NOTE: Everyone should familiarize themselves with the exact code that will govern their project. States are free to make changes, add details or delete sections.
PLANNING AND DESIGNING IS A PROCESS
There must be some good books on this subject, by people with significant experience with the planning process. I would assume that there are even lists of the various steps in the process, or maybe flow charts, if you will. Most books I find are oriented towards how to nail the thing together rather than actual design. If anyone knows of any such planning process and design process books that are oriented towards the DIY owner-builder, please bring them to our attention.
Good planning and design encompasses more than deciding on where the bathroom will be, or is the bedroom big enough for my king size bed or should that wall space be occupied by my wood stove or my big screen TV. There are many topics, many areas that need to be addressed. Some of these topics should actually be broached before even buying any land, or you could end up with property which you can't build on. Are there any special zoning requirements, easements, building setbacks, availability of potable water, sewer system options, utilities?
Many of us are planning to build in areas that have municipal or county building codes as well as zoning rules, well and septic system rules and permits. Some may be about to build in an area with a Home Owners Association and special rules that govern land use. Most areas now have some minimum zoning, building code and sanitary regulations which must be complied with. Others may be building in an area with few or poorly enforced rules. Some, at their own peril, may be building "under the radar". In any event, and ideally the prospective project planner should know what rules and regulations they will be facing before even purchasing the land. Knowing the costs of the various permits before land purchase would be wise; at times certain permitting costs can be surprisingly high.
Chapter 3 of the IRC is titled "Building Planning". Before we get there and have a look at some of the sub sections dealing with specific areas of planning that the IRC covers I'd like to begin with some thoughts from professional engineer PEte.
The actual building design process will seem bass-ackwards to many people until they actually think about it a bit. Ken Kerns or John Raabe said something like 'always work from the general to the specific,' or 'think in general terms first, then the details.,' I would say it only slightly differently; think of the big picture first, then narrow down your topic, but always thinking many steps ahead as regards the consequences of each action or detail. The layman's natural tendency is to think the first thing I have to build is the footings so I better get those figured out first. But, the footings are actually the last thing designed because you don't know the loads on them until everything else is designed. The actual process goes something like this:
Is the lot buildable? What is the access, road and utilities? Where will all the major functional areas be; septic tank and drain field, water well, some distance removed from waste system, where will major buildings be located and do they have proper drainage and elevation? Can you set building elevation for proper drainage around and away from the building and also to account for proper flow to a septic tank and drain field, preferably by gravity.
1a. What are the soil conditions and potential soil bearing capacity, drainage and water level conditions, etc., building loading conditions (wind, earthquake and snow) for my area, these will lead me to my choices of foundation types. Dig some small pits on your site to learn the soil conditions below the footing bearing elevation, and to understand the water level, perched water tables, sub-surface drainage levels, etc., and perc tests to start to understand drainage on the site for waste disposal systems and general site drainage. Many times you can case a hole dug with a post hole auger or digger, with a piece of 3 or 4" PVC with a loose cap, and study the water level, over the seasons. In a general way, consider the location of septic system, water well which must be some distance removed from a drain field, and house and out building locations on the site. If you put the building in the only place the septic tank and drain field can go, you may be up sh** creek without the proverbial paddle. Footings on undisturbed soil; piers and sonotubes have very small bearing areas, and no soil/pier frictional interaction, except as related to freezing uplift. How does my foundation take lateral loads from the building?
1b. When you are locating your buildings on the land, pay attention to natural contours of the land and the new final contours from any excavating you do so that you can blend the two back together after construction. Pay attention to how these relate to paths, sidewalks, stoops, driveways and garage aprons, etc. as they set the elevations for the lowest floor and all other floors and important features of the building. You should set a bench mark someplace on the work site, which will not move or be moved, so you can always go back to that to set or check relative project elevations. This can be done with something as simple as a water level or as refined as a laser level or surveyors transit. All finished grades should slope away from the building for 10 or 15', at a slope of an inch or two per foot, so it's sure to drain away from the building. but still be mowable. It is far easier to dig a swale 20-30' away from and partially around the building as part of the rough & final grading than to bail out your garage and basement after every rain or snow melt.
2. What types of framing systems am I considering for the floors and walls, etc., these will influence spacing for footings, piers, foundation walls, etc. And, what are my general gravity load requirements, and any heavy concentrated loadings, like fireplaces, hot tubs, pianos, etc.
