Modern Trus Joists

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Old 03-02-07, 09:53 AM
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Modern Trus Joists

I am planning on placing 3/4 oak strip flooring in my townhome. I have an open web trus joists system, where they are for the most part 24" between on center, above that is 3/4 tung and groove subflooring. This floor system has move flex then traditional joists.

Are there any special preparation that is needed?
 
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Old 03-05-07, 09:01 PM
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Basically I am worried about the movement or deflection of the subfloor. One could call my floor a little bouncy. I don't what the hardwood's nails to loosen or anything. The only thing I could really do is to add another layer of plywood.

I was looking at my sisters new house. They have engineered joists with the partical board stuff between 2 2x3's that are 24" appart on center with 3/4 partical board. They have Bruce installed above that. That floor feels very firm. Ofcourse their carpeted areas feel firmer them mine too, but I only have sub and no underlayement unlike them.

Just trying to make sure my floor is strong enough, so the hard wood doesn't fall apart!

Thank!
 
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Old 03-07-07, 09:59 AM
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Man, I guess not may poeple have worked with the type of structure. That or my title sucks because I miss spelled truss must be the reason I am not getting a response
 
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Old 03-11-07, 08:45 PM
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I'm not the expert, but I found a deflection calculator online last year, before doing my ceramic tile. You provide details, and it tells you what kind of flooring it can support (mostly tells you what size ceramic/marble/slate you can support, but mentions hardwood in the notes). I have engineered joists, and it's held my tile incredibly well (no cracks, grout problems, etc.). I don't think I've ever seen the type you have.

You also didn't provide details of the subfloor type - tongue and groove can be cdx, osb, etc. A pic of that joist might help folks too... but like you said, folks may not be familiar with this type of structure, and therefore may not be able to help.

My 2 cents (and worth less - I'm still preparing for my first hardwood install, but I can at least offer some comfort.
 
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Old 03-15-07, 02:00 PM
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I have the same type of engineered joists as you... and they are also spaced at 24" OC .. OSB subfloor on time. I just put down ~800' of engineered hardwood and i wish I put down a layer of plywood to make the floors stiffer, but that would have been a lot of work. My first section of flooring I put the staples every 6" or so, but soon found out that there was a lot of creaking and popping I finished the other 80% of the job with spacing the staples about 1.5-2" apart with much better results... hardly any popping there.

Here's what my joists look like:

http://photos.graeme.org/_/cimg!0/28qp8p86itw5c.jpeg
 
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Old 03-16-07, 08:22 AM
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Smile

Originally Posted by boomertsfx View Post
I have the same type of engineered joists as you... and they are also spaced at 24" OC .. OSB subfloor on time. I just put down ~800' of engineered hardwood and i wish I put down a layer of plywood to make the floors stiffer, but that would have been a lot of work. My first section of flooring I put the staples every 6" or so, but soon found out that there was a lot of creaking and popping I finished the other 80% of the job with spacing the staples about 1.5-2" apart with much better results... hardly any popping there.

Here's what my joists look like:

http://photos.graeme.org/_/cimg!0/28qp8p86itw5c.jpeg
Those look like the trusses I have! You don't say what thinkness your engineered hardwood is? Not the distance they span where you layed the floor. That may make some difference in the feel and durability?

In my living room and dinning room the span is only about 10 feet. I am thinking that is should be ok there, but unstairs it's closer to 20 feet, I may install the plywood up there.


I just did some reading on the different types of underlayment. In my previous post, the stuff at my sister's place is OSB not partile board.

My subflooring is plywood. I am not sure if it's CDX or exterior or grade or what. For the most part it looks in good condition, but in some places the layers are alittle flaky.
 
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Old 03-19-07, 07:50 AM
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Originally Posted by fumoffu View Post
Those look like the trusses I have! You don't say what thinkness your engineered hardwood is? Not the distance they span where you layed the floor. That may make some difference in the feel and durability?

In my living room and dinning room the span is only about 10 feet. I am thinking that is should be ok there, but unstairs it's closer to 20 feet, I may install the plywood up there.


