We are continuing our series on Passive House Design. LEAP’s intelligent design process consists of four main steps, each with the aim to maximize human comfort, energy efficiency, and real cost savings. Today we explore the importance of good windows and doors, along with what constitutes them as such.
Passive House Design Process
- Site Analysis
- Doors and Windows
- Air Sealing
We Aren’t Living in the Dark Ages, or Are We?
So you took a perfectly good, well insulated structure and put holes in it. Oops, I mean windows. You put windows in. But that’s one of the reasons we crawled out of caves and stopped living like mole-people. Our homes and offices are more pleasant with natural light and vitamin D.
Let’s look at an example somewhere between mole-people era and modern times—the reign of castles. I think we can agree that castles were not the pinnacle of energy efficiency. To support this claim, Eric “Outlander” Davenport, traveled back in time to report the effective R-values of castles as 4… Well, in comparison, the effective R-value of a passive house is 42. (Well really it’s 40, but we all know the answer to life, universe and everything is 42).
So what the heck is this effective R-value you speak of?
R-value stands for resistance to heat flow. The higher the R-value, the greater the insulating value.
Effective R-values are the TOTAL resistances provided by all components in a wall assembly. This equates to patience and higher math—tallying up the thermal bridging, air infiltration, radiant heat loss or gain, and moisture impact on the overall structure. These factors usually reduce the effectiveness of the labeled R-value, on say conventional cavity-filled insulation.
Poor window quality can totally tank your whole effective R-value. You can construct your walls from the most insulating material in the world, but if you’re then installing crap windows, you might as well tack an oil cloth over the opening and call it good.
Which brings us to the puffy sleeves of the 1980’s. Building designers deemed “Windows for all” & “Architecture is above human whims!”, as a backlash to the 1970’s energy crisis and inoperable windows. This equated to: we can put windows everywhere, (even on the—gasp—west side of the building) and a window, is a window, is a window. We shall install the same windows in New York, California, and Alaska—climate dependence be dammed!
Well, to give you an idea of how well that worked out—the one design fits all approach—the effective R-value of these buildings dropped back to 4. Yes, 4. Your new, beautiful, big-hair building is the energy equivalent of living in a drafty castle. Back to the dark ages. (Weren’t puffy sleeves popular in the middle ages too? Coincidence?)
So we continue to claw our way out of the dark days of the 80’s, towards the light of Passive House Design. Good windows (and doors) equals a good thermal envelope, which equals a high effective R-value (42!), which spreads comfort and energy efficiency across the land.
What Constitutes a High Efficiency Window?
Soft, but what light through yonder window breaks? It faces east, and 2″ is the notch. Or rather, placement and construction—a high efficiency window doth make. And who pray tell constructs the finest windows in the land? Well, the Europeans do. Perhaps it was those long, drafty years of castle living that haunt their collective consciousness. But at any rate, they have figured out how to build a great window. And the big secret? A deep notch.
A deep notch accomplishes two things: makes the structure stronger, and reduces thermal bridging. The wood/glass interface is the weakest part of the window, and also where most of the energy is lost. European windows have a 2″ notch, whereas most American made windows are only 1/2″. This extra 1.5″ seats the glass securely in the frame and significantly reduces air leakage.
The Passive House Institute has a database of Passive House Certified windows and doors (and no, they don’t have to be European). When manufacturers from anywhere meet Passive House specifications, they can become certified. Below is an example of what a Passive House Institute certification seal looks like. Notice the list of 7 different climate regions.
Types of Windows
The type of window is also important. Double hung are out. Casement, awning, and fixed windows are in. Tilt-turn windows are a good option for functionality and air sealing, see image below. The three positions (fixed, tilt, turn) allow for security, venting and ease of cleaning, respectively.
Placement is another key factor. For balanced daylighting, large and floor to ceiling windows are typically placed on south and east facing walls. Small windows are placed high up on the north facing wall. As a rule of thumb, window area is no more than 10% of the total floor area for a given room. This helps prevent overheating in the summer and losing heat in the winter.
Tilt Turn Windows are a good choice for Passive House Design. Image from Glo Windows.
We didn’t really touch much on doors, but the same principles apply: good sturdy frames and good sealing will be more energy efficient. Bad doors are like installing a portcullis? It’ll keep the critters out, but not much else. The payback for spending a little more money upfront on good doors and windows is well worth it. Want to know how much? Contact LEAP Architecture today, and we can fill you in!