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How to Install a Subfloor on Joists

October 13, 2011 |

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We are DIYing our moms a Duplex in Alaska! Check out our progress so far as we owner build a home, step by step. Read the Momplex blog here.

posted by Ana White

Momplex Stats

Money Spent So Far: 
$47,000 + Cost of Property (we haven't spent much since the truck load arrived with weeks of work)
Time Spent So Far: 
920

It has been torture waiting for plywood day! We put the upstairs floor joists up, and I thought the very next day I'd be getting a sun tan on a roof top deck.

Not so much the case ... we built stairs, backfilled, insulated ... just to name a few projects that had to get done as I tried not to glance up at those open floor joists ... and finally it's plywood day. (I'll be blogging about all the other projects we've been up to as well in the next coming bit).

Hooray for plywood day!

How to Install a Subfloor on Joists

Every once in a while, I have been sneaking up to sit on the floor joist, just dreaming of this day! In my mind, there's even a waiter with a tray full of drinks with little umbrellas. We put the floor joists in in this post.

And this is how we lay the subfloor on top of those floor joists ...

How to Install a Subfloor on Joists

On the tops of the floor joists, we measure and mark every 4 feet - this will be the plywood seams. Chalk lines are pulled all the way across all the joist tops at the 4 foot marks so we can check our accuracy with each sheet of plywood being attached to the joists. These chalk lines run the entire depth of the Momplex, perpendicular across each floor joist, every four feet.

The chalk lines serve as guides. When you are going 44 feet wide, if you get off 1/8" here, 1/4" there, a hair over there ... you'd be surprised at how fast that can add up to inches!

How to Install a Subfloor on Joists

For subflooring, you use tongue and groove plywood. The tongue and groove are only along the 8 foot edges. On the four foot edges, your seams will fall on joist tops, so no need for tongue and groove.

But to start off, we will need to remove the tongue so the plywood is tight with the exterior ICF walls.

Pretty simple step here ... I just set my saw blade to the depth of the plywood and ran it down the edge, removing the tongue. Remember, you only do this for the first row of plywood.

How to Install a Subfloor on Joists

Sheets of 3/4" plywood weigh as much as 90 pounds!!! I was so thankful our cousin Justin was here to pack plywood upstairs. We started first with a 1/2 sheet.

Tell me, does anyone else feel like they are getting stretched apart hauling a full sheet of anything? Here's wishing plywood was like 45" wide, or I was like three inches taller.

How to Install a Subfloor on Joists

Subflooring glue is applied to the tops of the joists. The right glue is very important here, it's what keeps your floor from squeaking.

How to Install a Subfloor on Joists

And the plywood is layed on top of the joist

How to Install a Subfloor on Joists

Matching up with the chalk line, reaching the center of the joist. You can see on the non tongue and groove side of the plywood, joints are made in the center of the joists.

How to Install a Subfloor on Joists

We consulted the manufacturer of our floor joists for nailing recommendations. Nails need to be 8d, spaced every 4" and staggered.

How to Install a Subfloor on Joists

We are using ring shank nails, or nails with rings on their shanks. The rings help to keep the nails from easily popping out (creating a potentially squeaky floor). Also, these nails come coated in a glue on the shank, further helping keep the nails nailed down. Nobody likes a nail popping up in the floor!

How to Install a Subfloor on Joists

And then the plywood gets nailed down!

Coming from past experiences of screwing down subfloors, this really felt like we were cheating.

How to Install a Subfloor on Joists

More plywood sheets are nailed down, staggering seams for a stronger fit. When you build, you always stagger. It's what makes a pile of boards and materials into a solid structure. Stagger stagger. We did this by simply starting with a 1/2 sheet of plywood on the first row, followed by a full sheet of plywood on the next row. You guessed it, we'll be back to the half sheet on the next row.

How to Install a Subfloor on Joists

New sheets are carefully pounded in place with a block protecting the open groove side of the plywood. If you did this without a block, it would destroy the groove and make fitting the next row of plywood very difficult.

How to Install a Subfloor on Joists

Just a tiny bit more!

How to Install a Subfloor on Joists

When we got to the stair openings, we kept to the pattern (pretending there is no stair opening) and nailed the subfloor down on the other side.

