5 Parts of a Double Glazing Specification That Matter
Replacement windows are sold on the number of panes and perform according to details that rarely feature in the sales conversation.
1. The glass
Low-emissivity coatings reflect heat back into the room and are the single largest factor in thermal performance.
The gap between panes matters, as does the gas filling it; argon is standard and improves insulation over air.
Warm-edge spacer bars around the perimeter reduce heat loss and condensation at the edges.
Window energy ratings summarise this and allow comparison between products.
2. Frames
Plastic frames are cheapest and vary considerably in quality of construction and reinforcement.
Timber performs well and needs maintenance.
Aluminium is strong and slim but conducts heat unless thermally broken, which good products are.
Composite frames combine materials and cost accordingly.
3. Installation, which decides the outcome
A well-specified window badly fitted performs poorly.
Ask how the perimeter will be sealed and insulated, and how the reveals will be made good.
Poor sealing causes draughts and condensation at the edges, which is then blamed on the window.
Trickle vents are required in many jurisdictions and are frequently omitted, causing condensation problems later.
4. Triple glazing
Improves insulation and adds weight and cost.
The gain over good double glazing is real and smaller than the gain from single to double.
Worth considering for exposed elevations, noise, or where you are already at a high specification.
5. Buying
Get three quotes on the same specification: same glass, same rating, same frame, same fittings.
Ask for the specification in writing rather than a product name.
Be wary of pressure selling, discounts that expire during the visit, and prices that fall dramatically when you decline.
Check the guarantee, who provides it, and whether it is insurance-backed against the installer ceasing to trade.
Confirm the installation will be certified under the relevant competent person scheme, since you will need the paperwork when selling.
Final Thoughts
Replacement windows are sold on pane count and perform according to coatings, spacers and fitting. Get three quotes on an identical written specification, and be wary of discounts that expire during the visit.
Author: This article is general information only and does not constitute professional advice. Circumstances vary, and you should consult a qualified professional before making decisions based on this content.
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