The standard rule for do-it-yourself projects is that they will take twice as long and cost three times as much as you expected. Or maybe it's take three times as long and cost twice as much. Either way, the reason is the same. DIYers make mistakes. Lots of mistakes. The good news is that you can learn a lot from mistakes. The bad news is that mistakes always wind up making your home improvement project more expensive and more time consuming than you wanted. With that as a premise, Bankrate.com asked home improvement experts for their lists of the top DIY goofs, with advice on how to avoid repeating the errors in the future. 1. Not taking out the required permits Considered a bother at best by many DIYers, permits actually serve a greater purpose than just raising money for the government. People in permitting offices aren't really evil. They're there to make sure the job is done right and that you don't hurt yourself. Plus, for some jobs, such as putting in a wood stove, you need proof of the permit or your insurance carrier won't cover it. Not sure if your job requires a permit? A general rule of thumb is that you need one for anything larger than painting and wallpapering. It doesn't hurt to call the building department and ask. 2. Inadequate preparation of the job site If you do a small addition, they'll be delivering materials. You don't want them out of stock, exposed to weather while you are working, or worse, they could be stolen if they're not properly stored. If you have a septic tank, make sure you know where it is. If a supplier delivering materials in a heavy truck drives over it, you could end up with a cracked tank. 3. Skimping on materials DIYers often use quarter-inch drywall for building walls, but you need at least five-eighths-inch. Three-quarters-inch works well for a good sound barrier. The same rule applies to plywood for subfloors. Go with three-quarter-inch. It creates a much stronger floor, especially if you're installing wood floors over them. 4. Using the wrong paint One of the most popular DIY projects around, painting can sure make a place look great. You have to be careful to use the right type of paint though. Flat paint should be used only for ceilings. Interior paints should have at least an eggshell or satin finish so you can scrub it. On outdoor decks, the sun and rain are really hard on wood. Clear sealers don't block the UV rays, and they peel. Use a linseed oil-based stain; it drives the pigment into the wood and preserves it. 5. Improper preparation of walls for painting A good quality paint job is 90 percent preparation. Clean the walls, sand them, and patch any holes before you paint. Painting experts recommend a coat of primer or stain blocker if you're trying to cover over oil based paint or stains, or if you're painting a lighter color over a darker color 6. Unsafe job conditions Nothing diminishes your return on investment like a trip to the emergency room. Wear safety goggles when using power tools or working with drywall or wood, wear hard hats when you're working under other people on scaffolding, and open some windows when you're painting, staining or stripping old finishes off floors or walls. Be careful when wearing loose, hanging clothing, especially when you're using power tools. Wear gloves when you're carrying wood, metal, and rock, or when hammering, and wear a nail or tool pouch to prevent damage to your floors and more importantly, the feet of people and pets. 7. Inaccuracy Experienced remodelers all live by the simple rule "Measure twice, cut once". It's so important for things such as building walls, cutting baseboards, counter tops, or pipe. If you're going to err, err on the side of too long. You can always make something shorter; you can't make it longer. Spackle can cover up to an eighth of an inch seam; if it's a quarter of an inch, the seam will pop the spackle and show. 8. Working beyond your limits Everybody has their limits. Yours might be plumbing, electrical work, or roofing. Don't stand on the top steps of ladders and don't try to work beyond your reach. 9. Lack of experience You don't want to start to learn how to do a project on your own house. If you have a friend who is a contractor or an experienced DIYer, offer your assistance on a project. No one will turn away free labor. 10. Not getting the proper help If you need to remove a supporting wall, have an engineer look at it to see what kind of beam you need to replace it. If you have a saw in your hand and have a question about what you're doing, just stop for a minute and make sure you don't make a big mistake.