Subfloor help needed regarding edge blocking
Hello all – I’m back again for some help on my bathroom remodel. This time it’s regarding the subfloor.
I’m trying to decide what is the best way to add blocking around the edges to help support the subfloor. I’m going to be using Advantech 4×8 22/32 t&g unless you feel that there is a better alternative. The room is 110×73. My calculation is that I require 3 sheets, unless I screw up! I cut out the previous subfloor as clean as I could using an oscillating tool.
I’ve attached some pictures. These were taken with a wide-angle lens so there will be some distortion.
I’m planning on either using tile or LVP. Since this can influence the answers, let’s assume tile and 12×12.
The wall that runs parallel with the joists and has the batt insulation in the cavities currently has trapezoidal blocking that doesn’t extend to the joist (see pics). However, those blocks are between 1″ and 2″ below the level of the joists (each block’s height is different). I didn’t think of this until writing this question but is there a way that I could simply add to the height of these blocks to bring them level with the joists? I saw online someone using shingles to make a subfloor level. Any ideas? The joist next to this wall is 10″ away.
The wall with the doorway has no edge blocking. Considering the amount of traffic in this area, it obviously will need some. I don’t think this blocking would be for structure for the walls but for something that the subfloor can screw into so that there is minimal deflection. Correct me if I’m wrong. If this is the case, I was reading Roger German’s excellent book Remodeling a Basement where it talks about blocking using 2x4s wide face down. Page 62 at this link:
https://books.google.com/books?id=3ZGRaLqdvhAC&pg=PA62&lpg=PA62&dq=%22blocking+in+an+awkward+spot%22&source=bl&ots=mJhAebBiR9&sig=ACfU3U28aK3q1GEzHKoBpwPQ0iIehPdUZg&hl=en&sa=X&ved=2ahUKEwjl-P6DsfvsAhWLbc0KHRUzCEAQ6AEwAHoECAEQAg#v=onepage&q=%22blocking%20in%20an%20awkward%20spot%22&f=false
Would this work? And if so, how would I screw/nail them to the wall? The previous subfloor was wooden planks (you might be able to see the remnants of them underneath the wall in the pics). Is that where the nails/screws should go? Or do I need to cut more of the wooden planks away under the wall (maybe 3/4″) to fit these 2×4’s underneath the wall, and then screw down into them from the floor plate of the wall? The joist next to this wall is 12″ away.
Finally, do you think I need edge blocking around the walls that run perpendicular to the joists? If so, any suggestions are appreciated. Regarding the joists in this room, there are a number of joists that are close to each other. Others are 16″ apart except for the joist surrounding the ductwork, which is 19″ apart OC.
Hopefully this makes sense. I appreciate any comments. Oh, and if you see anything else, please let me know. The electrical wires will be properly fastened to the walls/joists before covering up in case you were wondering.
Thank you for your time!
Replies
ok - i'm at a point where i need to get going on the subfloor installation. hopefully someone will chime in here on this post.
i think i have an idea here that i want to check out. regarding edge blocking, i've attached 2-3 pics to show what i've thought to help with blocking a wall that runs parallel with the joists.
i've screwed together two 2x4s and will place them horizontally between the last joist and underneath the old subfloor under the wall. i'll glue and screw them under the wall (screwing down), and screw into the ends against the joist. i could do this every 12 inches or so.
does this make sense? am i over/under thinking this? hopefully the pics show what i'm trying to do. again, i'm trying to provide support for the subfloor against the wall area.
thank you.
Can you fit the 2x4 vertical instead of stacking them? (do you have 3.5 inches between the 1 x which catches the edges of the ceiling drywall below and the bottom of the 1x subfloor under the wall bottom plate?
if so, you might be better off gluing and screwing to the joist under the wall, instead of trying to suspend your blocking from the bottom plate.
what is the geometry of the bottom plate of the wall and the hidden floor joist? it looks like it is sitting on the now-cut 1x subfloor, hanging over the joist.
you can cut the blocking at a slight angle (2-3 degrees) and offset the cuts, to make it easier to insert between the floor joists. (make the sides of the 2x4 the same length)
Thanks Mike for chiming in here. To give you some dimensions, the joist bay is 7.5" deep. The distance from the wall (the edge of the subfloor that has been cut off) to the hidden joist is 2.75".
