by SECTION R 310.2.1 shall be permitted to encroach a maximum of 6 inches (152mm) into the required dimensions of the window well.
  
• LADDER AND STEPS: SECTION: R 310.2.1 Window wells with a vertical depth greater than 44 inches (1,118mm) shall be equipped with a permanently affixed ladder or steps usable with the window in the fully open position. Ladders or steps required by this section shall not be required to comply with SECTIONS R311.5 and R311.6. Ladders or rungs shall have an inside width of at least 12 inches (305 mm), shall project at least 3 inches (76mm) from the wall, and shall be spaced not more than 18 inches (457mm) on-center vertically for the full height of the window well.

• BULKHEAD ENCLOSURES: SECTION: R 310.3 Bulkhead enclosures shall provide direct access to the basement. The bulkhead enclosure with the door panels in the fully open position shall provide the minimum net clear opening required by SECTION R 310.1.1. Bulkhead enclosures shall also comply with SECTION R 311.5.8.2.

• BARS, GRILLS, COVERS, AND SCREENS: SECTION: R 310.3 Bars, grilles, covers, screens or similar devices are permitted to be placed over emergency escape and rescue openings, bulkhead enclosures, or window wells that serve such openings, provided the minimum net clear opening size complies with SECTIONS R 310.1.1 to R 310.1.3, and such devices shall be releasable or removable from the inside without the use of a key, tool, special knowledge, or force greater than that which is required for normal operation of the escape and rescue opening.

• EMERGENCY ESCAPE WINDOWS UNDER DECKS AND PORCHES: SECTION: R 310.5 Emergency escape windows are allowed to be installed under decks and porches, provided the location of the deck allows the emergency escape window to be fully opened and provides a path not less than 36 inches (914 mm) in height to a yard or court.

In summary, non-conforming bedrooms are rooms that unlawfully serve as bedrooms, as the occupant would lack an easy escape in case of emergency.

 

One Source Real Estate Inspection your local certified home inspector @ www.onesourceinspection.com.

From Non-Conforming Bedrooms - InterNACHI http://www.nachi.org/non-conforming-bedrooms.htm#ixzz2z7SlkDM7

Plants and Indoor Air Quality - One Source Real Estate Inspection your certified home inspector @ www.onesourceinspection.com.

Plants and Indoor Air Quality

by Nick Gromicko and Kate Tarasenko

 

 

Raising plants indoors is a home-healthy move because of their ability to clean the air of carbon dioxide, but their benefits don't stop there. According to several studies, the average houseplant can remove formaldehyde, benzene, and a host of other toxins that plague typical indoor air.

 

It may come as a surprise, but indoor air is often much more polluted than the air outside. Off-gassing from paints, adhesives, and even unsuspected items, such as clothing and tap water, infuse the air we breathe will a host of chemicals, many of which are proven carcinogens. Newer, tighter homes are especially problematic, since they limit the amount of fresh air that can make its way into the interior. Compound this with the average time that citizens of developed nations spend indoors –- approximately 90% -– and the need for remediation becomes clear. Answering this need can be as simple as the addition of green, leafy plants to the living space.

 

Interesting Facts

• Removal of environmental airborne toxins with the aid of plants is called phytoremediation.
• Plants can reduce stress, increase work performance, and reduce symptoms of ill health.

Study Performed by NASA

While researching the ability of plants to cleanse air in space stations, NASA made some fascinating and important discoveries concerning the role that houseplants play here on Earth. They tested the ability of a variety of plants to remove common volatile organic compounds (VOCs) from the air. The toxins tested include:

