In This Article
Setbacks, Well & Septic
Building on a Slope
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What is the perfect building site for you is highly subjective. Some like windswept mountain tops with dramatic views, others like shady hollows. Some like open fields; others mature woods. Ideally, a house should be designed to fit the building site – or a building site found that is a perfect fit for the house design you have in mind.
In reality, most people have a house design in mind and then try to adapt it to the site they are able to afford. In some cases, this works fine, but it’s good to keep an open mind about changing the house design to truly fit the site. In any event, it is important to know what you are looking for in a building site, what are your top priority must-have’s, and what you would like to have, but can live without.
In selecting a lot, imagine where a house would fit best and where to locate the main rooms, garage, driveway, and yard space. A quick sketch on the site plan will help you visualize this. Making cut-outs to move around can be a big help. Some of the key elements to consider are discussed below:
SETBACKS, WELL & SEPTIC
On many smaller lots, there is little flexibility about siting the house. After accounting for the front and side-yard setbacks, the “buildable envelope” may be pretty tight. If you also needs a well and septic system, these require specific setbacks from property lines and clearances from the house, further limiting your options.
On older lots, check with the town as the lot may be “grandfathered” under more lenient zoning rules in place when the lot was originally subdivided. You can also apply for a variance or special permit (a simpler process) to bend the zoning regulations, but consider this a last resort as the process can be onerous and success is not guaranteed.
Even if the house location is set, you can still decide where to locate each room to get the best views, privacy, sunlight, and breezes. Read on.
BUILDING ON A SLOPE
A gentle slope of 10% (one foot of rise for every 10 feet across) or less is ideal. It simplifies site drainage and is easy to regrade to make a level yard if desired.
Slopes of 15% to 20% are ideal for a walk-out basement, which can be finished for relatively inexpensive living space. Beyond 20%, the slope may start to impact construction costs and may leave you with little level land for lawns and gardens.
The compass orientation of the slope acts similarly to sun exposure, as described above. A south-facing slope is particularly nice in cold climates as it tends to be warmer, and more sunny for more hours than a north-facing slope. An east slope receives more morning sun and a west slope receives more afternoon sun.
Also pay attention to whether the land is upslope or downslope from the road, assuming the lot has road frontage. On an upslope lot, you may be looking over the road at views. A downslope lot may have more privacy, but depending on the topography may feel like it’s in a pit. Also runoff from the road may end up in your yard. Again, spend some time walking the site to get a good feel for what it would be like to like to live there. See also Evaluating Sloped Sites.
Who doesn’t want a sunny house other than vampires and zombies? Anyone with the slightest interest in solar energy would love a gentle south-facing slope for their dream home. Conversely, living on the north side of a steep hill will mean very limited winter sunshine, and in cold climates, snow will remain on the ground for and extra couple of weeks in the spring, essentially making a long winter even longer. Of course, people in hot climates might find extra shade appealing, especially on the west side, where the low afternoon sun can turn any home into a slow cooker.
Sun Angles. To assess the a site’s sun exposure is not difficult, although for a precise analysis you’ll need some basic solar design tools that show sun angles throughout the year. You can do a quick assessment with the chart below, which shows the noontime sun angles throughout the year from the deep South (28° north latitude), to the northern U.S. (44° north latitude). If the winter angle shown is obstructed by tall trees, a hillside, another building, or other obstacle, you won’t get much sunshine at that time. Hardwood trees, which lose their leaves in winter, will allow a good percentage of winter sun to reach the house – the amount depending on the density of trees and branches. Pines and other conifers will block the sun year-round. Spend some time walking around the site at different times of day to get a good feeling for sun exposure.
|South-Facing Sun Angles for the Continental U.S.|
|Latitude||Cities||Sun Angle at Solar Noon*|
|June 21||March 21/Sept. 21||Dec. 21|
|28°||Tampa, San Antonio||85.4°||62.0°||38.6°|
|32°||Dallas, San Diego, Charleston||81.4°||58.0°||34.6°|
|36°||Albuquerque, Nashville, Raleigh||77.4°||54.0°||30.6°|
|40°||Pittsburg, Columbus, Salt Lake City||73.4°||50.0°||26.6°|
|44°||Sioux Falls, Bangor||69.4°||46.0°||22.6°|
|* Solar noon is when the sun passes directly overhead, usually within one hour of 12:00pm standard time.|
Fixed Overhangs. The summer sun angle is useful for designing fixed overhangs or awnings to block out the summer sun (see illustration). Because of the high angle of the summer sun, special shading is usually not needed on vertical south-facing glass unless your building has extensive south glazing. Skylights and sloped glass, however, often lead to summer overheating.