3. What sort of lateral loads do I have to deal with in my area: such as wind, or hurricane, which can involve both direct pressures on surfaces and negative pressures, or suctions, on the leeward side, and uplifts on horizontal or sloped surfaces such as roofs; earthquake loads which can involve lateral loads in any direction, plus vertical loadings, acting on the mass of the building as a vibrating system; tidal or flood loadings, maybe the building should be on stilts and be able to withstand these drastic lateral loads on its foundation All of these can be done, but not with 24" high, 4x4 posts sitting on sonotubes.
4. How am I going to frame the roof, for snow, wind loadings, etc.
5. The above are all done in a general way, with general and quick estimates of loadings, etc. to start to hone in on the options for the various major components, and with an eye on the costs of the various options. But, keep in mind that a buck saved now, which ends up costing you a $1000 to fix in a year, may be a false economy. Obviously, considerable building experience and judgment are a distinct advantage at this point in the process, dare I say engineering judgment and experience.
6. FINALLY, the design actually starts at the roof, since you won't know what the wall loads are until you are finished designing the roof framing system. I understand the want to save money by investing your own labor, but manufactured trusses are generally a great engineered roof system, and usually fairly competitive when compared to labor and materials for a rafter framed small building and they really help you get the building enclosed more quickly. They are also an engineered system which usually resolves issues of lateral thrusts at the tops of bearing walls, but some truss systems still leave that issue for the building designer to resolve.
7. Now, we know the loads on top of the walls and high beams and can design the walls; paying particular attention to concentrated loadings from the roof system, window and door openings and their headers and associated jack studs, and the lateral loads on the walls, both from direct wind pressure loads on that particular wall, and also with that wall acting as a shear wall against lateral loads on perpendicular surfaces. In addition to gravity loads, all walls must span vertically or horizontally to take lateral loads perpendicular to their surface. Shear walls (braced walls) take the reactions from these walls, that is, loads applied to the building parallel to the plane of the shear wall or shear diaphragm.
8. Floor framing is next; it might be a 2nd floor or a loft, which then bears on another wall below, or it might be a 1st floor which will bear on the foundation and foundation level beams or girders.
9. NOW, we finally know the loads on the foundation and can design it. It must take all the loadings from the building above; uniform and concentrated vertical loads (gravity and uplift) as well as all lateral loadings on the building These must all be taken solidly into the ground before the design job is done.
Just because someone can use a CAD program does not make them a competent designer, in fact in many cases that just gives them a false sense of confidence in their abilities and knowledge about good design and construction details. They can draw things that they couldn't before, which seem to fit together, but are not based on any knowledge or experience about how that detail actually works, or whether the way they have shown it can even practically be built and stay standing under all the possible loading conditions.
We'll get into some specifics soon.
This thread or forum topic is not intended to provide a complete architectural and engineering design education. Rather it touches on some of the planning aspects as covered in Chapter 3 of the IRC. As such the editor has taken liberties in deciding what to include or exclude from this topic. This is not to be taken as indication that any area of the IRC is more important than any other. It is simply editorial license. You should really review and read Chapter 3 for your own edification. Trying to understand the intent of the IRC, or asking questions based in its various sections might help us all communicate better here.
Criteria to be considered even before laying down a pencil line for a floor plan include; what is the snow load, wind load, seismic category, what is the frost depth, are there termites, is ice barrier underlayment required for the roof, is there a flooding hazard. Zoning and flood plane considerations go pretty much hand-in-hand in most areas, and particularly flood plane considerations can affect mortgages and homeowner's insurance.
The location of a well and or a septic system should be considered before the home location is fixed. It is entirely possible that the prime location for the home may be the same as the only prime location for the septic system; they both can not be in the same spot. The septic would take precedence, or may make the lot unbuildable.
When considering the location for building on a piece of land measured in acres one location or another may have certain aesthetic advantages over others. Sometimes there are seasonal variations that should be considered; sun angles and prevailing winds may make certain north-south, east-west orientations advantageous.
Chapter three has maps indicating winter temperatures, snow loads, seismic zones, wind speed and termite infestation. Many locations in the country are special case study areas when it comes to some of those. Areas of the mountainous west, for example, require local knowledge for snow load data. Moving a distance of only a few miles or a change in elevation can make a difference of 30 or more pounds per square foot in snow load. There are also special case study areas regarding wind. High wind zones include most coastal and near coastal areas but also include many areas deep inland. Most of the area of the USA is considered to be in a 90 mph wind zone. Many of us will likely never encounter winds in the 90 mph range, but that should not absolve one from considering winds when planning. Many times complying with the code requirements involves only a small cost increase over a bare bones design, and saves many future headaches, and wind loads on roofs is a good example of this.
