8 Upgrades Every Landscape Architect Should Spec
A technical guide to specifying hardscape assemblies that perform, drain, and hold up for decades.
When a plaza heaves, a driveway ruts, or joints wash out of a feature walkway, the instinct is to look at the installation. More often, the story begins earlier, in decisions made at the design stage that seemed reasonable at the time and only revealed their consequences two winters later.
After years of reviewing hardscape performance across North America, I see the same handful of specification gaps resurface on otherwise well-executed projects. Each one is also an opportunity: a place where a targeted upgrade to the spec changes how a surface performs for decades.
This matters most at the landscape architect’s desk, because the spec carries your design intent through bidding, substitution requests, and a job site you may never visit. The clearer and more complete it is, the better it protects both the design and your professional reputation through years of service. What follows are the eight upgrades I recommend most consistently, why each one affects long-term performance, and how to work it into your documents.
Upgrade 1: Switch to an Open-Graded Base in Freeze-Thaw Climates
WHAT TO SPECIFY
Specify clean, angular, open-graded aggregate (commonly ASTM No. 57 or No. 2 for the base layer), with compaction requirements written to achieve aggregate interlock per CMHA guidelines. Where you specify ROMEX TRASS BED as the bedding layer, the data sheet requires a load-bearing, firm, and water-permeable subsurface, so the base specification and the bedding specification must agree with each other.
Upgrade 2: Replace General Slope Notes With Spot Elevations and a Defined Drainage Path
Permeable does not mean drainage-proof. Water that infiltrates the surface still needs somewhere to go, and water that cannot infiltrate fast enough during a major storm event still needs to shed. A surface that appears to drain in normal conditions can pond during a 25-year event, and ponding on a hardscape assembly creates a cascade of problems: saturated bedding layers, accelerated efflorescence, freeze-thaw damage from trapped water, and potential water intrusion at the building envelope.
The ROMEX TRASS BED data sheet calls for a minimum slope of 1.5 to 3 percent on load distribution layers and slab coverings, with collected water directed to corresponding drainage measures. On watertight outdoor areas and over-structure installations where water can pond, the data sheet recommends a capillary-breaking drainage mat. Those numbers exist because flat assemblies fail.
The practical risk in most projects is not that the designer does not know this, it is that a general note on the drawing set is not the same as a specified minimum. When grading and hardscape details are produced by different people or in different drawing packages, a conflict between them may not surface until a site visit after installation.
WHAT TO SPECIFY
Write a minimum 1.5 percent slope away from structures on every hardscape sheet, with spot elevations rather than a general note. On rooftop and on-slab assemblies, detail the drainage mat and its outlet location. Review the grading plan and the hardscape details together before issue to confirm they agree.
Upgrade 3: Select Jointing Products by Joint Width and Load, Not by Habit
Jointing products are engineered for specific joint geometries and traffic loads. A product chosen because it worked on the last project may be outside its performance envelope on this one. Joint width in the field covers a wide range, from the narrow joints of interlocking concrete pavers to wide, irregular flagstone joints that can exceed 400 mm in feature installations, and no single product covers all of it.
The ROMEX jointing range maps to that spectrum in defined bands:
- ROMEX FUGENSAND is a stabilized jointing sand for unbonded interlocking paver construction with narrow joints up to 5 mm (1/4 in). It suits patios and residential driveways with standard paver geometry, not wide-jointed slab or flagstone layouts.
- ROMEX D1 is a commercial resin jointing mortar for joints over 3 mm (1/8 in) on porcelain and natural stone, or over 5 mm (1/4 in) on concrete pavers. The data sheet rates it to 7.5 tonnes on its own and to 40 tonnes when installed over ROMEX TRASS BED.
- ROMEX D2000 is a heavy vehicle jointing mortar rated to 25 tonnes, with a minimum joint width of 3 mm (1/8 in) and a compressive strength of 7,528 psi. Both D1 and D2000 require joints cleaned to a minimum depth of 30 mm (1-1/4 in), or two-thirds of stone height under traffic loads.
