April, 2018
Inspection News and Views from the American Society of Home Inspectors

Anchoring a Home to its Foundation: An Important Inspection Issue


A homeowner requested my help with assessing the severity of water intrusion into his home. As a result of the intrusion, exposed mud-sill plates (where damaged drywall required removal at the west exterior walls) revealed questionable foundation-anchoring methods used by the builder. The anchoring methods became a point of inquiry that I will address in this article, focusing on the following questions:

  • What are the codes for home anchoring and how can they be checked?
  • Why is this information valuable to the homeowner?

Fortunately, most state regulations follow the International Residential Code (IRC) and direct builders to abide by its requirements. The anchors exposed at my client’s home were powder-actuated fastener shot pins that were 2½ inches in length with a washer (see photo below). When the home was originally built in 2009 and inspected by the local city and county inspector during construction, it’s possible that the officials accepted powder-actuated fasteners.

Shot pin anchor, which was removed for record from a sill plate at the client’s home, where water intrusion was occurring. The anchor is placed next to an IRC-specified anchor bolt for comparison.

The property was reinspected by a home inspector associated with a real estate agent. At the time of purchase, my clients felt assured that everything was in order. In addition to the anchoring issue, the water intrusion inspection noted foundation and grade code violations, improper siding installation, including the absence of underlying water-resistant barrier (WRB) (building paper), fasteners and flashings, plus additional structural framing and fire code violation issues. All of these issues had been previously inspected and overlooked, but yet approved by local and real estate inspections. The anchoring, grade, mis-installed siding and absent WRB issues were the only observations included in my water intrusion report due to relevancy.

Some Background on Building Codes 
The Uniform Building Code (UBC) was first published in 1927 by the International Council of Building Officials. In 2000, the new International Building Code (IBC) and the IRC, published by the International Code Council (ICC), replaced the UBC. Most states have accepted the IRC and IBC.

Model building codes depend on referenced standards, as published and promoted by organizations such as the American Society for Testing and Materials (ASTM), which develops and publishes voluntary technical standards for a wide range of materials, products, systems and services. ASTM International does not require or enforce agreement with its standards. The standards, however, may become mandatory when referenced by an external contract (for example, in conjunction with architectural drawings and specifications, by a corporation or the government).

As stated in the 2015 IRC, Chapter 4, Foundations, Section R403.1.6, Foundation Anchorage:

“Wood sole plate at all exterior walls on monolithic slabs, wood sole plates of braced wall panels at building interiors on monolithic slabs and all wood sill plates shall be anchored to the foundation with…anchor bolts spaced a maximum of 6 feet (1829 mm) on center or approved anchors or anchor straps spaced as required to provide equivalent anchorage to ½-inch-diameter (12.7 mm) anchor bolts. Bolts shall extend a minimum of 7 inches (178 mm) into concrete or grouted cells of concrete masonry units. The bolts shall be located in the middle third of the width of the plate. A nut and washer shall be tightened on each anchor bolt. There shall be a minimum of two bolts per plate section with one bolt located not more than 12 inches (305 mm) or less than seven bolt diameters from each end of the plate section. Interior bearing wall sole plates on monolithic slab foundation that are not part of a braced wall panel shall be positively anchored with approved fasteners. Sill plates and sole plates shall be protected against decay and termites where required by Section R317 and R318.”

Furthermore, Section R317.1, Location Required, states the following: “Protection of wood and wood-based products from decay shall be provided in the following locations…2. Wood framing members that rest on concrete or masonry exterior foundation walls and are less than 8 inches (203 mm) from the exposed ground.” 

Removed shot pin next to mudsill for length and depth of penetration verification. 

I visited several different construction sites locally for reference of common foundation anchoring methods and discovered the prominent use of the MASA mudsill anchors. Unfortunately, I found that the method of a CMU stem wall being attached to a belowground footer was the most typical. The type of mudsill anchors being used by builders is depicted by the manufacturer as installed in solid concrete, where the mudsill anchor can be embedded at the outside edge of the foundation, enabling the strap to be wrapped tightly around the sill plates without compromising the manufacturer’s installation specifications. 