• benzene:
  • found in petroleum-based indoor coatings, gasoline, inks, oils, paints, plastics, rubber, cleaning solutions, plastics, and exterior exhaust fumes emanating into  buildings;
  • an irritant and probable carcinogen. Inhalation of benzene has been reported to cause dizziness, weakness, euphoria, headache, nausea, blurred vision, respiratory diseases, tremors, irregular heartbeat, liver and kidney damage, paralysis and unconsciousness.
• trichloroethylene (TCE):
  • found in a wide variety of products, such as inks, paints, lacquers, varnishes and adhesives;
  • is a potent liver carcinogen.
• formaldehyde:
  • found in virtually all indoor environments due to its widespread use in many kinds of products. Specifically, it may be found in:
    • urea-formaldehyde foam insulation (UFFI), particleboard and pressed-wood products;
    • paper products, such as grocery bags, waxed papers, facial tissues and paper towels;  
    • common household cleaning agents;
    • stiffeners, wrinkle-resisters, water-repellents, fire-retardants and adhesive binders in floor coverings, carpet backings and permanent-press clothes; and
    • heating and cooking fuels, such as natural gas and kerosene, and cigarette smoke.
  • Formaldeyde causes watery eyes, nausea and wheezing. More seriously, the chemical is classified as carcinogenic to humans by the International Agency for Research on Cancer.
• toluene:
  • found in adhesives, disinfectants, rubber, printing ink, lacquers, and leather tanners;
  • Symptoms in low doses include sleepiness, confusion, weakness, memory loss, nausea, loss of appetite, and hearing and color-vision loss. High levels of toluene may cause light-headedness, unconsciousness, and death.

In the NASA testing, flowering plants, such as chrysanthemums and gerbera daisies, effectively removed benzene from the chamber's atmosphere. Golden pothos, spider plants and philodendron were the most effective in removing formaldehyde molecules. Other top performers were red-edged dracaena and the Peace Lilly. The rest of the plants tested, with the exception of Chinese evergreen (Aglaonema modestum), were effective at removing at least one of the chemicals from the air. NASA researchers found that plants absorb airborne substances through tiny openings in their leaves, but roots and soil bacteria are also part of the purification process.

The study concluded that in an 1,800-square-foot house, occupants should incorporate 15 to 18 houseplants in 6- to 8-inch diameter containers to improve air quality. The larger and more vigorously they grow, the better. 

India Study

The government of India published the results of a groundbreaking study in September of 2008 that analyzed the effects of certain species of plants on indoor air quality. Three plant species –- areca palm, pothos (known as Mother-in-Law's Tongue), and the Money Plant -– were tested for 15 years at the Paharpur Business Centre and Software Technology Incubator Park in New Delhi. The building was 20 years old and 50,000 square feet, and it housed more than 1,200 plants for 300 workers. The study found that the building had the healthiest indoor air in the city. Specifically, compared to other buildings in New Delhi, the building showed reductions of:

• eye irritation by 52%;
• respiratory conditions by 34%;
• headaches by 24%;
• lung impairment by 12%; and 
• asthma by 9%.

In addition, energy costs were reduced by 15% because less outside air infiltration was required. Worker productivity showed an increase of 20%, perhaps as a result of fewer sick days and increased blood-oxygen levels.

 

Is There a Downside to Indoor Plants?

 

Some controversy exists regarding how healthy it is to keep plants indoors.  In a recent paper about plants and indoor air quality, co-authored by BuildingEcology.com editor Hal Levin, it was concluded that the positive effects of keeping plants indoors were negligible, at best, and, in some cases, it could possibly be harmful. 

 

The authors conclude that there are "significant methodological issues" for previous research conducted.  The positive gains, they argue, were likely the result of the potting soil and its abilities to cleanse or aerate indoor air, rather than the leafs of the plants themselves.  Additionally, they point out, some of these earlier studies were conducted under circumstances that do not reflect real-world conditions, so testing results can be skewed.  Experiments conducted in a sealed chamber, such as some of those performed by NASA, will have very different results than one conducted where ventilation rates mimic those in the average office building.  And, these days, there are many interpretations for what an "average" work environment is.  Every workplace is different, and every variable -- from the number of people, the level of ventilation, other airborne pollutants (such as personal scents, cleaning supplies, office printers, etc.) can confuse any reasonable measurements, making an across-the-board recommendation realistically difficult.