If one is planning a home or recreational cabin in a seismic area there are special rules and techniques recommended. This is not to say that there will be no damage if an earthquake occurs. However, the use of seismic approved techniques may likely prevent total collapse with the resultant increased danger to life and limb. Some foundations in particular are more susceptible to damage and dislocation than others.
Great stuff, as always. I read several other home-building forums (not necessarily people building their own home, though) and it's amazing how much people ignore this stuff. They're going to build their McMansion on 1/10 of an acre in a yearly flood zone, but they're agonizing over what granite to have in the kitchen.
We spent a lot of time researching our chosen geographical area, and then spent a lot more time researching individual properties to find the right one. By the time you eliminate the unbuildable properties, there isn't much left! There are a lot of tools for this- online real estate listings, GoogleEarth, GIS, even topo maps that a lot of colleges and universities make available. We even researched the future planning of the community to find out if they were planning a six lane highway or a sewage treatment plant in the area. A friend of mind found out (too late) that they built very close to a local stock car track. Saturday evenings on the porch are out of the question during racing season.
Now that we have the property, we've done a lot of research on sun angles, views, etc. at different times of the year to help us decide on siting the buildings. After all that, then I started sketching houses, working with the land to make it a good fit. Generally, the more you want to modify the lay of the land, the more it costs.
Designing requires a feed-back loop, so as you make changes to the general floor plan, you go back to your structure to see what, if anything, changes. Then back to the floor plan to see if the structural changes have made a change in the feasibility of what you wanted in a floor plan. I've designed a number of different styles in the last 4 years, and each one required studying the structure and seeing if it worked with the floor plan, and vice versa.
Excellent discussion of the planning processes----no matter how small or "off the grid" one builds, most if not all these processes and decision points should be honored. Mtn Don, you made mention of those who want to build "under the radar". Risking making too broad a generalization, It has appeared to me that most taking that track are expressing an ideological position of resistance to any direction from the government at any level. Maybe it is particular to our American propensity for independence---like the New Hampshire license plate slogan; "Live Free Or Die". A noble goal indeed but, taken too literally and applied to empirical wisdom like building codes, sometimes sounds more like cutting your nose off to spite your face. Granted the codes are not perfect, are always works in process, address only minimum requirements but, I have never understood why anyone would want less than the minimums and wear that like a badge of honor. Of course, King George couldn't understand how those stubborn colonists could get so fired up about a couple pennies tax on tea either-----it is an old and beloved American trait.
I see under the radar as....
1. those who have done their best to floow good practise and code rules. Probably as well built as any code inspected home, but the owner-builders are so far off the beaten track they thumb their noses at authority and take a chance. There are a few of those in my neck of the woods.
2. those who "know best" and do things their own way while also thumbing their nose at authority. Some of those I am sure contain dangerous elements. There are two of those I know of near us. The faults of one are obvious to
most many people. The other has many hidden faults I have seen and those could be trouble if and whenever someone else gets the property. Those kind of things are a concern to future users. Maybe not dangerous structurally, but the virtually non existent window flashings will be a source of troubles to someone down the road.
I can identify with those who want to avoid the whole permiting fee process. However I can also appreciate some of the reasons building codes are in place.
Tables R301.5, R301.6 and R301.7 contain useful minimum Live Load, (LL) values for attic, room, and other loads as well as allowable deflections for different members. These can be especially useful when using calculators for rafter and floor joists sizing. The footnotes should be read where applicable.
a. Elevated garage floors shall be capable of supporting a 2,000-pound load
applied over a 20-square-inch area.
b. Attics without storage are those where the maximum clear height between
joist and rafter is less than 42 inches, or where there are not two or more adjacent
trusses with the same web configuration capable ofcontaining a rectangle
42 inches high by 2 feet wide, or greater, located within the plane of the
truss. For attics without storage, this live load need not be assumed to act
concurrently with any other live load requirements.
c. Individual stair treads shall be designed for the uniformly distributed live
load or a 300-pound concentrated load acting over an area of4 square inches,
whichever produces the greater stresses.
d. A single concentrated load applied in any direction at any point along the top.
e. See Section R502.2.1 for decks attached to exterior walls.
f. Guard in-fill components (all those except the handrail), balusters and panel
fillers shall be designed to withstand a horizontally applied normal load of50
pounds on an area equal to 1 square foot. This load need not be assumed to act
concurrently with any other live load requirement.
