It is cold near the window
Then the U value counts. Triple with a good spacer goes furthest, provided your profile carries the weight and the junction around the frame is insulated too. Otherwise you simply move the cold to the edge.
Glazing
Triple is not
always better
Three panes insulate against heat loss better than two. Against noise they often do worse than a well chosen double unit, because symmetrical packages pass vibration straight through. Which unit you need depends on what is actually bothering you.
Choosing
What is bothering you?
Start from the complaint, not from the product. These three situations cover nearly everything we meet on the northern edge of Brussels.
It is noisy
Then asymmetry counts. Two panes of different thickness, or one laminated pane with an acoustic interlayer, do more than adding a third pane. We first ask where the noise comes from and at what hour.
It gets too hot
Then solar control counts, or better still external shading. Glass that stops the sun also stops light in winter. On a south facade a screen is almost always the smarter answer.
Honestly
When we advise against triple
- When noise is your real problem. A symmetrical triple unit can perform worse than a well chosen asymmetric double.
- When the rest of the house is not insulated. The window then becomes the warmest point and the moisture condenses elsewhere, against a cold wall.
- When the profile does not carry the weight. Triple weighs half as much again. On a large opening sash it will drop over time.
- When there is no ventilation. Better insulating windows close better, and without fresh air supply you get moisture at the coldest point of the room.
For the grant that last one is not advice but a condition. Anyone replacing exterior joinery without meeting the ventilation condition receives no grant. More about that on the grants page.
Questions
About glass
What does Ug actually mean?
It is the heat transfer of the glazing alone, in watts per square metre per degree. Lower is better. Note: Ug is about the glass, Uw about the complete window including the profile. A good Ug in a poor profile achieves little.
Does laminated glass also help against noise?
Yes, and that is exactly why we often propose it. The interlayer between the two panes damps the vibration. That same interlayer holds the fragments together during a break in attempt.
My glass is misted between the panes. Can that be repaired?
No. The seal of the unit has failed and moisture is inside. The glass is replaced, not dried. Sometimes that can be done in your existing frame, which is a completely different figure from a new window.
Tell us what is bothering you
Cold, noisy or too warm. The answer to that question sets the glazing unit, and that usually matters more than the brand of the profile.
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