“Double glazing with Low-E” is not a complete glass description: coating product, substrate, surface position, heat treatment, cavity and spacer all belong to the configuration.
A schedule says Low-E but does not say which coating or surface. One supplier prices a solar-control coating on surface #2; another proposes a passive coating on surface #3. Both quotations appear compliant until the buyer compares SHGC, U-factor, colour and climate intent. The missing surface number concealed a different product decision.
Design boundary: Energy, condensation, thermal-stress, appearance and code decisions require project-specific analysis by responsible professionals. This guide is a procurement review—not a glass design or energy model.
1. Number the glass surfaces before discussing coatings
For a conventional double IGU viewed from outdoors, surface #1 is the exposed exterior face, #2 faces the cavity on the outer lite, #3 faces the cavity on the inner lite and #4 faces the room. Triple glazing adds further surfaces. Draw the actual make-up and mark exterior/interior; do not rely on ‘inside pane’ language.
NGA’s architectural-glass description guidance shows that a usable specification identifies each lite, thickness, tint, heat treatment, coating designation and surface, spacer/cavity and seals. Use the same sequence in enquiries and approvals.
| Layer | Required description |
|---|---|
| Outboard lite | Thickness, substrate/tint, heat treatment |
| Surface #2 | Coating designation or none |
| Cavity | Width, gas and spacer/seal description |
| Surface #3 | Coating designation or none |
| Inboard lite | Thickness, substrate, heat treatment/lamination |
| Edges/processing | Edge deletion, frit, holes or special fabrication |
2. State the energy intent, not only the coating name
NGA explains that coating position affects product performance. Solar-control Low-E is commonly positioned toward the sun, often surface #2, to limit solar heat gain; passive Low-E is commonly positioned farther from the sun, often surface #3 in a double IGU, where heating-dominated designs may accept more solar gain while reducing long-wave heat loss.
These are design principles, not an automatic climate rule. Record project U-factor, SHGC, visible transmittance, exterior reflectance, climate/orientation and applicable whole-window calculation or rating route. Centre-of-glass data cannot be presented as whole-window performance.
| Question | Evidence |
|---|---|
| Heating/cooling objective | Project energy or envelope criteria |
| Solar-gain control | Required SHGC and orientation basis |
| Heat-loss control | Required U-factor and whole-window route |
| Daylight/view | Visible transmittance and glare review |
| Appearance | Exterior/interior colour and reflectance review |
| Compliance | Applicable calculation, test or rating documentation |
3. Verify the exact coating product and substrate
‘Single silver’, ‘double silver’ and ‘triple silver’ are family descriptions, not purchase specifications. Record manufacturer, exact product, substrate colour, nominal thickness, approved performance data and processing limitations. Confirm whether the fabricator is authorised or technically capable for that coating route where the project requires it.
Do not transpose data from another substrate, thickness or IGU build-up. Tinted substrates and multiple coatings can change absorption, appearance and thermal-stress review.
- Coating manufacturer and product code
- Substrate and nominal thickness
- Coating surface
- IGU make-up used for published data
- Heat-treatment and bending limitations
- Edge deletion and sealant compatibility
- Maximum/minimum sizes and processing route
- Document revision and responsible approval
4. Approve appearance under controlled viewing conditions
Electronic images cannot reliably approve coated-glass colour. Review representative samples or a mock-up with the intended substrate, coating surface, heat treatment, cavity, spacer and interior background. Record viewing distance, angle, daylight, sky and interior conditions.
Coated and heat-treated glass can show reflection, anisotropy, roller-wave or colour variation whose acceptance must follow project criteria and applicable guidance. A sample records an agreed reference; it does not guarantee every sky condition will look identical.
| Field | Record |
|---|---|
| Sample/make-up ID | [enter] |
| Coating/substrate/surface | [enter] |
| Heat treatment and IGU | [enter] |
| Viewing conditions | Distance, angle, light and background |
| Compared references | Adjacent glass/materials |
| Accepted observations/exceptions | [enter] |
| Reviewer/date | [enter] |
5. Check fabrication and edge details before release
Soft-coat Low-E is normally protected inside a sealed cavity. Fabrication may require edge deletion so sealants bond to appropriate surfaces; coating, spacer, primary/secondary seal, gas filling and quality controls form one IGU process. Obtain the fabricator’s controlled route rather than prescribing an unverified deletion width.
Resolve holes, notches, frit, lamination, heat treatment and post-temper operations before production. A coating substitution can affect processing, appearance, thermal stress and evidence even if nominal U-factor is similar.
