What Is Concealed Continuous Hinge Routing? (Mortise Depth)
Concealed continuous hinge routing means cutting matching, full-length recesses in the door edge and frame so the specified hinge sits as designed and moves freely. There is no universal mortise depth: use the selected hinge’s current template and instructions. Check the door, frame, clearances, fasteners, and any fire-door listing before cutting.
What concealed continuous hinge routing means
A concealed continuous hinge is a long hinge designed to be hidden or partly hidden when the door is closed. Routing is the controlled removal of material to make a recess, or mortise, for its leaf. The correct depth comes from the hinge maker’s instructions, not a general rule.
A continuous hinge runs along much or all of the door height, rather than joining the door and frame at just two or three points. Concealed designs differ in leaf shape, mounting method, and required door and frame geometry. Some are fully mortised; others are partly recessed or surface-mounted. Do not assume that a hinge that looks similar uses the same cut.
The goal is a hinge seated as specified, with no unintended high spots or excess recess. Its position must also preserve the door’s movement and the required clearances. A flush appearance alone does not prove the hinge is installed correctly.
ANSI/BHMA A156.26 covers continuous hinges. It does not give one mortise depth for every product. The hinge’s own template and instructions control the machining details; for a rated assembly, the door and hinge listing and applicable fire-door rules also matter.
Planning the hinge, door, and frame
Planning means confirming that the selected hinge suits the actual door, frame, swing, and use before you mark or cut. I start by collecting the hinge instructions and inspecting the door and frame. This simple check can prevent a clean-looking recess from weakening a part or blocking correct operation.
Record the door’s height, width, thickness, construction, and swing. Identify the frame material and any reinforcement. Check for glazing, thin skins, or concealed hardware and services near the planned cut. If you cannot confirm what lies behind the surface, stop and investigate before routing.
Then compare the door and expected use with the hinge’s published rating. Check its specified door size and weight limits, fastener type and locations, and any required reinforcement. A long hinge does not, by itself, show that it can carry every door.
Get the current template for the exact hinge model. Confirm whether the design calls for a recess in the door, frame, or both. Check the template’s mortise length, width, end allowances, and clearance notes. Do not scale an online picture or copy another model’s dimensions.
For fire-rated doors, check the door label and assembly documentation before any machining. A field cut can affect the listed construction even if the hinge works. Confirm that the proposed hinge and routing are permitted by the door listing and applicable requirements, including NFPA 80 where it applies. Use an authorized door shop when required.
Checking mortise layout and operating clearances
Layout means marking each hinge recess from the verified template and checking that the cut will leave the door and frame intact. Mortise depth is the depth of the recess, measured from the finished surface to its floor. Set it to the specified leaf thickness and fit, not to a generic number.
Measure the actual hinge leaf with a suitable gauge or caliper, then compare that measurement with the manufacturer’s stated depth and tolerance. The published instructions remain the authority if the measured part and drawing seem to differ. Do not add extra depth to make the leaf appear flush; first check for debris, a wrong datum, or a high spot.
Use the template to mark the hinge position from a consistent reference, such as the door top or a specified edge. Transfer the same reference to the frame. Check the hinge’s axis or pivot position, end clearances, and any required relationship between the door edge and frame. Small layout errors along a long hinge can make alignment harder to correct later.
Preserve the required operating gaps. There is no single gap value for every door, frame, hinge, or fire-door assembly. Use the door maker’s instructions and the applicable assembly requirements. Also confirm that the mortise will not break through a thin door skin, cut into glazing, or remove required reinforcement.
| Check | What to use | Decision before routing |
|---|---|---|
| Mortise depth | Hinge instructions and measured leaf | Recess only to the specified seat |
| Mortise width and length | Current hinge template | Include stated end and clearance allowances |
| Door and frame position | Template and measured assembly | Confirm hinge axis and swing geometry |
| Operating gap | Door and assembly instructions | Preserve required clearance; do not guess |
| Fasteners and load | Hinge rating and hardware schedule | Confirm size, type, locations, and capacity |
Routing and installing the continuous hinge
Routing is the machining step that forms the hinge recess. Secure the door and frame against movement, protect nearby finishes, and use a template-guided router or controlled machine setup suited to the work. Make shallow passes, test the setup on scrap where possible, and test-fit before removing more material.
Before cutting, confirm the router base, guide, bit, and template work together. A guide or cutter offset can make the recess wider or narrower than the template opening. Check that offset on scrap or a test piece. Keep the work supported, clamp it firmly, and follow the tool maker’s safety instructions.
Cut only the areas the hinge instructions call for. Where the design requires matching recesses in both door and frame, use the same reference logic on each part. Avoid a deep first pass. After each pass, clear dust and check the cut against the template and the hinge leaf.