Window Placement. Too many home designers and builders ignore the sun exposure when developing a floor plan and locating windows. Everyone loves a bright home with good natural daylighting, which you can maximize with south-facing glass. South-facing glass is also best for passive-solar heating as it receives the most heat gain in winter while naturally rejecting summer heat gain because of the high sun angle. Consider solar exposure when placing rooms and windows and you can have a light-filled home with natural warmth on sunny winter days.
- South Exposure.Whether or not you are designing a solar home, good south exposure is desirable in all but the hottest U.S. climate zones. For passive solar design, the southern exposure from 9 am and 3 pm are most important. To optimize solar gain, windows should be oriented within 15 to 20 degrees of true (solar) south. In a warm climate with significant cooling loads, southeast glass is better than southwest. South-facing windows will receive the most solar heat gain in winter when the sun is low and in short supply. In summer, the sun is high in the sky at mid-day, so south windows naturally receive less solar gain. With large areas of south-facing glass, you may need the additional protection of overhangs designed to block the summer sun. One caution: Vertical glass is best. Avoid sloped south-facing glass (e.g., in a sunspace), or overuse of south-facing skylights as these are prone to overheat in summer.In general, the total area south-facing glass should not exceed about 5% to 7% of your house’s floor area unless you use shading and thermal mass to prevent overheating on sunny days. A house with south glass up to 7% of the floor area is considered “sun-tempered”. Passive-solar homes typically have south glass equal to 9% to 12% of the floor area.In today’s tight, well-insulated homes, too much south glass without adequate shading can cause overheating on sunny days, especially in the spring and fall. A wall of glass can also cause excessive heat loss and a chilly feeling (from radiant cooling) on winter nights. Consult an experienced passive-solar home designer who will factor in climate, glazing type, and insulation levels to come up with a workable design.
- East Exposure. If you’re a morning person, it’s nice to enjoy breakfast near east- or southeast-facing windows. Look for site with unobstructed access to morning sun.
- West Exposure. West-facing windows are the most problematic. These receive a lot of solar heat gain in the late afternoon, when houses tend to be hottest in spring, summer, and fall. I’ve been in houses that overheat from too much west-facing glass in mid-winter. These problems can be controlled to some extent by using the right type of “spectrally selective” glass that blocks much of the solar heat gain. But, unless dramatic west views demand a lot of glass on that side of your house, moderation here is advised.
- North Exposure. Artists appreciate north light for its soft, even lighting quality and lack of glare and harsh shadows. While I wouldn’t overdo it in cold climates, new high-performance glazings allow you to put windows wherever you like without worrying too much about heat loss. On the other hand, if your building site has limited north sun exposure, that should not be a problem since north lighting is rarely direct in our hemisphere.
On a hot summer day, the more wind that blows through your house the better. On a cold winter night, the a blustery wind is less appreciated. Some areas have pretty predictable prevailing winds that you can rely on for summer ventilation. Winter winds are often from a different direction, so you may be able to orient your house and windows to get the best of both worlds. You can get data on local prevailing winds from the National Oceanic and Atmospheric Administration (NOAA) website.
Traditional New England Saltboxes faced their long roof and short walls on the north to shed the winter winds, while the more open two-story south face took advantage of southern summer breezes and winter sunshine.
The same obstructions that block sunlight tend to block winds as well. Again, walk the site to get a feeling for the wind exposure. If you’re down in a hollow, don’t expect a lot of natural ventilation. If you’re on a wind-blasted hilltop, plan to build a very tight shell and minimize the number of windows on the windward side in winter.
A great view of mountains, lakes, or the Golden Gate bridge can cost a bundle. A pleasant view of fields and trees might have to do. On a heavily wooded site, it may be hard to tell what views you’ll have after clearing. I’ve climbed trees, and once climbed on a neighbor’s house to see what I could see from the future second story.
A house design can take advantage of prime views, and minimize not-so-nice views (like a nearby road or collapsing barn) by the strategic placement of windows. If you want the light, but not the view, you can also glass block or windows placed above normal view lines.
