Welcome class to Economics 101. I'm your professor, Dr. Istockhouseplans. Today we'll be talking about poor house design and how you can avoid it.
The first thing to consider is the footprint of your house. While concrete can be molded into any shape or dimension, you need to consider that your framing and sheathing will be based off of this dimension. The easiest house to create would be a box. But you can't just choose any dimension for the size of your box. If you're truly trying to be economical, remember that most building material works off of a repetition of four feet. Would a dimension of 25' by 32'-6" make sense? Of course not! Anybody who thought this would be economical gets an 'F'. If you are going to save money, a 24' by 32' box is an excellent choice. However, mind your square footage, as this would be a rather smallish house, even at 2 stories.
You might believe (and rightly so) that a box would make a rather boring house. Suppose you would like to add some offsets. There are two ways to do this: one is to jog the foundation, keeping in mind your material parameters. The other way involves cantilevering the house over the foundation. Both methods are acceptable. Question?
"I want to add a fireplace bumpout, but four feet seems like an awful lot!"
Excellent question, please come sit at my feet and learn. There are three subsets of the 4' increment. One is the obvious 2' division. Two feet would make an adequate bumpout for a fireplace, but let us suppose that you have a tight setback to consider. In this case, you can use the second subset of 16", or one third of 4'. While 16" may seem a little odd, this is the standard spacing of studs that most builders use. A third subset is the 1' increment. While this last subset won't cause construction waste, use it sparingly. It can cause you to use more materials.
You may wonder if it is more economical to cantilever your bumpouts or pour a foundation under them. If the bumpout is not large it is ALWAYS better to cantilever unless there are extenuating circumstances. Extenuating circumstances are rare.
I mentioned the offset earlier as a way to bring volume to your box. This would also be known as a jog in the foundation. Jogs can follow the same increments as previously mentioned. However, keep in mind that each jog in a foundation costs more money to build, so use them sparingly.
Any questions so far? No? Good.
Floors are built upon the foundations. There are several floor systems, and a good foundation will accomodate all types. To do so, the 4' increment is ideal. The post and beam (AKA post and pier) style of floor utilizes floor beams running every 4' on center. The joist (AKA crawl space) style of floor depends on joists running every 16" or 12" on center. If your floor is 39 feet deep, you will use 31 joists at 16" on center. You can also build a 40' deep building using the same number of joists. You gain more square footage for the same amount of money. Also consider your joist support spacing. Beams 9' apart are less helpful than beams 8' apart. A 12' span is easy to cross and requires no cutting of joists.
Every house needs openings in the walls. These openings contain windows and doors. Most designers only place doors and windows so as to look aesthetically pleasing from the inside. If you can line up your opening so that one or both edges land on the 16" increment, this will save money, both in materials and time. Most openings are framed with 2 extra studs on each side. If one of these studs can be the same as a standard framing stud, you have saved money. Most openings need to be topped with a header of some sort. This header is 3 or 4" longer than the opening is wide. Therefore a 4' window will use a 4'-4" header. If all of your windows are 4' wide, you will end up wasting lumber with a bunch of 4'-4" cuts. Taking these from a 16' beam will leave you with 3'. This cannot be used for your front door. Taking these from a 20' beam will leave you with 2'-8". This makes good firewood.
"Can't I throw the 2'-8" remainder over a bathroom door?"
Excellent question. Yes, as long as you actually need bearing over your bathroom door. If your bathroom door is not in a bearing wall, this is just hiding your waste and uses extra nails and studs.
At the roof, the final test of your design skills plays out. If your roof is to be trussed, those trusses will set at 24" on center, not including gable end overhangs. If your house is 32' deep, you've done well. If your house is 32'-6", you have used an extra truss for very little extra square footage. Bad form. If you are stick-framing the roof, 16" is a better increment to keep in mind, but this will depend on the distances being spanned and the lumber being used. If you are stick framing the roof, keep in mind the length of the rafters. If your pitch is such that your rafters need to be 20'-8", this is poor planning. Either narrow your building or drop your pitch. The same concept applies to the roof sheathing. If you need 20'-8" of roof sheating from eave to peak, this is wasteful.
Not all concepts presented can be effectively used on every house designed. You will be able to use most of the techniques most of the time. There's the bell, for next week, design a houseplan using as many techniques presented as possible. Aesthetic is not important this time, but function is. If you need to, check out some examples.