Posted by
Message
WaWaWeeWa
Member since Oct 2015
13483 posts

Adding plywood flooring in attic

I want to add some plywood flooring to a walk in attic that already has about 50% of the area floored. I was thinking this would be a easy straightforward project but then I started googling.

Most sources are saying you shouldn’t do this without talking to a structural engineer

Is this necessary? Is there an easier way to determine if my joists can support plywood flooring for light storage? I’m not trying to convert it to living space.

Also, if I have an electrical wire running over a joist can I chisel out a shallow channel to run the wire in so I don’t pinch the wire between the joist and plywood?

The joists are 2x8 spaced 16 inches apart
This post was edited on 1/1 at 7:40 am


gumbo2176
Member since May 2018
11409 posts

I see no reason why 2 x 8 joists spaced at 16 inches apart would not be MORE than sufficient to support a plywood deck.

Besides, those joists going over the tops of walls that divide your living area offer a lot of structural support.

You could chisel down a bit into the joists to get the electrical wire off the top of the joists, but that surely won't be up to code as the joists should have bored through holes to run the wire well below the top surface of the joists.

But if you go the chisel route, put those small metal plates over the area of the wire so you won't accidentally run a screw or nail through the wire.


ETA: If you chose to set the wires below the surface of the joists, I'd suggest not using a chisel to do most of the work. Use a saw to cut the depth, then the chisel to remove the small piece of wood. Too much pounding on the joists could result in cosmetic ceiling damage with nail or screw heads being exposed.
This post was edited on 1/1 at 8:28 am


djangochained
LSU Fan
Gardere
Member since Jul 2013
18335 posts

Yes your good


Replies (0)
Replies (0)
21
WaWaWeeWa
Member since Oct 2015
13483 posts



meeple
USA Fan
Carcassonne
Member since May 2011
7763 posts

Just keep the heavier items like books over walls so the joists do not start to sag.


Replies (0)
Replies (0)
90
keakar
Member since Jan 2017
20603 posts

quote:

Most sources are saying you shouldn’t do this without talking to a structural engineer


maybe if you plan to store engine blocks up there and thousands of pounds of car parts

use 3/4" plywood if you expect to put a lot of heavy stuff in there, otherwise 1/2" is fine for normal storage, and be sure not to cover over any junction boxes so it meets code


Replies (0)
Replies (0)
80
junkfunky
LSU Fan
Member since Jan 2011
31113 posts

How far are the 2x8s spanning? Doubt you'll have an issue but I could tell you how much load they can carry.

Also, I'd recommend 5/8 deck. 1/2 just doesn't feel right especially if you are carrying something heavy.


Weekend Warrior79
LSU Fan
Member since Aug 2014
10870 posts
 Online 

quote:

Also, I'd recommend 5/8 deck. 1/2 just doesn't feel right especially if you are carrying something heavy.

Especially if the previous owner just missed a joist and you walk on it while carrying something large. You won’t go through, but it’ll flex enough to scare the shot out of you making you think you’re going through


Replies (0)
Replies (0)
100
MrLSU
Harvard Fan
Paris, Lake Como, Monaco, Marrero
Member since Jan 2004
21094 posts

I’m so glad you posted this because I was just about to post the same thing.

1.5 inch by 11 inch support beams spaced 14.5 inches apart.

Main support beam is 3 of the 1.5’s those together or roughly 5x 11.

The attic will be used for storage only above a detached garage. What size plywood do I need?


fwtex
Member since Nov 2019
1185 posts

quote:

Also, if I have an electrical wire running over a joist can I chisel out a shallow channel to run the wire in so I don’t pinch the wire between the joist and plywood?


Instead of chiseling a channel add shims on top of the joist to raise the plywood over the wires.


WaWaWeeWa
Member since Oct 2015
13483 posts

quote:

Instead of chiseling a channel add shims on top of the joist to raise the plywood over the wires.


This is exactly what I did. I used 1/2 plywood strips for shims and raised everything up over the wires.

Is that up to code?

Someone mentioned not covering junction boxes. Is there anything else I can’t cover? What about can lights?


Replies (0)
Replies (0)
00
Feelthebarn
Auburn Fan
Lower Alabama
Member since Nov 2012
1733 posts

2x8 on 16 centers is plenty


Popths
LSU Fan
Baton Rouge
Member since Aug 2016
3247 posts

Use screws instead of nails. Banging nails can crack the Sheetrock on your ceiling.


Replies (0)
Replies (0)
200
oldskule
USA Fan
Down South
Member since Mar 2016
8761 posts

I decked a large span over my carport and placed lots of junk up there....

ceiling in carport is now sagging and floating tape on sheetrock joints are failing.....

Be careful about the weight.


junkfunky
LSU Fan
Member since Jan 2011
31113 posts

quote:

Be careful about the weight.


And don't listen to people that say 2x8 @ 16 are fine. If your span is 25' they won't handle any additional load.

My offer still stands to run a check and get the actual allowable load but at least look into the tables or use one of the suppliers calculators. Weyerhauser's Forte is easier to use but Boise's BCCalc seems more accurate and both are free to use.


Replies (0)
Replies (0)
60
EA6B
Navy Fan
TX
Member since Dec 2012
14138 posts

quote:

1.5 inch by 11 inch support beams spaced 14.5 inches apart. Main support beam is 3 of the 1.5’s those together or roughly 5x 11.


In common construction terms what you have are 2x12 joists on 16” centers. You need to know what the un supported span length is. Once you have that you can look it up in a online “joist span table” if it shows it is adequate for 30 lb/sqft live load you are good to go, deck it with 3/4” plywood.

LINK
This post was edited on 1/2 at 1:08 am


tigereye58
LSU Fan
Montana
Member since Jan 2007
2496 posts

Use the span tables. 2x8x16 is dramatically different than 2x8x8.

I ran 2x12 anywhere I wanted to put decking in the attic of my shop. 2x8’s will work but the span makes a difference.


WaWaWeeWa
Member since Oct 2015
13483 posts

It looks like I have 2x8 on 16 and the span is about 19 feet. Yellow pine.

From what I can tell that’s close to the minimum for 20psf which is what is required for attic space that is usable for light storage

Am I doing that right?

What’s weird is that they already had decking laid out and it’s a walk in attic, I just wanted to extend the decking. They also have a water heater sitting up there and bracing to the roof.

Seems like they should have had thicker joists


VABuckeye
Ohio State Fan
Naples, FL
Member since Dec 2007
31550 posts

AKA 2" X 12" and 16" on center.


Replies (0)
Replies (0)
00
CarRamrod
USA Fan
Spurbury, VT
Member since Dec 2006
55379 posts

quote:

Most sources are saying you shouldn’t do this without talking to a structural engineer

they say this because most people are retarded as frick. It is a disclaimer because idiots will flor the attic, then proceed to stack the attic from floor to roof with shit, that COULD over load it.


first pageprev pagePage 1 of 2next pagelast page

Back to top

logoFollow TigerDroppings for LSU Football News
Follow us on Twitter, Facebook and Instagram to get the latest updates on LSU Football and Recruiting.

FacebookTwitterInstagram