Expert: Roger Zona - 9/3/2008

Question
I am remodeling my kitchen and dining room. I have torn out the wall between them (non load bearing) and am about to tile the new open space with 1/4" thk porcelain tile. I am also planning to replace the laminate countertops with 1-1/4" thk granite plus add an island in the middle of the kitchen space. Total granite area of approximately 45 sq ft. Of that, the island is approx 15 sq ft centered in the kitchen. All other counters are along the outer walls of the kitchen. My concern is that I may be overloading the floor joists at least from a deflection standpoint.

My home is a small 3 bedroom rambler (1040 sq ft main floor) in minnesota. It has a supporting wall running lengthwise down the center. The floor joists are 2 x 8s, 16" o.c. with a span of 11'5" contact to contact. The combined kitchen-dining space is approximately 21'5" long x 11'4" wide. The kitchen portion is 12'3" long. The subfloor in the kitchen is diagonally laid 1 x ? tongue and grove boards topped with 5/8" plywood and vinyl flooring. The dining area has the same tongue and grove subfloor covered with 1-1/2" x 3/4" thk red oak flooring which is then covered with linolium that has asbestos in the adhesive; that's why I'm tiling over it. I have already laid Hardibacker over the entire area (the cabinets have been removed); I was also going to tile under all the counters and new island but decided against it. Before I continue I want to confirm that I'm not going to end up with cracking tile joints or worse.

The approximate material weights/sq ft I've come up with are as follows:

Granite-average density: 17.5 lb/sq ft
Porcelain tile 1/4": 3.55 lb/sq ft
Hardibacker 1/4": 1.9 lb sq ft
Oak flooring: 2.75 lb/sq ft
Pine subfloor: 2.125 lb/sq ft
Plywood 5/8": 1.875 lb/sq ft

I don't quite understand how to deal with the dead and live weight issues in this scenario. Are the counters and island live weight since they are more or less concentrated loads? Also,

Thanks.

Rich Gundlach

Answer
Dear Rich,

Please excuse my delay in responding - we are preparing for hurricanes here in S.E. Florida.

I understand your concerns.  You gave an excellent description of the structural components of your home and they sound very typical and adequate and in compliance with code and structural safety.  Cabinets are not moveable and therefore are counted as "dead weight".  You have not exceeded the limits of your floor joists.

The live load refers to movable objects - people and furniture.  The dead load is a calculation of all the components of the structure and how it is distruted.

Your floor joists are well within the limits of carrying the loads you calculated as well as the live loads.  The only thing you didn't mention was the "bridging" of the joists.  For that span you may have one or two rows of bridging (cross bracing between joists).

You can tile after cabinets are installed.  Dishwashers are equiped with adjustable legs to allow for the tile thickness.  Another way is to lay a shallow row of tile against the walls to receive cabinets and then lay tile inthe field and just under the cabinet toe space so the base cabinets set on tile at the front and rear.  

Hope this has been helpful.

Roger