Midea PortaSplit Bracket Spacer Blocks for Flanged Windows

The Midea PortaSplit standard sill bracket is engineered for a clean, flat sill surface with a defined outer edge — a geometry common in brick-and-render European construction of the 1970s onward but increasingly uncommon in modern construction where window systems include projecting installation flanges, EPDM sill pan flashings, and deep architrave profiles. When the bracket meets a flanged or trimmed sill, the standard installation cannot proceed without custom Midea PortaSplit bracket spacer blocks that bridge the height difference between the bracket's bearing surface and the sill's usable flat zone.

Flanged windows are particularly prevalent in northern and central European new-build construction since the 2010s. The European standard for window installation (EN 14351-1) increasingly specifies installation systems that incorporate a factory-attached perimeter flange — a projecting aluminium or PVC fin that overlaps the exterior wall surface, sealing the window-to-wall interface and eliminating the need for a separate perimeter sealant bead. This flange creates a raised perimeter around the window opening that is typically 15–50 mm proud of the surrounding sill surface, directly blocking the rear hook of the PortaSplit bracket.

What Is a Flanged Window and Why Does It Block Standard Brackets?

A flanged window (also called a trim-flange or fin-flange window) has a projecting aluminium or plastic fin around its outer perimeter that overlaps the exterior wall surface during installation. This flange typically stands 20–50 mm proud of the window sill surface, preventing the standard PortaSplit sill bracket's rear hook from seating flush against the sill edge and requiring a custom spacer block to bridge the height difference.

The problem is straightforward geometrically: the bracket's rear hook is designed to drop over the sill's outer edge and grip its underside, applying a downward and inward force that presses the bracket against the sill surface. If the installation flange sits between the bracket's bearing foot and the sill surface, the bracket either cannot reach the sill edge (if the flange is on the sill face) or sits at an angle (if the flange is on the sill's outer edge). Either condition prevents the correct load path from developing and produces an insecure, tilting bracket.

Deep sill architrave profiles — ornamental timber or PVC trim installed on the sill interior and wrapped around the sill edge to the exterior face in some renovation styles — create an equivalent problem. The architrave raises the usable sill surface on which the bracket must bear, and its outer edge profile may be rounded or chamfered rather than the flat vertical face that the bracket's rear hook is designed to grip. Custom spacer blocks resolve both the height difference and the profile mismatch.

How Do You Measure for Custom Spacer Blocks?

Accurate measurement of three dimensions before fabricating spacers prevents the most common error — producing a spacer that either undercompensates (bracket still tilts) or overcompensates (bracket tips forward). The three measurements are the flange projection height above the sill bearing surface, the sill width available for the bracket front pin to bear on, and the sill outer-edge geometry (flat vertical, chamfered, or rounded).

Measure the flange projection height using a small engineer's square or a straight edge laid flat on the sill surface: the gap between the straight edge and the sill bearing zone behind the flange equals the spacer block thickness required. This measurement is taken at both the left and right bracket contact points, as flanges are not always symmetrically installed and a 2–3 mm height difference between sides will cause the bracket to twist unless the spacers are individually shimmed.

The spacer block's plan dimensions must span from the bracket's bearing foot to beyond the flange inner face, transferring load from the bracket to the sill surface behind the flange. A spacer that is too short in depth (measured from the wall outward) will bridge the flange but leave the bracket bearing only on the spacer's outer edge rather than distributing load across the full spacer width — a concentration of stress that can crack or compress the spacer material under the outdoor module's weight and vibration.

Which Spacer Block Materials Work Best Under a Bracket Load?

The spacer must be dimensionally stable under the combined static weight of the outdoor module (14–18 kg) and the dynamic loads from compressor vibration (peak force approximately 2–3× static at the compressor's fundamental frequency of 25–50 Hz). It must also withstand outdoor weathering across European seasonal temperature ranges of −15°C to +50°C without creeping, splitting, or losing structural integrity.

