Subfloor Thickness on 24" OC Joists

[chipbl]

Hi folks, great forum.

My BR-111 3/4" Angico 4” width flooring has arrived. During my sub-floor prep, I’ve removed the kitchen linoleum and the ~3/16 luan underlayment so that the kitchen is level with the adjoining great room. Therefore, the entire sub floor is Advantech (either 3/4" or 23/32” – hard to tell) on 24” OC joists.

BR-111 literature states that this is an acceptable subfloor thickness, but doesn’t state if 24” OC joists are acceptable with this thickness. Do I need to build this up, and if so, with what and by how much? Other townhomes have HW installed over the Advantech alone, but I want to make sure I’m doing this right and don’t have problems down the road.

Thanks!

[Bud Cline]

WELCOME.

I don't have an answer for you 'cause I'm not familiar with that type of flooring but someone here will know what to do. Standby.

[Floorguy]

I wouldn't do it without overlaying with ½" plywood underlayment.

This is some new building(make them cheaper) thing??? I have run into two like this. One I direct glued 5/8 engineered and the other I did ½ underlayment, and stapled ½" engineered.

[Jerry Thomas]

You'd be Ok if the OC spacing was 19.2 "....which is normally the case for floor trusses. If they are 24" OC you gotta add more plywood Chip ,or, block from underneath.

The 2007 NWFA guidelines state a minimum 7/8" T&G plywood or 1" OSB T&G. They consider AdvanTech same thing as OSB.

[William Mear]

If someone finds a sub-floor thickness spec. for a 24" o.c. floor joists I would like to know where. I had this problem 6 months ago and never saw 24" addressed anywhere.

[Nick Arrera]

How long are the joist ? what type , and dimension ? John Bridge has a deflection calculator on his site .. at least it will tell you what the floor is rated for ..

[chipbl]

Thanks guys for your usual prompt and detailed responses - I learn something every day here.

Since 24" OC joists just seemed odd, I checked another area of the kitchen/great room. There, the subfloor nailing patterns and the studfinder show joists 12" OC.

The kitchen/great room is 23' wide by 15.5' deep, but there is a bump-out that is 14' wide by 6' deep. That's the area that shows the 24" OC joists. Possibly the builder didn't foresee much traffic there or there is some 'engineering' concept at work.

Still think I should build up the bump-out (and thus the whole kitchen/great room area to make it all level)?

[Nick Arrera]

are the joist lams , 2x 10 , 2x 12 ? are they 14 ' long or 6 ' ? By all means build the floor up to level .. I would still put some kats in between the 24 oc joist to stiffen the floor ..

[chipbl]

Correction to my earlier post - joists are 16" OC not 12" OC. Not sure of the joist dimension, they're all sealed up now. If it helps, this is a townhouse, about 4 years old.

[Nick Arrera]

16 " is ok .. depending on width of joist ..

[chipbl]

Thanks - so now the question is the bump-out that is 14' wide by 6' deep. That's the area that shows the 24" OC joists. Guess it's a call as to whether I can live with possible flexing there or build it up as well as the entire kitchen/great room area...

[Nick Arrera]

can you get to those joist from underneath ?

[chipbl]

Ah, excellent point, but no - the bump-out is on all 3 levels of the TH. Below the area in question is a finished basement.

[Nick Arrera]

Would have to agree with floorguy and put at least 1/2 plywood on top of it , and not the Home Depot junk , good 4 to 5 ply .. It is my guess you have the lam joist under the floor @ 24 oc , if that is the case they are designed to flex then stiffen under the load .. Not good for hardwood ..

[chipbl]

Huge help, Nick, thanks. Guess I'm now in search of about 450 sq. ft. of decent 1/2" plywood!