How to Survey Windows for Replacement: A window Measurement Guide

Surveying your windows for replacement might seem like a daunting task, but with a little guidance, a tape measure, and some attention to detail, you can get accurate measurements that ensure a perfect fit. This guide will help you understand how to measure and survey your windows like a pro. Let's dive in!

Before You Start: What You Need to Know

1. View from the Outside: Always measure and view windows from the outside of the house. This ensures consistency and accuracy.

2. Tools Required:

   • Tape measure (preferably in millimetres)

   • Pencil and paper

   • Spirit level

   • String line (for bay windows)

   • Angle finder (for bay and bow windows)

   • Ladder or step stool (if needed)

   • Safety goggles and gloves (if chopping back plaster or handling rough edges)

3. Safety First: Ensure your ladder or step stool is secure if you need to measure at height. Always have a second person to assist when necessary.

4. Understand Window Types: The method of measurement may vary depending on whether your windows are flat, bay, bow, or casement. Identify your window type before proceeding.

Step 1: Window Measurement Guide

The aperture is the opening where your window will fit. Accurate measurements ensure a snug, functional fit.

• Width: Measure the width of the opening in three places: top, middle, and bottom. Record the smallest measurement.

• Height: Measure the height in three places: left, centre, and right. Record the smallest measurement.

• Diagonal Check: Measure from one corner to the opposite corner (diagonally) on both sides. If the diagonals differ by more than 10mm, adjustments might be needed.

• Deduct 10mm: Subtract 10mm from the smallest width and height measurements. This allows space for fitting and expansion.

Accurate measurements are key when replacing old windows—ensure a proper fit for your new double-glazed frames by carefully measuring the width, height, and depth of the existing opening

Step 2: Check for Obstructions

Look for any features that might interfere with your new windows:

• Overhanging Fascia's or Soffits: Ensure there is enough clearance for the window to open.

• Sills and Trim: Note if there are projecting sills or decorative trims that need to be retained or replaced.

• Internal Obstructions: Inside, measure the opening plaster to plaster and check for features like deep window ledges or skirting boards.

Step 3: Assess the Current Frame

Determine the position and condition of your existing window frame:

• Setback: Check whether the window is fitted to the outer edge of the wall, within the cavity, or flush with the interior.

• Structural Support: Ensure there is a lintel or support above the window. If unsure, consult a professional.

• Damp or Cracks: Note any damage to the surrounding structure, such as cracks, damp patches, or compromised brickwork.

Step 4: Consider Glass Requirements

• Safety Glass: Required if the window is close to the floor, a door, or part of a fire escape route.

• Egress Hinges: If the window is in a bedroom, ensure it has fire escape capabilities.

• Ventilation: For kitchens and bathrooms, trickle vents may be necessary to comply with building regulations.

Special Cases: Bay and Bow Windows

Measuring bay and bow windows requires extra care:

Splayed Bay Windows

• Back Span: Measure the internal width of the bay from frame edge to frame edge. Chop back plaster if necessary to locate the frame edges.

• Projection: Measure the distance from the back span to the inside of the front window using a string line. This determines how far the bay extends outward.

• Individual Facets: Measure each window segment separately. For instance, measure the width of each facet from one corner post to the next without including the post itself.

• Denoting Openers: On survey drawings, use arrows to point toward the hinge side of the opener. This visually indicates where the window will pivot or open.

Square Bay Windows

• Internal Facets: Measure the internal sizes of each facet and record these dimensions. The height should be measured from the outside.

• Angles: Use an angle finder to determine the angles between facets. This helps ensure the correct configuration for replacement.

Bow Windows

• Shallow Projections: Bow windows have a gentler curve compared to bay windows. Measure similarly to a bay window, focusing on the number of facets and the desired projection.

• Canopy Measurements: If you are replacing or adding a canopy, note its dimensions, as this affects the projection of the bow window.

Tips for Bay and Bow Windows

• Use an angle finder to simplify measurements and avoid calculation errors.

• Double-check measurements for back span, projection, and individual facet widths to ensure accuracy.

• Consider consulting a professional if the bay or bow configuration is complex or if the existing structure is compromised.

Filling Out a Survey Form

Once you’ve completed your measurements, it’s time to fill out a survey form to ensure all details are communicated accurately. Follow these tips:

1. Window Type: Specify whether the window is flat, bay, bow, or another style. Include details about the configuration (e.g., number of openings).

2. Dimensions: Record the smallest width, height, and diagonal measurements in millimeters. Clearly label each dimension.

3. Glass and Safety Features:

   • Note if safety glass is required.

   • Specify ventilation needs, such as trickle vents.

   • Mention egress hinge requirements for fire escape windows.

4. Frame Details:

   • Indicate the frame color and finish.

   • Note the setback position of the frame.

5. Structural Observations:

   • Record any structural concerns, such as cracks, damp, or missing lintels.

   • Mention any obstructions, like fascias or trims, that might affect installation.

6. Additional Features:

   • Include any add-ons like restrictors, child safety locks, or night vents.

   • Specify canopy dimensions for bow windows if applicable.

7. Bead Styles:

   • Ovolo Bead: Features a rounded, decorative edge for a traditional look.

   • Chamfered Bead: Offers a sleek, angled design for a modern and minimalist aesthetic.

   • Flush Sash: The sash sits flush with the frame, creating a flat, smooth appearance, ideal for modern or timber-style designs.

8. Final Confirmation: Review all the recorded details to ensure accuracy. Double-check against your physical measurements.

9. Sketch or Diagram: If possible, include a simple sketch or diagram of the window layout. Label key parts like back spans, projections, and facets for bay or bow windows. Use arrows to denote opener hinges and their directions.

Final Checks

Before finalizing your measurements:

1. Double-check all dimensions. The old adage, "measure twice, cut once," definitely applies here.

2. Confirm your measurements are in millimetres (mm).

3. If you’re unsure about anything, consult with your window supplier or fitter. Most are happy to help verify your measurements.

When to Call a Professional

While surveying windows can often be done DIY, certain situations may require a professional surveyor:

• Complex window designs like bays or bows

• Older properties with irregular apertures

• Structural concerns, such as damp or sagging lintels

By following these steps, you can confidently survey your windows for replacement. Remember, precision is key to a successful installation. If in doubt, don’t hesitate to seek expert advice—it’s always better to ask than to risk costly mistakes!