Set the depth stop from the specified mortise depth. Make a test-fit before the final pass. The hinge should seat as intended without rocking on chips or high spots. If it stands proud, find the cause and remove only the high material. If it sits too deep, do not treat excess depth as a harmless cosmetic issue; it can change support and alignment.
Install only the specified fasteners, in the stated locations and sequence. Do not replace them with shorter, thinner, or different types without approval from the hinge manufacturer. Confirm that the substrate and any required reinforcement can hold them. Do not force a screw into a misaligned hole, since that can pull the hinge out of position.
Verifying fit, swing, and assembly compliance
Verification means checking the installed hinge as a working part of the door assembly, not just judging its appearance. I check seating, alignment, swing, latch action, and required gaps after fastening. If any check fails, find the cause before making more cuts or changing hardware.
Use a straightedge across the hinge leaf and adjacent surface to check for an unintended proud or sunken seat. Compare the result with the maker’s stated tolerance, if one is given. Check the full hinge length, since a long leaf can sit correctly at one end and bind or lift at another.
Move the door through its full intended swing. Watch for binding, rubbing, uneven gaps, or a shift in the door as it moves. Check that the latch engages and that the door closes as intended. A smooth swing does not replace required gap checks or a review of the fire-door assembly.
| Result | Likely checks | Next step |
|---|---|---|
| Leaf stands proud | Chips, high spots, incorrect depth, wrong template | Clean and recheck; correct only as allowed |
| Leaf sits too deep | Over-routing or wrong depth setting | Stop; assess support and repair options |
| Door binds | Alignment, axis position, gaps, fasteners | Compare with template and instructions |
| Fasteners pull out | Wrong fastener, weak substrate, missing reinforcement | Stop use and correct the attachment |
| Rated door was modified | Listing and assembly requirements | Consult the listing holder or authorized shop |
Restore finishes without filling the hinge knuckle, blocking movement, or covering required labels. Keep the hinge instructions, door documentation, and any approval records with the building’s maintenance information. For a fire-rated assembly, confirm compliance before returning the door to service.
Installation scenarios: what the checks reveal
These examples are illustrative, not reports of tested installations. They show how the same routing question can lead to different decisions. The hinge model, door construction, and assembly documentation set the requirements in each case.
Solid-core interior door: A homeowner has a concealed continuous hinge and a solid-core door. The template calls for recesses on the door and frame. Before cutting, the installer checks thickness, hinge position, fastener locations, and the frame’s backing. A test-fit shows a high spot; the installer clears debris and checks the cut rather than deepening the entire mortise.
Rated corridor door: A contractor finds a fire label on the door and proposes a new hinge. The first step is not to route the recess. The contractor checks the door’s listing and the hinge documentation to confirm that the proposed hardware and machining are allowed. If that cannot be confirmed, the work is referred to an authorized door shop.
Thin or unknown door construction: A DIY builder cannot tell how much material lies under the door’s surface skin. The planned recess might break through or reach a core component. The safe decision is to identify the construction and confirm the permitted machining before routing. A template cannot answer whether an unknown door can safely accept the cut.
Conclusion and FAQ
The reliable mortise depth is the one specified for the exact concealed continuous hinge and door assembly. Measure and mark from the current template, route in controlled passes, and verify the seat, swing, fasteners, and clearances. If the door is fire-rated or its construction is uncertain, confirm permission before cutting.
Is there a standard mortise depth for concealed continuous hinges?
No. Use the selected hinge’s installation instructions and template. Depth varies by model and installation.
Should the hinge leaf sit flush with the door and frame?
Seat it as the manufacturer specifies. Do not assume that “flush” means the same thing for every hinge or design.
Do I mortise both the door and the frame?
Only if the exact hinge instructions call for recesses in both parts. Some designs use a different mounting method.
Can I use a depth based on the leaf thickness?
The leaf thickness is a useful check, but follow the maker’s stated depth and tolerance. Do not rely on a generic measurement.
Can I copy dimensions from an online hinge diagram?
Not unless it is the current, verified template for the exact model. Similar-looking hinges can have different dimensions.
How do I check a mortise before fastening the hinge?
Clean the recess, test-fit the hinge, and check the seat along its length. Use a straightedge and the manufacturer’s tolerance where provided.
What fasteners should I use?
Use the hinge-specified type, diameter, length, and locations. Confirm the door or frame has suitable backing or reinforcement.
How much door-to-frame gap should I leave?
There is no universal value. Follow the door maker’s instructions and applicable assembly requirements.
Can I route a fire-rated door in the field?
Only after confirming that the door listing and applicable requirements allow the proposed hinge and machining. Use an authorized shop when required.
What should I do if the mortise is too deep?
Stop and assess the hinge support and alignment. Do not assume that a deeper recess is acceptable; consult the hinge maker or a qualified door professional.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
