The San Francisco 49ers own 13 picks in the upcoming NFL draft, and five in the first three rounds — Nos. 31, 34, 61, 74 and 93. The 49ers have very few obvious needs.

If the NFL were a gated community of 32 mansions, the 49ers would own the biggest mansion in the neighborhood, three stories and an elevator and a fountain out front, stone Cupids wearing 49ers helmets shooting water out of their mouths, five Maseratis parked around the fountain, the whole house painted red and gold.

Upon first glance, a visitor might say: "Here's a house that's got it all, no need to make any additions. A new paint job should cover up the few blemishes."

But a closer look might reveal that the 49ers need some major overhauls on their mansion. The kitchen needs a complete remodel and the Maseratis need new engines, and the retaining wall in the backyard is shot.

In other words, the 49ers have specific issues they need to address in the draft to keep their roster elite. If they draft shrewdly, they should handle most of them. Of the 49ers' 13 picks, only six or seven rookies will make the roster, so they have picks to play with.

They can try to package them and trade up to get premier prospects, not B-level guys.

Think of the 49ers' kitchen as their cornerbacks. This involves serious remodeling. Two of the corners — Carlos Rogers and Nnamdi Asomugha — will be 32 years old next season.

Rogers' job is to cover the quick slot receiver, and he is no longer quick enough to do that. Asomugha is even slower <NO1><NO>and was one of the worst cornerbacks in the NFL last season before the Eagles released him.

General manager Trent Baalke easily could replace them with younger, better models.

Tarell Brown has one year left on his contract and is short — he can't cover the big receivers. Chris Culliver gave up a passer rating of 115 over the final five games of the season, including the playoffs.

The 49ers could stand pat at the 31st pick and draft D.J. Hayden from Houston or Jamar Taylor from Boise State — two good cornerbacks. Or the 49ers could package several draft picks and trade up to, say, the 18th pick and take Xavier Rhodes from Florida State or Desmond Trufant from Washington.

Think of the 49ers' safeties as the retaining wall in the back yard. Starting free safety Dashon Goldson signed with the Tampa Bay Buccaneers this offseason, so there's a hole at that spot.

Strong safety Donte Whitner will be a free agent after next season, and he gave up 12 touchdowns in 2012. Baalke must pay attention to upgrading these positions. The 49ers probably could draft D.J. Swearinger from South Carolina or Eric Reid from LSU in the second round.

Think of the Maseratis as the 49ers' wide receivers. Two of them — Mario Manningham and Kyle Williiams — tore up their knees last season.

A.J. Jenkins has done nothing in his career. He's stuck in neutral. He was drafted last year at No. 30 in the first round and never caught a pass the entire season, including playoffs.

He is by far Baalke's most controversial draft pick, and because of his lack of success, the 49ers may need to draft a wide receiver all over again.

Trade acquisition Anquan Boldin has one year left on his deal. He's 32 and has slowed, although he's still a quality receiver.

Michael Crabtree has two years left on his deal, and isn't particularly fast, either, although he has great hands and desire. He's probably going to sign the highest offer sheet he receives in free agency, which means he probably will not be a 49er in 2015.

The 49ers eventually will need new and better wide receivers, state-of-the-art Maseratis that can go from zero to 60 in a flash. And there are plenty in the draft — Cordarrelle Patterson from Tennessee, available in the first round, Markus Wheaton from Oregon State, <NO1>probably available in the second round and Quinton Patton from Louisiana Tech, perhaps available in the third round.

Sooner or later, the 49ers will need new running backs and tight ends, too. The 49ers have one very good tight end, Vernon Davis, but the backups — Garrett Celek and Cameron Morrah — are unproven. Celek was an undrafted free agent, and the 49ers just signed Morrah to a one-year non-guaranteed contract. The 49ers could take Zach Ertz from Stanford with the 34th pick, or Travis Kelce from Cincinnati with the 93rd pick.

At running back, Frank Gore will turn 30 this year, which means this could be his last productive season.

Running backs don't last long into theirs 30s.

His backup, Kendall Hunter, ruptured his Achilles' tendon last season, and it's unclear how well he will play.

Hunter's backup, LaMichael James, weighs only 195 pounds. He can make yardage as a change-of-pace back, but he cannot carry the load. There will be good load-carriers available late in the draft, like Latavius Murray from Central Florida and Knile Davis from Arkansas.

The one position the 49ers probably cannot address in the draft is backup quarterback. The supply is limited and lacks talent.<NO><NO1>. Most disturbing, there are cracks in their foundation. Their best player, defensive tackle Justin Smith, is the foundation of the franchise.<NO1> The 49ers built their defense around him, and on top of him. When he hurt his elbow last season, the defense transformed from one of the best to one of the worst in the NFL, transformed in one game against the New England Patriots. Smith has one year left on his contract and he turns 34 this year.

The 49ers may choose to wait until next year to find Smith's replacement. If they want to get the replacement in the upcoming draft, they could trade up in the first round for Florida State's Cornellius Carradine, who had 11 sacks for the Seminoles before tearing his ACL late in the season.

Before long, the 49ers need to find Smith's replacement so the mansion doesn't crack and crumble.