Converting Garage into Den

Old 01-25-05, 10:01 AM
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Red face Converting Garage into Den

I am in the process of planning to convert my garage into a den/office. We are expecting a new baby and now need the room my husband uses as his home office. A friend of ours that has done this type of conversion in his own home is helping us with planning, but we have one question we can't seem to agree on - leveling the floor. It has a slight incline we have to level before we can do much else. He poured concrete on top of the existing concrete to level his room. I think that it would be better to build a wood subfloor and go from there. Our house has a slab foundation, with the tile and carpet directly on the concrete throughout the rest of the house. He is of the opinion that this is why pouring the concrete floor would be better, easier, and cheaper. I have about 6-9 months in which to complete this project and a pretty roomy budget, so I want to do it the RIGHT and BEST way possible. We have on our team an experienced carpenter, a professional drywaller/finisher, an electrical engineer and electrician, and a professional brick mason (to match up new enclosure with current brick of house). The one thing no one seems to know much about is the best way to go about this floor.

Any help, suggestions, ideas anyone has would greatly help end this chaos and confusion. We can't go forward until we can decide on the floor. HELP!
Old 01-25-05, 01:55 PM
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You can read an article I wrote and use what seems appropriate. It is for more cold climate areas rather than Florida. I guess my first questions is if you had a permit for this, plans would have been sumbitted outlining what needs to be done. In fact calling the City as to what is allowable is the best thing to do. I am assuming that no permit was obtained based upon your question.

"On any garage conversion into habitable space, first thing is to see if this legal within your municipality. Contact your local code enforcement office. Many code jurisdiction DO NOT allow garage to living space conversions. Yours may not and that kills the deal before it starts. Assuming you can convert, you're on the right track with framing 2x4s and then insulating the walls with an R-13 fiberglass or what the current requirements are where you live.

Assuming that there is no existing living quarters above, the existing attic space should be can be upgraded to at least an R-19 and possibly and R-30 depending on the depth of the ceiling joists. This should be based on current Code requirements.

The garage walls are typically built on top of concrete curbs which hold the wood sill plate above grade level (to reduce the chance of dry rot and termite infestation); a good water barrier. **One thing to note, the existing concrete curb may require you to furr it out to get beyond the curb and new drywall installed. If not, you should plan how you are to make the finished look appealing with this deviation at the baseboard level.** You will install one in the form of a new 6" tall, 6" wide concrete curb, bonded to the existing garage slab with a structural epoxy. Follow the manufacturer's directions regarding the cleaning of the existing concrete surface so the new curb concrete achieves a watertight bond when poured. Drill and set a few 1/2" diameter x 8" long machine bolts with the threads embedded in the garage slab about 3" to anchor your curb in place. Keep the spacing under 24" and use the same epoxy to hold them firmly in place. Wire two 3/8" diameter reinforcing bars just below the heads of the embedded bolts to give the curb strength and prevent cracking. Your new sill bolts (for the infill wall) can be held between these reinforcing bars, which helps keep them in the proper position. Should this space be planned for an exterior door, this should be taken into account at the initial design stage.

Most garage slabs of yesteryear were not insulated and possibly not installed with vapor barrier below so we need to address the issue of concerns about the occasional seepage of moisture up through the slab (capillary action). Water may also seep up through the gap between the garage slab and the existing perimeter curbs. A liquid sealant should be applied prior to the sleeper (floor joist) installation.

So with all the above done, then we need to take care of the new floor joist installation. So is the floor of the garage lower than the floor of the house, most have at least one step down. This is good if it is and most are at lwast 4 inches down. What we are going to do is make both existing floor and new space finish floors even with the use of 2x Wood Treated stock.

The other concern is ceiling height. Most garage ceilings are usually level with the existing home. In some cases they can be lower but you need to measure the proposed finished height to meet code. Estimating this means that you determine the height from the existing home floor, such as the garage service door that may be entering the home from the garage.
Most garage floors do have a slight slope towards the big garage doors. This means that you must determine the “tapered” cut line for the 2x stock that will be used as your floor joists. To determine this, use a 4 ft level, by placing the level in a “level state” you can scribe the treated 2x stock. This will be the angle of the cut line for the sleepers. The size of this 2x stock sleeper will be determined by the distance that you have from the slab to the floor height of the existing home less the sublfoor. In some cases this can be a 2x4 or a 2x12, so taking good measurements is essential. In some cases, joist hangers are used to hold one end, depending if there is a gap between bottom of joist and floor.

You need to place 6 mil poly vapor barrier over the concrete slab. Then by cutting 2x spacers – 14 ½” long you can use these as your guide in laying out your floor. I suggest a powder actuated hammer (Hilti) gun and ramset concrete nails through the 2x. This is easy, fast and it will hold.
Put plastic under on the floor under the joists to keep moisture from coming up into them. Install R-10 – 2” rigid insulation between each sleeper.
Once this is done, you can glue and screw the ¾” T & G plywood to the sleepers in preparation of the finish flooring."

Since the neighbor poured concrete to level his floor, I am assuming that he took precautions against moisture. If not, they will have problems.

Hope this helps!
Old 01-25-05, 03:43 PM
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Converting Garage

I'm thinking that I may want to just hire a specialist on this step so that I can be sure it's done right. I have to complete the plans so I can submit them for the building permit, I just needed to know what route I was going on the floor. The carpenter I have that's helping us is not experienced on flooring as much as the framing and the built-ins we're putting in, so I need to find someone who can do the flooring as you suggested. Would I go to a general contractor for this? A flooring specialist? The flooring person I talked to said he does the tile, etc. AFTER the subfloor has been laid, so that was no help. What kind of contractor would I need to do this? And what can I expect as far as cost for an area that is approximately 12' by 20'?

Thanks for all your help!
Old 01-26-05, 09:25 AM
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A framing carpenter, who is in fact experienced, understands the process of floor joisting, wall, ceiling and roof framing.

The process for your project is the use of sleepers and involves treated lumber, shot pins and shimming.

What is the difference in height between the garage slab and the finished floor, at the high end, 10' and at the low end.

In most areas, the required slope will be 2%.
Old 01-26-05, 10:05 PM
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In most places in Florida, it is not permitted to convert a garage into living space under most zoning regulations...

But presuming you have the right to convert and depending upon the width of the garage....

And since concrete garage floors already, by code, need to be below existing living spaces....

It is usually enough to simply frame 2x10s or 2x12s across the width of the garage without having to level it with concrete to get a same height floor as the rest of the house and have it insulated as well.
Old 01-27-05, 10:21 AM
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Thank you all for your great info. I found a more experienced carpenter to do the floor framing for my garage. We got the permit needed to start work on this and are getting started after Superbowl weekend since my hometown is hosting it this year and all is chaos until it's over! We're all going to hunker down in our homes and not leave until things return to normal! LOL!

Again, thanks for your help. I will post again if I need anything more! LOVE this website!

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