This is the second installment in a series of posts aimed at educating customers who are interested in new construction, with a focus on implementing sustainable design and building practices. This series will cover nearly every aspect associated with new construction, starting with design and moving through the building phases sequentially. The previous installment can be found here.
“An ounce of planning is worth a ton of fixing.”
In our first post we talked about a few concepts to keep in mind when designing your new home. These included simple ideas such as keeping your structure small and avoiding a convoluted building shell and bump outs; to siting principles such as orientation (to maximize passive solar gain as well as create a roof plane for solar panels) and utilizing objects or trees for shading and wind breaks. In this post we continue to explore the design side of things, though we will examine some features more related to the specifics of the building shell itself.
The following features on your new home can have an incredible impact on your energy use (and thus cost of ownership), durability, and overall comfort. It is absolutely imperative that the proper attention to detail is paid to these components of the building shell, because if they are designed improperly it can lead to unforeseen expenses down the road (at best) or catastrophic failures of the building (at worst). No pressure though!!
First things first, let’s clear something up. The term “glazing” refers to windows (in their many forms) and glass doors to the exterior of the building. There are entire books and websites dedicated to this topic; but for the purposes of this post, we’re going to keep it simple and avoid all the nitty gritty details in terms of solar heat gain coefficient, u-value, visible transmittance, etc. These values aren’t necessarily pertinent at the design stage, rather what is important is the total surface area of glazing, and where it is located on the building (e.g. North, South, East, West).
A simple principle you should espouse in your home design in terms of window location starts with a significant amount of south facing glazing. South facing windows allow for ample amounts of daylighting opportunities as well as passive solar heat gain in the winter months. These windows are also easily shaded in the summer through the use of overhangs (as we’ll soon learn below). Both daylighting and passive solar gain mean less energy used for lighting and heating, which translates into dollars saved by you!
The next most important glazing design principle to bear in mind, is limiting the amount of north facing windows – for obvious reasons. The north sides of buildings are considerably colder, and lack that passive solar component associated with south facing glazing, therefore will shed more heat from the house than they could ever possibly gain.
In terms of East and West facing glazing, you have to keep in mind that it is possible for overheating to occur if you have an excessive amount of West facing windows (even in the winter!)- due mainly to the fact that the sun will be shining through these windows during the hottest part of the day. Windows on an East or West wall are also harder to shade with overhangs due to the nature of the sun’s path in the sky.
However, this should all be taken with a grain of salt. Windows are extremely poor insulators compared to your wall assembly. So if you have a sweeping vista to the east, or a gorgeous lake to the north, by all means, place your windows where you will enjoy them most!
If there is one motif you glean from these blog posts it’s that ‘simpler is better’. That logic applies to your roof design as well. There are many ways to make your roof convoluted but the most common come in the form of dormers and valleys. There is no doubt that these features can add to the “curb appeal” of your new home, but you must understand the negative attributes that come along with them. First and foremost – there are many more flashing details that must be done right the first time; lest you are fond of tearing your roof apart in search of elusive leaks. Another detail that is harder to get right with convoluted roof lines (as opposed to a simple gable roof) is air sealing. It is absolutely imperative that all new construction pays close attention to a continuous air barrier – which is made that much harder when your have many roof lines joining at different angles, or in the case of dormers, knee walls to contend with. Knee Walls in particular are easy to bypass in air sealing efforts.
At this point, you already plan to orient the long axis of your building in the East/West direction, which plays well with a large simple roof plane. A large south facing roof allows for an ideal scenario for installing solar. additionally, because you don’t have a plethora of adjoining roofs at different levels, you run no risk of shading your new solar array!
A few other details to consider when designing is to cluster penetrations close together, but more importantly, put them on the north slope of your building (think: continuous, large solar array with no obstacles interfering with it).
Houses with little to no overhangs shouldn’t exist; whoever designed them and those who chose to live in them should be ashamed!! They not only pose major problems down the road but they are eyesores! Ok, so the latter is an opinion, but the point still remains that overhangs serve very important roles, and houses without them are susceptible to some major problems that are easily avoidable with properly sized overhangs.
Overhangs fulfill two key functions: sheltering the building from the elements (namely wind driven rain and runoff); and controlling solar gain throughout the year. The first is straightforward and is an easy concept to grasp. Without overhangs – or overhangs that are too small for that matter- runoff from the roof is allowed to saturate the siding, greatly increasing the risk of a bulk water entry problem. This can reduce the life of your siding, and if the building doesn’t have the proper attention to detail in terms of flashing, it can ultimately lead to water entering the building shell. BAD! Additionally, there are typically weaknesses at the roof/wall interface that are even more susceptible to leaks when the water isn’t shed away from the building.
