Short answer: start with HT-508 when the design calls for a shallow, extensive planting profile dominated by sedum or other low-growing ground cover. Start with HT-5020 when the design calls for a deeper, semi-intensive profile for ornamental grasses, herbs or other herbaceous planting. This comparison is a selection guide, not final engineering approval. The completed roof build-up must still be checked against structural capacity, waterproofing, drainage, wind conditions, irrigation needs, local climate and the approved plant schedule.
What Do 8 cm and 20 cm Mean?
The published external dimensions of HT-508 are 500 × 500 × 80 mm, while HT-5020 measures 500 × 500 × 200 mm. In this guide, “8 cm” and “20 cm” therefore refer to the nominal module height.
Module height should not automatically be written into a project specification as the exact growing-medium depth. The usable planting profile can be affected by the module geometry, fill level, mulch or surface finish and the planting detail. Confirm the current product drawing and the proposed roof build-up before stating a final substrate depth.
HT-508 vs HT-5020 at a Glance
| Selection point | HT-508 | HT-5020 |
|---|---|---|
| Published module size | 500 × 500 × 80 mm | 500 × 500 × 200 mm |
| General design category | Extensive | Semi-intensive |
| Typical planting direction | Sedum, succulents and low-growing ground covers | Ornamental grasses, herbs and herbaceous plants; any shrub selection requires project-specific review |
| Useful starting point when | The brief prioritizes a shallow planting profile and a simple, repeatable plant palette | The brief needs a deeper planting profile and a more varied landscape composition |
| Still requires confirmation | Completed saturated load, plant root requirements, roof assembly, drainage outlets, irrigation, wind design, fire strategy, maintenance access and local regulations | |
When HT-508 Is the Better Starting Point
HT-508 is intended for extensive planting schemes. It is the more relevant model to review when the selected vegetation consists mainly of sedum, succulents or other low-growing ground covers and the design team wants a shallow modular profile.
It can suit projects in which the same planting approach is repeated across a broad roof area, provided that the complete assembly has been approved for that roof. A shallow module does not, by itself, prove that a finished system is “lightweight.” Structural assessment must use the completed saturated build-up, including the module, growing medium, stored water, mature vegetation and any other permanent or temporary loads.
Do not select HT-508 solely because the roof area is large or because a low-maintenance roof is desired. The plant species, climate, exposure, water strategy and maintenance plan must also be compatible with a shallow profile.
When HT-5020 Is the Better Starting Point
HT-5020 is intended for semi-intensive planting schemes and provides a deeper module profile than HT-508. It is the more relevant model to review when the landscape plan includes ornamental grasses, herbs or herbaceous plants that need more planting volume than a shallow extensive scheme.
The deeper profile can support a more varied planting composition, but plant suitability is not determined by module height alone. Root habit, mature size, climate, irrigation, maintenance and the detailed growing-medium specification all matter. Small shrubs should be assessed species by species by the landscape designer; HT-5020 should not be presented as a universal solution for every shrub.
A deeper module also changes the roof design inputs. The project engineer must assess the completed saturated load, and the waterproofing and drainage teams must confirm how the system interfaces with outlets, overflows, inspection zones, edges and adjacent roof elements.
Five Checks to Complete Before Choosing a Model
1. Confirm the plant schedule
List the proposed species, mature size, root characteristics and maintenance expectations. “Sedum roof” or “rooftop garden” is not a detailed enough planting brief for final module selection.
2. Confirm the complete roof load
Ask the structural engineer to review the finished system in its relevant design condition. The review should account for the module, saturated growing medium, retained water, vegetation and other roof loads. Do not substitute an empty-module weight or a generic “light” or “heavy” label for a project-specific calculation.
3. Coordinate the roof assembly
Confirm the waterproofing and root-protection strategy, protection layers, drainage path, outlets, overflows, inspection access and perimeter details. Module selection cannot correct an incomplete roof drainage or waterproofing design.
4. Review climate, irrigation and maintenance
Rainfall, dry periods, temperature, wind exposure and plant establishment all affect water demand. Water-retention features do not automatically remove the need for irrigation. The irrigation and maintenance plan should be agreed for the selected plants and local conditions.
5. Approve current product information
Before procurement, request the current model drawing and confirm the proposed build-up with the project team. For a new specification or an unfamiliar plant mix, consider a sample or project mock-up before approving the full quantity.
Common Selection Mistakes
- Treating 80 mm or 200 mm as an automatically guaranteed substrate depth. These figures are published module dimensions; confirm the actual planting profile in the project detail.
- Calling a system lightweight without a saturated-load calculation. The completed build-up, not the model name, determines the design load.
- Choosing from plant names alone. Species, mature size, climate, root volume, irrigation and maintenance must be considered together.
- Assuming a deeper module is always better. Greater depth is useful only when it supports the approved planting and roof design.
- Adding raised edges or extra fill without an engineered detail. Deeper planters and tree planting require a separately coordinated structural, waterproofing and drainage solution.
A Practical Selection Workflow
- Define the planting intent and preliminary species list.
- Use HT-508 as the initial extensive option or HT-5020 as the initial semi-intensive option.
- Request the current product drawing and prepare the complete proposed roof build-up.
- Coordinate the proposal with the structural engineer, landscape designer, waterproofing consultant and drainage team.
- Confirm irrigation, access and maintenance responsibilities.
- Approve the model, planting detail and bill of materials before ordering.
Need the published dimensions, system overview and project-supply information in one place? Compare HT-508 and HT-5020 on our main product overview.
HT-508 vs HT-5020 FAQ
Is an 8 cm module always an 8 cm growing-medium layer?
No. The 80 mm figure is the published external height of HT-508. The usable growing-medium profile depends on the module geometry and the approved planting detail. Confirm the current drawing and fill level before specifying substrate depth.
Which model is the usual starting point for sedum?
HT-508 is the usual starting point for an extensive scheme based mainly on sedum, succulents or low-growing ground covers. Final suitability still depends on the species, climate, roof exposure, irrigation and complete build-up.
Which model should be reviewed for ornamental grasses or herbs?
HT-5020 is the more relevant starting point because it provides a deeper semi-intensive profile. The landscape designer should confirm that the available planting volume and proposed growing medium suit each selected species.
Can HT-5020 be used for shrubs or trees?
Some shallow-rooted shrubs may be considered only after project-specific review. HT-5020 should not be described as suitable for every shrub, and it should not be assumed to provide the engineered planter depth required for trees. Larger planting requires a separately coordinated design.
Can the model be selected from roof area alone?
No. Roof area affects quantity, but model selection also depends on the plant schedule, saturated design load, roof assembly, drainage, wind exposure, irrigation, access and maintenance plan.
What information should I send when requesting a recommendation?
Provide the project location, roof area, proposed plants, target planting profile, any known structural limits, roof and drainage drawings, irrigation approach, estimated quantity and project schedule. This allows the two models to be screened more accurately before the project team gives final approval.
Request a Model Review
Send us your project location, roof area, proposed plant palette, target planting profile and available roof details. We can help identify whether HT-508 or HT-5020 is the more relevant model for technical review. Final specification and structural approval remain the responsibility of the project’s qualified design team.