Also think about the future. Will that beautiful meadow to your south be a field of cows or a field of condos in five to ten years. Also, remember that trees tend to grow taller over time and may block your cherished view in five years. If the trees are on your land, maybe you can cut or trim them, subject to any restrictions put in place by zoning or protective covenants. If the trees are on your neighbors land, your distant water view could become a treetop view over time as the trees mature.
See also Site Planning Basics Site Evaluation
Minimum Lot Size for Septic System
Considering land purchase near 20% grade. I will need septic and well. I wanted to avoid a terribly long driveway by building near the road. Maybe 30-40 feet back. I am assuming septic needs to be same elevation or lower elevation than the house. And well needs to be a certain distance away from the septic. How wide of a lot will I need to accommodate this? (Assuming my upslope is perpendicular to the road.)
These are all good questions to consider when evaluating a lot. The size of your leach field will depend on the number of bedrooms, soil conditions, and local codes. Once the leaching area is determined, the septic system designer will figure out a way to fit it to your site. Leaching trenches are usually limited to 100 to 150 ft. in length. Many local codes also require space for a “replacement field” to be used when the original field reaches the end of its service life. Overall size of the leach field can vary a lot – but an average size field for a 3 bedroom house in average soil might require 500 to 1,000 sq. ft. for the leach field.
The shape of the leach field is typically rectangular with the trenches running across the slope of the hill, not down the hill. The maximum allowable slope for a leach field is typically 20% to 30%, so that could also be an issue.
Where conventional trenches won’t fit, the designer might use leaching pits rather than trenches or reduce the area of the trenches with manufactured components – allowable in some areas.
Required clearances are also governed by local code. Some typical minimum clearances for the drainfield are:
to house: 20 ft.
to property line: 10 ft.
to private well: 50-100 ft.
to open water: 100 ft.
to dry gulch: 25 ft.
The septic tank, itself, can be 10 ft. from the house. In some cases, you can fudge these numbers with a variance or special permit, but there is no guarantee that your request for a variance will be approved.
Hope that helps you figure out a configuration that will work for you. It’s always a good idea to make any offer contingent on a perc test. In this case, you might also want to make your offer contingent on a preliminary septic design. Once you have perc test numbers and an approximate footprint for your house, a designer could tell you the feasibility of making everything fit in compliance with local codes.
Best of luck with your land search!
Should I Orient House For Solar or Wind?
We purchased a building site that will allow us to orient the back of our home to the south or a little to the southwest. We live in Lansing, Michigan and I looked at the NOAA website mentioned in your article. It indicates that the prevailing wind in Lansing in the summer months is from the W and from the W/SW in the winter months. Would you suggest we turn the back of the house a little to the SW or keep it oriented straight to the south?
Building design is full of trade-offs. What might be best for summer ventilation (lots of windows oriented to catch the summer breezes) might be worst for winter air leakage. The best views might be to the north or west, where you don’t want a lot of glass for energy design. So you need to establish your priorities and strike the right balance for your design need and building site.
Also, modern spectrally selective low-E glass, now standard on most premium windows, does a good job of balancing solar gain, insulation value, and summer heat rejection. So you have more flexibility nowadays in where you place your windows, with fewer energy penalties. True passive solar designs that maximizes solar heat gain (but reduces window R-value) uses high-solar-heat-gain glass, a special-order item.
That said, it is still best to place more glass on the south side than the north and to avoid overglazing on the west, where summer overheating can be a problem. To optimize passive-solar gain, you want to place windows within about 20 degrees of true south. (In Lansing, true south is about 7 degrees to the east of compass south due to magnetic “declination”.)
If you want to maximize summer cross-ventilation, then you want the longer axis of the house oriented toward the west. Orienting the house to the southwest might be a good compromise in your case. However with too much glass too far to the west, you run the risk of overheating on summer afternoons. Plan on good quality solar-reflective shades to control heat gain on summer afternoons.
If you are planning on using casement windows, these can be effective at scooping the summer breezes at an angle. For example, these can do a good job of catching a west wind from a southwest or northwest-facing window. Just make sure you specify windows hinged on the correct side (and communicate this to your contractor). Fixed projections called “wing walls” can also be used to capture and steer breezes through your home.
You can find good information on maximizing wind ventilation at this link.
A home designer who specializes in passive-solar design can help you figure out the best design and model the performance on software, taking a lot of the guesswork out of glazing decisions.
Best of luck with your new home!
