I think that can depend a lot on the footprint of your house. A small lot with a 2 story house may have a lot more yard space than one with a 1 story house since it is all on the ground floor.

What is the placement like on your lot?

Before you even can answer that question from a design and investment standpoint, check into your local zoning ordinances. That will drive the design direction of many pool/projects in general. Things like lot/impervious coverage and set backs for example.

Second, the driver of this project should be the use and function of the desired body of water. A pool or spa should be equally beautiful, but functionality should be strongly considered first.

Never build a pool or spa from an investment standpoint or for the other guy. It should be considered because you see the value and benefit. This site is a great tool to quantify your style, taste and preference, so start making your own personal scrapbook.

To answer your question from a financial standpoint, pool size vs. spa size, a concrete spa (opposed to a prefabricated) can cost close to a small pool because the needs and effort are very similar. Just like building a home and a pool house, the square footage is less, but it still requires many of the same amenities (in this case, I am referring to square footage costs).

So we are back to the desired functionality and recreational use you desire.

Remember, it is not just a pool, but a pool environment (pool deck, fencing, furniture, lighting, landscaping, etc.), so you want to plan out the entire space from a zoning, design and financial standpoint. I hope this helps.

In general we do not recommend pools of less than 30 feet in length to any type of residence. swimming becomes a frustrating task and the opportunities for water play are limited as well. The saved cost for a smaller pool are minimal , the overall costs are still very high.

Dimensions for a "typical lap pool" are ~ 40 feet long and ~ 10 feet wide, but lot size, house site orientation, and zone restrictions are critical. If space is a huge consideration and lap swimming is the goal, you might consider an endless lap pool where a machine is put into place (either new construction or retrofit into existing pool), that creates a constant current the swimmer can swim against. Often a pool such as this only takes up ~8 feet wide by 10 or 12 feet in length.

Thank you for all the great responses! We don't love the endless lap pools. I think we are considering scraping an actual pool idea and going with a nice hot tub like this: It tends to be pretty cool here year round (San Francisco Bay Area) and the kids can still splash around a bit in it.