I need to create a hatch in my floor to get to the crawlspace below. I have cut the desired hole into the subfloor, being careful that the sides of the hole are centered on the floor joists so that the lid will be supported when shut.

The problem is my hole spans 3 joists. Obviously the center joist is in the middle of my hole. Can I simply cut this joist out of the hole, then frame in a window like opening?

 

I ain't gonna ask......yes I am. Why are you doing this rather than accessing the crawl space normally through the side of the house? I smell an escape route in the event of attack.
Cutting the joist will weaken the floor substructure to where it will be noticeable. Spanning across the cut joist to the full joists is an answer, but I would support the area with more from underneath, like a post and beam at either end of the opening across the cut joist.
There's no tunnel associated with this, is there?

 

funny anecdote (I hope)

I used to sell real estate. I actually had the opportunity to view and list to buildings that had been used as "massage parlors" "wink wink". Each of them had several hatches as well as false walls and hidden passages.

BTW, they were not in use at the time I was in them.

also in my area (SW Michigan) we have several homes in the area that were owned by gangsters (most notable, Al Capone). Two of the homes he owned are on a river and had secret hatches and tunnels to access the river from the houses.



If you do cut the floorjoist, as chandler noted, you will weaken the structure. The problem is that a floor doesn't just hold up loads. Pressure in one spot is transferred across the joists and can actually, depending on how the floor is designed cause upward lift at some point of the joist if you were to cut it. It becomes a cantilever and depending on what loads and where it is supported, it could lift rather than fall but that would allow another portion of the floor to fall. They are designed to work as a complete unit.

With that said, chandlers framing and the support from below would be required to hold up those "loose ends" of the joist that was cut. Without PROPER support from below, you can have a lot of undesirable movement.

 

Thanks for the responses. This house was built in 1908, and the crawspace is only 4' high, all below grade so there is no entrance on the side of the house. I imagine at one time there was entrance to the space, but I can't find any now.

Anyway, as I said I would install a window type frame out of 2x10 into the hole and secure the cut joist as well as the uncut joists to the frame with nails and joist hangers. I suppose I could pour a footing down there for extra support if needed.

 

You need to sister the joists on the side. Cut the middle joist & install double headers between the side joists.

Cut the middle joist & install 1 board of the double header on each side of the opening. End nail through the side joist & end nail the header to the cut joist with (3) 16d for each connection. Do this on both sides of the opening.

Next, face nail the other board of the double header to the one you just put in. Stagger nails 12" o.c.

Then sister your side joists. Face nail 12"o.c. staggered.

 

This is pretty much exactly what I did. I put in a standard interior door just as one one when entering a basement stairwell. You open the door as if leading to the basement but instead you head down a short set of stairs to a crawl space. I do have a hatch in this floor so I can use the space as a closet. I do not see any difference in framing this as one would to frame a standard basement entrance to a full cellar. Double up and sister with full headers!

 

Thanks guys. Much appreciated. Now I can access my plumbing to fix it.