 

Additionally, keeping plants indoors will affect the moisture content of the air, which must be regulated so as not to promote mold growth.  Some people may have allergies to certain flowering plants, and moisture, along with airborne pollutants that are not effectively mitigated by plants, can exacerbate such problems for building occupants.

 

Finally, as with any study promoting a point of view, consumers should be wary of who is behind it.  Just as some of the most publicized research on heart health in the 1990s recommended eating oatmeal every morning was paid for by Quaker Oats, some plant studies have been scrutinized for their funding sources, as well. 

 

Inspectors should note the presence of indoor plants, and whether their containers are leaking, or if there are water stains.  Over-watering indoor plants can lead to cosmetic and even moisture-related structural problems, as well as mold and other serious indoor air quality issues.

 

In summary, plants can generally be used to enhance the aesthetic environment and the air quality inside buildings, but care must be taken to account for potential allergies, the use of fertilizers and pesticides indoors, adequate ventilation and air flow, and the level of moisture maintained for the plants -- all factors that can affect the building and its occupants.

 

One Source Real Estate Inspection your certified home inspector @ www.onesourceinspection.com.

From Plants and Indoor Air Quality - InterNACHI http://www.nachi.org/plants-indoor-air-quality.htm#ixzz2yu3umJfI

For Home Inspectors: Evaluating Problems with Fasteners -  One Source Real Estate Inspection your certified home inspector @ www.onesourceinspection.com.

by Nick Gromicko and Kenton Shepard

 

 

 

The term "fasteners" typically refers to nails, screws, bolts, and sometimes anchors. Fasteners may directly join together two pieces of material, or the material may be held together by connectors that are, in turn, held in place by fasteners.  A good deal of the difficulty in evaluating fasteners is the fact that most home inspectors inspect existing structures, as opposed to homes under construction, so, by the time the inspector sees a fastener, there’s usually not much visible except its head. Certain problems affecting fasteners, such as corrosion, may be visible, but other problems may be apparent only to inspectors who understand their properties and those of the materials they join.  In addition to becoming aware of visible issues, inspectors should understand some of the basics about fasteners that will help them spot less obvious problems.

There are many different types of fasteners.  Let’s examine the most common types, as well as the problems they are subject to.

 

FASTENER TYPES AND THEIR APPLICATIONS

 

Anchors are receptacle devices installed in very soft or very hard materials that alone wouldn’t hold or accept nails, screws or bolts well.

This photo shows a metal connector called a joist hanger held in place by fasteners, 

some of which are correct for this particular connector, and some of which are not.

 

In designing or specifying a fastener for a particular purpose, a designer has to take into consideration:

1. the types and extent of the force the fastener must resist;
2. the properties of the materials into which the fastener will be driven;
3. the various environmental elements that will act upon the fastener during its lifespan; and
4. the fastener’s lifespan requirements.

STRUCTURAL FORCES

Fasteners are designed to resist two structural forces:  withdrawal and shear.

Withdrawal

The withdrawal force is parallel to the shaft of the fastener, called the shank.  If you were to grab the head of a screw or nail with a pair of pliers and try to pull it straight out, the fastener would resist withdrawal.

One method used to help improve fastener resistance to withdrawal is to deform the fastener shank. This improves withdrawal resistance by increasing the friction that has to be overcome in order to withdraw the fastener.

Shank deformation takes a number of different forms. Adding threads to a fastener shaft to form a screw is one good way to achieve resistance.

Drywall screws

#1 is a coarse-thread screw designed for use with wood studs.

 

#2 is a self-drilling, fine-thread screw designed for use with light-gauge steel studs.

 

#3 is a self-drilling, fine-thread screw designed for use with heavy-gauge steel studs.

 

Coarse-thread screws can be installed faster but have lower withdrawal resistance than fine-thread screws.

 

Screws are more resistant to withdrawal than nails, but this does not mean that they can be substituted for nails for use with structural metal connectors. Fasteners used with metal connectors must be designed for use with each specific connector and approved by the connector manufacturer because connectors have load limitations that relate to a particular fastener’s properties and limitations.