I just did some reading on the different types of underlayment. In my previous post, the stuff at my sister's place is OSB not partile board.

My subflooring is plywood. I am not sure if it's CDX or exterior or grade or what. For the most part it looks in good condition, but in some places the layers are alittle flaky.
Thickness is 3/8" engineered, running parallel to the joists (yeah, I know its not recommended). I would definitely put plywood down, as my floors seem to flex a lot (I have a projector mounted on ceiling downstairs and when people walk, the image moves quite a bit...)
 
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Old 03-19-07, 09:29 AM
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You need a minimum of ½" plywood underlayment, installed before the flooring can be installed. That floor system does not meet the requirements. I have started to see this in a lot of new construction homes. I shake my head, in disgust! I'm losing a lot of bids, because someone will come in and do it without the additional plywood, and come in a much lower bid. I then get the call for the inspection!!
 
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Old 03-19-07, 12:24 PM
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Red face

Thank you so much for giving me your expert advice!

I realize that my house was built to meet and not exceed code. It's minimal.


I just found this link the other day, indicating NOFMA requirements.

http://www.gp.com/build/DocumentViewer.aspx?repository=BP&elementid=3201


It does indicate that my subfloor is suffficient.



But I think what it theorectically sufficient, and what feels bouncy are different. I am not leaning towards the safe side and just adding plywood everywhere. Just going to make some transitions more difficult!
 
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Old 03-19-07, 12:27 PM
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Originally Posted by boomertsfx View Post
Thickness is 3/8" engineered, running parallel to the joists (yeah, I know its not recommended). I would definitely put plywood down, as my floors seem to flex a lot (I have a projector mounted on ceiling downstairs and when people walk, the image moves quite a bit...)
eck! Parallel to the joists is even more problematic. Good luck with the flooring. I have been thinking (actuallly dreaming ) about getting a projector too, never thought about the vibration problem.
 
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Old 03-19-07, 03:34 PM
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http://www.gp.com/build/DocumentViewer.aspx?repository=BP&elementid=3201

The only thing it says about NOFMA is to follow NOFMA recommendations.

I suggest researching the NOFM website. You will see they call for more plywood over 19.8 joist centers, or greater. Then read what needs to happen if you want to lay with the joists, instead of across them.
 
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Old 03-19-07, 06:33 PM
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Originally Posted by Carpets Done Wright View Post
http://www.gp.com/build/DocumentViewer.aspx?repository=BP&elementid=3201

The only thing it says about NOFMA is to follow NOFMA recommendations.

I suggest researching the NOFM website. You will see they call for more plywood over 19.8 joist centers, or greater. Then read what needs to happen if you want to lay with the joists, instead of across them.
The GP article indicated the following tucked away in a foot note:
"When wood structural panels are used for subfloors under hardwood flooring, the NOFMA recommends minimum 19/32-inch plywood (Span Rating 40/20 or 20 oc), or 23/32-inch OSB (or COM-PLY; Span Rating 48/24 or 24 oc). Thicker panels with a higher Span Rating also may used."

From the NOFMA website:
"Q. Can I install hardwood flooring on wood joists systems with other than 16" on center spacing?
A. NOFMA’s subfloor tests (1992) concluded that good performance of 3/4" thick strip and plank flooring could be obtained with 16" on center spacing and proper subflooring, see NOFMA’s Installing Hardwood Flooring at www.nofma.org. Today, with “Engineered Joists and Trusses,” spans and spacing are often encountered which are longer and wider than with the solid wood members previously tested. Even though these systems are properly engineered for loads encountered, more deflection along the length of the span and across the spacing is also often encountered.
3/4" thick hardwood flooring can be installed over these properly engineered systems, but the expected “in use performance" of the flooring may suffer. The added movement may influence the flooring to have more than expected creaking and cracking between strips. Also, as pieces flex and move against each other, surface finishes may be stressed and show whitening along edges. These possible results most often should be noted to the end user.

Comparable performance of these floors to tested systems may require an additional layer of subfloor material to stiffen the system and/or stiffer joists or trusses."

So they recommend it but then say it may suck.

I am not interesting in running the boards parallel.
 
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