- ROMEX FLEX JOINT is a flexible, permeable resin mortar for any joint width over 8 mm (3/8 in), with no narrow upper limit, rated to 25 tonnes. It is the right specification for wide and irregular joints, permeable pavers, and control joints in bonded construction.
- ROMEX W1000 is a cold-climate jointing mortar for joints over 8 mm (3/8 in), rated to 25 tonnes and installable down to -5 C (23 F) for winter work or northern climates.
Irregular flagstone deserves its own note. It is one of the most widely specified natural stone surfaces and one of the most commonly mismatched with jointing product. Joint width varies piece to piece within a single installation, and feature layouts can run very wide by design. A jointing product for flagstone has to tolerate that full range, which is where a flexible resin mortar with no narrow upper limit fits the geometry. Flagstone also varies in thickness, so it should be set on a bonded mortar bed such as ROMEX TRASS BED rather than a loose course, to ensure every piece is fully and evenly supported regardless of individual unit thickness.
WHAT TO SPECIFY
Name the joint width range, the design traffic load, and the required cleaning depth in your spec section, then select a product whose data sheet matches all three. If a substitution request arrives, those three parameters give you an objective basis to accept or reject it without relying on brand comparisons.
Upgrade 4: Keep the Bedding Layer Within Its Thickness Limit
The bedding course is a leveling layer, and an important one. It compensates for minor variation in the finished base surface and brings the paving units to the correct final elevation. For conventional unbonded construction it should be held to a nominal 25 mm (1 in), and never more than approximately 50 mm (2 in). Beyond that maximum, the bedding becomes an unstable layer. A bedding course that is too thick consolidates unevenly under load, and that consolidation is a direct cause of rutting and low spots in the finished surface. The bedding is doing its job within its thickness limit; outside that limit it is a liability.
When a base comes in low or uneven, the field instinct is to make up the difference in bedding sand. That instinct is understandable, but once the bedding exceeds its maximum thickness it is no longer a stable layer. It will consolidate under load, and that consolidation shows up as settlement in the surface above it. The specification call that prevents it is correcting grade in the base, where compaction can lock it in, and keeping the bedding within its designed thickness range.
A bonded mortar bed behaves differently from a loose course and follows different rules. ROMEX TRASS BED is screeded to depth, ranging from 40 to 100 mm (1-1/2 to 4 in), with the depth selected for the expected load and the type of unit. Because it is a bonded structural bed rather than loose aggregate, it carries load instead of consolidating under it. Its cure schedule is specific: the surface can be walked on after 7 days, accept vehicles up to 3.5 tonnes after 14 days, and reach full load capacity at 28 days.
publicly available and structured for permit and bid documentation.
WHAT TO SPECIFY
Hold conventional bedding to a nominal 25 mm (1 in) and 50 mm (2 in) maximum. The bedding layer functions as a leveling course within that range; beyond it, the layer becomes unstable under load. Specify that grade corrections beyond the bedding tolerance occur in the base, where compaction locks them in. Where you specify a bonded mortar bed, include the screed depth for the design load and the full cure schedule, so site phasing and logistics do not put a vehicle on a green bed.
Upgrade 5: Call Out Lateral Force Zones on the Plan
Vertical load is only half the structural picture. Braking, acceleration, and repeated vehicle turning generate horizontal forces that push paving units out of position, and unbonded assemblies are especially vulnerable. A parking entry that performs well on the straightaway can creep and gap at the turn radius within a season or two.
This is a design-stage problem because the high-force zones are visible on the plan before a single paver is placed. Braking and stopping zones, entry radii, and sloped surfaces are all identifiable at the drawing stage, and specifying displacement protection in those zones at that point costs nothing. Addressing it after the surface has migrated costs considerably more.