g. For attics with limited storage and constructed with trusses, this live load
need be applied only to those portions of the bottom chord where there are
two or more adjacent trusses with the same web configuration capable of
containing a rectangle 42 inches high or greater by 2 feet wide or greater,
located within the plane of the truss. The rectangle shall fit between the top of
the bottom chord and the bottom of any other truss member, provided that
each of the following criteria is met:
1. The attic area is accessible by a pull-down stairway or framed opening
in accordance with Section R807.1; and
2. The truss has a bottom chord pitch less than 2: 12.
h. Attic spaces served by a fixed stair shall be designed to support the minimum
live load specified for sleeping rooms.
i. Glazing used in handrail assemblies and guards shall be designed with a
safety factor of 4. The safety factor shall be applied to each of the concentrated
loads applied to the top of the rail, and to the load on the in-fill components.
These loads shall be determined independent of one another, and loads
are assumed not to occur with any other live load.
... more later...
The following is from PEte, the engineer.
A couple of notes on this table R301.6 about min. roof LL (Live Load):
1.) Their rise of 4 inches per foot, 12 inches per foot, and greater; are shown as (1:3), (1:1) and (?:?), and are kinda confusing, even though the ratios are correct and I assume greater would be shown (1.33:1), etc. We usually express these as 4 on 12 pitch, or 4:12 pitch, 12:12 pitch and finally 16:12 pitch, and mean 4" rise in 12" of run, etc.
2.) Note that roof design loads are expressed in lbs./sq.ft. on a horizontal projection, that is in lbs./sq.ft. of run, not lbs./sq.ft. of rafter length. And, we actually calculate the roof weight (DL, dead load) of the roof structure in lbs./sq.ft. in its own plane, just as we do the DL of the house floor system. Thus, we must convert the roof system DL from its inclined weight to its horizontal projected weight, and a roof weighing 15 lbs./sq.ft. in its plane would have a horizontal projected DL of (1.414)(15) = 21.2 lbs./sq.ft., on a 12:12 pitch roof, which would be added to the snow load.
3.) This table may actually be confusing to the DIY/builder because it recognizes two things which are probably well beyond the realm of their design work and, first glance, understanding. You notice that the minimum load decreases with increased roof pitch, and that's because a steeper roof is less likely to hold snow or other loading. You also notice that the minimum load decreases as tributary area increases, and this is in recognition of the fact that over larger areas it is statistically and probabilistically unlikely that the higher load will exist over the entire area at the same time. Note that not many members a DIY'er might be looking at supports more than 200 sq.ft.
4.) I believe that most building officials (BO's) talk in terms of 20 lbs./sq.ft. minimum roof LL, but I wouldn't want to try proving this. If in doubt, ask your local BO.
Note #4 may be all the DIY/builder really needs to know.
Note: L =span length, H =span height.
a. The wind load shall be permitted to be taken as 0.7 times the Component and
Cladding loads for the purpose of the determining deflection limits herein.
b. For cantilever members, L shall be taken as twice the length of the cantilever.
c. For aluminum structural members or panels used in roofs or walls of sunroom
additions or patio covers, not supporting edge of glass or sandwich
panels, the total load deflection shall not exceed L /60. For sandwich panels
used in roofs or walls of sunroom additions or patio covers, the total load
deflection shall not exceed L/120.
Comment from PEte:
Note that a 10' long joist implies (10')(12"/')/(360) = .33" allowable deflection. And, the table doesn't show this but special attention should be paid to deflection of headers and the like over glazing and doors, etc., and requires smaller allowable defections, so doors and windows operate and glazing doesn't crack.
Comment from MtnDon. Some flooring treatments require even less deflection. Natural stone for example should be limited to L/720 according to my source, the John Bridge Tile Forum http://www.johnbridge.com/vbulletin/deflecto.pl Of course a floor like that would also require the joist and foundation calculations take the extra weight into account.
That was a great post, planning is key to the build.
;D Just remembered an old saying from my military days.....
"Remember the Seven P's----Proper Prior Planning Prevents Piss Poor Performances"
Section R303 covers light, ventilation and heating. Habitable rooms are recommended to have their windows area equal to a minimum of 8% of the floor area. Half of the glazed area should be openable. There are special exceptions to the glazed rule when mechanical means of ventilation is supplied.