 

Simpson structural screw

 

Although there are structural screws on the market, most screws used with metal connectors are considered a defective installation. Structural screws are made from high-strength steel and heat-treated to further enhance their strength.

 

The SD wood screw is not approved for use with metal connectors.  The structural screw is.

Head markings for Simpson screws

The structural screw in the diagram above is made by GRK. The CEE thread is designed to enlarge the hole in the uppermost of two pieces being joined so that they’ll be more tightly pulled together.

Ring-shank nail

Another method used to resist withdrawal is to roughen the nail shank by adding a series of rings. These are called ring-shank nails.

Roughened shank

Yet another method is to roughen the shank with coatings. In the photo above, compare the hot-dipped galvanized nail to the uncoated (bright) nail. Rough coatings are usually added to resist corrosion, but resistance to withdrawal is an additional advantage.

A spiral shank can also help resist withdrawal,
although it’s one of the less common types of fasteners used in building construction.

Head-shank connection

In addition to the properties of the fastener shank, the strength of the connection of the head to the shank and the thickness of the head are important in resisting withdrawal.

EXPERIMENTS

Inspectors should be aware of several experiments that have been conducted relative to withdrawal.

Gas & Wax

Before framing nails coated with vinyl became available in the mid-1970s, production framers working on large housing tracts in California found that uncoated nails took more of an effort to pound than they wanted to exert.  So, to make nails easier to drive, they would toss a bar of paraffin wax onto an open 50-pound box of 16d nails, pour on a little gasoline, and touch it off with a match. The wax would melt down through the box, making the nails much easier to drive, but lowering their withdrawal resistance dramatically. It also made it easier for the framers to hold onto a wood-handled hammer in hot weather.  Baby powder was occasionally poured into the open box of nails for the same purpose, but it didn’t work as well as a lubricant.

Shrunken, Roughened Shanks

In the early 1990s, in an attempt to save money, some framing contractors substituted a slightly smaller nail with a roughened shank for the industry-standard, 16d hand-driven framing nail.  However, this can lead to unexpected nail pull-out during construction with disastrous and potentially dangerous results.

Both gas and wax and the smaller substitute nails were used on many homes in California and a number of other places during the ‘90s, so if you see structural failures related to nail withdrawal, including head parts that are merely glued in place to give the appearance of being nailed, one of these issues or something similar may be the source of the problem.  But there are some things you just won’t be able to spot.

SHEAR

Shear force is exerted perpendicular to the shank of a fastener. Fasteners that fasten metal connectors to wood are primarily designed to resist shear, although, in many applications, there will also be some withdrawal force involved, too.  That's why fasteners for connectors also have minimum length requirements. The properties important to resisting shear are the strength of the alloy from which the fastener is made, its diameter, and the strength of the connection between the fastener shank and its head.

A defective installation

The fasteners used to connect the hanger to the wall pictured above are defective because the gold deck screws used are designed to resist withdrawal when holding deck planking to floor joists. They have inadequate shear strength to support the structural roof load. Also, because the drywall does not support the shank of the screw as adequately as wood does, the shear force is increased. Imagine that instead of resting against drywall, a ½-inch gap was left between the hanger and the framing. That’s almost the case. The roof of the garage next to this one collapsed under a snow load.

A similar defect with roofing nails

SCREW FAILURE

Screws fail in one of four ways:

1. Failure occurs through the shank. An example of this occurs when driving screws into a hard material. Screws often snap off just below the head. Deck screws may appear to be securely in place when, in fact, the shank has snapped.  Although it looks secure, the head is detached from the shank and the screw has no holding power. You might find this problem by pushing on the materials the screw is designed to join to see if they move separately.
   
   
               
2. Stripping of the screw thread is common with a hard material and soft screw. The photo above was taken with an electron microscope and shows partially stripped threads.
   
3. Stripping of the internally threaded material is common with hard screws and soft material. Consider the example depicting a screw going through a marshmallow (see below).
   