Two approaches address lateral displacement. A fully bonded assembly using the ROMEX RSG-10 system bonds each paver to the bedding layer through a wet-on-wet connection with ROMEX ADHESION ELUTRIANT, so units cannot migrate under horizontal force. For unbonded assemblies, ROMEX ISATEC EARTH ANCHORS placed per an engineered anchor layout plan, combined with ROMEX FLEX JOINT or ROMEX FUGENSAND, are designed specifically for sloped surfaces, braking zones, and frequent turning areas.
WHAT TO SPECIFY
Identify the braking, turning, and sloped zones on your plan and specify displacement protection or a bonded assembly in those zones by name. Generic notes such as ‘stabilize as required’ transfer a design decision to whoever bids lowest.
Upgrade 6: Match Joint Rigidity to Whether the Assembly Is Bonded or Unbonded
WHAT TO SPECIFY
Treat base, bedding, and jointing as one assembly in your documents, with consistent load assumptions across all three sections. Match the rigidity of the jointing product to whether the assembly is bonded or unbonded. If the jointing product requires a stable, non-moving substrate, the base and bedding specifications must be written to deliver one.
Upgrade 7: Specify a Warrantied System Rather Than Individually Sourced Components
- Load rating follows the assembly, not just the unit. ROMEX D1 is rated to 7.5 tonnes on its own and to 40 tonnes installed over ROMEX TRASS BED. The bonded bed spreads load into the base, so a pedestrian-rated paver or thin slab can be specified into a vehicular application it could not carry as a loose unit.
- Joint width becomes a drainage decision, not a structural constraint. Because a bonded assembly does not rely on tight joints to hold units in position, joints can be opened up and a permeable mortar such as ROMEX FLEX JOINT specified to meet the infiltration the design requires, rather than sizing joints around stability.
- A bonded assembly with ROMEX TRASS BED provides what I call invisible edge restraint. Because the units are bonded to the bed, they cannot migrate laterally, which means no mechanical edge restraint is required at the perimeter. Grass can grow right up to the paving surface, flush and clean, with no plastic edging, no steel restraint, and no spike line interrupting the design. It removes a routine failure point and a line item from the detail, while opening up design possibilities that a dry-laid spec simply cannot achieve.
WHAT TO SPECIFY
Where long-term performance and documented accountability matter, write the system into the spec rather than assembling equivalents. Reference the manufacturer’s data sheets directly in your documentation. ROMEX publishes full technical data sheets for every product, and assemblies are available through BIMsmith for direct inclusion in drawing sets and permit packages.
Upgrade 8: Specify a Bonded Assembly Under Porcelain and Large-Format Slabs
Outdoor porcelain tile is one of the fastest-growing surface choices in North American landscape design, and for good reason. It is durable, design-forward, and performs exceptionally well when installed correctly. Right now it is also one of the most common sources of post-installation callbacks, and the problem is almost never the tile itself. It is the installation method.
Outdoor porcelain tile is an excellent surface choice, and it is stronger than its reputation suggests. At 3 cm thickness it can support vehicle loads. The issue is not strength. It is movement. Porcelain tile has no mechanical interlock. In a dry-laid assembly there is nothing bonding the unit to the substrate, so under repeated loading the unit moves, however slightly. That movement, sustained over time, is what causes cracking, not the load itself.
Aspect ratio amplifies the risk. The larger the unit relative to its thickness, the more any micro-movement at the base translates into stress across the face of the tile. Large-format outdoor porcelain tile, 600 by 600 mm or larger, concentrates that stress and is where failures cluster. The terminology also matters for specification accuracy: the correct term is outdoor porcelain tile, not porcelain paver. Paver implies mechanical interlock and a unit geometry designed for dry-lay construction. Outdoor porcelain tile is a different product category and requires a different installation method.
