Measuring a front door opening for replacement requires recording the brick-to-brick width and height in three places each, taking the smallest dimension as the working size.
The new door frame is then ordered roughly 10–20mm smaller than the smallest measurement to allow space for fitting, sealing and adjustment. Installation involves removing the old door and frame, preparing the opening, fitting and squaring the new frame, fixing with appropriate fixings into the structural opening, foam-sealing the perimeter gap, and finishing with internal and external trim.
A standard front door installation takes a competent installer 3–5 hours. While DIY installation is possible, most homeowners use a FENSA or Certass registered installer to ensure Building Regulations compliance.
A proper measurement isn't just two numbers. To order the right door and avoid problems at installation, you need to record several dimensions and characteristics of the opening, the door itself, and the surrounding context.
The door's "handing" describes which side the hinges are on and whether it opens inward or outward.
To determine handing, stand outside the door looking at it. If the hinges are on the left and the door opens away from you, it's a "right-hand outward opening" door.
(The convention can vary; some suppliers use different terminology — always clarify when ordering.) Recording the existing handing is essential unless you specifically want to change it.
Glas in der Haustür wirft beim Thema Sicherheit Fragen auf, denn eine Glasfläche könnte eingeschlagen werden. Auch hier gibt es gute Lösungen.
An gefährdeten Stellen, besonders wenn Glas in Reichweite des Schlosses sitzt, ist Sicherheitsglas sinnvoll. Verbundsicherheitsglas (VSG) besteht aus mehreren Scheiben mit einer reißfesten Folie, an der die Splitter bei Bruch haften, sodass kein durchgreifbares Loch entsteht.
So bleibt der Lichtgewinn erhalten, ohne dass das Glas zur Schwachstelle wird. Glas und Beschläge sollten dabei zusammen betrachtet werden. Unsere Türen entsprechen den aktuellen Anforderungen an die Sicherheit; mehr dazu im Ratgeber zum Sichern der Haustür.
Always measure twice. A 5mm error at order causes 5mm of unwanted gap or 5mm of unwanted forcing at installation — both create problems that are hard to fix retrospectively.
British front doors come in a small number of standard sizes that cover most properties. Custom sizes are available but have longer lead times.
Imperial sizes (with widths in inches) are the dominant standard in older British housing. The 33" × 6'6" door fits most Victorian and Edwardian properties without modification.
If your opening doesn't match any standard size, you have three options. The choice depends on how far off-standard the opening is and how much building work you want to involve.
Option 1: Custom-made door
Order a custom-sized door frame to fit the existing opening. This is the cleanest option but typically adds lead time (often 4–8 weeks rather than 2–3) and a custom-size surcharge.
Option 2: Resize the opening
For openings just slightly smaller than the standard nearest size, the opening can be enlarged by removing some brickwork. This requires a builder or experienced installer and may need a new lintel if the opening is widened. For openings slightly larger than standard, the gap can be filled with packing and timber blocking under the trim.
Option 3: Choose a different size
Sometimes the nearest standard size can be used with appropriate fitting adjustments. A door slightly smaller than the opening can be fitted with thicker frame timbers and wider trim to cover the gap. This is more common than people expect and usually invisible once installed.
Once the door is ordered and arrived on site, installation typically follows a standard sequence. Understanding the steps helps when discussing the job with installers or supervising the work.
The old door is unhung from its hinges. The old frame is then cut into sections (usually quartered) and pried out of the opening, working carefully to avoid damaging the surrounding brickwork or plaster. This is often the messiest stage — expect dust and some plaster damage that will need patching.
The opening is cleaned of loose mortar, old fixing screws and any debris. The threshold area is checked for damp and treated if necessary. If the opening is out of square or has damaged brickwork, this is the stage to address it - adding shims, repointing, or repairing the lintel as needed.
The new door frame is offered up into the opening and packed with wedges or shims until it sits square and plumb. Spirit levels are checked on the head (horizontal) and both jambs (vertical). Diagonals are measured to confirm squareness. The frame must be square before fixing - any twist or out-of-plumb at this stage will affect door operation permanently.
The frame is fixed to the structural opening with long screws (typically 100mm or more) that pass through the frame into the masonry behind. Fixings are placed at the top, middle and bottom of each jamb, plus across the head. For PVC frames, special frame fixings or wall anchors are used; for timber frames, conventional masonry screws into plugs work well.
The gap between the frame and the masonry - typically 10–20mm - is filled with expanding polyurethane foam from the outside in. The foam expands to fill the gap completely and cures to form a thermal and air seal. Once cured (usually 1–2 hours), excess foam is trimmed flush with the frame edges.
On the inside, a vapour barrier tape is applied between the frame and the wall structure to prevent moisture migration into the wall. On the outside, an expanding tape or weather sealant is applied between the frame and the brickwork to prevent water ingress.
The handle, lock, letterbox and any other ironmongery are fitted. The door is hung and adjusted on its hinges. The multi-point locking is tested by closing and locking the door several times - points should engage cleanly without forcing.
The visible gap between the frame and the surrounding wall is covered with architrave (inside) and external trim or render-stop bead (outside). This finishes the appearance and protects the foam seal beneath.
Some homeowners install their own front doors. Whether this is sensible depends on three factors: your DIY experience, the complexity of the opening, and regulatory considerations.
For most homeowners, professional installation is the better choice — both for compliance reasons and because the cost of getting a front door installation wrong is high. A door that doesn't close cleanly, leaks air or water, or fails security inspection costs more to fix than the original install would have cost done properly.
In England and Wales, replacement external doors are subject to several Building Regulations parts. The relevant parts for most installations are:
Installation by a FENSA or Certass registered installer provides self-certification under each of these. For DIY or non-registered installation, separate Building Control approval is required, with submission to local authority Building Control or an approved inspector.
FAQ
Can I order a new door from the size of my current door?
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How long does a front door installation take?
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What if my opening is out of square?
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Do I need to remove my old front door before the new one arrives?
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