Stop wa­ter mess with garage floor drains

Baltimore Sun Sunday - - REAL ESTATE - By Tim Carter

Q: I’m about to build a new home with both an at­tached garage and a sep­a­rate free-stand­ing three-bay garage. The house I grew up in had floor drains in the garage and they were won­der­ful. My builder has never heard of garage floor drains and in­sists on slop­ing the con­crete floor so all liq­uids flow to the doors. What would you do if you were me, and how do you in­stall garage floor drains in your jobs?

A: I can tell you, I live this night­mare each win­ter here in snowy New Hamp­shire. I didn’t build the house I live in, and my garage doesn’t have mag­i­cal floor drains like the house I grew up in. Wa­ter melts from my car and truck and pud­dles down at the closed garage doors.

It’s im­por­tant to re­al­ize the build­ing code is a set of min­i­mum stan­dards. You can al­ways build things bet­ter than what the build­ing code man­dates. The build­ing code is re­vised ev­ery few years, and I can tell you that some fan­tas­tic things have been for­got­ten or changed in past re­vi­sions.

I checked sev­eral ci­ta­tions of the In­ter­na­tional Build­ing Code, and there was lan­guage that garage floors must slope to the door so liq­uids drain to the door or to a drain. Another key point is that cities or towns can make their own re­vi­sions to the code. What’s ac­cept­able in one town may not be al­lowed in another city nearby. You al­ways need to check with your lo­cal code of­fi­cial and see what you can do.

This past year my daugh­ter and son-in­law built a new home on Mount Desert Is­land, Maine. I spec­i­fied that floor drains be put in the garage and made sure with the lo­cal build­ing in­spec­tor that she al­lowed this. Not only did she per­mit the floor drains, she in­di­cated the wa­ter from the drains could drain to the sur­face be­yond the house just like down­spout wa­ter from the roof.

The floor drains in older homes were piped in al­most all cases with a sim­ple P-trap, just like you might find un­der your bath­room sink. The U-shaped pipe un­der the drain cre­ated a wa­ter seal, but it also al­lowed sand and dirt to ac­cu­mu­late fast. You had to be care­ful in older garages not to clog the drain line past the P-trap.

I in­stalled modern side out­let box drains in my daugh­ter’s garage. Th­ese mea­sure about 14 inches square and are about 10 inches deep. The drain­pipe ex­its out the side of the box drain and the bot­tom of the pipe is about 1.5 inches up from the bot­tom of the box.

This al­lows sand and grit to set­tle out and not be car­ried into the drain­pipe leav­ing the box drain. How­ever, you need to keep up with mak­ing sure this sand, dirt and grit never get any thicker than the 1.5-inch catch area.

Down­stream from the box drains I in­stalled a self-made P-trap us­ing 90-de­gree fit­tings. I also used a tee fit­ting so I could cre­ate a sur­face cleanout that rises up from one end of the P-trap un­der the slab.

This cleanout al­lows my son-in-law, or a fu­ture home­owner, easy ac­cess into the P-trap us­ing the hose from a wet/dry vac­uum. If the P-trap gets clogged, it will be very easy to clean out.

Some peo­ple worry about oil get­ting into the floor drains and caus­ing pol­lu­tion of the ecosys­tem. That’s a valid con­cern if you have a mas­sive oil spill in a garage. I main­tain this is a rare oc­cur­rence. If you’re wor­ried about oil pol­lu­tion, you can in­stall a com­mer­cial oil sep­a­ra­tor as part of your drainage pipe in­stal­la­tion. And as for car and truck oil pol­lu­tion, imag­ine how many gal­lons per day leak onto the road­ways around your town or city from pesky drips from en­gines, trans­mis­sions and hy­draulic hoses.

Com­mon sense also is re­quired if you have a car or truck that has a tired en­gine or trans­mis­sion. If th­ese do leak small amounts of oil, for good­ness sake lay out some card­board to soak up the leaks and re­place the card­board once it be­comes sat­u­rated. There are also dry gran­u­lar prod­ucts made to soak up oil spills. You see this prod­uct at many gas sta­tions when some­one spills diesel fuel or other oil prod­ucts.

It’s very im­por­tant to make sure the tops of the floor drains are about 2 inches be­low the pri­mary level sur­face of the garage slab. The con­crete con­trac­tor needs to cre­ate large shal­low fun­nels around the floor drains.

The size of the fun­nel de­pends on the size of the car or truck. At the very least, the fun­nel should be a to­tal of 10 feet wide and 22 feet long. Cen­ter the floor drains so they’re ex­actly un­der the cen­ter of the car or truck when it is parked in the garage.

Another side ben­e­fit of hav­ing garage floor drains is that you can wash your car or truck in­side on blis­ter­ing hot days or in colder months. You can buy a spe­cial hose bib that has both a hot and a cold han­dle like an in­door sink. This way you can use warm wa­ter to rinse off your ve­hi­cle.


If you’re build­ing a new garage, it’s easy to in­stall floor drains, a sim­ple P-trap and a sur­face cleanout.

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