The Great Enheightenment

In recent surveys, readers have asked for instructional articles with practical knowledge they can use on the job. In response, Interlock Design is pleased to present this first installment of its new how-to series of feature articles that will run throughout the year. We welcome reader feedback and invite you to contact us at with any suggestions or topics you’d like us to cover in the new how-to series.

Why a Raised Patio?

As this issue’s cover story explains, residential outdoor living is a booming market for the hardscape industry. An integral component of an outdoor living space is a raised patio.

Traditionally, a raised patio allows movement from house to backyard without a change in elevation. A homeowner steps out the back door and into the outdoor living space as easily as walking from one room to the next inside the house, creating a seamless transition from interior to exterior space.

Initial Precautions

“If not done properly, a raised patio can do significant damage to the building that it’s constructed against,” says ICPI Director of Engineering Robert Bowers, P. Eng. The main factors that can cause damage are moisture accumulation and the increased lateral load placed on the foundation, and possibly on exterior above-grade walls.

Most exterior above-grade walls of a house are not designed to have moisture continuously against them, explains Mr. Bowers. Whether they’re brick, wood siding, vinyl or another material, these exterior walls are designed to resist water and shed it—to get wet and then dry out. They cannot withstand a continuously moist environment. Placing compacted soil against these types of walls can trap moisture, resulting in mold, decay and deterioration.

Regarding foundation walls, in most cases they are constructed to bear the weight of the supported structure, the lateral pressure from the soil and not much more. By constructing a raised patio, the lateral pressure against a foundation increases. This presents an increased risk of blowout and basement wall collapse, because the increased load to the wall is not counterbalanced. This is called an unbalanced fill condition. When taking on an unbalanced fill project, an engineer should be consulted to ensure the stability of the project. Additional reinforcement of the foundation wall is sometimes necessary. The cost of the engineer’s involvement will increase the cost of the construction, so it’s important for contractors to include this in the price of their proposals.

 “A homeowner should be able to appreciate it,” Mr. Bowers says, “if you say, ‘Hey, I’m concerned that we don’t damage your house in any way and I’d like to have a professional engineer tell us the best way to do this.’”

At the outset of planning, be sure to thoroughly document the existing conditions of the site. Take photos of the exterior walls, the foundation and the basement walls inside and out, carefully inspecting for cracks, bulging and any signs of dampness or water damage.

Design Considerations

The most effective way to raise a patio adjacent to a building is with a retaining wall (aka stress relief wall) that faces the building, offset from it by 3 to 4 in. This creates an air gap that prevents the patio from touching the building’s exterior cladding and also allows airflow so any moisture that gets in can dry out (See Figure 1). Additionally, the air gap prevents a raised patio from covering up weep holes. Covering weep holes compromises the exterior above-grade wall venting system, leading to deterioration and potential collapse. For this reason, covering weep holes is a building code violation. At the top of the air gap, cantilevered pavers and screens are common solutions to prevent debris from falling into the gap. A drainage system at the bottom of the air gap is also required. Another option is applying aluminum flashing against the house. This surface, however, cannot block weep holes designed to wick moisture from the walls.

The higher the patio is raised, the greater the complications and potential risks to the foundation. Most homes are constructed with 8 to 12 in. of foundation wall above grade, atop which sits another 12 in. of floor joists. That means the threshold of the back door is typically 20 to 24 in. above grade. For every foot of elevation a wall is built up, roughly 50 to 100 pounds of additional load is applied to the foundation walls. Depending on a number of conditions, it could be even more.

Coincidentally, a raised patio height of 20 to 24 in. is a gray area for determining if additional measures are required to reinforce the foundation wall. For any patio raised above 24 in., it is recommended to have an engineer review the design, test soil quality, evaluate foundation walls and make recommendations.  Heights of 20 in. or less generally carry less risk in relation to the loads. Ultimately, each contractor must decide on his or her level of comfort and corresponding liability.