4. The driver may strip the head. Slotted and Phillips-head screws strip more easily than screws with square or star drive profiles.

Square drive

Star drive

Screws used for fastening trim have heads smaller in diameter.

FASTENER LIFESPAN

The lifespan of a fastener is related to its base material, which is usually carbon steel or one of a couple of different types of stainless steel. The type and thickness of the coating or plating will also affect the lifespan, with zinc being one of the most common coatings. The lifespan will also be affected by the properties of the materials that the fasteners are joining together and the environment in which the fastener is used.

MATERIAL PROPERTIES

Density

Dense materials provide a better anchoring substrate for resisting both withdrawal and shear.

To use an extreme example, oak holds fasteners more effectively than marshmallows.

Dense wood may need to have pilot holes pre-drilled to prevent it from splitting, especially near the ends. Dulling the end of a nail also helps prevent splitting, since the dull nail point crushes through wood fibers instead of wedging them apart as a sharp point does.

Some types of screws are designed to cut their own pilot holes.
This screw is designed to fasten wood to steel and will cut its own pilot hole through steel.

Some materials, such as plastic-based composites used for decking, vary in density according to temperature and moisture content, so fastening requirements can vary from day to day. Extreme expansion and contraction have also made fastening these materials a challenge. According to an article in the September 2007 issue of Building Products Digest magazine, there were about 750,000 decks built in 2006 using plastic composite planking.

A screw for fastening plastic-based composites

With as many as 80 manufacturers now offering composites of different formulations that are installed in widely differing climate zones, you may find decks with a large percentage of their fasteners that have spun out and have failed to hold the deck planking securely in place. Fastener manufacturers have been quick to provide solutions to these problems, and screws are now available for fastening composites used in a number of different environmental conditions.

In this illustration, you can see how the tips of various screw types are designed
to penetrate the materials that the screws were designed to fasten.

Thickness

Materials that allow a fastener to remain in contact along its full length will provide more effective anchoring than a thinner material through which most of the fastener has penetrated and is no longer in contact.

When thin materials, such as sheet metal, are joined together,
screws with fully threaded shafts are used.

When thicker materials, such as wood, are joined together, screws with a smooth section near the head allow the two pieces to be pulled tightly together.

This is a gold deck screw designed for fastening deck planking to joists.

CHEMICAL REACTIONS

Metal fasteners can lose their load-bearing capacity when exposed to corrosive environments and materials. These include:

• preservative-treated wood;
• ocean salt air;
• fire-retardants;
• fertilizers;
• fumes; and
• acid rain.

Part of learning the inspection profession is learning not just about common conditions that can affect fasteners, but about conditions unique to the local region where you work that may affect fasteners.

Preservative-Treated Wood

Several types of water-borne preservatives were used in the past to increase wood’s resistance to attack by wood-destroying insects and decay fungi. Each type included chemicals that corrode some metals. Chemical formulas vary by manufacturer and region, and those formulas may change without warning.  The level of retention of preservatives can vary by wood species and by the method used to treat the wood. Complicating the issue even further is that the industry is still evolving.  So, although fastener manufacturers make recommendations about compatibility with their products, choosing the correct fastener or confirming that the right fastener has been used can be difficult, especially if all you can see is the fastener head in the spot of a flashlight in a dark basement or crawlspace.

Chromated copper arsenate (CCA) was used for many years, but its use has declined due to the inclusion of substantial amounts of arsenic as one of the treatment chemicals. U.S. EPA regulations in place since 2004 call for pressure-treatment chemicals to be arsenic-free. Generally, hot-dipped galvanized and stainless steel are the recommended fasteners for CCA.

The next generation of wood preservatives commonly used in buildings includes alkaline copper quat (ACQ), copper azole (Types A and B), as well as SBX/DOT (sodium borate) and zinc borate (for wood composites). The formulations for these products also vary.  Although they don’t contain arsenic, some types contain chemicals that are more corrosive to fasteners than CCA.

