Sealed units made in London, for people who fit them

What you are buying when you order sealed units in London

A sealed unit is four materials asked to stay bonded to one another through twenty years of expansion and contraction: glass, a spacer, a desiccant and two seals. Almost every failure you will see in sealed units in London traces back to one of those four components or to the way the unit was glazed after it left the factory. We make double glazed sealed units to your sizes in our own workshop on Atlas Road in Wembley, on trade terms. You measure, we manufacture, you fit.

That division of labour is the whole business. We are not quoting against you, we are not surveying your customer behind your back, and we do not want your fitting work. What we want is a clean cutting list and enough notice to make the units properly.

If you are a homeowner with one misted window, you are on the wrong site

This is a trade manufacturing supply. We do not sell single units over the counter to the public, we do not come out and measure your bay, and we do not glaze. If you have one cloudy window in your own house, our sister site handles misted double glazing for homeowners, measures the units itself and fits them.

The split is not snobbery, it is risk. When a window company sends a cutting list, the measurements are theirs, the glazing is theirs and the clearances in the rebate are theirs. When a homeowner orders a unit from a drawing they made with a tape measure, somebody still has to carry the consequence of a unit that is two millimetres too wide, and it should not be the person who cannot do anything about it. Different jobs, different pricing, different paperwork.

Why sealed units fail early, and whose fault it usually is

A unit that mists in its first two or three years has almost always failed for one of four reasons, and they leave different evidence. Poor adhesion of the seal to the glass, which is a factory problem. Excessive movement or point loading in the rebate, which is a glazing problem. Ultraviolet attack on an exposed edge seal, which is a design or edge cover problem. Or standing water in the rebate, which is a drainage problem and by a wide margin the most common of the four.

You can usually tell a manufacturing failure from an installation failure in five minutes without taking anything apart. A factory fault tends to show up across a batch rather than in one unit, appears regardless of which elevation the unit is on, and shows an even haze or a perimeter bloom all the way round. An installation fault is local. It starts in the bottom corners, it is worse on the sills that hold water, it affects the units in the worst-drained frames and leaves the identical unit two metres away perfectly clear.

Lift the bead and look at the rebate before you phone anybody. Tide marks, silt, a damp timber base, a drainage slot full of paint or sealant, or a unit sitting flat in its own puddle all tell you what happened. If the secondary seal has gone soft, dark and spongy along the bottom edge only, that unit drowned. It did not fail.

If a customer rings us about a misted unit, the first question is which edge it started from and what the bottom of the rebate looks like. We would rather spend ten minutes establishing that than send a free remake into the same wet rebate and do it all again in two years.

Standing water kills more units than bad manufacture ever will

The secondary seal on a sealed unit is water resistant. It is not designed for permanent immersion, and nothing on the market is. Put a unit in a rebate that holds water and you are asking a polysulphide or hot melt seal to behave like a tanking membrane. It will manage for a while and then it will let go, usually along the bottom edge and up into the corners first.

So the drainage is the job. The rebate has to be drained to the outside, the slots have to be clear and they have to stay clear after the decorator has been round. On timber the base of the rebate should be sound, primed and never left bare. On aluminium and uPVC the drainage path is designed in, which means it can also be blocked by a bead of silicone applied by somebody who thought they were weatherproofing it. Sealing the outside of a drained and ventilated system traps water inside it.

This matters commercially as well as technically. Every manufacturer in London writes a guarantee that excludes units glazed into frames without working drainage, because every manufacturer has paid for remakes that were never their glass. If you are the fitter, five minutes clearing a slot protects your margin more than any upgrade you can sell.

Setting blocks, bridging and edge cover

A unit should sit on setting blocks, not on the frame, and not on a smear of silicone. The blocks hold the glass clear of the drainage path, spread the weight into the sash where the sash can carry it, and keep the unit square in the opening. Two blocks positioned in from the corners, sized to the rebate width, is the whole technique. Units glazed with no blocks end up bearing on one bottom corner, which concentrates load into the edge seal and the glass edge at the same time.

Bridging is the other common error. A packer, a fixing, a screw head or a lump of mortar touching the glass across the cavity transfers movement straight into the edge seal. Anything hard in contact with the edge of a unit becomes a lever. The seal also needs covering: leave too little edge cover and you expose the secondary seal to direct sunlight, which degrades anything that is not silicone. A stepped unit, a shallow bead or a frame modified on site to take a thicker unit are the three ways people accidentally leave an edge seal in the sun.

How to price sealed unit work so you do not lose money on it

The glass is rarely the thing that hurts. What hurts is the second visit. If you price a job on the supply cost of the units plus a day of labour, one wrong size or one chip discovered during glazing turns a profitable job into a break-even one, because you are paying a fitter twice and remaking at your own cost if the error was on your list.

Price with those realities visible rather than hidden:

• A breakage allowance. Glass gets broken during glazing, by fitters, by other trades and by weather, and the job that carries no allowance is the job where the breakage comes out of your margin.
• A remake policy you have read. Know before you order which errors are ours and which are yours, and what a remake does to the programme.
• Minimum chargeable area. Very small units are priced on a minimum area, because the labour to cut, wash, seal and press a tiny unit is the same as a large one.
• Toughened and laminated content priced separately, because it changes lead time as well as cost.
• Collection or delivery, chosen deliberately. A collection from Wembley on a day you are passing costs you nothing but time; a booked delivery into central London costs real money and is sometimes still the cheaper answer.
• Access and handling. Two-man units, long carries, scaffold lifts and staircases are labour, and they belong in the quote rather than in the apology.

The other half of pricing properly is sequencing. Measure after the frames are in, not before. Order toughened content first because it has the longest tail. Confirm anything shaped from a template rather than a dimension. And never let a customer talk you into ordering glass from a drawing that has not been built yet, because the drawing is not the building.

What a good trade customer looks like from this side of the counter

The accounts that run smoothly for years all behave the same way. Their cutting lists arrive in writing with the units numbered against the openings, their sizes are glass sizes rather than frame sizes, they tell us the thickness and the specification per line instead of per order, and they ask before assuming. They also check a delivery while the driver is still there, which is the single habit that prevents most disputes.

The accounts that go wrong usually go wrong in the same three ways too. Sizes given verbally and then disputed. A change made halfway through a batch that nobody wrote down. And damage reported a fortnight after a clean signature, by which time nobody can honestly say whether it happened on our rack, on your van or on the scaffold. None of that is about trust. It is about evidence, and evidence is cheap to create at the moment of handover and impossible to create later.

We would rather lose an order than take a cutting list we do not believe. If a size looks wrong against the others on the same elevation, we will query it before we cut, and if you confirm it we will make it exactly as written.

Who we make sealed units for across London

The sealed units trade in London is more varied than the phrase suggests, and the four groups we deal with want quite different things. Window companies making their own frames want consistency and a lead time they can plan a fitting diary around. Joinery shops and builders want someone who will take a template seriously and make one awkward shaped unit without sighing. Shopfitters and conservatory installers want large units, often toughened, handled and delivered without damage. Maintenance contractors doing sealed unit replacement across London on managed housing want small quantities, quickly, repeatedly, with the make-up recorded so the next visit matches the last.

All of it is double glazed units made to measure from your sizes, out of the Wembley workshop, on trade terms. There is no stock range to choose from and nothing is cut to a catalogue size. If what you need is one unit for your own house, go to the homeowner site instead, and if you need technical help deciding a make-up before you price a job, phone 020 4634 6045 and ask. We would rather answer a specification question for free than remake a unit later.