“If you think there’s the slightest possibility you might need an engineer, then you need an engineer,” Mr. Bowers says. “I can’t tell you how many calls I get from contractors who say, ‘I’m not sure but I think I might be doing something that requires an engineer.’  They describe the situation and yes, they should’ve had an engineer involved weeks ago.”

Local building codes also come into play at heights around 24 in. or greater and when adjoining the raised patio to a building exit like a back door. Every building code has specific requirements for steps including tread depth, riser height and pitch, as well as for hand railings and guards. Because many aspects of raised patio construction are governed by building codes, raised patio construction often requires first obtaining a building permit.

Raised Patio Construction

Raised patios are constructed using three basic components: walls, flatwork and steps. But before building anything up, the ground must be broken.


When new home construction is completed, often the soil against the foundation wall is excavated backfill of the soil consisting of silty, clay soil unsuitable for the subgrade of a raised patio. A soil probe or test pit will confirm this and is recommended to determine soil type and quality. A common way to reduce the lateral load applied to a foundation wall is to remove poor quality soil and replace it with a higher quality dense-graded, crushed stone aggregate. As a rule of thumb, the height of the patio determines how deep to excavate and how far out from the building foundation. If a raised patio will be 48 in. (1.2 m) high, dig down 48 in. (1.2 m) and out from the building the same distance.

Subbase, Drainage, Base

Dense-graded, compacted aggregate is commonly used for the base of the wall and the raised patio. For some projects, flowable fill may be advantageous because it’s lighter and does not require compaction. However, it can be more expensive to install and may require time to cure.

Once the subgrade and base for the wall are set, install a 4 in. (100 mm) diameter perforated drainage pipe along the length of the wall that slopes to a drain. For the drainage layer above the drainage pipe, use open-graded, compacted aggregate with ¾ in. (19 mm) minus clean stone (See Figure 2).


When using segmental retaining wall (SRW) units to raise a patio, a conservative rule of thumb is that the maximum height of the wall should be approximately twice the depth of the SRW unit. For heights three times the depth of the SRW unit or greater, geogrid should be used to help stabilize the wall. Most building codes require walls over 48 in. (1.2 m) in height to be engineered, and some jurisdictions have set limits even lower.

A conservative initial design incorporating geogrid could specify continuous layers every 12 to 16 in. (300 to 400 mm) vertically with a length equal to the height of the wall, and not less than 4 ft (1.2 m). This design would only be suitable for typical conditions: dense graded aggregate backfill; pedestrian-only loading with no slope or terraced wall above; a stable, undisturbed subgrade to a maximum total height of 8 ft (2.4 m). If these typical conditions do not exist on the site, or the decision is made to optimize the design, an engineer should be consulted to develop the initial design.


Every building code has requirements for steps. For outdoor applications, a common pitch requirement is 6:12: a 6 inch (150 mm) riser and a tread depth of 12 in. (300 mm). Maximum riser heights of up to 8 in. (200 mm) may be permissible, so check local building codes. The steps must have a consistent tread depth and riser height to prevent a tripping hazard. Complete compaction of base material is extremely important. Flowable fill or a well-compacted, cement-treated aggregate can help minimize the potential for settlement.

SRW units (Figure 3) or concrete pavers (Figure 4) can be used to construct steps. Either way, choose a material that has freeze-thaw durability. Snow removal and deicers can destroy concrete materials not manufactured to freeze-thaw resistance. Some SRW systems have cap units that are not meant to support regular pedestrian traffic, so be sure to choose the proper units if using for steps. If pavers are selected for the steps, it is necessary to build the base out of concrete to prevent “roll over” that occurs if paver steps are not properly supported.


For patios with elevations greater than 24 in. (600 mm), most building codes require a guard or handrail, including minimum height requirements, as well as specifications for resistance to lateral loads. For code compliance, the railing, mount and foundation all must resist the applied load. Generally, there are four types of mounts used to connect the post to the stabilizing foundation: surface, core, side and direct.

