# Attic Flooring Questions



## 1victorianfarmhouse (Feb 4, 2012)

Im in the process of planning out completion of the attic floor in my 1895 house.  Right now it has joists with several areas of plywood or fiberboard nailed in place for access to some areas.  Nothing is consistent.  The rest of the floors in the house have the original wooden planks, with decorative wooden flooring on them, usually oak and birch.   

I am wondering what is considered the proper base material and thickness, keeping in mind that a another layer of wood flooring will eventually be placed on it.  As this is the third floor, am I wrong to be keeping in mind the weight of the various thicknesses of flooring as well?

Thanks!


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## Dionysia (Feb 4, 2012)

What size are your joists, and how long is the span?


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## BridgeMan (Feb 4, 2012)

Dionysia, don't forget to ask what the joist spacing is too, before performing your calculations!


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## 1victorianfarmhouse (Feb 4, 2012)

Attic  Joists
1.75" x 5.5" actual
length varies; many are hidden by insulation. 6, 7 + feet

Spacing is 14" (side to side, not center to center)

Attic max Width
362.5 inches
30' +

Attic max Length
402"
33.5'

Another factor is that it might be pretty tough to get anything larger than 4' x 4' sheet of plywood into into the stairwell because of a sharp turn into the stairwell before going up the stairs.  Gotta love these old Victorian houses and their quirky design!

Thanks,

vince


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## Dionysia (Feb 5, 2012)

[blushes] I am impressed that you think I could do the calculations, Bridgeman! As you know, we are dealing with similar issues on our infamous moneypit...


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## BridgeMan (Feb 6, 2012)

Dionysia, I've heard they sell face make-up that should easily cover the blushing.  So go ahead, and calculate away!

But to answer the OP's attic flooring question, if the joists are only 2 x 6s, they obviously have some support from load-bearing interior walls in the living space below.  I'd suggest using 3/4" T&G for a uniform subfloor, glued and screwed, followed by a finished floor of choice.  By far, the heaviest loading the attic is likely to see will be from interior walls, furniture, storage items and people.  Total flooring/support deadload is usually computed at around 10 PSF (3/4" plywood weighs just 3 PSF), while other applied loads are usually figured at 40 or even 50 PSF, total.  Heavier design loads (80 PSF) are usually used for exclusive storage areas.


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## 1victorianfarmhouse (Feb 8, 2012)

Thank you. Mr Bridge.

The attic does indeed have an I-shaped load bearing interior wall underneath it that extends to the outer walls.  The flooring in the other two floors is also 3/4" T&G.  I've also thought it was be good to screw it down, less plaster dislodging impact shock than nails and better holding power.  Any preferences on glue type or brand?

Thanks,

vince


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## BridgeMan (Feb 8, 2012)

You can buy adhesive made exclusively for subflooring, in the large (30 oz. tubes) at commercial construction supply places.  If it weren't so cold outside, and late in the early AM, I'd walk out to the shop to tell you what I've been using.  It's probably a tad better than Liquid Nails, which is available in all the big box stores, in 11 oz. tubes.


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## joecaption (Feb 17, 2012)

The spans may be to long for that width of joist. 
Very likly to crack the plaster below.
http://www.awc.org/calculators/span...d=10&submit=Calculate+Maximum+Horizontal+Span


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## 1victorianfarmhouse (Feb 17, 2012)

Thanks, Joe.  That is very interesting, want to see how it computes for the distances from the load bearing walls.  I wonder if there are ways to reinforce the joists or other ways to stiffen the floor.


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## BridgeMan (Feb 18, 2012)

Don't forget to throw in an "inverted reduction factor" if the joists are continuous over the interior load-bearing walls, vs. just simple span.  Not likely they are, but one never knows until looking.  There were a lot of old growth, large trees being harvested when the place was built.  

A rough rule of thumb is the inverse of 80% (0.8), or 1.25.


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## kalawn (Feb 27, 2012)

My experience with older homes like yours is that they used 2x6 ceiling house up to 18 +feet. I have done a couple things to stiffen the floor up to usable living space loads. 1-- Build a knee wall nailing the studs to the side of the rafters down to the side of the ceiling joist. 2--widen the ceiling hoist by laying another member on top of the existing hoist and gusset together with plywood. Example, stand on edge a 2x6 on top of the existing 2x6. Rip plywood strips 10 3/4" apply glue to the sides of the 2x6s and heavily nail the plywood to both 2x6s. It will pass code.


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## nealtw (Feb 27, 2012)

kalawn; When you have doubled the 2x6 like this do you stop at the knee wall or do you go full length.
BTW. welcome


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## kalawn (Feb 28, 2012)

You go the full length so you have bearing on the walls. The knee wall is not required if you do the hoist this way.


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## GBR (Mar 3, 2012)

You may have to completely rebuild the stairway though....
Adding 2x4's to the bottom of joist- similar to an "I" beam, steel strapping wrapped around the joist, simply doubling (sistering) the joist, plywood &#8220;T&#8221; floor stiffening, LVL&#8217;s sistered, depending on purpose and application involved. http://www.finehomebuilding.com/PDF/Free/021184090.pdf
http://boards.hgtvremodels.com/eve/forums/a/tpc/f/4891014781/m/9591011862


Be sure to glue the groove of the T&G for maximum strength and correct application as per manufacturer of the sub-flooring.

Gary


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## 1victorianfarmhouse (Mar 4, 2012)

Wow, lots of great info, it takes a while for a newbie like me to absorb it all and fully understand it.

Thanks Kalawn for jumping in with great info on your first posts!

This is what I like about this forum, not only are there a number of experienced people with knowledgeable answers, but others chime in with more than one correct way to approach the issue.

vince


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