concrete slab vs/ wood floor - pros and cons


Audiogoners, given the choice, with sound quality being a top priority, which choice is usually better?

I have been given the green light from my wife, bless her heart, to convert our stand-alone 1935-era garage into a dedicated music/theater room - woo hoo!! The fact that it's a separate structure will be ideal for playing loud movies whenever without bothering anyone in the house. The space is roughly 11.5 x 17' and I think it will make a terrific intimate theater. It's completely unfinished inside and has a sturdy stucco exterior. It's a very solid structure. However, the concrete floor has some large cracks lengthwise due to settling so it is pretty crowned in the middle. If I keep the concrete, I will need to build a floor over the slab and shim it quite a bit to level it out enough to install the underlayment. Headroom is limited as the walls are just over 7 feet, although the roofline peaks at just over 10' in the center, enough height to hang my projector.

If I removed the concrete, then I could dig down and build a normal floor over wood joists with a nice hollow space underneath. My house is built over a crawlspace with hardwood floors and I like the quality of bass and overall sound I get in our living room. The downside is that it would be more difficult to convert the garage back later to use for parking a car if we move. I was thinking it might be cool to design this type of floor and then have space below for insulation, wiring, etc. without sacrificing any height. Maybe the floor could even be designed as a sort of bass trap to help with the sound. Any thoughts? -thanks, -jz


john_z

Showing 5 responses by nsgarch

After 60 years, the slab ain't goin' anywhere, but it most certainly wasn't waterproofed underneath (not in those days.) So what you want to do is cover the existing slab w/ construction grade polyethelyne sheet, the a layer of 2x2 or chicken wire mesh propped up on 4x4 squares if 3/4" thk plywood or fir, then call the concrete truck and tell them you need 2,5 yards of lightweight concrete topping layer (2" over the highest existing spot) and to notify you when they have extra from a job they're finishing. If you and the garage are ready when they call, you'll make out like a bandit because they hate having to dump that stuff!
The older concrete gets, the harder it gets -- and I mean jackhammer hard!! You have two problems: levelling, and (potential) moisture. So far, you haven't said if your garage floor ever gets damp or even floods. So is moisture a problem or not? If not (the garage is on high ground?) then you could just level the floor with a fine sand bed and sand-set pavers (brick, stone, terrazo, slate) to make a very beautiful floor, with a really nice oriental rug on top. And if it's cold where you live (where was that?) you could lay some radiant heating elements in the sand bed. The 7' wall height shouldn't be a problem if the roof ridge is at 10', but there are probably cross members at 7'. There is a solution for this too: knee braces at the walls and cross braces near the peak.
John, tell Z you'd like to pay him to "tear out" the old slab for you. The laughs alone will justify the cost!! Just remember to invite us ;-) The driveway and garage floor of my little 1928 house in Hollywood, was poured at the time of construction, and jackhammering it out would have brought down the garage as well as the house, ha, ha!!
Zzzzzzzz -- I have far more than a 'clue' about both subjects, and more than enough experience to refute your bombastic assertions; many of the nice folks on Audiogon are already quite aware of my credentials and background, so troll away, you won't be here long ;-)
John, you can move the cross ties closer to the peak (a lay term for ridge) so you get better headroom (they're there to keep the walls from splaying outward under the weight of the roof ;-) Make sure you do it to every pair of rafters to be safe. Placing 18" diagonal knee braces nailed near the bottom of each rafter and the top of the corresponding wall stud (put an xtra stud in if there's not one near the rafter) will keep the building from racking. You should also put in diagonal metal bracing (two metal straps nailed across the wall studs in a big "X" on each sidewall of the garage) to insure earthquake resistance.

Removing the existing slab is an unnecessary expense, if you don't have moisture problems. A level sand bed over an electric radiant heating pad with sand set pavers on top would make an easy and attractive floor.