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How to Size a Security Door: Step-by-Step Guide for New Orleans Homes
Getting the size right is the first and most important step in any security door project. Order the wrong size, and you are looking at return shipping costs, fabrication delays, and potentially an opening that cannot be filled with a stock door at all. In New Orleans, where historic homes frequently have non-standard openings that do not match modern door sizes, accurate measurement before purchase or fabrication is non-negotiable.
This guide walks through the complete measurement process, explains the difference between rough opening and finished opening dimensions, and addresses the specific sizing challenges created by New Orleans’ most common historic home types. For a full overview of security door options available in the New Orleans area, visit our New Orleans security doors page.
Standard Security Door Sizes in the United States
American security doors are manufactured in standard sizes that correspond to the most common rough opening dimensions in modern residential construction. Knowing these standards tells you immediately whether your opening is within stock range or requires custom fabrication.
| Standard Door Width | Standard Door Height | Typical Application |
|---|---|---|
| 30 inches | 80 inches | Secondary entries, older homes |
| 32 inches | 80 inches | Common residential, back/side doors |
| 34 inches | 80 inches | Common residential |
| 36 inches | 80 inches | Standard front door, most common residential |
| 42 inches | 80 inches | Wide entry, typically custom or special order |
| 36 inches | 84 inches | Taller opening, available as special order |
| 36 inches | 96 inches | 8-foot ceiling construction, custom |
| Double (2 x 30 to 2 x 36) | 80 to 96 inches | French door / double door openings |
These are finished door slab dimensions. The rough opening in the wall must be larger than the door, typically 2 inches wider and 2 to 2.5 inches taller than the door size, to allow for the frame, shimming space, and clearance. More on that below.
How to Measure Your Door Opening Correctly
Accurate measurement requires taking multiple measurements at different points in the opening. A single measurement is not sufficient because New Orleans homes, particularly older ones, have settled, shifted, and been repaired over decades in ways that make openings consistently inconsistent.
Tools You Need
- A quality steel tape measure (not a cloth tape, which stretches)
- A 4-foot level
- A pencil and paper or notepad
- A bright light source (flashlight or headlamp) for inspecting frame condition
Step 1: Measure the Width at Three Points
Measure the width of the opening at three horizontal positions: the top, the middle, and the bottom. Measure from the inside face of one jamb to the inside face of the other jamb at each position. Record all three measurements. For ordering purposes, use the smallest of the three measurements. This ensures the door will fit the narrowest point of the opening without binding.
A typical result for a New Orleans older home might look like: top 35.75 inches, middle 35.5 inches, bottom 35.25 inches. In this case, you order for a 35.25-inch opening, which typically means a 34-inch door slab in a frame that allows for shimming to fill the difference.
Step 2: Measure the Height at Both Sides
Measure from the floor to the underside of the door head (the horizontal framing member above the door) on both the hinge side and the latch side. Floors in New Orleans pier-and-beam homes are notoriously uneven. The floor may be a half-inch or more lower on one side than the other. Use the shorter of the two height measurements for ordering.
If your floor is significantly uneven, discuss this with your installer before ordering. The threshold and weatherstripping must accommodate the floor level difference, and this may affect which door system is appropriate for your opening.
Step 3: Understand the Difference Between Rough Opening and Finished Opening
This is where many DIY measurement attempts go wrong. There are two distinct dimensions in every door installation:
- Rough opening: The unfinished opening in the wall framing, measured from stud to stud in width and from subfloor to the underside of the header above. This is the largest measurement.
- Finished opening: The opening after the door frame (jambs and head) are installed. This is what you measure when the existing door and frame are in place.
If you are measuring an existing finished opening (existing door frame in place, measuring between the inside faces of the jambs), you are measuring the finished opening. A pre-hung door sized to this measurement will typically fit correctly with normal shimming allowances.
If you are measuring a rough opening (no frame in place, just the wall framing), subtract 2 inches from the width and 2.5 inches from the height to get the approximate door size you need. Your installer or door supplier should confirm this math for your specific product.
Step 4: Check for Plumb and Square
A perfectly sized door in an out-of-square frame is an installation problem waiting to happen. Use your 4-foot level to check both jambs (hinge side and latch side) for plumb. Then measure diagonally across the opening from corner to corner. Measure both diagonals. If they are equal, the opening is square. If they differ by more than 1/4 inch, the opening is out of square.
Out-of-square conditions are extremely common in New Orleans historic homes. A slight out-of-square condition can be corrected with shimming during installation. A severe condition may require reframing the opening before a new security door can be correctly installed. Flag any significant out-of-square measurements when communicating with your installer or door supplier.
