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Joist support for kitchen cabinets, island and tile

Joist support for kitchen cabinets, island and tile

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  #1  
Old 02-17-09, 11:18 AM
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Joist support for kitchen cabinets, island and tile

We're remodeling the kitchen in our 100-yr-old twin home. The joists below are on average 8.0"x2.5", and spaced on average 18" o.c. The unsupported span is about 15'.

We're adding a porcelain tile floor over hardibacker, new cabinets, and a new kitchen island including a couple of barstools, all with quartz countertops, so the kitchen will weigh much more than before.

Here's my question: One of the joists (right below where the island will be) has a 2.5" or so hole drilled in it for a drain pipe. The hole is about 18" away from the middle of the joist span, and is very close to the bottom of the joist (within 0.5").

Is there a concern here for joist strength or stiffness? I was going to glue/nail a couple of 4' strips of plywood to the joist with the hole, centered above the hole. Is this sufficient?

Thanks!
 
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  #2  
Old 02-17-09, 10:19 PM
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" Is there a concern here for joist strength or stiffness?"

There always is whenever a joist is cut/drilled.

"I was going to glue/nail a couple of 4' strips of plywood to the joist with the hole, centered above the hole. Is this sufficient?"

Without seeing it, I would say yes, maybe so, maybe not.

If it is possible I would add a beam in the middle or close to the center to support those joist's.


"8.0"x2.5"," 2.5" wide ? that is unusual. After 100 yrs it is still 2.5" wide.

What kind of wood is it? Is that a normal thing to find in 90 plus year old structures in the N.E.?
 
  #3  
Old 02-18-09, 03:16 PM
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Thanks DE. Yes, it's definitely not like new construction joists. The individual joists vary in thickness and even depth, and are not evenly spaced -- what I posted was just the average. I would imagine they were probably even larger when installed 100 years ago.

I don't know what type of wood. How would I find out? There are certainly no markings on the joists!

And yeah, I think this is pretty typical of homes of this age in the Philly Main Line area.

When you say "add a beam", do you mean a column to support the joists? If so, which joist? The one with the hole, or do you mean something else? Sorry, I've made great advances with wiring over the last year but I'm still pretty new with framing.
 
  #4  
Old 02-19-09, 10:40 PM
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"When you say "add a beam", do you mean a column to support the joists? If so, which joist? The one with the hole, or do you mean something else?"

I mean run a 2x10" or 12" beam perpendicular to the floor joist's in question half way between the center beam and the outside support/foundation.
 
  #5  
Old 02-20-09, 11:06 PM
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I think he means add a joist where the damaged one is. And from wht you described that hole is damn near a notch due to its location. And it is located in the wrong place(only notch on the top). It probably fine, the house is 100 years old but since its open you might aswell sister it up around the hole.
 
  #6  
Old 02-21-09, 09:28 PM
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I was referring more to adding an extra support beam. You have the joists supported on each end by something, foundation, center support beam, something is holding them up on each end.
2.5" x 8" spanning 15' with 18" center is approaching the max, if not exceeding it.

So add another support beam under/across all the floor joists.

That will go a long way with reducing the deflection with the " hard floor" you are installing and the extra weight of a modern kitchen.
 
  #7  
Old 02-24-09, 12:35 PM
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Thanks DE. Just weighing risk vs. cost/effort. Right now there doesn't seem to be a lot of deflection -- and adding a beam across the joists would reduce headroom by almost a foot, right?

Do you know of an easy way to do a calculation of how much stiffness/strength a couple of strips of plywood would add to the joist, vs. sistering the joist or adding a beam across the joists?
 
  #8  
Old 02-24-09, 01:13 PM
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"adding a beam across the joists would reduce headroom by almost a foot, right?"
If you used a 2x12 yes. You could use a double 2x6 or 8 depending on where and how many support posts you can put in the basement.

"Do you know of an easy way to do a calculation of how much stiffness/strength a couple of strips of plywood would add to the joist," No, can't help ya there.

If a support beam is not an option is it possible to sister the joist on both sides with 2x6 slightly notched ( from the measurements you gave it should only be a 1/2 " or so) and bump them up to your sub floor, nail and carriage bolt as needed?

What about angle iron on each side of joist and bolted?
 
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