By Abricos Glass · Last updated 2026-07-27
Written and reviewed by the Abricos Glass team from field practice on Colorado projects. Cost ranges are budget guidance, not quotes, and code notes are background rather than a code determination — see our editorial and content accuracy policy.
Low-E coatings for curtain wall thermals
How the right Low-E stack quietly does more work for your building envelope than any other spec decision.
The decision this page is about is narrow: which low-emissivity coating stack belongs on which façade of your building, and how to write that into a specification a fabricator can price without guessing. It is not a product review and it does not rank brands — every number that matters for your project comes from the NFRC label of the exact insulated glass build, not from a coating family in general.
Low-E coatings are microscopically thin metallic layers deposited on a glass surface. Uncoated glass radiates heat freely in both directions; a coating changes how much long-wave infrared it re-radiates and how much of the solar spectrum it lets through. Two properties describe the result on a label: solar heat gain coefficient (SHGC), the fraction of solar energy admitted, and visible light transmittance (VLT), the fraction of daylight admitted. A third, U-factor, describes conductive heat flow and is influenced by the coating but set mostly by the gas fill, spacer and frame.
The reason this becomes a per-façade decision in Colorado is that the sun does not treat the four sides of a building equally, and neither does the design intent. A west elevation with an afternoon load and a north elevation whose only job is daylight rarely want the same coating.
How coating families behave — directional, not a substitute for label data
| Coating family | Typical behaviour | Where it tends to fit | What to verify on the label |
|---|---|---|---|
| Hard-coat (pyrolytic) low-E | Durable, can be handled and used monolithic; less selective than sputtered coatings | Storm and single-glazed retrofits, some interior and specialty conditions | Emissivity and whether the coating is rated for the exposed surface it will occupy |
| Single-silver soft-coat | Strong U-factor improvement with relatively high solar transmittance | Heating-dominated and passive-gain elevations, north glass, mountain residential | SHGC, U-factor, and that the coating is on a protected IGU surface |
| Double-silver soft-coat | Balanced daylight with noticeably reduced solar gain | General commercial glazing across mixed orientations | SHGC and VLT together, not SHGC alone |
| Triple-silver soft-coat | Lowest solar gain of the clear-appearing stacks, with more selectivity | West and south commercial elevations with real cooling load | VLT, exterior reflectance, and colour consistency across the façade |
| Coating plus tint or reflective layer | Adds visual character and further gain control, with appearance consequences | Where a design intent or an energy target cannot be met by a clear stack | Exterior reflectance, mock-up approval, and reflected-glare exposure to neighbours |
Surface positions, and why they change the answer
Surfaces in a sealed unit are numbered from the outside in: #1 is the exterior face of the outboard lite, #2 its cavity face, #3 the cavity face of the inboard lite, #4 the room-side face. In a triple-glazed unit the numbering continues through the middle lite.
A solar-control coating placed on surface #2 intercepts solar energy before it enters the cavity, which is why gain-control stacks normally live there. Move a coating inboard to #3 and it does more to keep interior heat from radiating outward, which is a heating-climate strategy. In triple glazing the two roles can be split across two coated surfaces, which is precisely why triple-glazed performance cannot be inferred from a double-glazed cut sheet.
A room-side #4 coating is a distinct product decision, not a free upgrade. It sits in an occupied, cleanable, condensation-exposed position and changes both interior surface temperature and cleaning requirements. Treat it as a specification item with its own maintenance note rather than a default.
Soft-coat stacks degrade if exposed to air, so the coating must be edge-deleted at the perimeter and captured by the sealant system. That makes coating choice, edge deletion and sealant compatibility a single package rather than three independent decisions.
Choosing per orientation on a Colorado façade
West elevations carry the hardest condition on the Front Range: low afternoon sun, high summer air temperature and, on tall glass, direct occupant discomfort near the glass line. This is where the most selective clear stack usually earns its cost, and where exterior shading, if the design allows it, does more than any coating change.
