I am building a mahogany built-in cabinet/bookshelf system for some friends of mine.
The built-ins will be in the basement, and set on a naked concrete slab. I went with off the shelf RTA cabinets for the base portion of the main built in, and will be custom building the upper shelves on top of that. On the adjacent wall (90 degrees from the end of the big cabinet/shelf system), I am building a low bookcase (30in tall) from the floor up. These cases will be built on a slab that is 3 years old, in an area where slabs must be floated due to expansive soil problems. The slab is a bit wavy – 16 ft long, largest difference from my high point is 1/2″, most spots are within 1/4″ of the high point. I spoke with a friend who is a structural engineer, and he says that the slab won’t move more than a 1/2″ up or down at this point, and it won’t change in its wavy profile materially, if at all.
I have a few quick questions for our resident experts.
1 – Leveling and moisture – Since this slab is floating, I am not supposed to tie into the walls* as I would do with setting base cabinets in a kitchen. I am not sure if I should scribe some pressure treated for the front and back edges of the cabinets to get a sturdy and level base, or go with floor leveling cement or just go with shims. Any thoughts? Also, can cabinet plywood be in direct contact with concrete in a basement, or should I make sure it is all resting either on cedar shims or pressure treated?
2- Since I cannot really tie into the back wall, should I tie into the floor like it is an island in a kitchen?
Any thoughts or advice?
Thanks in advance!
* – I will be attaching the case to the wall, but only to ensure it doesn’t tip over and it will likely be some sort of flexible strap to accomodate for potential rise and fall in the slab.
Replies
OK I thought someone would bite by now!
I laid off this all day because I don't live in Denver area and am not an expert on building techniques in the west.
But I'm wondering Who told you this? With this design, there could be no internal load bearing walls or columns in the basement? Furthermore, systems like the furnace and ductwork, gas, and hot water must require some sort of flex connection so items like the furnace and water heater which sit on the floor can "float" as the ground beneath it shifts.
It is pretty common in the front range of the Rockies
And depending on what location, it is often code.
Bentonite (and many other clays) expands and contracts based on soil moisture content. We have a lot of bentonite out here, but it varies by neighborhood. I think Littleton is the worst in the Denver metro area, but I am certainly no expert.
The problem is that a solid (somewhat structural?) wall could, under the right circumstances, lift structures off of the foundations when the soil is wet and the expansion lifts the slab, and drop it back on a then compromised foundation when dry, or twist and not put it back on the foundation properly, etc... Posts in basements will have separate footers, typically. Yes, HVAC, gas, water heater connections, etc. is usually done with a flexible connection. Once again, I am not an expert.
I was out of town when my friend had it framed, so all the walls hang from the 1st floor joists. If I had been thinking before he did that, I could have/should have had the framers put that wall on the floor and then put the gap up near the top of (but still behind) the bookcase where no one would have been able to see it. Hindsight is 20/20...
A guy at Rockler today told me that he thought the best way would be to put down a vapor barrier and then use heavy duty adjustable furniture legs. I did the load calculation for the weight of the materials and the max potential load on the shelves, and there is plenty of margin. I worry about using the bottom panel of an RTA cabinet for this, but may look at beefing it up a bit to handle the point pressure.
Any thoughts on that approach?
I am concerned about your thoughts of scribing the front and back of the cabinet to the floor.
Over concrete, in your conditions, I think free air-flow would be desirable. I had some boxes stored directly on concrete. They soon developed mold and stain. I built a grid of 1' x 2's that kept the boxes off the floor and all problems disappeared. Aesthetics could be an issue but your innovation should overcome that.
Frosty
Late reply but I found this information that may help.
http://timberwindland.com/3_projects/1_thesprings/pdf/Lot_15_Soils_Report.pdf
I founf you question something I became qurious about. Not sure if this pdf applies to your situation but see page 8.
As I read it. 'The floating flore should be 'free floating' and isolated from all bearing members.....' Included are cabinets....
Good luck on your job.
PS.. I have never thought of interior walls hanging from the rafters! Amazing....
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