HOW TO MEASURE FOR A NEW FIRE DOORSET

Accurate measurements are essential when ordering a new fire doorset. All Masterdec doorsets are manufactured to the dimensions provided, therefore incorrect measurements may result in installation difficulties, excessive fitting gaps or non-compliance with certification requirements.

Before measuring, please ensure that all dimensions are taken in millimetres (mm).

STEP 1 – MEASURE THE STRUCTURAL OPENING WIDTH

Measure the structural opening width in three locations:

  • Top
  • Middle
  • Bottom

Record the smallest measurement.

The measurement should be taken from the finished wall substrate on one side to the finished wall substrate on the other side.

STEP 2 – MEASURE THE STRUCTURAL OPENING HEIGHT

Measure the structural opening height in two locations:

  • Left side
  • Right side

Record the smallest measurement.

The measurement should be taken from the finished floor level (or threshold bearing surface) to the underside of the structural lintel or finished opening above.

STEP 3 – ALLOW FOR INSTALLATION TOLERANCES

Fire doorsets require an installation gap between the outer edge of the frame and the surrounding wall substrate.

IMPORTANT

The maximum permitted gap between the doorset frame and the surrounding wall substrate should not exceed 20mm.

However, based on practical installation experience, Masterdec recommends allowing a fitting gap of approximately:

  • 10mm to 15mm per side
  • 10mm to 15mm above the frame

This provides sufficient space for:

  • Levelling and packing
  • Compensation for uneven wall lines
  • Installation tolerances
  • Correct fire stopping around the frame

Using excessive gaps can make installation more difficult and may affect compliance if appropriate fire stopping solutions are not used.

OVERALL DOORSET DIMENSIONS

All Masterdec products are supplied as complete doorsets, meaning the frame dimensions are included within the overall size specified.

IMPORTANT

When ordering a doorset, the dimensions provided must represent the overall doorset size, including the frame.

DOORSETS WITH THRESHOLDS

Where a threshold is specified, the threshold forms part of the overall doorset assembly.

IMPORTANT

Any threshold selected will be included within the overall doorset height.

For example:

  • If you order a doorset with an overall height of 2100mm
  • And a threshold is selected

The complete doorset, including the threshold, will still measure 2100mm overall

The threshold is not supplied in addition to the specified height.

CHECK FOR UNEVEN OPENINGS

Many existing openings are not perfectly square.

Before ordering, check:

  • Width at top, middle and bottom
  • Height left and right
  • Floor levels
  • Wall alignment
  • Plumb of side walls

Always use the smallest measurement when assessing available opening dimensions.

MEASURING EXISTING FIRE DOOR REPLACEMENTS

When replacing an existing fire doorset, Masterdec recommends measuring the structural opening wherever possible rather than relying solely on the dimensions of the existing door or frame.

Existing installations may contain:

  • Packers
  • Large fitting gaps
  • Multiple frame layers
  • Additional linings

which may not accurately represent the true opening size.

IF YOU ARE UNSURE

If you are unsure how to measure your opening, please send:

  • Photographs of the opening
  • Existing doorset details
  • Approximate dimensions

to:

info@masterdec.co.uk

Our team will be happy to provide guidance before ordering.

MEASURING GUIDE SUMMARY

Width

✔ Measure top, middle and bottom

✔ Use the smallest measurement

✔ Allow approximately 10-15mm fitting gap per side

Height

✔ Measure left and right

✔ Use the smallest measurement

✔ Allow approximately 10-15mm fitting gap above the frame

Thresholds

✔ Thresholds are included within the overall doorset height

✔ Overall ordered size always includes the frame and threshold (where specified)

Maximum Installation Gap

✔ Maximum gap between frame and wall substrate: 20mm

✔ Recommended gap: 10-15mm per side

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