I would never do that, a real PIA to repair properly

for every joist bay cut would need 2 blocks plus replacing the subfloor

The benefit of the insulation would never come close to the cost of the repair

tedious work to do properly, need pine subfloor because ply is not as thick as the old pine, just a real pain all around

 

Joe, this crawl is only about 12" and there are HVAC ducts running through it. Nobody is crawling in there.

for every joist bay cut would need 2 blocks plus replacing the subfloor

Explain why. I am going with another layer of 3/4" ply over the top of existing 1x subfloor. Screwed into the joists. Why is the structural integrity of the 1x subfloor necessary? Thx

 

I'm guessing there is a standard practice in parts of the country where crawls are common.

Minimum crawl space height is 18" which is plenty tall enough to crawl in.

 

1 block to hold the existing cut floor, 1 block along outer perimeter to hold new sufloor

 

I say if you're putting down another layer of 3/4 ply, then all you have to do is snap a chalk line along the center of the floor joists, set your skil saw depth to whatever the pine subfloor thickness is, cut the man some slots.

Let him do his insulation thing, staple the pine boards back onto the exact same place they came from, then just make sure your 3/4 ply is secured with screws long enough to go through the old pine and well into the floor joists. I'd be using 3" deckmates myself. It's my go-to screw.

 

I say if you're putting down another layer of 3/4 ply, then all you have to do is snap a chalk line along the center of the floor joists, set your skil saw depth to whatever the pine subfloor thickness is, cut the man some slots.

Let him do his insulation thing, staple the pine boards back onto the exact same place they came from, then just make sure your 3/4 ply is secured with screws long enough to go through the old pine and well into the floor joists. I'd be using 3" deckmates myself. It's my go-to screw.

if he can do what he has to do through 1 missing board that would be fine as long as the board is not going under the bottom plate. But you will be about 24-25" from the wall it total if everything lines up more if not

A few months ago I had to fix a sub floor where the plumber cut the diagonal subfloor at the edge of the bottom plate and again 15" away. Miserable to fix with pipes in the way

 

18” is like an ocean for a minnow. My foam sub could ace it up w/holes drilled w/a hole saw. Glue & screw 1x2 blocks like a drywall patch. Plenty of glue circling the plugs. 10th of time



Mike

 

18” is like an ocean for a minnow. My foam sub could ace it up w/holes drilled w/a hole saw. Glue & screw 1x2 blocks like a drywall patch. Plenty of glue circling the plugs. 10th of time
Mike

4" X 4" cut outs and he wouldn't even need to repair the holes since he's applying another layer of subfloor.

 

It's easy to see who has done this before and who has not

 

 

Gentlemen, I appreciate the input. All good points. Maybe I'm a bit thick, but there is one thing I still don't understand. Since I'm applying a whole new 3/4" subfloor on top of the existing pine 1x, screwed into the joists, why does it matter if the 1x pine is all butchered up and some missing? At that point isn't the pine just a 3/4" shim? What am I not getting?

@rrk: Bear with me please. So what happens if I have a board that goes under the bottom plate and I cut it off 6" from the bottom plate? Yes I have a board cantilevered out 6" with no support under the cut end. How is that a problem when I put a ply subfloor over it?

 

Leaving some holes is not that big an issue. You can usually just sub over it if the lower sub floor is reasonably secure.
When you make a cross cut along a rafter all the sub flooring that is cut loose is just flapping. This can lead to increased deflection in those areas along with a slap noise and squeaking.
Depending on the finish flooring used, this can cause cracking of tile joints and separation between wood flooring planks over time.
Especially if it ends up in a high traffic area or near an opening with increased vertical pressures.
Now place some heavy furniture or a hutch full of ceramics over the area and the problem exacerbates.
It's just a simple CARP 101 rules to always stabilize a flooring system to 100% of your capability to avoid many problems from arising.

 

Do as you like, I’m not leaving holes anywhere. Only sayin that’s how I would do it. Hell, canti the 18” if you like


Mike

 

Thanks Joe. I get all that and I don't disagree. Just want to make sure I am not missing anything specific to this new to me situation. I don't know what I don't know.
The finish floor is LVT.

 

It will still flex down especially if they put a bed or a dresser along the wall. A point load along that 14 1/2 is going to flex. it it was under a sink you could get away with it but not much other places. I always have the perimeter of the room supported by the rim joist or blocking

 

How does it flex more than if it was just 3/4" subfloor right to floor joists without the pine under it?

 

We may be confusing the situation more
draw out what you want to do

I have dealt with tons of 1x6 t&g subflooring

 

Here is a sketch. My point was that when we put a new 3/4" ply subfloor over this, and screw it all the way into the joists, it is basically no worse than having NO pine 1x10 at all, rigidity-wise. And rigidity is not an issue with a simple 3/4" ply subfloor. At most, I would want to fill in the "slot" with long 1x pieces so there is no gap between joists and ply anywhere.

The existing is 1x10 flat boards with gaps between, NOT t&g.

 

I totally agree with what you are saying here. I would cut it out like in your drawing and fill it in with some 1x and plywood over it. I wouldn't even think twice about doing it that way. It will be fine.

 

So it makes it easy to just place a rip of plywood in the gap.

 

I would probably put pine 1x in the gap, I can use fewer pieces if I get 12ft boards. Cut the slot to the width of 2 boards so I don't need to rip anything.

 

Why is this sounding more difficult than it actually is?

 

Mostly because I don't know what I don't know and overthinking is a lot cheaper than a major mistake in a client's house.

 

1x10? wow I usually see loose or cracked 1x6. A 1x10 is over a foot wide when cut at a 45 which helps tremendously
you may have an occasional loose or unsupported board then would put a block in, and you are not cutting right at the plate so I doubt you would have a big issue.

 

When I cut tongue and groove like that. I always cut it to a joist so there are no hanging tails. Then either back fill with plywood or pine.

Along the wall would need to run perpendicular to the joists to not get any hanging tails, so plywood probably makes the most sense.

The idea of taking a four inch hole saw and spraying through that is a good idea, if the operator can see what they're doing. It would save a lot of time work and material.

 

Another option is to drill and PLUG LINK but if you are going over it with 3/4" I wouldn't even do that. This is the definition of overthinking a situation.

 

What's the size of the crawl, anyway? How many holes does the foam guy need?

 

This is not complicated at all. Install blocking as needed .
Reinstall subfloor and cover with your ply.

 

We have very few houses on crawl in my area, so I haven't dealt with this problem before. I have a crawl space to encapsulate, but it is too shallow for anyone to actually crawl in there. I need to spray foam the outside walls of the crawl. My spray foam guy says no problem, just cut me a slot out of the subfloor about 18" wide near the outside walls and I can spray it from above. Sounds reasonable. Now the subfloor is 1x on the diagonal. Cutting an 18" slot will leave a bunch of board ends hanging unsupported. Do I need/want to add blocking to support them? Do I need/want to replace the boards I cut out? Is any of it necessary? There will be a second layer of 3/4" ply subfloor, as there was before. Finish floor will be click LVT on top of the plywood. I'm guessing there is a standard practice in parts of the country where crawls are common.

What you describe is not a crawl space. Walk away from the job.

 

 

What you describe is not a crawl space. Walk away from the job.