The recommended fasteners for these include hot-dipped galvanized, stainless steel, or triple-coated zinc polymer materials. Carbon steel and aluminum fasteners should be avoided. Aluminum nails are not common in building and, in general, their use is limited to fastening aluminum flashing, so watch for bright nails used with treated lumber, and comment on this if you find them.

A nail approved for used with treated lumber

Most stainless-steel fasteners are acceptable for use with pressure-treated wood. Testing has shown that Types 304 and 316 stainless steel perform well with CCA-C, ACQ-C, ACQ-D carbonate, CBA-A, and CA-B treated woods.

The large number of variables that affect the rate of corrosion of fasteners in contact with pressure-treated wood makes it impossible to provide an accurate, estimated long-term service life for these fasteners.

PROTECTIVE COATINGS

There are two basic types of corrosion-protection methods used to protect steel-based fasteners. Barrier coatings bond to the steel and serve as a shield between the steel and the corrosive elements in the environment. Sacrificial coatings often serve as a barrier coating.  Additionally, because they’re lower on the anodic chart, they will corrode before steel so that even if the protective coating is damaged, exposing the steel, the sacrificial coating will corrode first, protecting the steel base metal.

Bright

Steel fasteners with no protective coating are called bright fasteners. Bright fasteners should be used in low-corrosive environments only. Even humid air will cause any exposed portions to eventually rust.

A hot-dipped galvanized hanger nail above a bright hanger nail

Galvanization

Fastener galvanization is the approved coating process most commonly used with pressure-treated lumber. Galvanization is the process of coating fasteners with zinc. The zinc coating acts as both a barrier coating, preventing corrosive agents from reaching the underlying steel base metal, and as a sacrificial coating, because zinc, as the more cathodic metal, will corrode before steel. There are several types of galvanization processes, including hot-dipped, electroplated and mechanically galvanized. The thicker the galvanized coating, the longer the expected long-term service life of the steel fastener.

Hot-dipped galvanized fasteners are used in regions where a maximum amount of protection is desired. To hot-dip galvanize steel fasteners, the steel is first cleaned, pickled, fluxed, and then dipped in a molten bath of zinc.  The fasteners are allowed to cool prior to inspection and shipping. Some concrete anchors and metal connectors can also be hot-dip galvanized. Hot-dipped fasteners are manufactured to ASTM 153 standards.

Electro-galvanized fasteners are used in mild-weather conditions and in areas with low humidity. Electro-galvanization plates the nail in a zinc coating by using an electrical charge. The nails are submerged into an electrolytic solution and an electrical current coats them with a thin layer of zinc. However, after prolonged exposure to the elements, the thin layer of zinc oxidizes, leaving the fastener subject to normal rusting and staining.

A hot-dipped roofing nail is shown on the left, and an electroplated roofing nail is shown on the right.

Mechanical galvanizing is a process of providing a protective zinc coating over bare steel. The bare steel is cleaned and loaded into a tumbler containing non-metallic impact beads and zinc powder.  As the tumbler is spun, the zinc powder mechanically adheres to the parts. The coating of mechanically coated nails is porous and brittle compared to electroplated and hot-dipped fasteners and is prone to flaking off.

Two zinc-coated screws

Zinc-based coatings are one of the most common.  Gold deck screws are simply zinc-plated screws dyed yellow to make them look like cadmium. Cadmium screws were used in the past because of their strength, but due to cadmium's toxicity, it’s no longer used in fasteners that are typically used for building.

Vinyl-Coated Nails

A 16d vinyl-coated checker-head sinker, which is the industry standard

Framing nails manufactured today are coated with vinyl, which acts as a lubricant when the fastener is being driven.  It also provides a small amount of barrier protection against corrosion. It’s a common coating on hand-driven framing nails, such as 8d and 16d sinkers.

Resin-Coated Nails

Some nails are coated with a resin that acts as a lubricant for easier driving, and also as an adhesive. Driving the nail raises the temperature of the fastener enough to liquefy the resin. Once in place, the resin hardens and acts as an adhesive, bonding the shank to the wood fibers.