If you take a look at the 4th picture in my original post (with the blue level in it), you'll get a more bird's eye view of it. You'll also see two pieces of wood that are for some reason attached to the drywall underneath for some of the bay. That wood is 1.5" thick.
The opposite wall joist bay has a similar situation. If you look at the first picture (which shows trapezoidal shaped "bridging" that doesn't extend the width of the joist bay), there is also 1.5" thick wood pieces.
These wood pieces have made it more complicated for me to figure out how to do traditional bridging where the bridging wood would be on it's end. That's why i thought of my solution and wanted to run it by people here. Based on your response, it doesn't appear to be a great option.
I guess i could get some 2x8 wood and use that for bridging? Cut off the 1.5" from the height of this wood if I'm using it where there's already some wood attached at the bottom of the joist bay. and make it a snug fit between the first joist and the hidden joists on each end.
Is that a better solution? I'm not sure if i'd have the ability to "notch" the bridging wood so that it has more attachment to the bottom of the bay. remember i'm trying to provide support for the subfloor along the walls here where there is no support. i'm less concerned (correct me if i'm wrong) for the walls where the joists are perpindicular and extend all the way to the wall and are mostly either 12" or 16" OC (one is 24 i believe).
thanks again. let me know if i'm not clear here and if you have any more questions. again, i appreciate your help.
Sounds like there is an inch of the wall setting directly on the inset joist, so that is a good thing.
you could use a 2x6 under that wall, screwed and glued to support not only your new subfloor, but the existing wall.
those angled parts... in the first and second photo of your first post... did there used to be a roof that was cut out?.
you certainly have an interesting set of challenges. looks like there has been some work more recently than the original structure.
Regarding the wall without the angled parts:
there's actually 2.75 inches of wall inside the hidden joist (wall overhang). if i use a 2x6 for blocking, i think it will not be wide enough to support the wall and fit snugly between the wall and the drywall underneath. the distance between the added pieces of wood and the removed subfloor underneath the wall is 6". that's too wide for a 2x6 if i understand correctly.
so if i'm understanding you right, i'll get a 2x8 and cut it down to fit this section. Other sections (without the added wood) should be fine (hopefully) with 2x8 to fit snugly underneath the overhang and attached to the first joist.
Regarding the wall with the angled parts:
there is only 1 inch of wall overhang before hitting the hidden joist. You are right on the roof part - before i purchased this place they did work to this section (the upstairs). beforehand, it was a 45 degree roof. They decided to make more headroom for half of the upstairs by changing the roof angle. so that explains the angled parts.
you have me a little nervous about the comment "interesting set of challenges". I was thinking I would do with that floor (angled part section) the same as the floor on the other side - add blocking and even though there's only 1" overhang, it might help with support. Am I wrong here?
thanks so much. appreciate your help.
without looking a bit more, it seems that the wall below is only holding itself and some drywall up. you may not want to rest the floor on it.
if you put the 2x6 in, and attach each end securely to the top of the joists, it should be able to support the load of the existing wall, and your subfloor.
I think it a fine idea to do the same thing to the other wall. since it was holding up the old roof, the concern with resting weight on it is not as much. (depending on what was done with the wall below when the roof was raised) But I still would want the blocking to be supported by the floor joists, and not the wall below.
With some tile going in, you want the whole floor to move together.
By the interesting comment, I only mean that with the mix of old and older, figuring out what is load bearing can be a bit of a puzzle.
just to confirm Mike, your indicating that the 2x6 should not rest on the bottom of the joist bay?