HDPE sheet is the recommended first choice for most DIY fabricators: it is available in various thicknesses from plastics suppliers and DIY markets, cuts cleanly with a jigsaw or circular saw, drills without cracking, and has excellent long-term outdoor durability with no surface treatment required. Aluminium flat bar is the structural optimum for high-load situations (outdoor modules placed in high-wind-exposure locations or on sills of unusual depth) but requires more machining effort. Kiln-dried hardwood is the easiest to source and work but requires annual oiling or varnishing to prevent moisture absorption that can cause dimensional change and eventual splitting.

How Spacers Affect the Bracket's Wind-Load Geometry — and Why You Must Recalculate

Adding spacer blocks under the bracket changes the effective lever arm geometry of the mounting system. The standard bracket is designed so that the outdoor module's centre of gravity falls directly above the rear hook's sill contact point, minimising the overturning moment that wind and vibration must resist. When spacers raise the bracket above the sill surface, the effective hinge point of any overturning movement shifts from the sill edge to the spacer block's outer lower edge, which may be 20–50 mm further inward. This reduces the effective anti-overturning moment arm by the same distance, meaning the rear hook must resist greater force for the same wind load. For spacers thicker than 30 mm, increase the anti-tipping strap's pre-tension by tightening the anchor screw more firmly, and reduce the bracket's front pin extension to move the outdoor module's centre of gravity as far rearward as the conduit routing allows. For spacers thicker than 50 mm, consult the module supplier before installation — the standard bracket's rear hook geometry may not provide adequate engagement depth to compensate for the additional moment arm.

Step-by-Step: Fabricating and Fitting Spacer Blocks

Fabricating a pair of spacer blocks is a straightforward workshop task using only basic hand tools. Each block serves as one of the two primary bearing points of the bracket, so the pair must be identical in thickness and flat on both faces to within 1 mm to prevent the bracket from twisting.

1. Measure the flange projection height at both bracket contact points; if they differ by more than 1 mm, fabricate a thin shim (cardboard laminate or aluminium foil tape layers) to correct the difference.
2. Cut two spacer blocks from HDPE sheet: each block should be 80–100 mm wide (direction parallel to the wall), 60–80 mm deep (direction outward from wall), and equal in thickness to the measured flange height plus 1 mm (the extra 1 mm ensures the block bears on the sill behind the flange even if the flange height was slightly underestimated).
3. Drill two 9 mm holes in each spacer at the positions corresponding to the bracket's front pin contact and rear foot contact, allowing the bracket fixings to pass through without binding.
4. Test-fit the spacers on the sill behind the flange; confirm both spacers sit flat and level with no rocking; check the bracket rear hook now engages the sill outer edge cleanly.
5. Apply a thin bead of clear silicone sealant under each spacer's bottom face where it contacts the sill surface — this prevents water pooling under the spacer which could freeze in winter and cause movement.
6. Re-fit the bracket with spacers in place, set the front pin position to keep the module's centre of gravity as far rearward as possible, tighten all hex bolts to specified torque, and re-attach the anti-tipping strap with increased pre-tension as described above.

How Do You Verify That the Modified Bracket Installation Is Safe?

After fitting spacers and before placing the outdoor module on the bracket, apply a static load test: press down firmly on the bracket's module support surface with both hands (approximately 50 kg force simulation, comparable to double the 12K module's weight) and hold for 10 seconds. No movement of the spacers, no rotation of the bracket, and no compression deflection of more than 1 mm indicates adequate spacer strength. Perform the standard push-test on the outdoor module after mounting: upward push (simulating bracket-hook lift-off) and forward push (simulating wind overturning) should both produce less than 3 mm movement.

Check the spacer-to-sill interface after the first 72 hours of operation, particularly if the sill material is stone or tile with a polished surface. Some vibration-induced creep of the spacers laterally is possible if the anti-vibration pad was omitted or insufficient. A lateral movement of more than 5 mm in 72 hours indicates inadequate friction — add rubber anti-vibration pads between the spacer base and the sill surface and re-test.

Took one look at my new build window flange and thought the bracket was never going to work. Cut two HDPE spacers in about 20 minutes, and the bracket seated perfectly. The whole installation including spacer fabrication was under an hour.

Flanged windows represent an increasing proportion of the European housing stock as new-build rates recover, and the spacer block solution described here will be relevant to a growing number of PortaSplit owners in the coming years.