Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Welcome to John Bridge / Tile Your World, the friendliest DIY Forum on the Internet


Advertiser Directory
JohnBridge.com Home
Buy John Bridge's Books

Go Back   Ceramic Tile Advice Forums - John Bridge Ceramic Tile > Tile & Stone Forums > Tile Forum/Advice Board

Sponsors


Reply
Thread Tools Search this Thread
Unread 08-06-2012, 03:27 PM   #1
gbrny
Registered User
 
Join Date: Aug 2012
Posts: 5
Does knee wall count?

Does knee wall count as a mid joist support for the deflecto calculator?

In other words I got 2x8 joists, 3/4 osb subfloor for a span of 12 ft. Not a good "L" number.

If I use the fact the knee wall is there my span is now 6 ft. Very very good "L" number.

Getting ready to install marble could really use the advice.

Thanks guys...
__________________
Greg
gbrny is offline   Reply With Quote
Sponsored Links
Unread 08-06-2012, 03:30 PM   #2
pgc555
Registered User
 
Join Date: Aug 2009
Location: Chicago NW Burbs
Posts: 1,227
Greg,
Your talking about a "knee" wall ( half wall ) on top of the existing floor?
I don't think that gives any added support to the floor joists?????
__________________
Phil,

http://www.edgestripkits.com/
pgc555 is offline   Reply With Quote
Unread 08-06-2012, 03:45 PM   #3
gbrny
Registered User
 
Join Date: Aug 2012
Posts: 5
Phil,

The top of the knee wall is fastened to the roof rafters the bottom nailed to the joists. doesn't the knee wall support the joists by hanging the mid point of the joist from the rafters?

Greg
__________________
Greg
gbrny is offline   Reply With Quote
Unread 08-06-2012, 03:48 PM   #4
gbrny
Registered User
 
Join Date: Aug 2012
Posts: 5
Maybe I should clarify...this is upstairs in a Cape Cod house
__________________
Greg
gbrny is offline   Reply With Quote
Unread 08-06-2012, 04:02 PM   #5
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 95,749
Welcome, Greg.

We'd need to know a good deal more about the structure and method of fastening to determine if your floor joists are actually benefiting structurally from the roof rafters or vice-versa.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is online now   Reply With Quote
Unread 08-06-2012, 05:32 PM   #6
gbrny
Registered User
 
Join Date: Aug 2012
Posts: 5
Hi Cx,

1st off thanks for your time...

This cape cod house is a very typical 1 1/2 story. It is 24 ft wide. there is a center load bearing wall that runs the length of the house. The downstairs ceiling joists are laid perpendicular to the bearing wall. They are 12 ft.
The upstairs room is made by adding a 5 ft wall from joist to rafter midpoint on each 12 ft joist.
The knee walls are nailed to joist and rafters.
__________________
Greg
gbrny is offline   Reply With Quote
Unread 08-06-2012, 06:45 PM   #7
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 95,749
Still not enough information for a good guess, Greg. Sorry.

Without knowing anything about the roof rafters and the design intent, or at least the as-built result, we simply don't know what you've got.

The fact that you say the "knee walls are nailed to joist and rafters" makes me all the more skeptical.

Are the knee walls built with a plate across the rafter bottoms and the joist tops and studs fastened to these plates?

Or is each stud nailed to the side of each rafter and each joist without any plates at all?

What size are the rafters?
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is online now   Reply With Quote
Unread 08-07-2012, 03:37 PM   #8
gbrny
Registered User
 
Join Date: Aug 2012
Posts: 5
Plates are on top and bottom of knee wall.
Short wooden plates are installed to anchor top of knee wall to 2"x8" rafter on a 12/12 pitch roof.

Also, load bearing wall runs the length of room dead center, therefore i'm not too worried about tiles in center of room, i'm worried about the tiles at the base of the knee wall.

I plan on adding another layer of 3/4" plywood screwed to joists. Won't this fact help with joist length deflection as well as between joists? Doesn't this make a "T" configuartion between joist and plywood?

Would ditra help as well? Or is ditra only for side to side movement not up and down?
__________________
Greg
gbrny is offline   Reply With Quote
Unread 08-07-2012, 04:22 PM   #9
cx
Moderator emeritus
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 95,749
Tough to tell without at least a photo, Greg, but from your description I'd say no, your design is not such that the roof rafters are at all helping to support your floor joists. Best case, the knee wall is probably not adding to your joist deflection problem unless you get a wet snow that sticks to even that steep roof. Very high wind loads could also factor in.

Hint: If you'd add a geographic location to your User Profile we'd be able to tell at a glance if that was at all likely.

The support in the center of the span is a positive thing only if the joists are full length from one side of the house to the other and sitting on the support, or if there are two joists, one from each side, and they are properly overlapped and fastened at the center support. Or if the individual joists from each side are attached properly to the sides of the support. Or some such arrangement to prevent any lever action at the center.

Adding another layer of subflooring attached to the joists will not in any meaningful way diminish your joist deflection, especially when installed over only half the span. Adding another layer of subflooring not attached to the joists will help substantially with your between-joist deflection, which is usually the more serious problem for a ceramic tile installation.

Ditra, like any other tiling substrate, depends upon the floor structure already meeting the deflection requirements. It adds no strength to the subfloor.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!

Last edited by cx; 08-07-2012 at 04:27 PM.
cx is online now   Reply With Quote
Reply

Stonetooling.com   Tile-Assn.com   National Gypsum Permabase


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Knee Wall Waterproofing question sck0006 Tile Forum/Advice Board 12 03-12-2012 10:12 AM
tiling a knee wall steve10112 Tile Forum/Advice Board 2 09-09-2007 11:33 PM
3-wall tub w/knee wall - how to tile and top it? biondanonima Tile Forum/Advice Board 6 08-11-2007 04:54 PM
Knee wall question Northwest Tile Guy Professionals' Hangout 6 03-24-2007 06:56 PM
Knee Wall Heights YuHu Tile Forum/Advice Board 9 08-10-2006 07:34 PM


All times are GMT -6. The time now is 10:29 AM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
Copyright 2018 John Bridge & Associates, LLC