Phosphate-Coated Nails

Adding a thin coat of phosphate helps resist withdrawal and also provides a small measure of resistance to corrosion.

Galvanic Corrosion

Galvanic corrosion occurs when certain dissimilar metals come into contact with each other.  Two conditions must exist for galvanic corrosion to take place:

1. There must be two dissimilar metals present.
2. There must be an electrically conductive path between the two metals, such as water.

This means that fasteners used with metal connectors or flashing should be made of the same metal as the connector. For instance, using stainless steel fasteners with galvanized steel connectors will likely lead to corrosion.

Cathodic Protection

A third type of basic protection from corrosion is called cathodic protection and consists of metals highly resistant to corrosion. Stainless steel Type 304 and especially Type 316 are the industry standards for fasteners used in building construction. Type 316 is recommended for salt environments, but you won’t be able to tell just by looking.

The photos above and below show stainless steel fasteners.

Copper nails resist corrosion well and are often used with copper trim and to attach slate roof tiles.

 

Moisture Cycles

 

Many commonly used construction materials, such as wood, expand and contract with changes in moisture content. This process is called moisture cycling. Over the long term, moisture cycling causes the holes around fasteners to enlarge, and when the fasteners used are nails, they eventually loosen in their holes and increasingly protrude as moist wood expands, gripping the nails and forcing them up and out of their holes slightly. As the wood dries, the holes enlarge, and the wood shrinks away from the nails.

As this cycle is repeated, nails can be raised above the wood surface significantly. Protruding nails are a common problem on decks with wood planking.  This condition is also common on metal roofs with exposed fasteners, including screws.

FASTENER SIZES

Screws are sized by number.  This is a self-tapping, hex-head #10 zinc-plated screw.

Nails are sized by the “penny” shown as a “d.”
This photo shows a 16d or 16-penny vinyl-coated checker-head sinker.

MASONRY ANCHORS

Mechanical Anchors

Masonry wedge anchor

 

Wedge-type masonry anchors in sizes 3/8-inch, ½-inch and 5/8-inch, like those shown in the photo above, have a code stamped into the end that’s left exposed after the anchor is installed.  Anchors 1½ inches are labeled A, 2-inch anchors are labeled B, 2½-inch anchors are labeled C, and so forth, with subsequent letters that correspond to length increasing by half-inch increments, as shown in the chart below.

 

A wedge anchor code mark

The code table

Although you may see other fasteners with codes stamped into their heads like this stainless steel screw, codes are not standardized, so don’t assume you can tell the length by using the same chart that’s used for wedge anchors.

Anchoring in cracked concrete has been a problem in the past,
but a new type of wedge anchor is available for this use.
 It’s the anchor on the left in the photo above.

Other Types of Concrete Anchors

Hammer drive

T-anchor

Bear in mind that concrete anchors don’t work well in concrete masonry units (CMUs), commonly called concrete blocks, unless the cells are filled.

Testing Anchor Connections

Manufacturers of masonry anchors recommend confirming that the anchors are properly installed by testing them to the proper torque using a torque wrench. They do not recommend tapping anchor heads with hammers or tightening them with a socket wrench.

Adhesive Anchors

Adhesive anchors are usually threaded steel bar (commonly called all-thread) or re-bar that’s inserted into pre-drilled holes and held in place with an adhesive.  The manufacturer’s instructions should be carefully followed for the anchors to attain their full strength. Holes should be drilled to the correct depth and diameter and then brushed and blown clean with compressed air.

Adhesive formulations can vary, resulting in widely differing performance characteristics among products with similar chemistry, including temperature-related performance. One problem with adhesive systems is known as “creep.”  Some types of adhesives are designed to resist short-term loads only, such wind and seismic loads. When subjected to long-term loads, anchors will slowly pull loose. 

