Living in a house from 1920, which is now renovated and mostly finished, but I have one project left, the basement.
The ceiling height in the basement varies from 165 to 185 cm and since it's not possible to excavate the basement floor (the foundation is level with the basement floor, discovered during drainage work a few years ago), I'm wondering if it's possible to replace the existing wood floor joists in the basement ceiling with some other joists that take up less height?
The room I plan to start with is 4.5x2.9 meters and the span of the joists is 2.9 meters. Ceiling height is about 170 cm.
The goal is to increase the ceiling height by at least 10 cm and the first 4-5 cm can be gained by tearing out the gypsum, studs, and plank ceiling and replacing with gypsum directly against the joists or possibly between the joists.
Some ideas that I'm wondering if they are possible:
1: Is it possible to reinforce the floor joists by nailing/screwing/gluing new lower joists and then cutting away 5 cm at the bottom?
2: Can I install new lower joists between the existing joists and then cut the existing joists 5 cm?
The basement space will be used as storage, hence I don't want this to become too expensive but at the same time, I don't want to hit my head on the ceiling.
Grateful for any ideas I can get.
The ceiling height in the basement varies from 165 to 185 cm and since it's not possible to excavate the basement floor (the foundation is level with the basement floor, discovered during drainage work a few years ago), I'm wondering if it's possible to replace the existing wood floor joists in the basement ceiling with some other joists that take up less height?
The room I plan to start with is 4.5x2.9 meters and the span of the joists is 2.9 meters. Ceiling height is about 170 cm.
The goal is to increase the ceiling height by at least 10 cm and the first 4-5 cm can be gained by tearing out the gypsum, studs, and plank ceiling and replacing with gypsum directly against the joists or possibly between the joists.
Some ideas that I'm wondering if they are possible:
1: Is it possible to reinforce the floor joists by nailing/screwing/gluing new lower joists and then cutting away 5 cm at the bottom?
2: Can I install new lower joists between the existing joists and then cut the existing joists 5 cm?
The basement space will be used as storage, hence I don't want this to become too expensive but at the same time, I don't want to hit my head on the ceiling.
Grateful for any ideas I can get.
It is possible to replace the existing floor joists with, for example, glue-laminated beams that can be split in half to achieve a lower height than standard. Whether this is interesting depends on the height of the existing beams. You can achieve a joist height of around 100 mm with glue-laminated beams, although the last few mm can be quite expensive. The method for replacing the floor joists isn't very important. However, my experience with 1920s houses tells me that it's best to remove the old beams. This will likely make it easier to lay a new level floor.
ThanksJ justusandersson said:
Unfortunately, I can only access the floor joists from below (from the basement) since there is a relatively new kitchen on the floor above. During this renovation, beams were placed on the side of the floor joists to level the floor. This makes it difficult to remove the existing floor joists, but it should be possible to fit new glulam joists between the existing ones, right?
Regarding the height of the existing floor joists, they should be about 200mm, but since I haven't yet torn down the basement ceiling and have only drilled a peephole, I'm not entirely sure.
Is it possible to go down to the dimension 145x45 (not glulam) if building with cc 300mm?
I suspect that your old floor joists have the dimension 75x175 (i.e., 3x7 inches). It was almost standard at the time.
If you don't want to touch the old joists, it's naturally fine to install new ones from underneath, even though it might be a bit tricky. 45x145 at c/c 300 mm works for the short span. However, I suspect you gain too little from it. Open up so you can measure accurately.
If you don't want to touch the old joists, it's naturally fine to install new ones from underneath, even though it might be a bit tricky. 45x145 at c/c 300 mm works for the short span. However, I suspect you gain too little from it. Open up so you can measure accurately.
Thank you, I hope to have time to open up and check the measurements this coming weekend, will get back with exact measurements.J justusandersson said:
Finally, I have cleared away to be able to measure the existing beams, the dimensions vary in width between 60-70 mm, the height is 210 mm.
210 mm was unusually much for a house from the 1920s. Then you can gain a lot by doing as you planned.
Adding a new idea that a friend of my father came up with and he has also done the calculation below, I am now wondering if someone can say if this is strong enough?
The goal is to achieve as high a ceiling as possible, meaning every cm that can be saved on the height of ceiling/floor beams is valuable.
If I understand my father's friend correctly, I leave the existing beams in place but cut them to a height of 120mm and then insert 2 new glued-together 120mm beams at 30cm centers. I also think I can reinforce the existing beams by screw-gluing a 120mm beam to them.
Span 286cm
Dimension Proposal
Cut existing beams down to h= 120 mm.
Combine two screw-fastened beams 45x120 mm in each section to increase cooperation.
These screw-fastened beams provide Vx 216 cm³, more than required.
Checking the actual bending stress in the modified beam structure.
Zigma b = M: Wx= 19670 : 456= 43 kp/cm². Acceptable.
The goal is to achieve as high a ceiling as possible, meaning every cm that can be saved on the height of ceiling/floor beams is valuable.
If I understand my father's friend correctly, I leave the existing beams in place but cut them to a height of 120mm and then insert 2 new glued-together 120mm beams at 30cm centers. I also think I can reinforce the existing beams by screw-gluing a 120mm beam to them.
Span 286cm
Dimension Proposal
Cut existing beams down to h= 120 mm.
Combine two screw-fastened beams 45x120 mm in each section to increase cooperation.
These screw-fastened beams provide Vx 216 cm³, more than required.
Checking the actual bending stress in the modified beam structure.
Zigma b = M: Wx= 19670 : 456= 43 kp/cm². Acceptable.
Your father's friend has calculated the bending strength, and his calculation shows it holds. When it comes to floor structures, one usually looks at deflection and bounce, which involve stricter requirements. The problem is that the construction does not provide acceptable bounce in the floor (it becomes too large). It can only be fixed with glulam (and steel) if you want to reduce the construction height that much.
What type of steel beam would you recommend?
A HEA 100, smaller versions of this type do not exist. Steel, however, becomes almost twice as expensive as glulam. Additionally, there are usually some fastening problems that arise when combining steel and wood. I do not recommend it in this situation.
What dimension would be needed for glulam if I choose it and place them with cc30cm?
If you purchase glulam with dimensions 215x225 mm of the homogeneous quality and have them cut to 110 mm in height (alternatively special order that dimension from the factory) then a c/c of 600 mm is sufficient.
Thank you, I will consider whether it will be glulam according to your suggestion or 145mm studs at cc30
I would dig deeper in the middle of the room and cast a sturdy concrete ring around it so that the foundation cannot collapse. So it becomes like a cast concrete ledge, let's say 10 or 20 cm high and half a meter wide around the entire room with full standing height in the rest of the room. The ledge becomes a good dry shelf to place things on.