Surface mounts are common but also typically the weakest. A plate is welded to the bottom of the post and then connected to the top of the retaining wall with lag bolts or self-tapping concrete screws. Core mounts involve drilling down 18 to 24 in. (450 to 600 mm) into the retaining wall and grouting or epoxying the post directly into the wall. Core drilling can be time-consuming and costly and risks splitting the SRW units under certain conditions in freezing environments. While core-drilled guards are potentially more stable than surface mount guards, neither should be relied upon as the only means of securing the guard.

Side mounts attach handrails to the face of a side wall. When side-mounted handrails are combined with a guard system, they contribute to the stability of the entire guard assembly. The most effective way to secure a guard system is with the fourth type, a direct mount, which attaches to a solid fixed object like a building or caisson (See Figure 5).

Site Prep

The main task in job layout is transferring the final design from paper to the site. Verify access and staging areas; identify slopes and drainage conflicts; install erosion control and containment measures; and provide protection for trees, plantings and structures. Confirm the location of all utilities and buried utility lines, making sure everything is clearly marked. Outline the extent of excavation and the patio, install string lines, and designate finished elevations with stakes, string lines and markings on adjacent structures. Make plans for equipment storage and vehicle parking. And always maintain a clean, organized site to make a favorable impression.

When defining the elevations of a project, identify the critical elevations on existing structures like a doorsill. Typically, critical elevation determines the finished elevation, so it is necessary to calculate backward from the finished elevation down to the starting elevation. Repeat this calculation in several locations on-site and double-check them.


Care must be taken when compacting adjacent to a foundation wall; excessive force may cause cracking. Less force can be used by placing soil in thinner lifts. For the first course of SRW units, dense-graded aggregate base should be compacted to a minimum of 98% standard proctor density (SPD). Although industry guidelines call for 95% SPD for the fill behind the retaining wall, ICPI recommends 98% SPD to minimize the settlement of the pavement surface above. It is important to watch the alignment of the SRW units to ensure they are not pushed out of alignment or rotated forward during compaction.

For bases and fill, in addition to the flowable fill alternative previously mentioned, geotextile or geogrid, cement-treated base (CTB) and asphalt-treated base (ATB) are also options. Installers who have limited experience with these materials and methods should receive technical support prior to selection. A geotechnical engineer’s input may also be necessary to determine the strength of the subsoil and the extent of remediation required.

Raised patios also require adhesives for retaining wall caps, treads and other materials. Adhesives that remain slightly flexible after curing are preferred. Though mortar can be a cheaper option, its use is not recommended in areas with freezing and thawing conditions.

Close Out

Equipment removal and cleanup are standard operating procedure. After running down punch-list items and performing final inspection, secure a certificate of occupancy and final payment. As a courtesy, provide the homeowner with spare pavers, sand and cleaner. Photograph the completed project for the company’s portfolio and be sure to write a thank-you note for a high-dollar job.

Continuing Education

The information provided in this article is from the ICPI Advanced Residential Paver Technician Course manual. To sign up for this course or any other offered by ICPI, visit


Backyard Project Boom

Some spa owners might be jealous of the newly revamped backyard of a Wayne, NJ family: 5,000 sf of outdoor living space, complete with an elevated patio area, pool and hot tub lined with natural rock, a waterfall bubbling gently down from a walkway above, and a cozy fire pit tucked off to the side. The era of kiddie pools, Coleman grills and fold-up lawn chairs may be officially over.

“Our backyard residential projects are all becoming high-end, and even people who are watching their budgets are asking for elements like fireplaces, outdoor kitchens and extensive living spaces,” says Joe Monello, owner of New Jersey-based Monello Landscape Industries. The recent project in Wayne makes significant use of hardscape, with concrete pavers playing a major role. Four different sections on the project — dining, pool entrance, lounging and fire pit — each used a unique paver style to differentiate one space from the other, with a repeating border that brings the hardscaped area together aesthetically.

