Tag Archives: window requirements

Solar Heat Gain Coefficient

Solar Heat Gain Coefficient aka SHGC

Hansen Pole Buildings’ Designer Rachel has a client who is looking for a SHGC rating of .45 or higher and found a window from Cardinal window (made by Marvin Windows) which had a rating of .65 SHGC.

Rachel read my blog https://www.hansenpolebuildings.com/2012/06/low-e-windows/  and Window SHGCwondered if I could talk more about the SHGC and U-Factor and if there is a rating which is too high for the SHGC?  She spoke with Dave from Anderson Windows and he said a .65 would bring in a lot of heat and they would be smokin’ with the sunlight coming in the window although he said it would NOT be energy efficient.  He also wouldn’t recommend these windows especially because these windows are going to go to Minnesota and it will have serious frost issues.

He said they should pay more attention to the U-Factor than the Solar Heat Gain.

I relayed this to the customer and he said he realizes how much heat it would bring in which is why he is putting a 3’ overhang so it doesn’t get too much light in. I wonder if he had read this article: https://www.hansenpolebuildings.com/2015/07/windows-5/

What even is SHGC?

The origin of solar heat gain is the direct and diffuse radiation coming from the sun and the sky (or reflected from the ground and other surfaces). Some radiation is directly transmitted through the glazing to the building interior, and some may be absorbed in the glazing and indirectly admitted to the inside. Some radiation absorbed by the frame will also contribute to overall window solar heat gain factor. Essentially, the lower the window’s SHGC, the less solar heat it transmits. SHGC is expressed as a dimensionless number from 0 to 1. A high coefficient signifies high heat gain; a low coefficient means low heat gain. The glazing type, number of panes, and any glass coatings influence solar heat gain. Solar heat gain of glazing ranges from above 80% for uncoated clear glass to less than 20% for highly reflective coatings on tinted glass. A typical double-pane insulating glass unit (IGU) has an SHGC of around 0.70. This value decreases somewhat by adding a tint and can be decreased substantially by adding a low-solar gain low-e coating.

The National Fenestration Rating Council (NFRC) has a nationally recognized rating method for the whole window, including the effects of the frame. Sometimes the center-of-glass SHGC is referenced, which describes the effect of the glazing alone. Whole window SHGC is lower than glass-only SHGC, and is generally less than 0.8.

Solar heat gain can provide free heat in the winter and can cause overheating in the summer. Finding the best balance solar heat gain with an appropriate SHGC depends upon climate, orientation and shading factors.

The U.S. Department of Energy has available a publication (https://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/measure_guide_windows.pdf) which includes a Window Selection Process which begins in Section 4, page 16.

Want the right window for your new pole building? The USDOE document will provide the guidance to assist in making the right choice

Egress Windows

Dedicated readers will remember my oldest step-son, Jake. Although he is a high school physics/biology/chemistry teacher by vocation – he seems to have a bit of the “builder gene” in him.

For those who missed out on some of prior adventures – they begin here: https://www.hansenpolebuildings.com/blog/2012/07/construction-time-2/

Home AdditionJake’s dad is a successful farmer in South Dakota. Growing up on the farm, Jake got plenty of dirt under his fingernails, and after spending several years in Tennessee, he, his lovely wife and their two children have returned to his roots – to farm with his Dad.

Needing a place to live which would be convenient to the farm, they are remodeling his paternal grandmother’s house – adding a 24’6” wide x 32’ two-story “wing”. In effect, they are making it a four-level home.

Of the 15,000 plus pole buildings I have been involved with over the decades, very few have intentionally been designed as houses (or at least I was not told they were going to be houses). When it came time for bedroom windows – I bounced the “minimum egress size” thing off Jake. Who (being the scientist he is) had the answers at his fingertips via the internet on his smart phone.

Now an egress window is one which is large enough to allow entry or exit if there is an emergency. Egress window requirements are used to guarantee a minimum window size and maximum height above a floor.

Egress window requirements are designed to make sure windows can open enough to climb through when there is an emergency. Egressable windows are only required in bedrooms and basements. The heights and widths of the clear openable space are designed to allow a firefighter with an oxygen tank on, to climb through the window.

From the 2012 IRC (International Residential Code):

R310.1 Emergency escape and rescue required. 
habitable attics and every sleeping room shall have at least one operable emergency escape and rescue opening. Where basements contain one or more sleeping rooms, emergency egress and rescue openings shall be required in each sleeping room. Where emergency escape and rescue openings are provided they shall have a sill height of not more than 44 inches (1118 mm) measured from the finished floor to the bottom of the clear opening. The net clear opening dimensions required by this section shall be obtained by the normal operation of the emergency escape and rescue opening from the inside. Emergency escape and rescue openings shall open directly into a public way, or to a yard or court that opens to a public way.

R310.1.1 Minimum opening area. 
All emergency escape and rescue openings shall have a minimum net clear opening of 5.7 square feet (0.530 m2).

Exception: Grade floor openings shall have a minimum net clear opening of 5 square feet (0.465 m2).

R310.1.2 Minimum opening height. 
The minimum net clear opening height shall be 24 inches (610 mm).

R310.1.3 Minimum opening width. 
The minimum net clear opening width shall be 20 inches (508 mm).

R310.1.4 Operational constraints. 
Emergency escape and rescue openings shall be operational from the inside of the room without the use of keys, tools or special knowledge.


The key phrase here is “net clear opening”. While a four foot wide by three foot tall sliding window would “appear” to have a sliding two foot by three foot panel, when physically measured the actual opening falls just below the threshold of 5.7 square feet.

Typically sized sliding windows for egress are four foot wide by four feet tall, or five foot wide by three feet tall.

With single or double hung windows, they must be at least three feet in width and five feet in height.

Building a new pole building to be your next home, or a mother-in-law apartment? Keep these sizes in mind when planning for sleeping areas – and help keep everyone safe