The original post: /r/diy by /u/Dick_Kickem12 on 2025-02-08 23:01:11.
Im going to put a TLDR at the bottom of this. It feels like the question needs a lot of explanation so if youre wicked smart hop to the end. I also made a video to better show the precise question. I will put that at the bottom as well.
Hi fellas, I am not a carpenter, but I am a tradesman. Ive taken on a project that has lead to me having my subfloor pulled up. Currently, I have numerous joists in my house that are, somehow still standing, but not resting on the main support beam. The end of the joists are sistered and then attatched to the joists on the other side of the beam. I am going to try and include a picture of that right here
I know the fix, its very easy, install new joists. I can do that competently. I removed all the wiring that would get in the way, but there is a problem. The dimensions of the 2x8 floor joists are not the modern standard. some are truly 8" and others are 7.5" but none are 7.25 of course. You may also notice those 2 joists being different sizes would definitely cause waviness in my subfloor, and you are correct. Managed to self diagnose on that one.
It seems to me, that the easiest solution to this problem is to buy a 2x10 and notch the corners of it down to the correct size (7.5), and run them resting on the sill to resting on the beam. Then, sistering to the old joist. Function of that being basically just to hold them in place I guess.
I read online that if I notch the corners of my joists, it will damage their integrity and a lot of people seem to advise against it. Ive also seen a lot people say you can notch the ends of a joist if its within a certain depth in relation to the joists size. I do not know enough about how wood works to know which answer is right, as both of them seem like valid points. I do not need the support of a 2x10 only the support of a 2x8. I do not care if the 2x10 being notched reduces its carrying capacity to that of a 2x8 as thats all it needs to be anyway. What do?
TLDR: Replacing (not sistering) floor joists that are true 8" dimensional 2x8. Modern lumber is not 7.25". I want to use a 2x10 and notch it down on the corners to fit between the subfloor and load bearing surfaces. I do not need the support of a 2x10 so I do not care if notching it to 2x8 reduces its carrying capacity to 2x8, as thats what it already is. Can I do this?