Currently, Mr. Monello is working on several similar projects, including one that involves about 7,000 sf of concrete pavers. He certainly isn’t alone in garnering more extensive backyard projects like these. The trend is toward elaborate, sumptuous living spaces that replicate and expand indoor layouts, complete with a kitchen, dining and lounging areas, and a fireplace. “There’s no question that this is going to continue,” he says. “If anything, these projects are just going to keep getting bigger.”

Going Backwards

The shift toward larger backyard projects comes as the result of several factors, including a continuing interest in staying home and connecting with nature. Even though the 9/11 terrorist attacks happened over a dozen years ago, the dramatic move away from travel as recreation never really returned in a big way, notes Justin Hampton, co-owner of Paver Designs in Omaha, NE. And the sputtering economy of recent years has put “staycation” in the American lexicon firmly if not permanently.

“Instead of going on vacations, people learned how to stay home and have fun,” he says. “They’re turning their backyards into places to hang out. They’re going from a small patio or deck to grill islands, pizza ovens, seating walls and fire pits.”

Most of these projects incorporate several natural elements like fire, water and stone, as well as edible plants like grape arbors or herbs, says Julie Moir Messervy, a landscape architect based in Vermont who helms JMMDS, a creative design firm. “I’ve been pushing for people to put these things in their front yards and actually talk to their neighbors,” she says. “But there’s a sense of privacy in the backyard, and intimacy when you’re entertaining.”

Another part of the reason for the larger scale is lower cost compared to renovation, adds Frank Gandora, president of Creative Hardscape Company in Englewood, CO. To build an addition onto a home is usually around $300 per sf, he says, but for 10 percent of that price, a homeowner can have a large outdoor space for entertaining.

Mr. Gandora experienced this phenomenon firsthand. He spent almost $100,000 to refinish his home’s basement but less than $20,000 for a sumptuous backyard patio area. Where do guests prefer to spend their time? “Everyone wants to be outside, it just has a better feel to it,” he says.

The recent recession also reduced material costs, notes Jeff Zock, a landscape architect with Ryan Hughes Design in Florida. That incentivized homeowners, prompting them to increase the scale of outdoor projects. The recession made people retreat from interior renovations and put funds toward backyard projects instead. As the economy has improved, those projects got larger and more elaborate, Mr. Zock says. “People felt like they couldn’t justify remodeling, but they could see the sense in spending money on outdoor spaces. As a result, there’s been a huge surge in people wanting to invest in their backyards.”

Then, there’s Pinterest. More than any other social media site or marketing campaign, the online bulletin board has driven interest in backyard landscaping and remodeling. “Basically, people spend hours on that site getting ideas,” says Mr. Gandora. “Then they go to Google and spend more time looking at separate features, like fire pits or concrete pavers. People used to want to keep up with the neighbors. Now, they want to keep up with everybody on Pinterest.”

Bigger is Better

The trend many contractors and landscape architects are noticing is more larger pavers and slabs that require special handling and installation to prevent cracked units. Big pavers and slabs give a more natural look, believes Mr. Gandora. “The sense of scale is bigger, so what we’re seeing is a preference for bigger pavers,” he says. “If you have a very large project with smaller pavers, it can tend to look busy, and homeowners don’t like that, especially with so many elements in the space.”

Mr. Gandora thinks the paver industry may see issues with this trend in the near future. If homeowners start asking for larger pavers on driveways, they won’t work well there. Another disadvantage to larger pavers and slabs is weight; some can weigh up to 60 pounds, requiring specialized equipment to place them. But larger pavers are bringing advantages as well, Mr. Gandora says. Since each paver or

slab takes up more area, they install faster, which increases production efficiency. They also create an expansive aesthetic similar to natural stone, he adds.

Addressing Challenges

With the trend toward large outdoor residential projects, particularly in backyards, unique challenges emerge. One of the major difficulties can be access, especially with homes that have landscaping or narrow passageways along the sides of a house. That can increase a project’s cost because it takes more time to get materials into the backyard, says Mr. Hampton. For example, on a recent backyard project that involved a grill island, fire pit, retaining wall and extensive pavers delivered along the side of a mansion-style house, Mr. Hampton and his team couldn’t use a skid loader, so they used smaller equipment that required more trips. Overall, the project took five weeks, which was longer than it would have been with better backyard access.