Porcelain performs when it is fully and uniformly supported across its entire underside, and that is what a bonded bedding assembly delivers. ROMEX TRASS BED screeded to depth, with ROMEX ADHESION ELUTRIANT applied across the full underside of each unit, creates a wet-on-wet bond with complete contact and no voids. There is nowhere for water to collect, nothing for the unit to rock on, and no unsupported span for it to crack across. For larger slabs, the ROMEX ADHESION ELUTRIANT data sheet specifies the bonding slurry across the whole underside, with the outer 6 mm (1/4 in) kept clear so it does not squeeze into the joint.
WHAT TO SPECIFY
For outdoor porcelain tile and large-format slabs, specify a bonded wet-lay assembly rather than a dry-laid detail. Note the full-underside back-buttering requirement explicitly in the spec. Pair it with a jointing product matched to the joint width, such as ROMEX D1 for joints over 3 mm, or ROMEX FLEX JOINT for wider or irregular joints.
Specifying Hardscapes That Outlast the Warranty
None of these eight upgrades requires exotic knowledge or specialized detailing experience. They come down to treating the hardscape as one engineered assembly: a draining base, a thin and uniform bedding course or a screeded bonded bed, joint materials matched to joint width and traffic load, rigid surfaces given full continuous support, lateral forces addressed where the plan shows them, and a specification written tightly enough to survive the bidding process intact.
Get those decisions right on paper, and the installation crew inherits a buildable design instead of a set of ambiguities. That is what keeps projects performing, and professional reputations with them, a decade after ribbon cutting.
Frequently Asked Questions
What is the most common specification gap in hardscape design?
Inadequate base specification is the most consistent root cause of long-term performance problems. A dense-graded or fines-heavy base retains water, becomes frost-susceptible in freeze-thaw climates, and leads to ice lens formation, heaving, and differential settlement. An open-graded base of clean, angular aggregate drains freely and does not develop the conditions for frost heave.
How much slope does a permeable hardscape surface need?
Plan for a minimum slope of 1.5 percent, up to 3 percent on load distribution layers, directed away from structures. Even fully permeable assemblies need a defined drainage path for major storm events and for water that reaches the bottom of the profile. Detail the outlet, not just the slope.
Which joint width requires a flexible jointing mortar?
Joints over 8 mm (3/8 in) generally call for a flexible resin jointing mortar such as ROMEX FLEX JOINT, which has no narrow upper limit and suits wide and irregular flagstone joints as well as control joints in bonded construction. Narrow joints up to 5 mm (1/4 in) in unbonded interlocking paver installations are typically handled with a stabilized jointing sand such as ROMEX FUGENSAND.
Can outdoor porcelain tile be dry-laid?
Outdoor porcelain tile is an excellent surface material and genuinely strong, capable of supporting vehicle loads at appropriate thickness. The problem with dry-laying it is not strength, it is movement. Without a bond to the substrate there is no mechanical interlock, and repeated loading causes micro-movement that accumulates into cracking over time. Installed correctly on a bonded bed such as ROMEX TRASS BED, with ROMEX ADHESION ELUTRIANT applied across the full underside, outdoor porcelain tile is one of the most durable and design-forward surfaces available in the North American hardscape market.
How thick should the bedding layer be in a conventional unbonded installation?
Hold conventional bedding to a nominal 25 mm (1 in) and 50 mm (2 in) maximum, and specify that grade corrections occur in the base rather than the bedding. Excess loose bedding consolidates unevenly under load and is a direct cause of rutting. A bonded mortar bed such as ROMEX TRASS BED follows different rules: it is screeded from 40 to 100 mm (1-1/2 to 4 in) depending on load and unit type, and carries load as a structural layer rather than consolidating under it.
What CMHA guidelines apply to jointing and base specifications?
CMHA guidelines for permeable interlocking concrete pavement (PICP) address open-graded base aggregate, infiltration requirements, and paving unit stability requirements for jointing. Specifically, CMHA specifies that all paving units must be fully stable before and after jointing is applied, and that the base and bedding assembly must meet defined performance standards before jointing begins. These requirements align directly with the performance specifications published in ROMEX product data sheets.