If i understand this correctly, then I'm assuming using a 2x4 instead would simply not provide as much support as the 2x6.
if i understand you correctly, i'll pick up some 2x6 from HD or lowes and get to work! Thanks again for your help.
That is what I would do.
You can also put some blocking in between other floor joists to help stiffen up the floor. (where you can do so)
From the photos, some of the structure under your floor joists is hanging from the joists, and the joists are supported by others.
https://s3.amazonaws.com/finehomebuilding.s3.tauntoncloud.com/app/uploads/2020/11/11162157/DSC00627-700x467.jpg
in your second photo, above, the overlapping joists, newer and older, sit on what is a load supporting wall.
https://s3.amazonaws.com/finehomebuilding.s3.tauntoncloud.com/app/uploads/2020/11/11162224/DSC00615-700x278.jpg
In your third photo, the 1x holding up the drywall sits on and is nailed to a 2x that could just be part of a box hanging from the walls.
I think I've screwed up here Mike. I'm sure it's not a difficult fix but I'm thinking I just didn't read what you were wrote correctly. Let me know what you think.
I've attached a photo with the edge blocking that i put in. About every 10 inches. However, I didn't realize that I need to secure the edge of the subfloor every 6 inches.
Now that I read your posts again, I believe you were telling me to put the blocking PARALLEL to the joists and underneath the floor. Am I right?
The blocks in this picture were not glued but were toe-nailed(screwed) into the two joists.
Let me know if you have any suggestions. I could just add more blocking the way i've done it, every 5 inches or so, if that would work.
The subfloor you see in the picture hasn't been attached yet. I'm slooowww.
Thanks.
I was suggesting blocking at right angles to the floor joists.
Keep in mind that the 6 inch spacing for fasteners indicated in your photo is only along the outside edge, and only for the short side of a full sheet that spans joists that are spaced on 24 inch centers.. in this illustration, fasteners on the long edge are 24 inches apart.
Looks to me like you have plenty of support.
Thanks Mike - I'm glad I did understand you correctly. However, what wasn't clear was that according to the manufacturer the long side of the sheet has to go perpendicular to direction of the floor joists. I've attached another screen shot.
Based on this, would you suggest adding extra blocking or anything else, or do you think there's enough support without screwing in the edge of the subfloor against the wall?
Thanks!
What thickness are you using?
https://www.huberwood.com/uploads/documents/technical/literature/AdvanTech-InstallationGuide-2013-10-1.pdf
might be worth a read.
remember that you would stagger the edges if doing the whole house, and end up with 4x4 sheets or similar.
I do see your question.
(sorry, I was distracted by local news events)
It would be more solid if you had joists under the edges.
.
it does seem they advise edges should either be interlocked with the adjacent sheet or over a solid framing member. If you were doing an entire house, the whole floor would have a rim joist on the outside edges.
https://s3.amazonaws.com/finehomebuilding.s3.tauntoncloud.com/app/uploads/2021/01/06121105/IMG_1160-700x525.jpg
On the bright side, you are probably getting pretty good at measuring and cutting blocking by now.
Hey Mike - thanks for following up with me here and looking into this.
In order to do the edge screws on the short side, could i not lay a 2x4 flat (not on it's edge) underneath the lip so that some of it extends beyond the lip? I'd screw through the bottom plate into the 2x4, and this would leave an edge for the subfloor to screw into. hopefully the picture i've attached shows this well, with me holding it in place rather than screwed in.
Also, for the blocking I've already completed, I'd keep the current blocking as it is and just fit around it.
btw I am getting a bit better at cutting and measuring it. however, toe screws are not easy for me. i find that pre-drilling before putting it in place has helped.
Thanks again.
I think that will work. You can also use some construction adhesive to help hold it together. I find that holding with a clamp helps make sure the boards are flush when the screw goes in. (also helps me keep from putting the end of a screw into my finger)
The blocking you installed helps to hold that wall up. I too, would leave it in place.
Thanks for sharing your project.