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Building Homes or Extensions/Taking bounce out of floor and adding support from basement


Hi Bruce, I have a 100 yr. old house or so and real bouncy floors.  I have a unfinished basement ,the floor joists are 2"x8" 16" o.c. And the width of the basement is about 20'.  The length of the joists is  14' total length of the floor is about 42'. There is 2 main support beams that are 6"x6" timbers, so the overhead floor is divided into 3 14' x 20' sections.
 So anyways in order to take the bounce out of the front and middle sections I have attached the 4" side of a 2"x4" glued and screwed to the bottom of each joist that I had access to ( heat duct and such in the way of some.)  I chose this method because of cost and ease of installment , it seems to have worked pretty well.
 The back section is the kitchen and seems to have the most deflection , everything rattles when you walk through the kitchen.  I am worried about all the weight ( stainless steel appliances center island tile floors and lots of cabinets.
 What I was thinking is to use a 6"x6" timber beam or glue and lag bolt together 3 2"x 6" s 20' long to span the width and use either 3 or 4 adjustable lally columns one next to each wall ( I don't want to cut into the block walls though I know that's the proper way but I am not tying to support any load bearing walls or anything it will be in the middle of the 14' joist span which is in the middle of the kitchen ).  The kitchen floor is sloped a little not that worried about it .
 Sorry about the long text just wanted to provide a clear picture I just want to know if you think this will acomplish  A. Take out a lot of the deflection or bounce and provide good support for the extra weight. B. how about the column placement 3 or 4 ? Your recommendation. C. 6"x 6" timber or 3 2"x6" s or different recommendation?  D. How about footings what size ? I want to put them on the basement floor rather than breaking up the floor and all I thought it would be ok because I am not carrying the load of the house or a tremendous load ? FYI I am not getting a permit because I am not changing structure or anything.
Again thanks and sorry about the long text.

Hi David, a rule of thumb I use for structural wood is for joists, one inch of height per foot of run so your joists are 2x8 and with the new beam they will span 7 feet? This should suffice..For load bearing beams it's the same rule of thumb but with 4" if you are spanning 6' with a 4x6 that should your case you are making a laminated 6x6 which should allow you to span another couple feet..but if you are going through the trouble might as well beef it up good and stick with the 6x6 and a 6' span between columns.  There isn't much difference between laminated beams and solid wood..both are acceptable for what you are doing..a 2'x2'x 8" thick concrete pad with 4 number 4 rebars each direction should be sufficient..honestly since you are just shoring up your existing joists and if your slab is in decent shape you might get by without any pads..any slab worth its salt is at least 2500 psi and soil bearing 2500 pounds a square foot...your column base is probably 6x6 or 4x4 inches square.. sincerely, Bruce Johnson

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Bruce E. Johnson


I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.


Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

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