Cantilevered bump out/bay window

[Hank11]

I need to expand a bathroom just a bit (2 feet extension past the block foundation wall) for a large tub. Outside wall on gable end of structure. Floor joists parallel to rim joist. I need a 2 foot X 7 foot bump out. The tub will be sitting approximately directly over the block foundation. It seems a lot of work for 2 feet but will transform the bathroom. This is in Tennessee, so no long extremely cold winters and I can insulate easily and well.

If the joists ran the other way it would be simple, but they don’t. Do you have any ideas on how to frame this?

 

[The Cobbler]

cut back 3 joists , run the new joists perpendicular . probably double up the outer new joist

 

[strutaeng]

What's underneath the framing? Crawlspace or is this second story?

 

[carlaisle]

Rule of thumb on cantilevers of this type built with traditional lumber is 4:1. i.e. if you want 2' to extend past the rim joist you should have 8' inside it.

 

[The Cobbler]

I thought cantilever was 2:1
very likely a regional thing

 

[Hank11]

What's underneath the framing? Crawlspace or is this second story?

Crawlspace. One story structure.

 

[loganb]

Cantilever rule for floor framing as I recall is 3:1 ratio...so to extend it out past the wall 2' you need 3x that length to the inside of that wall.

But agree with the above on it means the joists need reframed to allow you to get 6' or more of joists to the interior side of the foundation wall so it can project out the 2'. If you're redoing the bathroom that much...you're likely pulling subfloor(or can without much additional effort) so that would make it much faster and more efficient. Remove subfloor, build some temp walls on each side where being cut....layout then cut out, install a bunch of joist hangers...install new joists....install lots of nails or screws, glue and screw new subfloor ...admire progress while slapping the floor saying "that's not going anywhere"

Even for short spans like this, I'm fan of overkill and would try and use LVL in place of sawn lumber here(assuming existing joists are sawn 2x). The LVL will be significantly more resistant to bending which is the concern here and the upcharge over conventional lumber shouldn't be a huge impact to the overall budget for 5 or 6 pieces.

 

[KansasArt]

Even for short spans like this, I'm fan of overkill and would try and use LVL in place of sawn lumber here(assuming existing joists are sawn 2x). The LVL will be significantly more resistant to bending which is the concern here and the upcharge over conventional lumber shouldn't be a huge impact to the overall budget for 5 or 6 pieces.

This seems like best advice considering it’s going to be supporting a bath tub.

 

[mm08822]

Large tub = lots of weight when full. I'd increase that ratio to as large as possible.

The previous ratios mentioned certainly dont account for this level of weight.

4 lvl's would be cheap insurance too.

 

[TRWham]

We did a similar project a few years ago, but a 4’ cantilever. We ran 4 LVLs above the space in the attic and suspended the addition. The LVLs ran back into the attic and were tied down to the rafter ties.

 

[Hank11]

Thanks for all the comments. The tub will sit directly above and on top of the floor joists sitting on the block foundation wall, so the floor structure is really not holding up a lot of weight on the cantilever. But it still needs substantial framing.

 

[caleb383]

I need to expand a bathroom just a bit (2 feet extension past the block foundation wall) for a large tub. Outside wall on gable end of structure. Floor joists parallel to rim joist. I need a 2 foot X 7 foot bump out. The tub will be sitting approximately directly over the block foundation. It seems a lot of work for 2 feet but will transform the bathroom. This is in Tennessee, so no long extremely cold winters and I can insulate easily and well.

If the joists ran the other way it would be simple, but they don’t. Do you have any ideas on how to frame this?

Since your floor joists are parallel to the rim joist, you will likely need to double up the existing joists and run new cantilevered joists perpendicular to them. Supporting a large tub in a two-foot extension requires serious structural support, so having an engineer quickly review your framing plan is a safe bet.