But the extended timeframe became a positive, Mr. Hampton says. As the crew worked, the homeowner kept adding to the project, wanting more pavers and additional features. Grades are another challenge with backyard projects. People often will want their hardscape floor to meet the back door or existing patio, but a contractor has to figure out how to create enough slope away from the house to prevent water problems. That usually means putting in more hidden drains and finding an appropriate area where they can empty.

Looking Ahead

Despite some of the challenges that backyard projects present, many landscape architects, designers and contractors expect these outdoor living spaces to get even more extensive, especially as the economy strengthens and more of the population ages. “Empty nesters are really taking hold of this trend,” says Ms. Messervy. “They’re creating these backyard-homestead kind of spaces, where they have an appreciation for the land and nature. They find ways for their backyards to simply work better for them.”

The backyard is no longer a mere grass patch the kid down the block grudgingly mows each week. These days, that space is a place as vital and lively as any indoors. In some cases, it’s even more enticing than hanging out in the kitchen. Messervy says, “People love what they can create for themselves in their backyards, and it doesn’t matter where they live or whether it’s winter for six months of their year. They all want to be outside.”


Why Specify an ICPI Certified Installer?

For commercial and municipal projects, ICPI promotes specifying certified installers in its webinars and continuing education presentations seen annually by hundreds of licensed civil engineers, architects and landscape architects. These ICPI presentations earn credits toward civil engineers’ professional development hours, and continuing education programs administered by the American Institute of Architects, the American Society of Landscape Architects and the Green Building Certification Institute.

The ICPI Concrete Paver Installer Certification can be supplemented with three additional courses resulting in three designations: Residential Paver Technician, Commercial Paver Technician and Permeable Interlocking Concrete Pavement (PICP) Specialist. Specifiers are encouraged to include the appropriate designation in residential, commercial/municipal or in PICP project specifications. By specifying that an ICPI Certified Installer be on the jobsite as foreman or crew leader, this can help assure that installation is done according to industry best practices.

To obtain and maintain certification, an installer must attend a course, pass an exam and meet minimum installation experience requirements. If a Certified Installer is in the specs, the contractor has a legal obligation to place a Certified Installer on the job. Obviously, it’s up to this person to manage the crew and jobsite according to ICPI best practices.

For residential projects, the contractor is often the designer and specifier who works in cooperation with the homeowner. For these projects, the homeowner’s big question is this: Can I trust this contractor to get the job done right? ICPI Concrete Paver Installer Certification is one of several things that can answer this question affirmatively. Other affirmative answers come from positive contractor job references, an impressive project portfolio and the manner in which the contractor relates to the homeowner.

Residential and commercial contractors can use ICPI Concrete Paver Installer Certification to promote their company to the homeowner and specifier markets. Certification is another marketing and sales tool accompanying a fair price, a history of quality jobs and timely service.

An ICPI member paver manufacturer might offer an “authorized contractor” service that refers residential customers to a group of reputable contractors that purchase concrete paving products from that manufacturer. Paver manufacturers should include ICPI certification as part of their requirements for qualifying contractors to participate in an authorized contractor program. This is one of several assurances to the manufacturer that its authorized contractors install segmental concrete paving systems according to industry best practices. This helps minimize complaints and callbacks.

ICP 021 KNOW 02ICP 021 KNOW 03


ICPI Certified Installer courses are offered multiple times each year in various locations throughout North America.

Concrete Paver Installer Course:

This is the introductory course. It provides a broad foundation of knowledge about all aspects on installation of segmental concrete pavements including materials, installation, estimating overhead recovery and job costing. This is a two day, classroom course immediately followed by an exam. Certification is obtained by meeting minimum installation and continuing education requirements over a twoyear period. Certification is renewed every two years. ICPI recommends that installers, specifiers and manufacturers’ representatives taking this course have at least one year of installation experience to receive the most from the information presented.

