Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect the construction industry to grow as the global economy eventually heats up again, the Dynamic Building & Construction Portfolio ETF (NYSE: PKB) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in a lot of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The building ETF's expense ratio -- its annual fee -- is 0.63%. That's a bit higher than many ETFs, but also considerably lower than the typical stock mutual fund. The ETF is small, too, so if you're thinking of buying, beware of occasionally large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF has not performed spectacularly, largely because of the lengthy recession we experienced recently. It underperformed the S&P 500, on average, over the past three and five years. It's the future that counts most, though; and of course, as with most investments, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

With a somewhat steep turnover rate of 75%, this fund, like many of its mutual fund peers, isn't committing to its picks for very long. Low turnover ratios can reflect more conviction. The fund holds only about 30 stocks, though, which does reflect some conviction. Many funds spread their assets over hundreds of holdings.

What's in it?
Several construction-related companies had strong performances over the past year. Tractor Supply (Nasdaq: TSCO), for example, gained 49%. The retailer serves tradesmen and small businesses, and repeatedly has been posting estimate-beating numbers and record revenue levels. Its profit margins have been growing steadily in recent years, too, and the company is expanding, aiming for 800 more stores.

Lowe's (NYSE: LOW), meanwhile, gained 17% as it beefs up its online business and tries to boost market share via its "Everyday Low Price," "Go Local," and "Specialty Sales" initiatives. Business has been hurt by the big housing slump, but even during the recession it served those who needed to remodel or make repairs that couldn't be put off.

Other companies didn't do as well last year, but could see their fortunes change in the coming years. AECOM Technology (NYSE: ACM), which offers architectural, engineering, and construction services, among other things, shed 18%. The company's revenue is growing and its debt is low, but these figures are still below industry averages. The company is racking up business, though, with recent orders for government agencies and foreign nations worth hundreds of millions of dollars.

Vulcan Materials (NYSE: VMC), down 4%, is the target of a hostile bid by Martin Marietta Materials. Vulcan is denying the legality of the bid. It also recently has made a case for its strong value proposition, citing debt reduction, cost-savings, and its presence in many growing markets.

The big picture
Demand for construction services and products will eventually rebound. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

Learn about 4 ETFs You Can Count On. And if you're looking for some great investments beyond ETFs, consider these 5 Stocks Growing Their Dividends by 20% Per Year.