Step 5: Measure the Frame Depth
If you are installing a security door that must fit within your existing frame depth rather than replacing the frame entirely, measure the frame depth as well. This is the thickness of the door frame from the interior face of the jamb to the exterior face. Standard frame depths run 4.5 to 6.75 inches to accommodate standard wall thicknesses. Non-standard wall thicknesses, which are common in older New Orleans construction, may require a custom-depth frame.
Step 6: Double-Check Every Measurement Before Ordering
Before you place an order or authorize fabrication, measure everything a second time, preferably at a different time of day when the temperature and humidity are different. In New Orleans’ climate, wood frames move seasonally, and a measurement taken on a cool December morning may differ from one taken on a humid July afternoon. For a custom iron door, the cost of a measurement error is high: fabrication is irreversible.
Non-Standard Door Sizes in New Orleans Historic Homes
This is where New Orleans diverges significantly from the rest of the country. The city’s historic housing stock was built across several centuries and multiple architectural traditions, few of which used the standard door sizes that dominate modern construction. Here is what you are likely to find by home type:
Creole Cottages (1790s to 1850s)
Creole cottages are typically smaller in overall scale, with front door openings that often run 32 to 34 inches wide, which is within standard range. However, the height is frequently non-standard, with some original openings as short as 74 inches (6 feet 2 inches) due to the lower ceiling heights of the period. A stock 80-inch door does not fit in a 74-inch opening. Custom sizing is required.
Shotgun Houses (1830s to 1920s)
The classic New Orleans shotgun house has a front door that is typically the full-width room entry, usually 32 to 36 inches wide. Height is generally in the 80 to 84-inch range, which can work with stock doors. The challenge is often the condition of the frame after more than a century of use, repair, and New Orleans weather exposure, rather than the size itself.
Double Shotguns and Camelbacks (1870s to 1920s)
Double shotguns share a center wall and often have two identical front door openings. The standard widths apply, but the paired configuration means any sizing inconsistency between the two openings is immediately visible. Both openings should be measured independently because they are rarely identical despite the symmetric facade.
Victorian and Italianate Double Gallery Homes (1870s to 1910s)
These homes frequently have the most generous front door openings in New Orleans residential architecture, with widths of 36 to 42 inches and heights of 84 to 96 inches. Widths over 36 inches and heights over 80 inches are outside standard stock dimensions, making custom fabrication necessary. Many of these homes also have elaborate original transoms above the door, which affects the sizing calculation if the transom is to be preserved.
Bungalows and Craftsman Homes (1900s to 1930s)
Bungalow-style homes in Mid-City, Gentilly, and Lakeview tend to have more standardized door openings than the older architectural types. Front doors are typically 32 to 36 inches wide and 80 inches tall, within standard stock range. Frame condition is the more common challenge in these homes rather than non-standard sizing.
Custom vs. Standard Size Security Doors
Once you have your measurements, the question is whether a stock door works or whether custom fabrication is necessary. Here is the decision framework:
Standard size works when: Your finished opening width falls within 1/2 inch of a standard size (30, 32, 34, or 36 inches) and your height is 80 inches or close to it. A pre-hung door sized to the next smaller standard size can be shimmed to fill the gap. Most standard openings in New Orleans post-WWII construction fall into this category.
Custom fabrication is necessary when:
- Your opening width is more than 1 inch away from a standard size in either direction
- Your opening height exceeds 80 inches and you need a door that fills the full height (rather than installing a fixed transom above an 80-inch door)
- Your opening is for a double door configuration with non-standard panel widths
- Your HDLC Certificate of Appropriateness requires matching specific historic proportions that do not align with stock sizes
- You want an ornamental iron door (custom fabrication is standard for all ornamental iron work)
Custom fabrication timelines at New Orleans iron shops typically run 2 to 8 weeks depending on workload and design complexity. Plan accordingly, especially if your project has a deadline driven by storm season, a renovation completion date, or HDLC approval timing.
Measuring for French and Double Security Doors
Double door openings require the same measurement steps as single door openings, with one additional consideration: the astragal or center post.
A double door opening with a center post (a fixed structural element in the center of the opening) is measured as two separate openings side by side. Each panel is sized to its own opening width.
A true double door opening without a center post is measured as a single opening. The two door panels together must fill the full opening width. For a 72-inch opening, two 36-inch panels is the standard solution. For a 60-inch opening, two 30-inch panels. Openings that do not divide evenly into equal halves may require one larger and one smaller panel, which is a custom fabrication situation.
