When we added on to our house several times, I had an idea of what I wanted. Called in a couple of contractors and had a rough sketch. They helped fill in the blanks. One even had a computer program that he loaded that could virtually walk you thru the rooms!!! Good luck! - Ellen

What kind of soil do you have? If you have clay, or clay subsoil, you might consider a cob addition to your house. It is basically free (use the soil in your yard, you may need to buy some straw) It stays cool in summer and warm in winter, and is a great conversation piece. You can make a foundation out of old chunks of concrete (urbanite) a nice poured adobe mass floor. It will take time, but you won't need contractors, and the planning is much simpler. You can bury the plumbing and wires right into the wall as you build it.

I am a bit of a cob enthusiast. Well, a wannabe enthusiast. I still haven't gotten my hands all the way dirty, but I have researched it a lot. Sorry if I tend to run on about it.

Eric in Japan

Go to a builders supply store and ask questions. Go to a Library and look for books about adding on. 2x4 wall studs are done on 16" centers because the other building material is made to fit that width, so that you will end up with joints over a stud for nailing. Floor joists can be either 16" or 24 inch center. If you use 2x10 or 2x12 floor joists, you can go 24" center. All these things depend on how much weight will be on it. Ad ons can get complicated where you have to match up the floor levels and especially joining to the existing roof. You really need to hire at least one person who knows what they are doing to work with you. A retired carpenter that would take part time work is ideal. Ask at the builders supply if they know someone like that.

Well now in jumps the 'expert' do it yourself guy ...me ;o)
Ha!!!!
Graph paper is simple and and oh so wonderful tool. I drew up the entire plans for my house on the stuff! Draw out the house you have then play with the add-on. This will give you the general idea as to the dimensions and layout. Think through what this add-on will be used for and draw in ideas.
As Millie points out unless you are completely crazed, like your humble writer of this note, you will need a carpenter friend to help you with the details.
If I may make a small suggestion as to getting your hands dirty first, try building a small shed. Sounds silly but you will learn a great deal from doing so like how to square a foundation (rule of 3, 4, 5 .... thats the right triangle .... a square triangle will be square if its ... lets say feet ... 3 feet on one straight side, 4 feet on the other then 5 feet on the Hypotenuse ... thats the long side .... any multiple of this works say 6,8,10 .. 9,12,15 ect.)
A good book is a must as the above shows.
Get a good general idea as to what you want then break down the tasks into small projects and it won't overwhelm you. Of course you work from the ground up.
I have built an entire house solo, all by my lonesome and I would not wish the job on another ;o)
Note that GW also has a link to "The Home Site". You can get good detailed info off of it but general info is ... well tough to answer.
Hope that helped some ;o)
Mike

Hey Dots2u, any progress?

Bigeasyjock seems to have some very good suggestions. I'm going to jump in and suggest a book: "The Very Efficient Carpenter." It's published by Taunton, the folk who do Fine Homebuilding magazine and others. It's a one book framing course.

When putting it all down on paper, you may want to look at your local building code, if you have one. Your library should be able to get you a copy. Think about what it says in terms of insect protection (termite shields on your foundation) and rot-resistant materials underneath. I generally don't hold with the idea that I need a building code to protect me from myself, but they can be good reality checks, and if you ever intend to sell the place, having it up to code makes the buyer getting a mortgage much easier.

Is your block foundation a wall of blocks, or just piers? Piers seem like an easier thing to deal with in terms of termite shields and seeing what's going on under there. Foundations are going to be easier there because you don't have to deal with frost heaving, but make sure your soil is stable and the area around the footings is well drained.

In terms of framing for plumbing: Consider making your walls out of 2x6, 24" on center, rather than 2x4, 16" on center, at least where the plumbing will go. It will give you much more room to work, especially where you have 4" drain pipes. In northern climates we now favor 2x6 because it gives more room for insulation. Will that be a consideration for you because of air conditioning, or will you go for good ventilation? It makes about the same strength of wall, and because you use fewer pieces of more expensive lumber, it costs something similar too. The other upside is that it's fewer pieces to nail together. The downside is that your sheathing and wallboard have to span a greater distance, so if they're marginal, they'll sag and undulate.

Dan

Lol, Jock is correct about the 3,4,5 triangle but that's an awful cumbersome way to get a square corner or square off the end of a board. A carpenters square or a machinist square are much easier, just as accurate and not very expensive.