To Ply or not to Ply


Old 01-07-19, 10:22 AM
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To Ply or not to Ply

Hi all,

I am doing a reno to a 1960s townhome. The home had 1” strip hardwood. The hardwood was installed the length of the rooms. And in the strips were run the length of the hallway; which just so happened to be opposite the rooms. I removed the old 1” strip hardwood flooring to find that there was 3/4” plank boards. The boards are about 3.5” in width. The planks are installed on a diagonal. I then realized that the 1” strips were installed perpendicular to the joists and that is why the hall is different to the rooms.

The Ύ” plank subfloor is in good condition. I removed any nails from the strip hardwood. I then hammered in the old nails and screwed in every plank to the joists (joists are 16” OC) with 2.5” flooring screws (5000 screws). I will end up taking a floor sander to the planks because I found that there is gritty grime on some of the planks (most likely because of the plaster that was installed in the 1960s on the floor and ceiling). I also want to get rid of any high spots (wood chips) because of the nail removal from the 1” strips.

So I want to install either Ύ” hardwood (4 or 5 inch wide) or engineered hardwood. Here are my concerns.

1) I want to run the new hardwood in one direction. The direction will be parallel to the joists in the rooms. Is that ok? Or should I put ply on top of the planks? If I should put down ply suggestions on thickness?

2) I really don’t want to put ply down because that will change the height from the bathroom. Also there is a guard rail along the stairs and code states that the rail must be 48” high from the floor. The guard rail is old wrought iron and secured really well into a joist. I am trying to avoid removing the guardrail if possible.

3) Also I have one closet that I want to run the same hardwood in but the closet is on a concrete slab rather than sub floor. There is vinyl tile on the slab currently. I can see that the tile is glued on with a black tar type adhesive. Can I glue the hardwood right on the tile?

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Old 01-07-19, 06:14 PM
czizzi's Avatar
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Running the flooring parallel to the joist on a single layer of subfloor runs the risk of your flooring having a "wave" to it. The joists are stationary, and sometimes there is a dip or deflection between the joists that cause the "Wave" to take effect. For that, it is always recommended that flooring be placed perpendicular to the joist system.

A large straight edge can guide you, but the deflection from body weight between the joists is something that you need to seriously consider. Single 3/4" on the diagonal, is the minimum standard for nail down. No guarantees on end result.
Old 01-08-19, 04:17 AM
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Can I block from underneath

Thanks for the clarification. I understand now. Can I block between the joists from underneath say every 16 inches with a 2x8 to prevent the wave?

Old 01-08-19, 08:22 AM
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I am doing a reno to a 1960s townhome.
You already have the wave, it's the slight depression that the sub flooring gets with time. Probably dont see it now but put down a nice shiny floor and it may pop out!

If, it's a floating engineering floor it would not necessarily have the same requirements to be installed perpendicular to the joists, but you need to check with the manufacturer!
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