Installing new manhole cover

[Pete F]

I presently have a manhole that sits between the joists in the bathroom of my 1969 house, however (I guess) the joists are on 18" centres so it's quite a small access.

I'd like to install a new manhole in the hallway and make it larger so I can store larger boxes etc, I was thinking something like 600x600 or even 600x800. If I finish up using the storage area a lot I may even later install an attic ladder. The problem is the new manhole will be going across the joists instead of along them, so I will need to cut them.

I was wondering if there were any specific precautions to take before I start hacking away? Should I install nogs before cutting the joists or is it generally safe to just cut the joists and then frame the opening? I chose that location as I thought the top plates of the walls on either side would basically support the joists.

Thanks for the advice.

PS Sorry that title should be "Installing new manhole" not sure what the heck I was thinking about "covers" for
Pete

[Skew ChiDAMN!!]

If the joists run across the hallway (not along) and are definitely supported by the top plates (ie. you've actually physically eye-balled the connections) then you could probably get away with simply cutting and framing.

However, it doesn't take much to install a hanging beam on each side before cutting. It increases structural strength (especially if you're the sort that grabs the sides of the manhole to pull yourself up and in ) and practically eliminates any risk.

Why do things half-arsed?

[Pete F]

Ok thanks for that, I really appreciate the time guys spend helping each other out here.

I haven't been up there for a while so will need to confirm the actual arrangement but by the same token I tend to over-engineer things so why take a risk? Particularly if I later install the stairs.

I'm pretty new to this sort of thing so do you mind if I confirm I have the correct idea? I would install 2 hanging beams on top of, and tied to, the wall plates and hang each cut joist form them. I'm not sure how far I would need to extend them out though, just 1 uncut joist of more?

Thanks again.

[Skew ChiDAMN!!]

For a 3' span (ie. only cutting one joist) you can get away with the hanging beam(s) running from the uncut joist on one side of the opening to the one on t'other, if the joists run across the hallway. (Personally, I'd have it covering two joists on each side)

If the joists run along the hallway, then yes, I'd run a pair of hanging beams from one top plate to the other.

I guess it's pretty obvious, but I also prefer to over-engineer: it can save so many headaches later. Especially as you've stated you want to store boxes up there... (ie. it'll be supporting more than just you and the ceiling's own weight - I'm assuming you'll also be laying sheets of MDF or similar across the joists as "false flooring?")

Edit: a picture is worth a thousand words...

Attachment 60074

I didn't include the frame, etc. for simplicities sake.

[Pete F]

Excellent, thanks for that, I can now see the arrangement of the hanging beams from the diagrams. Yes the arrangement I expect would be similar to diagram #2. Seems it would make sense to frame it up at 600mm as it appears the stairs are designed for joists on those centres and it would make later retrofit easier if I decide to later go that way.

Cheers,
Pete

[billbeee]

Good answer Skew,
spot on.
I remember in my second fix days we had a government inspector who used to test the manhole fixing by swinging off it, just as you say, until one time he finished up on the floor with it around his neck. He stopped after that.

Of course this wasn't on one of our jobs, honest. (we used to put four two inch nails in, not two)

Cheers
Bill.