subfloor/underlayment replacement...

MLO · 05-21-2006, 01:02 PM

I'm extensively reworking the floorplan an a 1250 sq.ft. 1950's ranch home. The current subfloor is a diagnal run siding (shiplap?) with plywood underlayment (where there is vinyl flooring). I was going to replace the underlayment (where needed) as I moved the interior walls around but am now thinking I should consider replacing the entire subfloor as well.

The flooring in the living, dining, kitchen, hallway and mst.b/r will be hardwood (most is currently). Two bedrooms, bathrooms and laundry will be carpet and vinyl etc.The current hardwood floor (red oak) creaks in many places and has gaps. I was going to pull the existing hardwood up and re-use/add to it, though now I'm wondering if it should be installed over a different subfloor. I'm thinking the subfloor is responsible for the hardwood floors demise/condition as the "planks" appear to have shrunk and seem to flex a bit. The homes crawl space (concreted) is now dry and has been for over 3-4 years, it was previously seasonally wet before some needed site excavating was done.

What I am not sure on, is how to deal with the possible subfloor replacement where it runs under the exterior framed walls. Obviously I would have to cut it and "butt" the new subfloor to the old "near" the wall plane. Am I weakening the structure doing this? Would I just add some nailers between the floor joist under the "butt" near the wall? what subfloor (if any)/underlayment materials should I consider for a "nice" floor?

Any advice, opinions or pointers would be great, TIA.

MLO · 05-23-2006, 12:33 PM

After doing some research it seems that exterior grade 3/4" in plywood glued and screwed should suffice for the subfloor. While I am not looking forward to this added element of repair, it is very apparent the original subfloor will continue to be problematic. Some research on this site seemed to back that up.

Should a gap be left between panels?

Bonus · 05-24-2006, 12:50 AM

How about renailing the shiplap and then going over it with 5/8" t&g? This will add to the thickness of your floors but it seems to me it should solve your problems with the movement without cutting out the sub from the ext. walls. If nothing else it will be faster/cheaper.
Yes, leave a gap at the ends of the sheets, not much, an 8 penny nail is good.

MLO · 05-24-2006, 11:00 AM

I had not thought of that...the boards have shrunk considerably and some are quite cupped/warped. I did try to drive some nails in a few and they are like concrete!

Bonus · 05-25-2006, 12:35 AM

Even if you wind up having to cut out the occasional board you'll still be way ahead of the game by just renailing (rent a nailer, use 2-3/8" galv. ringnails in it) the existing subfloor and then installing new over it. If you're going to be redoing the whole house then the extra height won't bother you, and you're going to end up with a solid floor. Good for tile, hardwood, whatever you like, plus it's cheaper and easier. Good luck.

05-21-2006, 01:02 PM	#1
MLO Member Join Date: Jan 2006 Location: Great Northwest Posts: 85	subfloor/underlayment replacement... I'm extensively reworking the floorplan an a 1250 sq.ft. 1950's ranch home. The current subfloor is a diagnal run siding (shiplap?) with plywood underlayment (where there is vinyl flooring). I was going to replace the underlayment (where needed) as I moved the interior walls around but am now thinking I should consider replacing the entire subfloor as well. The flooring in the living, dining, kitchen, hallway and mst.b/r will be hardwood (most is currently). Two bedrooms, bathrooms and laundry will be carpet and vinyl etc.The current hardwood floor (red oak) creaks in many places and has gaps. I was going to pull the existing hardwood up and re-use/add to it, though now I'm wondering if it should be installed over a different subfloor. I'm thinking the subfloor is responsible for the hardwood floors demise/condition as the "planks" appear to have shrunk and seem to flex a bit. The homes crawl space (concreted) is now dry and has been for over 3-4 years, it was previously seasonally wet before some needed site excavating was done. What I am not sure on, is how to deal with the possible subfloor replacement where it runs under the exterior framed walls. Obviously I would have to cut it and "butt" the new subfloor to the old "near" the wall plane. Am I weakening the structure doing this? Would I just add some nailers between the floor joist under the "butt" near the wall? what subfloor (if any)/underlayment materials should I consider for a "nice" floor? Any advice, opinions or pointers would be great, TIA. Last edited by MLO; 05-22-2006 at 01:39 AM.

05-23-2006, 12:33 PM	#2
MLO Member Join Date: Jan 2006 Location: Great Northwest Posts: 85	subfloor/underlayment replacement... After doing some research it seems that exterior grade 3/4" in plywood glued and screwed should suffice for the subfloor. While I am not looking forward to this added element of repair, it is very apparent the original subfloor will continue to be problematic. Some research on this site seemed to back that up. Should a gap be left between panels?

05-24-2006, 12:50 AM	#3
Bonus renovations Join Date: Aug 2005 Location: Canada Posts: 430	subfloor/underlayment replacement... How about renailing the shiplap and then going over it with 5/8" t&g? This will add to the thickness of your floors but it seems to me it should solve your problems with the movement without cutting out the sub from the ext. walls. If nothing else it will be faster/cheaper. Yes, leave a gap at the ends of the sheets, not much, an 8 penny nail is good.

05-24-2006, 11:00 AM	#4
MLO Member Join Date: Jan 2006 Location: Great Northwest Posts: 85	subfloor/underlayment replacement... I had not thought of that...the boards have shrunk considerably and some are quite cupped/warped. I did try to drive some nails in a few and they are like concrete!

05-25-2006, 12:35 AM	#5
Bonus renovations Join Date: Aug 2005 Location: Canada Posts: 430	subfloor/underlayment replacement... Even if you wind up having to cut out the occasional board you'll still be way ahead of the game by just renailing (rent a nailer, use 2-3/8" galv. ringnails in it) the existing subfloor and then installing new over it. If you're going to be redoing the whole house then the extra height won't bother you, and you're going to end up with a solid floor. Good for tile, hardwood, whatever you like, plus it's cheaper and easier. Good luck.

subfloor/underlayment replacement...