Choosing Conservatory Glass

roof detail

In a conservatory, glass choice and climate control are factors to consider. Glass technology has come a long way since the first orangeries of the 16th century. High performance low-E glass options, site orientation, naturally occurring shade, and weather are appropriate to consider when choosing glass.

In general, glass uses solar heat gain to advantage in winter, especially for a conservatory in Boston or Chicago. Conversely, a conservatory located in New Orleans will need a lower (better)shading co-efficient than a building located in Seattle with its low number of sunny days. Solar control glass would be more appropriate for many northern climates, while a north or east facing conservatory in a northern climate zone would require less solar control glass.

Understanding Conservatory Glass Specifications

Steps to consider:

  1. Glass which has the lowest shading co-efficient (most solar gain reduction) tends to have low visible light transmittance and thus less natural light. The benefit however is reduced air conditioning loads. Even in northern climates, with hot summers, this is an important consideration.
  2. In overcast or rainy climates high visible light transmittance may be preferred and thus the clearer the glass, the better.
  3. Low-E glass, especially in colder climates reduces U-values (increases R-values) with minimal effect on visible light values and reduces air-conditioning costs.
  4. High performance Low-E products manage to achieve an impressive balance of U-value, Visible Light Transmission and Shading Coefficient.
  5. Roof shading in combination with glass choice can reduce solar heat gain, reduce heat loss and permit adjustment to varying conditions throughout the seasons and the day (shades open on overcast days and closed on bright sunny days).

Based on our experience in most North American climate zones, we use Cardinal High-Performance Low-E 272 glass as a standard throughout the conservatory with an option to upgrade the roof glass (or roof and sides) to a slightly better shading coefficient. We also specify that the Low-E coating be placed on the second surface for better shading as is common in southern and western U.S. building practices (no deleterious effect on U-value).


Performance Specification

Standard roof and side glass is detailed below, along with the next upgrade option.

(1″ Overall)
Typical Low-E Glass .33 .66 .76 73% 17%
LoE² -272 High-Performance Low-E Glass (our standard) .26 .40 .46 70% 11%
LoE² -366 High Performance Low-E Glass (upgrade)** .25 .27 .31 64% 11%


*The lower the U value, the better the insulating properties. The lower the Shading Coefficient, the better

the glass is at reducing heat gain.  The higher the Reflectance, the shinier the exterior appearance.


 **Low-E 366 improves the shading coefficient by over 30% from 272 while only decreasing visible light by 6% from 272 glass.