Another related problem is splash-back: that is, water that careens from your roof and strikes the ground, causing splashing onto the structure. This has all the same problems that are noted above – all of which could be avoided if the overhang is large enough to get the falling water away from the building.
The second key feature of properly sized overhangs is their ability to control solar gain. When the sun is higher in the sky during summer months, the overhang creates shade and thereby helps to keep your home cooler by blocking solar heat gain. Inversely, during winter months when the sun is lower in the sky the overhang doesn’t block (or blocks much less) solar gain, allowing that big ball of plasma in the sky to heat your house! And in case you weren’t aware, the sun doesn’t send you a bill at the end of the month asking for your hard earned money in exchange for this heating!
South facing windows are the easiest to size and plan for to achieve the solar gain (or lack thereof) benefits. East and west facing windows generally require deeper overhangs, and may be more adequately served by other extension structures or vegetation. And of course, by now you know that your north facing glazing should be minimal!
One unforeseen benefit of a properly designed house is a reduction in construction waste. There are some simple rules of thumb you and your designer can follow that will drastically cut down on waste throughout all phases of the project. The first rule one should abide by is designing out-to-out dimensions on 2-foot increments.
Most sheet goods (e.g. plywood, OSB, gypsum board) come from suppliers in 4’x8’ dimensions (or something else equally as divisible by 2). Therefore, keeping the dimensions of your assemblies based on 2 -foot increments can reduce material waste by avoiding the need to rip down whole sheets for the odd measurement. This same principle can be applied to CMUs (concrete blocks), ICFs (insulated concrete forms), and SIPs (structural insulated panels).
A second rule of thumb is to provide a properly pitched roof. A quick bit of trigonometry can determine the dimensions of your roof plane, and thereby eliminate the need for small rips of plywood for sheathing and roofing.
Finally, doors and windows should be located on 2-foot grid increments to eliminate the need for extra framing material. “Small gap” studs in your house can add up in a hurry, and by utilizing this principle, jack studs and the framing lumber for the openings can be used to fasten your interior finish. As if that weren’t enough, any stud you nix from your house decreases the amount of thermal bridging your structure experiences (more on that in a later post).
If your inner hippie isn’t exactly getting excited at the prospects of reducing waste and the environmental effects associated with that waste, just remember, all that material is dollars out of your pocket. Over the many phases of construction related to building a house there are ample opportunities to throw money out the window – many of which can be prevented with a little foresight at the planning and design stage.
This is another topic that deserves its own series of posts – and rightly so! There are few things as critical to the energy footprint of your home than proper air sealing. First, what exactly is air sealing/air barriers? Simply put, an air barrier is any product that reduces the flow of air to 0.02 liters/(s-m2) @75 Pascals. Ok, so that wasn’t very simply put. What that means, is that air is essentially blocked from flowing through the material. Why is that important? Two reasons. The flow of air through your enclosure carries with it massive amounts of heat, as well as water (in vapor form). Not only does this cost you a lot of money in heating/cooling bills, but the mobilization of water into your wall and ceiling assemblies can wreak havoc to your home resulting in very expensive repairs down the road. Here are the keys to making sure your house is sealed better than your neighbors (bragging rights!)
- Impermeable to air flow (duh)
- Continuous over the entire building (can you take your plans and trace a line around the enclosure without lifting it?)
- Able to be resilient during and after construction
- Durable for the lifetime of the building
Now that you’ve come to realize just how important the air barrier is in your new home, there is one major thing that you should make sure happens at the design stage. MAKE SURE THERE IS EXPLICIT DETAILING AND A DEDICATED SPACE IN YOUR CONSTRUCTION DRAWINGS THAT DETAIL EXACTLY WHERE AND HOW THE AIR BARRIER IS TO BE INSTALLED! Sorry for the caps, but this is important stuff, people! There should be no such thing as improvisation on the job as it relates to the air barrier. Improvisation leads to failure. Failure leads to sky high heating/cooling bills, and what is more, huge potential for structural damage due to moist air leaking into building cavities – all of which costs you hard earned money!
Keeping a heads up approach to the design of your new home is absolutely imperative if you want to meet your goals. It is increasingly common for aspiring new home owners to find a set of plans on the internet and take them to a builder. Without the proper consideration in the design stage, especially to certain critical components of the building shell such as:
- Glazing area and location
- The overall roof design
- Roof overhangs
- And air barrier continuity and location
You are setting yourself up for potentially catastrophic building failures down the road as well as an immediate increase in energy consumption and therefore higher cost of ownership.
However, tackling these problems aren’t challenging, and being on top of these decisions will go a long way to ensuring your new home will be more comfortable, more durable, cheaper to heat and cool, as well as aesthetically pleasing.