# Non-standard spacing in between floor joists?



## SBay_ecologist (Apr 8, 2013)

Hello All:

If I were to put my joists 17" apart center-to-center, leaving a space of 15.5"-wide, would there be a problem? 

Thanks,


Al
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Here is the background:


I am planning to build a 12x10 shed at the back of my home.
I am planning to insulate it on all sides, at the top and bottom.
I understand that floor joist usually put 16" apart center-to-center. 
This leaves 14.5" in between the joists.
A standard-size fiberglass insulation pad measuring 15.5" wide drops in there nice and snug.


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## nealtw (Apr 8, 2013)

Insulation is ment to be a snug fit in 14 1/2" space. If you are using plywood sheeting, you will waist more than you can save with insulation. Don't forget to lose 3/4" to make your layout work for sheeting.


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## bud16415 (Apr 9, 2013)

In my 1880 farm house the spacing of things was done by the length of the builders hammer. There wasn&#8217;t any standard size materials everything was rough sawed to random length so this method worked out ok. Many of the Amish around here still build this way. 

With 48x96 sheet goods they factor into thirds with 16 and half with 24. And as nealtw mentioned all the rest of the products out there are made to work around these two spacing.


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## SBay_ecologist (Apr 9, 2013)

nealtw said:


> Insulation is ment to be a snug fit in 14 1/2" space. If you are using plywood sheeting, you will waist more than you can save with insulation. Don't forget to lose 3/4" to make your layout work for sheeting.



Thanks for writing. Not being in the trade I am not clear on what you wrote and have some questions.

What do you mean by "you will waist more than you can save with insulation"? Is 3/4" plywood a good insulator therefore I do not need any fiberglass insulation underneath? (My house does not have any insulation underneath, and the wood floors are cold to my barefeet, even though here in the SF Bay Are we have mild winters --some say "no winters"  )

What do you mean by "lose 3/4" to make your layout work for sheeting"? Allow for 3/4" thickness in my plans? If this is the case, since I am essentially building a 10x12 platform, a thicker or thinner platform will not really matter. I am adopting the following plan: http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH09JAU_DOLSHE_06.JPG "

Al


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## nealtw (Apr 9, 2013)

SBay: Sorry I wasn't more clear. If you change from 16" on center you will waist plywood as the end will not land on framing and would have to be cut. If you are heating or cooling insulating the floor is a good idea. You do want air below the insulation so some kind of wire mesh should be facing the ground to keep critters out of the insulation. What we do we a shed like yours is place the timbers in the ground where you need them straight and level, they will absorb moisture so you want a 6 mil poly to protect the rest of the framing from moisture Then we build the floor beside it, make sure it's square and attach wire mesh and then flip it over on top of the timbers. Attach it to 1 beam with treated nails or screws ( the treatment in the wood eats reguler nails and screws).
Check your frame for square and then attach to the other beam, now your ready for insulation. ( Measure on angle from corner to corner and compare to oposite corners, adjust until both measure the same)
Keep in mind that lumber is not cut to length except for studs so all framing bits and peices have to be cut to length ) a 12ft 2x6 will be 1/4 to 3/4" to long.
Dropping 3/4" is just a term used to make sure plywood fits the layout. So when you lay out the endframing members for floors and walls, put the two peices together and hook your tape to one end and mark it at 15 1/4, 31 1/4 , 47 1/4 and so on, this will make the 96" plywood land half way on the joist or stud.
For floor plywood, houses are built with 5/8 tongue and grove, 5/8 should be enough for your floor and tongue and groove is a must. There will be tips for that too.


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## Mightygiving (Apr 9, 2013)

SBay_ecologist said:


> What do you mean by "lose 3/4" to make your layout work for sheeting"? Allow for 3/4" thickness in my plans? If this is the case, since I am essentially building a 10x12 platform, a thicker or thinner platform will not really matter. I am adopting the following plan: http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH09JAU_DOLSHE_06.JPG "
> 
> Al


 
From looking at the floor detail in your image and although you are making the building 12' x 10' vice  the 12' x 8' depicted, the drawing clearly (upon enlarging), shows 24" oc as the joist spacing, which will allow for standard 24" wide insulation to be installed. 

That said, You are adding confusion by making a correlation for interior insulation standards which would be used for an occupied dwelling when you talk about how cold your floors get in the house, where this is appearantly an exterior play house/ storage shed application which aren't ment to retain heat the way occupied dwellings are. J/s


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## GBR (Apr 14, 2013)

As said, insulating the playhouse would do little unless adding a heat source, though reduce solar gain somewhat (walls/roof).  If trying to get a stiffer floor without keeping the same thickness sub-floor for the span, you could space 19.2"(look for black arrows on tape measure) on center (engineered wood standard) and use 19-1/4" f.g. batts; http://www.google.com/url?sa=t&rct=...TcE6slWItX4iSrQ&bvm=bv.45175338,d.cGE&cad=rja
Keeping in mind, any gaps around the insulation will lead to reduced R-values, as will leaving the backside open to exterior air movement, critters, and vermin. I would check with your local building department if the shed is even approved, before you start. Your house floor insulation is code required (minimum), R-19 for your location; cities below the map, http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_11_par002.htm

http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_11_sec002.htm

Gary


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