Once the exam is passed, an installer can apply to become an ICPI Certified Installer by submitting an application for certification. This document details concrete paver installation experience which must meet the required minimum. For more information on requirements visit ICPI then issues the applicant an ICPI Certified Installer document and lists the individual on the ICPI website as certified. ICPI Certified Installer status is only granted to individuals; certification does not apply to a company. To remain valid, an ICPI Certified Installer must renew certification every two years by paying a renewal fee and documenting completion of the minimum required hours of continuing education related to the industry.

Advanced Residential paver Technician Course:

This two-day course covers specialty applications typically built in backyards such as raised patios, outdoor kitchens, paving around swimming pools, lighting, water features, fireplaces and fire pits. The course also includes an introduction to residential permeable pavements. The course is typically taken after the above installer course. In addition to taking this course and passing the exam, there are experience requirements to qualify for the accompanying designation. Those who take the course and pass the exam earn a Record of Completion, which does not expire.

Commercial Paver Technician Course:

This two-day course on commercial, municipal and industrial applications includes stabilized bases, overlay/inlays, rigid applications, roof applications, grid pavements, machine-assisted installation and take-offs. The course is typically taken after the first installer course. In addition to taking this course and passing the exam, there are experience requirements to qualify for the accompanying designation. Those who take the course and pass the exam earn a Record of Completion.

ICPI PICP Specialist Course:

This is a one-day course on system types, estimating, materials, installation and maintenance. The course is typically taken after the first installer course. In addition to taking the PICP course and passing the exam, there are experience requirements to qualify for this designation. Those who take the course and pass the exam earn a Record of Completion.

GET CERTIFIED To register for an ICPI certification course, visit



The Transcendent Backyard

While this magazine typically focuses on commercial and municipal applications, this particular issue is about residential projects. Such uses consume about 75 percent of the concrete paving units made in the U.S. and Canada. This market is bread-and-butter to concrete paver producers, dealers and contractors. ICPI manufacturer members continually invent and promote new shapes/sizes, textures, patterns and colors that communicate a widening range of moods that fit with the house and yard.

Backyard living spaces with concrete pavers and segmental retaining walls are where most residential sales land. These products have helped expand other industries such as outdoor kitchens, countertops, lighting, grills, fire pits, fireplaces, furniture, trellises, fountains, pizza ovens, ponds and hot tubs. From the homeowner perspective, the return on investment into this backyard utopia is 100 percent or close to it when selling the home. So 100 percent enjoyment with 100 percent return resonates as a worthwhile deal for homeowners. Demographics underpin this investment trend with a growing number of homeowners over 55-years-old with no kids in the house.

The stars aligned in the market in the late 1990s. A second wave of development came in the wake of the 9/11 terrorist attacks. Homeowners invested in making their residences more secure and comfortable rather than risk traveling on vacations. With the recent recession in the rearview mirror, backyard living space reemerged as its own industry. You can explore a wide range of outdoor living displays and building materials at Hardscape North America ( held in Louisville, KY, annually in October.

This particular issue touches on some trends in backyard environments and the reasons for them from the owner, designer and contractor perspectives. My particular take on this growth market is its creation of unique residential spaces and places as a result of combining indoor functions with the outdoors.

An outdoor kitchen is not one space, but several. The space certainly has some key things normal to most kitchens, but also the sun, shade from trees, a cool breeze, birds, the wind and maybe water running through a fountain or nearby pond. The experience of a kitchen is transformed by integration with the natural environment.

The integration of tangible and intangible experiences from such outdoor living spaces fuels this market. It is magical. And backyard living spaces seem to be the only residential space perceived and received this way. The intersection of indoor functions with the outdoors transcends expectations and creates a new, refreshing reality for families and friends to relax and recharge, and segmental concrete pavements are vital to that transcendence.