Recessed type manholes (also called recessed manhole covers) are designed with a recessed tray on the top surface so the cover can be infilled with concrete, tiles, pavers, or asphalt. This makes them ideal where the manhole cover must visually blend into the surrounding surface—especially in streetscapes, footpaths, plazas, landscaped areas, and paved zones.
What is a recessed type manhole?
A recessed type manhole cover includes:
- Frame
- Recessed cover/lid with an infill tray (depth varies)
- Optional: lifting keys, locking, hinge, gasket/seal
The infill tray holds the surface finish (pavers, concrete, etc.) so the cover becomes less visible and more uniform with the surrounding pavement.
Where recessed type manholes are used
Recessed type manholes are preferred when appearance and surface continuity are important:
- Footpaths and pedestrian zones
- Paver/tile streetscapes
- Campuses, parks, and landscaped utility corridors
- Commercial areas with decorative paving
- Driveways and light-to-medium vehicle zones (when correctly load-rated)
They are also used when the design intent requires the manhole to be “hidden” within the pavement finish.
Recessed type vs solid top manholes (quick selection)
Choose recessed type manholes when:
- You need pavers/tiles to continue across the cover
- Aesthetic finish matters more than fast access
- Surface uniformity is a requirement
Choose solid top manholes when:
- Heavy traffic and durability are primary concerns
- You want faster maintenance access
- You want fewer infill-related failure risks
Load classes (EN 124): pick based on real traffic
The load class must match actual usage, not assumptions.
Common EN 124 classes:
- A15: pedestrian/cycle areas
- B125: footways, car parks
- C250: kerbside areas
- D400: carriageways/roads
- E600: industrial zones
- F900: airports/extreme loads
Important practical point: recessed covers are often used in paved areas, but if vehicles cross them regularly, you must specify B125/C250/D400 as required—otherwise the infill and seating will fail early.
Materials: Grey Iron vs Ductile Iron (SG Iron)
Ductile Iron (SG Iron)
Best for:
- Higher toughness and impact resistance
- Better safety margin under shock/vibration
- Reduced brittle cracking risk
Grey Iron
Used when:
- Loading is lower and predictable
- Cost sensitivity is high
- Installation quality is controlled
If the cover sees vehicle movement, vibration, uneven paving, or frequent access, ductile iron is generally the safer choice.
The critical engineering issue: infill behavior
Most recessed cover complaints are not “casting issues”—they’re infill failures.
Common infill problems:
- Cracking due to weak mix, poor curing, or wrong reinforcement
- Debonding between infill and tray
- Water ingress causing washout and settlement
- Mismatch between paver thickness and tray depth
- Edge spalling if the infill is not properly supported
To reduce failures, specify:
- Correct tray depth for your finish build-up
- Reinforcement requirements (if applicable)
- Proper curing time before opening to traffic
- Drainage control so water doesn’t sit in/around the tray
Design features that matter in recessed manholes
1) Tray depth and geometry
Tray depth must match the finish system:
- tiles/pavers + bedding layer
- concrete thickness and reinforcement
- asphalt layers if used
If the tray is too shallow, the infill will be thin and crack. If too deep, it adds weight and complicates handling.
2) Seating stability (anti-rocking)
Rocking causes noise, wear, and cracked infill. Look for:
- stable bearing surfaces
- anti-rocking seating design
- consistent dimensional control
3) Lifting and access
Recessed covers can be heavy once filled. Specify:
- safe lifting keyways
- handling method on site
- whether hinged design is required for frequent access points
4) Locking and safety (where needed)
Use locking where theft risk or public safety demands it.
5) Sealing (gasket)
If odor control or water ingress matters (utility/sewer), specify gasket/seal requirements.
Coating and corrosion protection
Choose coating based on exposure:
- Bitumen: general protection
- Epoxy: better corrosion resistance for harsh environments
- Powder coating: durable finish where appearance is also important
For outdoor paver zones, corrosion resistance still matters because moisture gets trapped around the frame.
Installation: the real make-or-break factor
Recessed type manholes need stricter installation discipline than solid top.
Key installation controls:
- Frame must sit on a level, stable bed
- No voids under frame flange
- Proper compaction around the frame
- Correct final level: cover must sit flush with finished paving
- Infill must be placed and cured properly before traffic
- Ensure paver/tile joints are detailed so water doesn’t continuously enter the tray
Common failure modes and how to prevent them
Cracked or loose infill
- Cause: thin infill, weak mix, poor curing, water ingress
- Prevent: correct tray depth, proper infill design, curing, drainage control
Rocking and noise
- Cause: uneven seating, settlement, debris
- Prevent: anti-rocking seating + good bedding and compaction
Settlement around frame
- Cause: poor backfill compaction or washout
- Prevent: correct compaction and edge detailing; control water flow paths
Difficult access/unsafe lifting
- Cause: heavy filled cover without safe lifting points
- Prevent: specify lifting/hinge solution based on maintenance frequency
Recessed type manhole checklist (copy for BOQ / RFQ)
Include:
- Standard reference: EN 124 (or required equivalent)
- Load class: A15/B125/C250/D400/E600/F900
- Material: Grey Iron / Ductile Iron (SG Iron) with grade requirement
- Clear opening size + frame depth
- Recess tray depth and intended finish system (pavers/tiles/concrete)
- Seating requirement: anti-rocking
- Locking/hinge requirement (if needed)
- Coating system + inspection requirement
- Testing/documentation requirements
- Installation notes: bedding, compaction, infill curing, final levels
FAQ
Are recessed type manholes good for heavy traffic roads?
They can be used only if the correct EN 124 load class is selected and the installation/infill is designed for traffic. In practice, recessed covers are more common in paved streetscapes and pedestrian-heavy zones than high-speed carriageways.
Why does recessed manhole infill crack?
Usually due to thin infill, weak mix, poor curing, water ingress, or wrong tray depth for the paving build-up.
What infill is used in recessed type manholes?
Concrete, pavers, tiles, or asphalt—selected based on the surrounding surface system and tray depth.