What size LVL beam to replace 17 foot load bearing wall (marriage wall) on first floor of two story colonial modular home

Question

We are currently in the process of opening up the space between the living room and family room on the first floor. The house is a 2 story, 2600 square foot colonial modular house.

The wall we would like to replace with a LVL beam is the marriage wall between the rooms that is 2- 2x4's and 2- 1/2" pieces of OSB. We have a full poured concrete basement with steel support beams spread. From the left the spacing is 7' from wall, then the next one is 9'from that beam then 5'from that beam. The section of wall would have to be replaced with a 17 foot beam. The LVL beam would between the red squares are in the photo. We want to keep the existing post where the red square is between the morning room and the foyer which is roughly 8"x8".

The house was designed with a 40 psf live load and a 12 psf dead load for the floor. Attempts be in contact with the manufacture/builder of the house have been unsuccessful.

Initial research has shown 3-14" LVL beams to cover that span but we would like to keep the drop to a minimum but maintain the full structural integrity of the house built which is very high.

Please let me know if you need any other information to provide.

Answer 1

You don’t indicate where this is located nor what the roof snow load is, so I’ll make some assumptions and you can tell me where I’m wrong.

The roof could be constructed with trusses that span the entire width of the house. However, to be safe I’m going to assume it spans to the center wall like the floor framing. Therefore, the contributing roof load is 25 per square foot (psf) snow load plus 10 psf dead load. Total roof load is 35 psf x 13’ = 455 per linear foot.(plf)

The first floor load is 40 psf live load plus 15 psf dead load for a total floor load of 55 psf. Therefore, the contributing load is 55 psf x 13’ = 715 plf.

Total design load is 455 plf plus 715 plf = 1,170 plf. Therefore you have three lvl options for a 17’ span and all are based on grade 2.1E 3100:

Option 1: 3 1/2 x 18” lvl = 1276 allowable load

Option 2: 5 1/4” x 16” lvl = 1530 allowable load.

Option 3: 7” x 14” lvl = 1393 allowable load.

As you can see, the height of the beam can be decreased by 4” if you use a wider beam. You may need to cut the length of each floor joists in order to fit the beam up between the joists.

Also you’ll need a minimum of 3 1/2” x 5 1/2” post under each end.

Also, you are adding about 10,000 lbs. load at each end that will need a footing. The end by the wall may be able to transfer the load to the wall footings, but there probably isn’t anything at the other end. (That would be a good “new” question for this site, but would need location.)

Remember, if you have roof trusses then the size could be reduced significantly.