Evaluating a Steep Site
Should I hire a geotechnical engineer to determine the soil condition on a residential sloping lot with a 35% grade (618′ – 580′ over 100′ distance) to determine the whether there exists a soil expansion issue and/or to determine if retaining walls on the lower levels of the lot are necessary?
By my math, the lot you are looking at has a 38% slope (618-580)/100 = 38%. Assuming the slope is more-or-less consistent across the property, and assuming your house is 30 feet wide, then the land will drop over 11 feet from the front of your house to the back.
You would either need to step the building down the slope or build level on a stepped foundation. In either case you will need to move a lot of soil around and probably need to bring in additional fill in addition to building one or more retaining walls.
If you need a septic system, that can also be an issue with steep sites.
So bringing in an engineer (geotech, soils, or civil) with experience on residential construction sites to help you evaluate site development costs and options would be an excellent idea. Read more about Site Evaluation
Overheating from West-Facing Windows
Thanks so much for this article. We are building our first home and the house orientation is going to be tricky. In our current home, the eat-in kitchen is totally unusable during the hours of 4:00 to 6:30 pm due to the giant windows cooking us out of there. I will not make that mistake with this home.
Too much west-facing glass is a common problem and can make rooms unusable on summer afternoons. The newest versions of low-E glass (called “spectrally selective”) are pretty effective in blocking out a lot of the heat. And you can also add heavy draperies and heat-reflecting shades. The best solution, however, is to not go overboard with west-facing glass in sunny climates.
Car Bottoms Out on Driveway
Hi, we bought a lot & are now in the process of building. When the builder started presenting us with his proposal, he said that they would have to move the building to the back of the lot; otherwise when we drive to our garage, the bottom of the car will hit the driveway. I cannot understand why they can’t fix this as both houses next door were built with a normal driveway. If we agree to that, we loose few meters from our backyard. As per the state guidelines we have to have 4 meters [setback] at the front. Please advise.
It’s hard to say what the problem is without seeing the building site. If the car is bottoming out (as we say here in the U.S.), it sounds like there is a steep drop-off or a hump in the driveway. It is probably possible to regrade this, but could leave you with other grading problems for your front yard such as steep slopes by the driveway, retaining walls, etc. By moving the house to the back of the lot, they can make the grade change more gradual, eliminating the hump.
I would suggest scheduling a meeting with the builder to ask if there is any way to fix the driveway other than moving the house. Ask for an explanation of why the neighboring houses do not have this problem. Hopefully, that will clear things up for you.
If you already own the land, then you can certainly contact a third party – an architect, civil engineer, or contractor – to suggest alternatives that are closer to what you are looking for. Sorry I can’t be more specific, but every site is different and requires site-specific solutions.
Best of luck with finding a suitable solution and getting your new home built!
Thanks so much for getting back to me. I can understand that without seeing the siting it’s difficult. But at least giving us some ideas was awesome. Have a great day.
Zo Benn says
Runoff Onto Sloped Site
I am thinking about purchasing a lot that has a slope in the back. Also the lot sits next to a water-runoff lot. Do you think this would be a good purchase?
There are many factors to weigh in your decision: location, views, vegetation, neighbors, solar exposure, noise, drainage, road access, site development costs (including well, septic and other utilities), and – of course – the cost of the lot.
A moderate slope in the back of the lot is certainly not a make-in or break it issue. Building into a slope can provide you with a walk-out basement, which some people find useful and attractive. It can also make for interesting landscaping and good site drainage. With steeper slopes, retaining walls can be used to provide level yard spaces.
I’m not sure what you mean by a “water runoff lot”? Do you mean that the lot you are considering is below an adjacent lot that drains storm water and snow melt onto the lot you are considering? If that’s the case, then it is certainly something to consider. If a large area naturally drains onto your lot, then it can be challenging (and expensive) to provide the necessary surface drainage and subsurface drainage to keep your lot and house free of water problems. This is especially true if your lot sits in a depression surrounded by higher land.
If the lot is very attractive otherwise and priced well, you might consider making your offer contingent upon inspection for site development and drainage issues. Then you could have an engineer (civil or geotechnical) come out and take a look. For an hour of his time, he can probably give you a pretty good idea of the work required and rough cost to steer clear of site drainage problems.
If the site is very wet and soggy in the springtime, or has wetlands-type plants such as cattails, make sure that the site is not been designated a protected wetlands, which can make development difficult or impossible. And whether or not is a regulated wetlands, it’s likely to be pretty soggy at least part of the year.