Section R308 has specific information regarding glazing in hazardous areas. Hazardous areas include glazing in doors, glazed shower or tub enclosures and hot tub enclosures, glazing near walkways and stairways to only mention a few. The size of the glazing, glass strength and temper, distance from floor or adjacent doors also influence the recommendations. See Section R308 (PDF page 86 in the Minnesota IRC document for complete details. From the IRC: Heating is required when the winter design temperature in Table R301.2(1) [below] is below 60̊F , every dwelling unit shall be provided with heating facilities capable of maintaining a minimum room temperature of 68̊F at a point 3 feet above the floor and 2 feet from exterior walls in all habitable rooms at the design temperature.
Looking at that map there doesn't seem to be many locations that would meet the criteria; maybe the tip of Florida or someplace in the locale climate and topography area? I believe the above may be interpreted to mean that dependence on solar or wood heat requires a backup such as gas or electric, though I do not find specific mention in the IRC.
NOTE: Some adopted versions of the IRC may include an exemption for the heating requirements if the building is for seasonal use, not a permanent residence (often defined as use for more than 90 days per year).
Section R304 covers minimum room areas. Recommended is one room of at least 120 square feet with other habitable rooms being no less than 70 square feet. Kitchens are excepted. For very small cabins this may be negotiable with the local building code officials; best to check with them before making assumptions. Portions of a room with a sloping ceiling measuring less than 5 feet (1524 mm) in clear height or a furred down ceiling measuring less than 7 feet (2134 mm) from the finished floor to the finished ceiling shall not be considered as contributing to the minimum required habitable area for that room.
Section R305 covers ceiling height. It states: Habitable rooms, hallways, corridors, bathrooms, toilet rooms, laundry rooms and basements shall have a ceiling height of not less than 7 feet. The required height shall be measured from the finish floor to the lowest projection from the ceiling. For rooms with sloped ceilings, at least 50 percent of the required floor area of the room must have a ceiling height of at least 7 feet and no portion of the required floor area may have a ceiling height of less than 5 feet.Bathrooms shall have a minimum ceiling height of 6 feet 8 inches over the fixture and at the front clearance area for fixtures. A shower or tub equipped with a showerhead shall have a minimum ceiling height of 6 feet 8 inches above a minimum area 30 inches by 30 inches at the showerhead
There are some other exceptions listed. Refer to Section R305 for complete information.
Section R306 covers sanitation.
R306.1 Toilet facilities. Every dwelling unit shall be provided with a water closet, lavatory, and a bathtub or shower.
R306.2 Kitchen. Each dwelling unit shall be provided with a kitchen area and every kitchen area shall be provided with a sink.
R306.3 Sewage disposal. All plumbing fixtures shall be connected to a sanitary sewer or to an approved private sewage disposal system.
R306.4 Water supply to fixtures. All plumbing fixtures shall be connected to an approved water supply. Kitchen sinks, lavatories, bathtubs, showers, bidets, laundry tubs and washing machine outlets shall be provided with hot and cold water.
Figure R307.1 provides recommended bathroom fixture clearances.
I believe a wood stove is OK if it meets the above criteria. With multiple rooms, you'd have to have multiple stoves, or a way to duct the heat.
One thing that I think would be helpful for many folks is to read the sections along with these postings rather than take MD's posts as the whole enchilada. I've seen kudos but not too many questions. We are moving fast and light.
The section of hazardous locations of glazings has cost me hundreds of dollars before, and I've saved clients hundreds of dollars when the designer inappropriately called out tempered glazings where they were not needed. Make certain you understand exactly what that means and where those locations are. If anyone needs some untempered $200 Anderson sashes for a chicken coop... we can talk ;D.
The woodstove as a primary heat source I've seen interpreted differently in different jurisdictions, I've also seen energy code revolve around renewable sources of heating. In our house they were fine with just the one woodstove. I was very happy when we put in a Monitor, which I've also seen viewed both ways. It meant we didn't have to drain down to go away visiting in winter and I can come home to a warm house at the end of a day outside.
Quote from: Don_P on May 27, 2011, 08:06:57 PM
One thing that I think would be helpful for many folks is to read the sections along with these postings rather than take MD's posts as the whole enchilada. I've seen kudos but not too many questions. We are moving fast and light.
Thanks Don_P. I believe I have mentioned in a couple of places that owner builders should spend some time reading. Perhaps I should mention that more frequently. I have found myself searching for one thing or another more than twice. Thewre is no way I am going to cover everything. Questions may be more valuable than kudos. Kudos are appreciated but questions indicates someone is reading, thinking and so on.
How does R305 fit in with the 1.5 story plans?
I suspect the discussion would revolve around the word "habitable". Also the section is referring to the portion of the required minimum area not the total area.