Simpson Strong-Tie MASA mudsill anchor and the manufacturer’s depiction of a fully embedded installation in a solid concrete foundation. 

A typical compromised installation of MASA mudsill anchor with CMU stem wall

Another example of compromised anchoring.
The upper arrow points to a void in the slab made visible by daylight and the lower arrow points to a void that is visible because of a large depression.

In 2012, ICC Evaluation Service, LLC (ICC-ES) reported on and accepted Simpson Strong-Tie MASA and MASAP foundation anchor straps. Both the ICC-ES report and Simpson Strong-Tie require that the manufacturer’s published installation instructions be followed. Structural observation or inspection is a good way to make sure that happens. Special inspection may also be required by the building code or the local building jurisdiction.

All of the illustrations of specified MASA installations I’ve seen depict the foundation anchor straps embedded in a solid concrete foundation. During my visits to residential building sites within a 10-mile radius of my client’s home in Arkansas, I observed that these foundation MASA anchor straps (or “mudsill anchors”) often had been installed in CMU stem walls, making them questionable with respect to the ICC-ES report and the Simpson Strong-Tie product warranty, as well as possibly in violation of IRC and IBC building codes, which otherwise require anchor-bolt anchoring to the foundation. Simpson Strong-Tie emphasizes having correct installation drawings and specifications on site for reference where mudsill anchors are being incorporated for anchoring to the foundation. 

CMU block stem wall and mudsill with Simpson Strong-Tie MAB mudsill anchor installed with a ¾-inch center hole in the mudsill.

Simpson Strong-Tie MASB-type mudsill anchor, specified for masonry block foundation installation. The most noticeable difference between MASB and MASA is the wider-spread, horseshoe-like exposed attachment flange of MASA, compared with the longer, narrower MASB flange.

Simpson Strong-Tie has gone on to create MASB and MAB foundation straps, supported by IAPMO Uniform Evaluation Service (IAPMO UES) Evaluation Report ER-417 and evaluated according to the 2015 IBC and IRC for installation in CMU block-type foundations.

MASB and MAB mudsill anchors are noted in the 2015 IRC R403.1.6 as follows: “…approved anchors or anchor straps spaced as required to provide equivalent anchorage to ½-inch-diameter (12.7mm) anchor bolts” (note the emphasis on the word approved—which means by the local building inspection official). ER-417 under Section 5.0 Limitations, Sub-Section 5.6, lists some limitations.

It’s imperative that the manufacturer’s installation specifications are followed. Special inspection is one way to ensure that happens, and it may be required by the local building code or building jurisdiction. In addition, there are competitor manufacturers of mudsill anchors that have similar reports regarding “approval” in process with which an inspector will have to become familiar to be well informed. 

I was a builder for many years and always incorporated Simpson Strong-Tie hurricane ties, joist hangers and a wide selection of specially engineered added-attachment hardware where needed. Simpson Strong-Tie customer service is excellent, and they respond promptly and helpfully to all questions and requests for information. 

The Big Question: How can you inspect foundation anchors that are covered up by exterior cladding and interior drywall? 

Answer: You can’t, unless there is a basement or crawl space under a wood floor where exterior sill plates are visible, or a possible exposed area of sill plate on an exterior wall where a utility panel or fresh air vent of some kind has been incorporated and can be removed. 

Outside of an exposed sill plate area, an inspection requires the partial removal of drywall (possibly in the garage) about 1 foot back from any exterior corner that lines up with code attachment placement within 12 inches of all sill-plate ends. The best-case scenario is when a client requests an inspection during the construction process at the point of framing, where the sill plate-foundation attachment is exposed or, even better, an inspection incorporating a foundation examination that occurs before concrete is poured or before the foundation stem wall is placed; at which point, either anchor bolts or mudsill anchors (along with the manufacturer’s installation specifications) should be visible for inspection verification.

