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I have torn out the original flooring from by 1910 Victorian so that I can level the joists and install new sound subfloor. I'm using 3/4" AdvanTech T&G subfloor, glued and screwed to the new sisters.

What I'd like to know is if I need to install blocking to provide a nailing edge around the perimeter of the room where the joists deadhead into the brick walls. The original floor had no nailing edge. Installing blocking will be pretty easy in some places, but there are mechanicals that make installing it a challenge in others. There are places where I can't fit a nailing edge within 6" of the exterior wall.

Nailing Edge Here?

Some things I'd like opinions on are:

  1. If I don't install a nailing edge, is it likely I will have a noticeable bounce?
  2. If I should install a nailing edge, but can't fit a full height joist in place, will a 2x4 add enough rigidity to be worth the energy to install?
  3. If I should install a nailing edge, but can't get one within a few inches of the exterior wall, do I just install one as close as possible or is that just a waste?
  4. What would your typical contractor do in this scenario?

For you old house lovers who want to yell at me for chucking the old growth pine planks, please know that I did everything I could to try to salvage the original floor. For a wide variety of reasons, it just wasn't in the cards.

Update: Just as an FYI I did not install blocking around the perimeter. 5 months later and there is no noticeable difference between the rigidity of the floor system between the middle of the room and the perimeter. Thanks for you help!

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If I don't install a nailing edge, is it likely I will have a noticeable bounce?

No, because you can't stand that close to the wall. The only unsupported edge is right at the face of the wall

If I should install a nailing edge, but can't fit a full height joist in place, will a 2x4 add enough rigidity to be worth the energy to install?

Yes. A 2x4 is more than adequate for that span and use

If I should install a nailing edge, but can't get one within a few inches of the exterior wall, do I just install one as close as possible or is that just a waste?

Close as possible is adequate. Think about how much plywood can bend if you wanted to bend it at say 4" in from the edge, almost impossible

What would your typical contractor do in this scenario?

When I was a contractor I would usually not worry about it. 3/4" ply is very stiff (and rated for 24" oc) and as I noted, no one can stand close the wall anyway. If it were to be a tile floor, I might be more likely to add it since tile is so sensitive. I would consider that adding blocking would reduce air flow at the exterior wall in the crawlspace and therefore increase humidity and likely of decay or mold issues.

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I did it both ways in a laundry/powder room I completed last year.

Along the one wall, I installed the nailing plates your described.

Nailing plates for subfloor

Along another wall, I didn't, in part because the sole plate for the wall had to be down before the subfloor, in order to run the plumbing. Also this area holds the washer/dryer & a utility sink, so no foot traffic.

enter image description here

In any case, the inspector was satisfied.

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  • Thanks, Steve. Do you know if there was there a noticeable difference in stiffness between your two methods?
    – Doug Hill
    Commented Mar 30, 2020 at 20:03
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    Nothing I could notice. The one end is under the washer/dryer (stacked), and the other is in the powder room behind the toilet and vanity. There is one small area when the laundry goes into the kitchen with the blocking in place. But nothing un-blocked to compare than to,
    – SteveSh
    Commented Mar 30, 2020 at 21:03
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I chose if I need blocking by placing 2 pieces of flooring on top of each other and stepping in the middle of a span. If the deflection is excessive and it is a high traveled area like a entry door I will block (I normally block at perpendicular entry’s).

At a wall I don’t block in most cases unless the flex in 2 boards is noticeable, remember when you glue and nail the boards become fixed in place. If I feel the new T&G sub is flexing two much I go thicker but this is normally only needed for floors 24” OC however I normally use 1-1/4 T&G with a thin overlay. For vinyl and carpet. Tile I use a backer on top then tile.

What is your plan for the floor a little more info would be helpful.

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    Thanks, Ed. I'm likely going to use engineered hardwood flooring. I don't notice any flex with two AdvanTech board stacked on each other. But engineered hardwood won't be nearly as stiff as that second piece of subfloor, I bet.
    – Doug Hill
    Commented Mar 30, 2020 at 20:15
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    I meant the sub + the new floor stepping on that. if using an engineer floor on top of that t&g decking you should be ok. If there is no flex when laying flat there will be less when tied together glued & screwed . I am quite large at 6’5” so I really feel floor bounce and with a good sub floor it is not needed except for doorways where you would enter. This is about the only time your entire body weight will be on a small area heel to toe walking.
    – Ed Beal
    Commented Mar 30, 2020 at 20:48
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I would definitely put in blocking along the wall. The point isn't for support of the the floor the point is to deflect some of the bounce. 2x4 blocking as close to the wall as you can get is more than adequate.

Also not sure why you notched the new joist for electric (sure seems you could have went under) but I would block each side of that too.

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    I thought someone might comment on that notch. Good catch. That electrical was existing before the sister. Also, these are not full height sisters, rather they are glued and screwed (and nailed) stiffening sisters. Typically this is done with 2x4s, but I oversized to 2x6s to add additional rigidity (and since I was using them to also level the joists, in some places up to 1.5", I wanted enough meat of the sister to be on the side of the joists).
    – Doug Hill
    Commented Mar 30, 2020 at 20:12
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    So while the notch certainly does reduce the effectiveness of the sister, in my amateur opinion it should still be just as strong as a 2x4 which is typically specified. If my reasoning is wrong here, please let me know!
    – Doug Hill
    Commented Mar 30, 2020 at 20:13
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    Tough working with 100+ year old structures!
    – SteveSh
    Commented Mar 30, 2020 at 21:04

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