the greenest option
the greenest option
The SupaWOOD System; What's that?

In short, it's a Patent glazing system designed to ensure the longevity of the sealed unit within a pre-finished wood frame.

Unlike traditional timber windows, aluminium and uPVC frames were designed from scratch to take double-glazing, and all of the issues of protecting the sealed unit by draining and venting their edges were dealt with on the drawing-board. 

And that was how the
SupaWOOD System was born more than thirty-five years ago: On the drawing board, starting with a clean sheet of paper

The end result is a frame system assembled from pre-finished components, with the edges of the sealed unit surrounded by nothing but fresh air and located by self-aligning clips.  Self-centred, automatic heel and toe, in dry glazed, drained and vented profiles as slender as the single-glazed originals.

Truly, a Super Wood System.

Sealed units (DGUs) stay clean and dry inside because the spacer-bar - that strip of material around the edge keeping the panes apart - contains a dessicant (= drying agent) capable of holding a good deal of water.  Any moisture that does get into the unit during its lifetime is swiftly mopped up like a sponge, until the 'sponge' can hold no more. After which, moisture inside the unit may condense out inside the unit from time to time  (where you can't get at it) and - in a really serious failure - collect at the bottom of the unit, slowly filling it up.  Fogged DGUs are a sign that the dessicant is exhausted, and, while there are ways of unfogging the unit, the process always degrades it and the only real solution is a proper - and probably much better - modern replacement.  These days, the Building Regulations demand a very high insulation value from sealed units, so the best ones are widely available and it hardly makes sense to use any but the best.

BEWARE: Some DGUs are supplied with aluminium foil around the edge. While some claim that it adds to the seal, the truth is that the opposite occurs. The glue holding it in place is highly unlikely to be well attached, and capillary force will accelerate the penetration of water in some way, leaving the edge of the glass almost permanently wet. If the DGUs arrive with foil, my advice is to strip it off from the sealed edges of the glass. You will then see how badly it is attached to the edge-seal.

DGUs fail in the main through water vapour penetrating the edge seal. At a molecular level, even the best mastic or sealant is vapour-permeable to some degree, so even the very best sealed units will fail eventually.  Just when that 'eventually' is will depend on a number of factors, but if they are manufactured properly and installed properly they should last thirty years or more. Installing them properly means keeping the edge-sealant out of contact with water and fluids - particularly oil-based material that may well (= probably will) react with the seal of the unit to degrade it.  This means avoiding bedding the DGU into putty or mastic of any sort, as they all contain some sort of oil as a plasticiser.  This process of inter-mixing is known as 'plasticiser migration', where oils pass from one component to the other.  Think of wrapping cheese in cling-film: Within a very short time, the cheese will be slightly tainted with cling-film, and the cling-film slightly tainted with cheese.  That's why you are advised to choose your food-quality cling-film carefully.
ALSO BEWARE of cleaning your windows with washing-up liquid.  If this gets onto the edge of the DGU it will assist the penetration of water and shorten the life of the unit.  A bucket of clean water with a cupful of vinegar will do a great job of cleaning glass.

Traditional wood windows do not take sealed units well.  Originally designed to take single glazing, they were simply altered to take the new-fangled double-glazing when that appeared on the scene. To make room for the DGU and provide sufficient 'upstand' to cover the edge seal of the DGU adds to the bulk of the profile, and still fails to deal with the dry-glazing draining and venting of the void around the DGU, let alone issues of factory-finishing. 
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