How to Install a Subfloor on Joists

Then when we went to put the remaining piece in, everything keeps to the pattern, fitting just right, like a perfect puzzle, only the pieces are 48" x 96" and weigh 90 pounds. Not exactly a Melissa and Doug puzzle!

After each sheet of plywood is layed down, I went and marked the open edge, with a mark centered on the open floor joist.  Then I traced a line to the mark I had made on the previous sheet of plywood, making it easy to find the joist and nail the plywood to it.
Then I got in trouble for making bad marks ....
We all chuckled later when we realized I had had some help!
It was getting pretty late when we finally finished up.  My rooftop sun deck fantasy would not come true on this day.
But we are enjoying it now!  The view up there is amazing.  
Maybe we should go up one more level?
Happy Building!
Ana
clips
ferbit's picture

Yay!!!!

This is the part I remember most from my family building a house when I was growing up. As soon as the second floor plywood was done, my dad let us come up and dance around. :) Wonderful photo of you two!!! :)


posted by ferbit | on Thu, 2011-10-13 13:12
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emmarosemc's picture

That looks amazing!!

That looks amazing!!

posted by emmarosemc | on Thu, 2011-10-13 13:13

Great Job

Wow, not many can make carharts look that gorgeous!Beautiful picture of you and your daughter. Great job with the house, it's fun to watch go up! Now if only my husband trusted me with a nail gun...

posted by Guest (not verified) | on Thu, 2011-10-13 13:23

details, details

Ana - thank you so much for explaining things in both a basic way, and also with more details (spec sheets,etc).

My husband and I do our own trim work (crown moulding, baseboard, etc), have installed cabinets, laid tile, hung drywall (but hired out the mudding/taping, thank you very much!), and designed our new 16x20 deck to exceed code.

Many of your readers (like us!)will never tackle a project like yours, or even smaller ones like ours, but your explanations will help them have an understanding of the processes involved that will really help make them better consumers/customers when it comes to specing/hiring for remodeling projects.

Building codes are not just "suggestions". If anyone out there ever has a contractor suggest, "You don't really need that glue under the subfloor" or something else like that - you've got the wrong crew on your project!

Love, love, love your blog, & the new photo of you & Grace)!
Sara

posted by Sara (not verified) | on Thu, 2011-10-13 13:31
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loniwolfe's picture

That photo of you 2 is

That photo of you 2 is beautiful! And Yay! for a subfloor!

posted by loniwolfe | on Thu, 2011-10-13 13:31

Only you could look so good

Only you could look so good after a long day building a house!

posted by Nona (not verified) | on Thu, 2011-10-13 15:42

The best part of going on

The best part of going on vacation tomorrow, besides the actual vacation, will be that I'll have a few Momplex posts to come home to. :) Congratulations on getting to the second floor!

posted by Jenn Hoff (not verified) | on Fri, 2011-10-14 00:09

Momplex Details...

You rock! I love watching this process! Thank you!

posted by Robbi Montgomery (not verified) | on Fri, 2011-10-14 09:23

Carhartts are the new fashion accessory! Who knew?!

That is a gorgeous pic of you and the little one, Ana!

Thanks for keeping us updated. Someday DH and I will be building a house of our own and your posts do so much to keep us motivated and feeling like we really can do this! We're not afraid of some hard work, but we don't want to build something that will come down around our ears at the first summer breeze. :-0

Yay for the new sundeck! You guys are making great progress.

posted by Cindy from Indiana (not verified) | on Sat, 2011-10-15 11:29
clips
Ana White's picture

Thanks everyone! @ Cindy

Thanks everyone! @ Cindy LOL!!! You can't look good if you are freezing your bum off! Love my Carhartts so much, function beats fashion any day! You CAN build your own home, and my bet is it will be BETTER than what contractors would turn out for you!

posted by Ana White | on Sat, 2011-10-15 12:31

you are such an inspiration .. just amazing

I enjoy reading how you are coming along with your mom plex..... you are such an inspiration
.. Thank you for sharing....
and what a beautiful picture of you and your sweet baby girl... you both are so beautiful inside and out...
thank you again for sharing all this and all that you do... I know you are so busy...
Bless you ....

posted by Alanna B (not verified) | on Thu, 2012-03-15 21:19

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