Being aware, informed and attentive to this facet of your inspected structure could be not only a property liability investment for your clients, but also a life-saving one. Just the added inspection attention will confirm for your clients that they have chosen an inspector who is concerned with their interests.

Why is this issue so important?
Structures are only as strong as their connections, and structural systems can’t behave as a unit without proper interconnection of the components and assemblies. In residential wood construction, anchor bolt or mudsill connections are limited to wood-to-concrete connections with a significant purpose—the importance of transferring shear wall overturning forces. High winds from storms can overturn an improperly anchored home. In some cases, hold-down connectors are specified that attach the wall framing to the foundation where overturning forces are high. An inspector has a great opportunity to prevent disaster if provision is made to verify proper foundation attachment.

The Worcester Polytechnic Institute, a private research university in Worcester, MA, focuses on the instruction and research of technical arts and applied sciences. After the tornado disaster in Joplin, MO, in 2011, the Worchester Polytechnic Institute (WPI) conducted a study on the type of anchoring and its effect or lack thereof relative to residential structures. 

Here are excerpts from WPI’s report, titled, “Design of Residential Structures Against Strong Wind Forces: A Major Qualifying Project” (https://web.wpi.edu/Pubs/E-project/Available/E-project-042412-142801/unrestricted/Final_MQP_Report.pdf):

“Model building codes are codes developed by an organization autonomous to the group responsible for executing the code. The division between the group establishing the code and people operating under the regulations is imperative to ensure a reliable system where the well-being and safety of the building owner and occupants are first priorities.”

Simple changes in the spacing and quantity of connections can result in major damage when faced with abnormal wind temperatures and weather conditions.

(2.2 Importance of a Model Building Code)

“The International Code Council’s main objective is to provide safety to the occupants and owners of the building after construction. There are still common wind deficiencies in newer construction which need to be addressed. The most prevalent deficiencies from wind damage are the foundation anchorage with hold-downs, anchor bolt spacing, rafter ties and wall ties. The main issue in the most frequent wind deficiencies involves connections. The spacing, type and material used in each connection are what allow the shear walls to stay attached to the foundation or the roof to maintain its structural integrity” (2.2.4 Most Frequent Wind Deficiencies).

“Shot pins and cut nails are generally a violation of building code around the perimeter foundation but have been found in some houses. Instead of shot pins and cut nails, the IRC specifies that anchor bolts should be used (IRC, 2012)” (2.4.1 Concrete Slab Foundation Failures).

A Sobering Story
Over the past century, the earth’s surface and atmosphere have been gradually warming. A significant proportion of the scientific community believes this climate change will destabilize weather patterns and increase the frequency and intensity of natural disasters like hurricanes, tornados and flooding. Recently, we have experienced the warmest years on record, which coincided with the most active hurricane and tornado seasons. The devastating weather event of the Joplin tornado had readings of EF5, with wind gusts over 200 miles per hour.

The most recent years also have been the costliest to date for the insurance industry with regard to building claims for property damage. The foremost concern for the construction industry and inspectors should be the health and safety of building occupants, with the added consideration of protection of their greatest financial investment, their homes.

Unfortunately, the statute of limitations for reciprocity relating to a builder in my client’s state was five years, and reciprocity regarding any inspection (whether related to city, county or real estate) is just one year. With their home’s construction completed in 2009 and the water intrusion report requested and completed in 2016, they had missed any legal opportunity to regain some of the remedial repair financial loss they had suffered. All of their losses could have been prevented by having a well-informed, qualified home inspector conduct a complete inspection and provide a comprehensive report. Adding such an inspection to your checklist, could save your clients a lot of money and help protect their lives. 

The author thanks the Simpson Strong-Tie communications, marketing and technical support departments for all of their considerations, and the Worcester Polytechnic Institute for their admirable research regarding residential anchoring. 

Greg White began his career as a residential contractor (15 years) and then worked in commercial construction, which led him to become part of a specialized team of engineers who investigated and tested materials. White resides in northwest Arkansas, where he works as a building envelope consultant, a certified commercial building inspector and a property condition assessor. Visit his website at www.gregwhiteconstruction.com.