Necessary to glue subfloor?

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Old 09-15-20, 07:49 AM
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Necessary to glue subfloor?

I finished insulating my mudroom floor with rigid foam and it's time to secure the plywood subfloor (Advantech). The mudroom is on a concrete slab with stacked 2x4 sleepers (three high, to allow space for a duct and a copper plumbing line to an outdoor spigot). Can I skip the glue and just screw the floor down without issue? The idea of gluing the subfloor doesn't sit well with me with the plumbing going through there. If it were to ever leak, it would be a royal pain to fix. The area is not accessible from any other angle but from above. I could use extra screws to keep everything secure. I don't see it flexing at all since it has such a solid base. Mudroom is only 80 sq ft. Thoughts?
 
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Old 09-15-20, 08:16 AM
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I for sure would have used PEX instead of copper.
If you pressure test the lines for 24 hours and there are 0 leaks there should never be an issue in the future.
Gluing will make the whole floor stronger and far less chance of squecks.
 
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Old 09-15-20, 08:34 AM
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I agree with the suggestion of PEX. Less likely to burst if it ever freezes.

In any case you could cut a small section (or several) of the subfloor for access to the space below. Glue and screw the entire floor EXCEPT the access panel area--screw only.
 
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Old 09-15-20, 03:58 PM
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I can replace with PWC if necessary, but freezing isn't a concern. It runs parallel to the duct and there is a small opening to the finished basement so there is circulation in there.

 

Last edited by mossman; 09-15-20 at 04:21 PM.
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Old 09-15-20, 07:44 PM
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Pex, not PWC. Stupid phone.

Come to think of it, do I even need to add more than one layer of foam insulation over the slab? My plan was to fill the entire cavities with foam board from slab to subfloor (4.5"), but if I did only the bottom 1.5", the water line could lie on top of the insulation keeping it warm and at the same time the slab wouldn't sweat from the warm subfloor. I would be sure to seal all the seams.

The room is has two exterior walls, but the foundation wall has foam insulation and I already insulated around the band board, which is actually three stacked 2x4s.
 
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Old 09-16-20, 06:39 AM
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only the bottom 1.5"
That should be fine over a slab. Is there any insulation already under the slab? Maybe at the perimeter if not full coverage.

the water line could lie on top of the insulation keeping it warm
Are you planning to keep the line active through the winter? Are you going to use a frost-proof sill ****? You might need access to the sill **** connection on the inside for possible replacement if it malfunctions. You could leave an access panel there or just cut the floor if access becomes necessary.
 
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Old 09-16-20, 06:14 PM
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Yes, There is insulation under the slab as well as vertically along the inside of the foundation wall.

The sillcock is frost proof. I've already needed to replace the cartridge/stem once, which was done from the exterior.
 
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Old 09-17-20, 09:20 AM
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insulation under the slab
So 1.5 on top should be more than enough.
 
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Old Yesterday, 09:46 AM
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Great. Thank you so much!
 
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