Sealed unit recycling: how IGUs are processed

Installers pulling out warranty failures, fabricators with QC rejects and glaziers clearing the van all end up with sealed units, and they confuse people more than any other waste stream. They look like glass, but there's an aluminium or polymer spacer bar round the edge, two layers of edge seal, desiccant inside the spacer, and often a trapped gas. Drop one whole into a cullet skip and you've contaminated the load.

What an IGU is

An insulated glass unit (IGU) is two or three panes of float glass held apart by a spacer bar and sealed. The cavity between the panes does the thermal work.

• Panes. Usually 4mm float, sometimes Low-E coated on the inner face. They can be toughened, laminated or plain annealed.
• Spacer bar. Aluminium (older units, still common) or a warm-edge polymer or composite (TGI, Super Spacer, Swisspacer types). It holds the panes apart and contains the desiccant.
• Desiccant. Beads inside the spacer that keep the cavity dry so the unit doesn't mist.
• Edge seals. A primary butyl seal against the spacer and a secondary polysulphide, polyurethane or silicone seal round the outside. That's what keeps it gas-tight.
• Cavity fill. Dry air, argon, or krypton on high-spec units. Argon is standard on new build now.

That matters for recycling because everything apart from the glass has to go somewhere different.

What failed units look like

Most sealed units coming off install vans have failed seals. These are the terms you'll hear:

• Misted units. The edge seal has gone, moisture has got into the cavity, the desiccant is saturated, and you've got condensation between the panes that won't clear.
• Blown units. Same cause, seal failure, usually with water or chemical staining ("tide marks") between the panes.
• Stress-cracked. Thermal shock or installation stress. The glass is cracked but the unit is still in one piece.
• QC rejects. Fabricator failures: wrong size, wrong spec, wrong toughening, a scratch on the inner face. Usually intact.

To us a misted unit and a brand-new unit are the same, because we'd be cutting it open anyway.

Why IGUs can't go in mixed glass cullet

Cullet processors and glass manufacturers buy on contamination limits measured in parts per million. An aluminium spacer in a load of cullet is enough to spoil a furnace charge. The metal melts in the furnace and leaves inclusions in the new glass, and the manufacturer rejects the batch.

The contaminants in a whole IGU are:

• Aluminium or polymer spacer bar
• Butyl primary seal (sticky, smears across glass)
• Polysulphide or polyurethane secondary seal
• Desiccant beads (silica or zeolite, the wrong chemistry)
• Setting blocks if they're still attached

One whole sealed unit in a 16-yard skip of float drops the cullet grade. That's why our glass service keeps float and sealed units in different containers, and why a recycler who knows the job will always quote the two separately.

What happens to your IGU, step by step

1. Units still in a frame

When we collect old windows, the sealed units come out of the frames on site before collection, by the installer or by us. The frames go for uPVC recycling and the sealed units go through steps 2 to 6.

2. IGU handling and staging

Sealed units are stored on edge in stillages. Triples are heavier than they look (a 1500 x 1200 triple in 4-12-4-12-4 with argon is around 60kg) and snap easily at the corners, where the spacer concentrates the load.

3. Spacer bar separation

The spacer has to come out, and there are two ways to do it:

• By hand. A blade goes round the edge to cut the secondary seal, then the panes are prised apart. It's slow but works on every spec.
• Mechanical splitters. Purpose-built kit for volume that cuts, separates and ejects the spacer in one go.

Once the panes are split, any argon or krypton vents to atmosphere. It's harmless, as both are inert gases already in the air around you.

4. Pane cleaning and grading

The panes still have butyl on the edge, which is scraped, washed or abraded off depending on volume and where the glass is going. Then the glass is graded: plain float apart from Low-E (the coating affects re-melt chemistry), toughened apart from annealed (toughened can't go back to float manufacture).

5. Routing to reprocessors

Clean float cullet has three routes in the UK:

• Container and flat glass re-melt. Highest value, back into new glazing. Tight contamination specs.
• Glass fibre and mineral wool. More forgiving, takes mixed-grade cullet.
• Construction aggregate. Lowest value but still recovery, used as a sand replacement in concrete and as drainage media.

The Glass and Glazing Federation (GGF) and the glass industry publish cullet specs for each route, and we grade to them.

6. Spacer, desiccant and seal: where they go

Aluminium spacer goes to metals recycling. Warm-edge polymer spacers go to plastics recycling where the polymer can be recovered, or energy-from-waste where it can't. Desiccant beads are inert and go to general waste. Cured edge seal is mixed polymer and mostly goes to energy-from-waste.

Argon, krypton and triple glazing

A triple-glazed argon-filled unit is processed the same way as a double. The only differences are the weight and two spacers instead of one.

Krypton is rarer in UK housing. You'll see it in slim-cavity heritage units where the cavity is too narrow for argon, and it's handled the same way.

What we don't accept without prior arrangement

Our standard sealed unit collection covers double and triple-glazed IGUs in float or Low-E. These need a phone call first because they go a different way:

• Toughened glass in volume. It can't go back to float manufacture, so it's a separate stream.
• Laminated glass with PVB or EVA interlayers. The interlayer has to be separated. We can take it but quote separately.
• Shopfront security glass, especially anti-bandit and bullet-resistant grades. These are mixed laminate construction.
• Automotive glass. It has a different chemistry and supply chain.
• Container glass (bottles, jars). It's a different industry and we don't handle it.
• Wired glass. Old fire-rated stock with embedded steel mesh.

Each of these needs a different reprocessor, and mixing them spoils the standard load. Tell us up front and we'll route it correctly.

Compliance and paperwork

Sealed units are non-hazardous waste under EWC code 17 02 02 (glass from construction and demolition). Section 34 of the Environmental Protection Act 1990 still applies, and you need a duty-of-care chain from your site to the final reprocessor.

That means:

• Whoever moves the units must be a registered waste carrier with the Environment Agency. We are, and our registration number goes on every transfer note.
• You need a waste transfer note for every collection. We issue electronic waste transfer notes (eWTNs) within 24 hours.
• You keep the paperwork for two years and have it ready if the Environment Agency asks.

The paperwork is the same as for uPVC frame collection.

BPF Recovinyl, the GGF and the closed loop

The British Plastics Federation runs Recovinyl, the Europe-wide scheme that tracks and verifies PVC recovery. There's more on it in our closed-loop uPVC piece. For glass, the equivalent is the Glass and Glazing Federation (GGF), which sets the standards on glazing performance, cullet quality and end-of-life handling.

The closed loop on glass is only partial. Float cullet does go back into new glazing, but only the cleanest grades and only as a set share of the furnace charge. The rest goes to glass fibre and aggregate, which is still recovery and still better than landfill.

Booking a sealed unit collection

For a fabricator or installer with regular IGU waste, the best setup is a stillage or container on your site, emptied on a schedule that fits your shifts. For one-off jobs, a glazier with a van load or an installer clearing a warranty backlog, call or email photos and we'll book a collection from your nearest hub.

Collection is same or next day across the North West, Liverpool, North Wales, the Midlands and Yorkshire, and same week elsewhere. Phone 0330 043 5543 or email info@upvcrecycling.com.