Making your home bigger, or nicer, always makes it more valuable. But some projects offer a better return than others.

Although installing a new front door can boost the value of your home by more than the cost of the door, it's the exception to the rule.

The average return on home improvements has fallen for four straight years, slumping to 63.8% in 2009, down from 70% in 2007 and 67.3% in 2008.

That means every dollar spent improving a home now boosts its value by an average of 63.8 cents

To determine which projects provide the best return, we went straight to the mother lode of data -- the annual cost-versus-value home improvement survey by Remodeling Magazine and the National Association of Realtors.

We used that data to create Interest.com's list of the 10 best home improvements, based strictly on the percentage of the cost recouped at resale.

We pulled out variations on the same themes, such as one kitchen remodeling project instead of minor, midrange and upscale kitchen renovations, which the annual survey breaks out in great detail. In those cases, we gave you the version that produced the highest rate of return.

Our top 10 home improvement projects, with the national average for cost, resale value and the percentage of the cost that was recouped, are:

Improvement 1. Replacing the entry door with a midrange steel door costs $1,172 and adds $1,470 to your home's value, or 128.9% of the cost.

Improvement 2. Upscale siding replacement costs $13,287 and adds $11,112 to your home's value, 83.6% of the cost.

Improvement 3. Renovating an attic into a bedroom costs $49,346 and adds $40,992 in value, 83.1% of the cost.

Improvement 4. Adding a wooden deck costs $10,634 and adds $8,573 in value, 80.6% of the cost.

Improvement 5. Minor kitchen remodeling costs $21,411 and adds $16,773 in value, 78.3% of the cost.

Improvement 6. Replacing windows with midrange wood windows costs $11,700 and adds $9,044 in value, 77.3% of the cost.

Improvement 7. Finishing a basement costs $62,067 and adds $46,825 in value, 75.4% of the cost.

Improvement 8. Midrange bathroom remodeling costs $16,142 and adds $11,454 in value, 71% of the cost.

Improvement 9. Adding a second story costs $156,309 and adds $107,286 in value, 68.6% of the cost.

Improvement 10. Replacing the roof costs $19,731 and adds $13,133 in value, 66.6% of the cost.

A minor facelift would include things such as replacing faucets, adding new flooring, new wallpaper or tile, new towel bar and toilet paper holder, maybe new doors for the shower.

Midrange remodeling adds new vanities and countertops, mirrors, medicine chest and maybe pulling the toilet and doing a new tub surround.

A midrange addition involves building a new bathroom with moderately priced fixtures, such as $165 for a solid-surface countertop with built-in sink as opposed to $500 for a custom-ordered sink that you would expect in a luxury addition.

If the prices seem a little more than you expected, there are several reasons:

Averaging can skew costs higher than taking the mean of all costs. Let's say, for example, three people remodeled their kitchens at a cost of $10,000, $15,000 and $100,000. The median price would be $15,000, because half of the projects cost more and half cost less. But the average would be $41,666.

The prices include professional labor, which is about 30% of the cost. There are also substantial regional variations in home values, materials and labor costs.

So, how do you decide which project to do and how far to go?

The old maxim of "If a little is good, a lot must be better" does not always apply in the world of real estate.

If the goal of your project is to increase the value of your home for resale, your project needs to reflect the neighborhood.

It's completely within the realm of possibility to spend six figures on a kitchen renovation, but unless you live in a neighborhood of million-dollar houses, you'll want to scale things down.

The same goes with bedroom and bathroom counts. If your neighborhood is mostly three-bedroom, two-bath houses and your house has only one bathroom, you're at a serious disadvantage on the resale market. Adding on a bathroom would make a big difference.

Then, you have to consider all the costs involved with a renovation. A swimming pool is the perfect example.

Building the pool is just the beginning of the expense. The same is true of adding on a family room or remodeling a basement or attic. Not only do you have the structural costs, you also will need to furnish those spaces and heat and cool them year-round. So add those costs into your budget.

Finally, some decisions are made with the heart as much as the head. Maybe you've always wanted a gourmet kitchen, or a trilevel deck with a hot tub and an outdoor kitchen, or a home theater with enough space to have your own rock concert.

You have every intention of living in this house for the rest of your life, you know you'll never get the money out of it that you put into it and you don't care. If you can afford it, knock yourself out. It's your house, your money and your life.

Go for it.

By Darci Smith

Interest.com Contributing Editor