Being a handy guy runs in my family. My grandfather built beautiful cabinets as a hobby, my dad and I built a garage together when I was a kid, and it's still standing. I once built a guitar, and for years I've done all sorts of basic (and not so basic) car repairs by myself. I own good tools, and I like using them.

But I usually know my limits, unlike -- apparently -- the former owners of my current house. Our recent drive to spruce up our house to sell it has uncovered all sorts of minor horrors. We found non-water-resistant wallboard in a bathroom, right above a shower -- as we peeled off the wallpaper, the wall came with it. There was textured paint that (sort of) concealed badly aligned walls. The previous residents added on a bathroom that doesn't, on close examination, appear to have a single right angle anywhere in it, along with several oddly improvised plumbing "solutions." Unfortunately, I could go on.

Of course, these botched jobs didn't hurt the value of the house -- we bought it, after all, once a home inspector gave us the thumbs-up. Most problems were pretty well concealed from the casual eye, and many aren't really worth worrying about. But some have caused a few problems over the years, and the worst will take -- and have taken -- considerable time and effort to put right.

All of which raises an important question: When should you not attempt your own home repair or improvement projects?

The homeowner's Peter Principle
You've probably heard of the Peter Principle, the famous business axiom that says people tend to get promoted to one level above the limit of their abilities. I suspect that there's a similar principle at work in home improvement -- people are often tempted to try their hands at jobs that are one level beyond their skill, experience, and toolbox. Certainly, I've often gotten bailed out of big trouble with a quick phone call to my dad.

But not everyone has a handy dad to call, and even those who do may find it easy to bite off more than they can chew. Lowe's (NYSE:LOW) and Home Depot (NYSE:HD) have made huge amounts of money from the trend of do-it-yourselfing -- they've been busy selling the idea that plumbing, foundations, and electrical work are all straightforward. Even Sears Holdings (NASDAQ:SHLD), with the perennially popular and ever-expanding Craftsman tool line at its Sears stores, contributes to the sense that complicated jobs can be accomplished by the average Joe or Jane. After all, the reasoning goes, if Sears sells welding tools to anyone who enters the store, how complicated can welding be?

Yes, I know someone who asked that very question in all seriousness. Fortunately, cooler heads prevailed.

How high are your standards?
Well, it's not that hard to do many home-improvement tasks -- as long as your standards are low. But getting professional, quality results that will hold up over time is much harder, and it often requires tools and experience that many of us lack.

More to the point, even when doing a job correctly is within reach, it takes us amateurs a lot more time. Is blowing a whole weekend on a tough job really worth saving the money that a pro would charge?

Here are some key factors to keep in mind when considering whether you want to tackle a project yourself.

  • Do you understand what's involved? Most hardware and home-improvement stores carry reference books for do-it-yourselfers. Get one of these guides. Familiarize yourself with all the tasks required to complete your project, and make sure you're comfortable with every step.
  • Do you have the time? Make sure you understand how long it will take to do the project. Do you really want to spend your time swinging a hammer or hauling bricks?
  • Do you have the tools? There are worse things than being almost finished at 9 p.m. on a Sunday only to find that you're lacking a critical tool. But you won't think so if it happens to you -- especially if it means your shower or kitchen will be out of commission Monday morning.
  • Do you know how to use the tools correctly? You can buy a nailer and a roofing hammer and think you can replace your own roof. But using the tools to do the work to a high standard is something else again. Not every technique can be learned from a book, and the trial and error  involved in getting the hang of a new tool could add a lot of time, cost, and possibly injury to your project.

For all these things, it's important to be realistic. Put your ego aside, get your spouse or a friend to sanity-check your plans, take a deep breath, and decide: Can you really do this project, and will you feel good about it afterward, or will you be better off calling a professional? If in doubt, make the call. Your home, and its future owners, will thank you.

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Fool contributor John Rosevear (a.k.a. TMFMarlowe) welcomes your questions and comments. He does not own any of the stocks mentioned in this article. Home Depot is an Inside Value recommendation. The Motley Fool has a disclosure policy.