South elevations are the most design-dependent. High summer sun is comparatively easy to shade with an overhang or a deep reveal, while low winter sun is useful gain in a heating-dominated climate. A less aggressive stack plus real shading often outperforms the most selective coating with no shading at all.
East elevations get morning gain when the building is still cool, so the penalty is usually comfort and glare at desk height rather than peak cooling load. Interior shading strategy and VLT often matter more here than the last increment of SHGC.
North elevations mostly need daylight and a good U-factor. Specifying the same aggressive solar-control stack on the north face as on the west is a common way to lose daylight and pay for performance the elevation never uses.
Altitude and dry air are the Colorado overlay on all four. Higher UV exposure and large diurnal swings are hard on sealants and gaskets, and units fabricated near sea level and shipped up to the Front Range have to be built for the pressure differential — a coating decision does not solve that, an IGU-build decision does.
Writing the specification so it can be priced
Specify the complete build, not the coating name. That means the outboard lite thickness and heat treatment, the coated surface number, the cavity dimension and gas, the spacer type, the inboard lite, and the interlayer if the unit is laminated. A coating name alone lets two fabricators price two different products.
Ask for NFRC-certified values for the specific build rather than the product line. Manufacturer literature reports representative assemblies; the assembly you buy may differ in thickness, cavity or heat treatment, and those differences move the numbers.
State the appearance requirement explicitly. Exterior reflectance and colour vary between coating families and between heat-treated and annealed lites of the same coating, and a façade mixing both without a documented tolerance is where colour-uniformity disputes come from.
Name who owns the energy model. A glazier can supply label data for the build; whether that build satisfies the project's energy path is a design-team and Authority Having Jurisdiction determination, not a glazing warranty.
Spec checklist before the units are ordered
Coated surface number stated for every unit type, including any triple-glazed and any room-side coating.
Heat-treatment requirement stated per lite, with the appearance tolerance for mixed annealed and heat-treated glass on the same elevation.
Edge deletion and sealant compatibility confirmed in writing by the fabricator for the coating being used.
NFRC label data requested for the exact build, kept with the submittal record.
Elevation-by-elevation schedule showing which unit type goes where, so the field crew is not choosing at the opening.
Mock-up or sample approval for appearance where the façade is visually continuous.
Where coating decisions go wrong in the field
Reversed units are the classic failure: a unit installed with the coated surface facing the wrong way performs differently and may look different in reflection next to its neighbours. Clear factory orientation marking and a field check before glazing is cheaper than the discovery.
Mixed procurement is the second. When a replacement lite is ordered years later from a different fabricator against a generic description, it can differ in colour and reflectance from the surrounding glass. Recording the original build with the owner's closeout documents prevents that.
The third is treating the coating as the whole thermal story. Spacer type, gas fill and frame conduction move the whole-window number as much as the coating does, which is the subject of the companion piece on insulated unit specifications.
Frequently asked questions
- Does a low-E coating make glass look tinted or mirrored?
- Clear soft-coat stacks are designed to be visually subtle, but they are not invisible: exterior reflectance and a slight colour cast vary between families and between heat-treated and annealed lites. If appearance matters on a continuous façade, review a sample or mock-up rather than relying on a printed swatch.
- Can a low-E coating be added to glass that is already installed?
- No. Sputtered low-E coatings are applied in fabrication and have to sit in a sealed cavity. Retrofit films are a separate product category with their own performance and warranty implications, and they are not a substitute for a coated unit.
- Should the same coating be used on every elevation?
- Not necessarily. A single coating simplifies procurement and appearance, but elevations with very different solar exposure often justify different stacks. The trade-off between a uniform façade appearance and per-elevation optimisation is a design-team decision.
- Where do the actual SHGC and U-factor numbers come from?
- From NFRC-certified data for the specific assembly, supplied by the fabricator or manufacturer. Numbers quoted from a product family or an article are planning context only.
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