In Boston in 2006, a portion of a suspended concrete ceiling system in a tunnel collapsed, killing one person. The adhesive anchors holding the ceiling in place, which were subjected to a long-term gravity load, pulled loose, resulting in the collapse. If you inspect structures that may have adhesive anchors under long-term loads of some type, look carefully for signs of failure. One location where you might expect to see this in residential construction is where a concrete patio or porch has been retrofit to connect to a masonry foundation. Poor soil consolidation beneath the porch or patio slab that has resulted in settling may create a load on the anchors.

Concrete anchors have two test standards for creep, including the CC-ES AC 58, with the optional creep test. The other test is ICC-ES AC 308, which requires two sample tests taken at different temperatures.

DRYWALL ANCHORS

Different types of devices are available for anchoring screws into drywall. Some of the more common ones are shown below.

BOLTS

A typical zinc-plated, hex-head bolt

Two standards exist for grading bolts: the American National Standards Institute (ANSI) standard is for bolt strength. The International Standards Organization (ISO) standard is for both tensile and yield strength of the bolt.

A bolt graded by the ANSI standards is identified by
the number of lines arranged around the head of the bolt.

• 0 lines = Grade 2 tensile strength
• 3 lines = Grade 5
• 5 lines = Grade 7
• 6 lines = Grade 8

A bolt graded by the ISO standard, shown in the photo below, uses two numbers on the head of the bolt. The first number indicates the tensile strength; the second number signifies the yield strength.

Most bolts used in residential building are Grade 5. Applications such as for steel wind frames may call for Grade 8 bolts, but, as an inspector, you’d need to see documentation showing that requirement.  Seeking such confirmation exceeds InterNACHI’s Standards of Practice.

 

 

 

 This is a carriage bolt. The square section beneath the head

 is designed to prevent the head from spinning as the nut is tightened.

 

This photo shows the difference in appearance between
the head of a stainless-steel carriage bolt and a zinc carriage bolt.

This photo shows a plastic-lined lock-nut compared with a conventional hex-head nut.

LAG SCREWS

Lag screws are like heavy screws with hex heads.

FASTENER IDENTIFICATION

Nails

This is a cut nail. As an older style, they’re not used much anymore,
but you will see them used in older homes.

The photo above compares a galvanized finish nail above a stainless-steel siding nail.

Below are three views of nails commonly used for fastening metal connectors.

 

 

A masonry nail

This photo shows a TimberLok® screw designed for use
with log and timber-framed homes.

The photos above and below show structural and wood screws manufactured by GRK.

Screws designed for use in masonry are often colored blue.

NAIL GUNS & NAILS

The concern with fasteners installed with nail guns is over-driving the nails that are used to fasten structural floor, wall and roof panels made of materials such as plywood.  In these cases, it’s important that the nails not be over-driven.

Over-driving nails (or driving them at an angle) reduces
the effective thickness of the panel by breaking through its veneer.

Driver-Depth Adjustment Devices

Many newer guns have driver-depth adjustment devices built into the trigger mechanism.  On nail guns that lack this device, the depth of the driver may be regulated by adjusting the air pressure at the compressor.  This is less accurate, since the density of wood will vary.

A newer gun with a driver-depth adjustment device

An older gun whose driver depth is regulated by air pressure

Gun Nails

Framing nails for guns typically come in strips. Here are a few examples.

Galvanized 12d

Bright, ring-shank 8d

Hot-dipped galvanized 6d

Staples

A typical staple used in framing: 16-gauge galvanized 1½ x 7/16-inch

 

 

Home inspectors should be aware that fastener manufacturers do not give lifespans for their products because they vary too much based on where the fasteners are installed in a home, the materials in which they're installed, and the local climate and environment.  However, inspectors can use the information presented here to make educated judgments about the materials they inspect. 

 

 One Source Real Estate Inspection your certified home inspector @ www.onesourceinspection.com.

From For Home Inspectors: Evaluating Problems with Fasteners - InterNACHI http://www.nachi.org/home-inspectors-evaluating-problems-with-fasteners.htm#ixzz2ypiE5MYT