Change rule: Any change in coating, substrate, surface position, cavity, spacer, gas, heat treatment or seal system is a configuration change requiring documented review.
6. Verify delivered units without damaging them
Use labels, approved make-up records and appropriate non-destructive coating detectors or professional methods where required. Do not scratch, chemically test or dismantle glass. Reconcile opening mark, glass code and IGU marking with the packing and inspection records.
If orientation appears wrong, quarantine the affected units and request fabricator evidence. Reflections or handheld readings must be interpreted by competent personnel because multiple surfaces and coatings can confuse casual checks.
| Control | Evidence |
|---|---|
| Opening identity | Mark and glass schedule |
| IGU identity | Label/code and approved make-up |
| Coating orientation | Approved non-destructive verification |
| Appearance | Controlled comparison and exceptions |
| Damage/edge condition | Receiving and glazing records |
| Disposition | Accept, hold or investigate |
7. Issue a complete Low-E enquiry brief
Give every bidder the same glass make-up or the same performance-and-appearance decision route. If suppliers may propose alternatives, require a line-by-line comparison of coating, substrate, surface, performance data, appearance, heat treatment, processing limits, lead time and evidence.
Keep the approved glass schedule tied to drawings, samples, production and replacement records so a future remake does not rely on the phrase ‘same Low-E as before’.
- Identify exterior/interior and number surfaces.
- State project performance and appearance criteria.
- Name or require declaration of coating/substrate.
- Define complete IGU make-up and processing.
- Approve representative appearance evidence.
- Record calculation/test/rating applicability.
- Control substitutions and delivered-unit verification.
Work through two offers that both say Low-E
Consider a hypothetical enquiry where two suppliers return the same overall glass thickness. Offer A identifies a coating product, its surface and the glazing build-up. Offer B says equivalent Low-E but leaves the coating code and surface unstated. The missing details do not prove that B is unsuitable; they mean the two offers cannot yet be treated as the same configuration.
Return a marked comparison asking B to identify those fields and the configuration behind its performance figures. Also ask A to confirm that its sample and quotation describe the same make-up. A complete-looking quotation can still refer to a different sample. Keep each clarification connected to the offer revision rather than adding an untraceable note to a price spreadsheet.
This exercise deliberately supplies no performance numbers or preferred coating. Its output is an aligned comparison for the responsible project review, not a buyer-selected substitution based on a generic Low-E label.
Keep identity, performance and appearance in separate columns
Create one comparison row per glass code, with the opening marks it serves. Use separate fields for the proposed construction, the performance-document reference and the appearance sample. A visual acceptance should not silently approve a performance value, and an energy calculation should not silently approve the visible colour.
For the construction field, record the outside-to-inside make-up and named surface locations. For the evidence field, retain the applicable document and the configuration it describes. For the appearance field, record the physical reference and agreed observations. If one of these is provisional, name its owner and the decision still required.
When an alternative is offered, request a difference list rather than accepting the word equivalent. Record whether the supplier has changed the coating, substrate, cavity, spacer or processing route. Refer the technical and appearance consequences for review before revising the order.
Carry the accepted glass code through the order
Once the configuration is approved, use its code consistently in the opening schedule, quotation, sample record and production documents. Ask how it will be linked to delivery labels and any later replacement request. Retaining the code and revision is more useful than asking for the same blue-looking glass several years later.
Use the sample approval guide for appearance decisions and the whole-window thermal guide to check the scope of energy evidence. Send your glass schedule with the proposed alternatives and the fields that still need clarification.
FAQ
Is surface #2 always better in hot climates?
No universal conclusion applies. Coating product, building orientation, energy criteria and complete glazing system require project analysis.
Can centre-of-glass U-factor represent the complete window?
No. Frame, edge and system configuration affect whole-window performance.
Are double- and triple-silver coatings interchangeable?
No. These labels describe families; exact products differ in solar, visible, appearance and processing characteristics.
Can a phone photo approve coating colour?
No. Use controlled physical samples or mock-ups with the intended make-up.
How can coating orientation be checked after delivery?
Use approved markings and suitable non-destructive professional verification without damaging the glass.
Continue the project review
Connect this guide with the proposed window and door systems, then review how Cavorlen approaches manufacturing and quality control. When your schedule is ready, send it through the project review form.
Official sources used
NGA — Describing Architectural Glass ↗NGA — GANA Glazing Manual ↗NGA — Recent Technologies in Glazing ↗Related buyer guides
This guide does not select a Low-E product, promise an energy value, approve a coating surface or claim that surface #2 or #3 is universally superior.