For iron double doors, also specify:
- Which panel is active (operated daily) and which is inactive (pinned in place)
- The swing direction of both panels
- The astragal design (the overlapping element where the two panels meet) and whether it is fixed to one panel or removable
- The locking mechanism for the inactive panel (floor and head bolts)
Common Sizing Mistakes to Avoid
These are the most frequent measurement and sizing errors in New Orleans security door projects:
Measuring Only Once at One Location
A single width measurement in the middle of the opening misses the taper or bow that is common in older frames. Always measure at three heights. A door that fits the middle of the opening may bind at the top or bottom.
Confusing Rough Opening with Finished Opening
Ordering a door sized to the rough opening dimensions results in a door that is too large to fit inside the frame. Ordering a door sized to the finished opening dimensions when the plan is to remove the existing frame and reframe results in a door that is too small. Confirm which measurement type your door supplier requires before ordering.
Ignoring Frame Depth
A door frame that is shallower than the wall thickness creates a condition where the door casing cannot cover the gap between the frame and the wall finish on the interior side. This is a cosmetic problem that adds cost and complexity to the finish work. Measure frame depth and confirm it matches the door system you are ordering.
Not Accounting for the Threshold
The threshold at the base of the opening reduces the effective height of the opening. If a new threshold is being installed, its height must be subtracted from the opening height before ordering. This is especially relevant for raised entries common in New Orleans pier-and-beam construction.
Ordering a Standard Door for a Historic Opening
The single most common mistake in New Orleans historic home security door projects is assuming the opening is standard size without measuring. A 34-inch opening looks very similar to a 36-inch opening at a glance. The 2-inch difference means a stock 36-inch door does not fit without significant and often structurally problematic modification to the opening. Measure first, order second.
Frequently Asked Questions: Security Door Sizing
What is the most common security door size in New Orleans?
For post-WWII construction in neighborhoods like Metairie, Kenner, and Lakeview, 36 x 80 inches is the most common standard size and fits the majority of openings. For older historic neighborhoods, non-standard dimensions are the rule rather than the exception, and custom sizing is frequently required.
What if my door opening is not a standard size?
You have two options: modify the rough opening to accommodate a standard door (which involves framing work and may affect HDLC compliance on historic properties), or order a custom-sized door fabricated to your exact opening dimensions. For ornamental iron doors, custom fabrication is standard regardless of whether your opening matches standard sizes.
How much clearance should I leave between the door and the frame?
Standard clearance is 1/8 inch on the top and both sides of the door. At the bottom, the clearance depends on the threshold configuration, typically 1/8 to 1/4 inch above the threshold sweep. These small gaps allow for seasonal wood movement and smooth operation without binding.
Do I need to measure the door or the opening?
Measure the opening, not the door. Door manufacturers specify their doors by slab size. Your job is to determine what slab size fits your opening. Measure the finished opening (inside face of jamb to inside face of jamb) for width and finished opening height on both sides. Report those measurements to your door supplier, and they will help you select the correct slab size.
Can I make my door opening bigger to fit a standard size?
Yes, but with important caveats. Widening a door opening requires cutting into the wall framing, which may affect structural headers, utilities in the wall, and in HDLC-regulated properties, the exterior facade. Never widen a structural opening without consulting a licensed contractor who can assess the structural implications. On historic properties, opening modifications require HDLC review.
How do I measure for a security door on a raised New Orleans home?
The measurement process is the same, but pay particular attention to floor levelness. Pier-and-beam foundations in New Orleans homes frequently create floor variations of 1/4 to 1/2 inch or more across the door opening width. Measure height on both sides and use the shorter measurement. Discuss the floor condition with your installer so the threshold system can be selected to accommodate the variation.
What is the standard door size for a New Orleans shotgun house?
Shotgun houses vary considerably by age and neighborhood, but 32 x 80 and 34 x 80 are the most common front door sizes in this home type. Some older examples have shorter openings (76 to 78 inches) that fall outside standard stock sizes. Always measure before ordering.
Does a security door need to be the same size as my current door?
It needs to fit your current opening, which the current door presumably does. If you want to change the door size, the opening itself must be modified. For most security door replacements, matching the existing opening size is the right approach, as it avoids structural work and, on historic properties, complications with HDLC review.
Not Sure What Size Security Door You Need?
Bring in a professional to measure your opening correctly before you order. Call Big Easy Iron Works at 504-732-0066 for a free on-site measurement and estimate. We fabricate custom iron security doors for standard and non-standard openings throughout Greater New Orleans, including Metairie, Kenner, Gretna, Uptown, Mid-City, the Marigny, and the Garden District.