If you are using your own windows or doors in a SIP kit, the most important thing you can send us is accurate dimensions. We can cut SIP panel openings to suit customer-supplied windows and doors, but the openings are only as good as the measurements we receive.
This guide is useful whether you are buying new windows, second-hand windows, Facebook Marketplace doors, ex-display bifolds, wrong-order frames from a local manufacturer, or reusing windows you already have.
Measure the frame, not the glass
The biggest mistake is measuring the glass instead of the frame. For SIP openings, we normally need the overall external frame size. That means the full width and height of the window or door frame, not just the visible glass and not just the opening sash.
For windows, measure the overall frame width, overall frame height, whether the sill is included, and any add-on profiles, couplers or trickle vents. For doors, measure the overall frame width, overall frame height, threshold height, side panels, top lights, opening direction and hinge side.
Use millimetres
Please send measurements in millimetres. This avoids confusion and removes conversion errors from feet, inches or metres.
- Window 1: 1200mm wide x 1050mm high, sill included.
- Door 1: 1790mm wide x 2090mm high, outward opening, hinges left viewed from outside.
Avoid rough descriptions such as small window, standard door or around 1.2m. SIP openings need more precision than that.
Measure in more than one place
Used windows and doors are not always perfectly square. Even new frames can vary slightly depending on how they are stored or measured.
Measure the width at the top, middle and bottom. Measure the height at the left, centre and right. If there is a difference, tell us the measurements and send photos. Do not just average them without saying.
Photos help prevent mistakes
Send clear photos of the full front, full back, both sides, sill or threshold, labels, the tape measure across the width, the tape measure up the height, and any couplers or unusual profiles.
If you are unsure whether a sill is removable, photograph it. If a door has a low threshold, photograph it. If a bifold has a track, photograph it. These details matter.
Door opening direction matters
For doors, tell us whether the door opens in or out, which side the hinges are on when viewed from outside, whether it is a single door, double door, French door, sliding door or bifold, and whether the threshold is included in your height measurement.
If the door is second-hand, check that it has keys or budget for a locksmith to replace the cylinder.
Large openings need extra thought
Large openings such as bifold doors, sliding doors and wide French doors can affect structure. The wider the opening, the more likely a beam, lintel, glulam, steel or goalpost detail may be needed.
UltraSIPS can cut the panel opening, but the structural support around large openings may need to be confirmed by a structural engineer, especially if Building Control is involved.
Remember fitting gaps and installation details
The frame size is not always the same as the final structural opening size. Installers may need fitting tolerance, packers, foam, tapes, sealants, trims, flashings or membranes around the window or door.
If a supplier gives you a recommended opening size, send that too. Do not guess the tolerance if you do not know.
Second-hand windows and doors
Using second-hand or surplus windows can save money, but check for misted units, cracked glass, twisted frames, damaged handles, hinge issues, missing keys and poor seals before buying.
For more on this, read: How to Save Money on Windows and Doors for Your SIP Build.
Common measuring mistakes
- Measuring the glass instead of the frame.
- Forgetting to say whether the sill is included.
- Not mentioning a threshold.
- Sending inches instead of millimetres.
- Not saying whether the door opens in or out.
- Not checking if a frame is square.
- Changing window sizes after panels have been designed or cut.
A simple measuring template
- Item name: Window 1 / Door 1 / Bifold 1.
- Type: fixed window, opening window, composite door, French doors, bifold, slider.
- Overall frame width: ____ mm.
- Overall frame height: ____ mm.
- Sill included: yes / no / not sure.
- Threshold included: yes / no / not sure.
- Opens in or out: ____.
- Hinge side viewed from outside: left / right / not applicable.
- Wall location: front / back / left / right / wall number.
- Photos attached: yes / no.
The simple takeaway
We can cut SIP panel openings to suit customer-supplied windows and doors, including second-hand or surplus frames. The key is accurate information.
Measure the full frame, use millimetres, tell us about sills and thresholds, photograph everything, and send the details before the SIP kit is finalised.
Send us your window and door measurements or start your layout with the UltraSIPS configurator.