I own a 110 yr old wood frame rowhome, roughly 28' x 32'. The floor dips on both axis - most noticeably on the first floor - to the main support beam in the basement. It has some minor cracks. It deflects at the contact points with the 3 lally jacks that were installed by a previous owner, leading me to believe that I need to replace or sister the beam. The beam and foundation are stable where they meet, leading me to believe that sistering is both structurally sound and appropriate. The span measures 32'.
1. How do I go about sistering? Do I need to jack the old beam or can I jack with the sister beam?
2. Does the sister beam need to sandwich the old beam? I was considering placing two 2/10s on one side and a single 2x10 on the other, as this would provide plenty of support and I wouldn't have to move any plumbing on the single board side. Can I use 2 boards with a stagger to run the length (32') or would it be better to get a composite beam fabricated?
3. How many jacks will be required? I was planning to use a pair of 20 ton jacks, pressing on lengths of 6x6s under the new beam to raise it ~1 inch above the location of the current beam.