• Important! If you attempt to register and do not get an email within 5 minutes please check your spam box. This is especially true for Microsoft owned domains like Hotmail, Outlook, and Live. If these do not work please consider Gmail. Yahoo, or even AOL email which works fine.

Attic Floor -- Plywood question

FinlayZJ

Doing hoodrat things
VIP
I'm guessing your joists are 2x4's? The best way would be roll out batt insulation in the current joists, and then build the new floor the same depth going perpendicular again with batt insulation. Unfaced would be okay. This would be the best in terms of creating a great thermal barrier. Blow-in insulation settles over time and loses some of its effectiveness.

Edit: I used 3/4" MDF for my floor. HD had it on sale and I bought some damaged pieces and it has held up fine.
 

synonymous

Better than you.
VIP
Edit: I used 3/4" MDF for my floor. HD had it on sale and I bought some damaged pieces and it has held up fine.
UGH. They had laid 1/2" MDF on top of 3/4" plywood for the subfloors in the kitchen and baths of htis house. It did NOT hold up well.
 

synonymous

Better than you.
VIP
Is there some way to keep the 12 inches of blown-in insulation and still put down the plywood without having to do rather ridiculous things like trying to put 2x10's on top of the current joists?
Sister the current truss with 2x12s, glue and nails for the sistering.
 

synonymous

Better than you.
VIP
The best way to do it is cut out everything and lay it the opposite direction with 4x6s and blocking all over the place.



<


 
Does sistering mean fastening to the side of the 2x4 so that I've got a total of 12 inches of height?
Yes. One thing to be careful of is extra weight. By the time you add all those new joists and the plywood, that is a lot of weight, and if your current joists/rafters/trusses are really 2x4s, you might get into trouble. You just need to make sure that your new sistered joists are supported propertly.
 

synonymous

Better than you.
VIP
Yes. One thing to be careful of is extra weight. By the time you add all those new joists and the plywood, that is a lot of weight, and if your current joists/rafters/trusses are really 2x4s, you might get into trouble. You just need to make sure that your new sistered joists are supported propertly.
They'll be sitting on the plates of load bearing walls. The 2x12s won't deflect anywhere near what 2x4s do, so he'll probably be good. I've found blocking goes a rediculously long way to increasing rigidity as well for little added weight.
 
They'll be sitting on the plates of load bearing walls. The 2x12s won't deflect anywhere near what 2x4s do, so he'll probably be good. I've found blocking goes a rediculously long way to increasing rigidity as well for little added weight.
They *should* be sitting on the plates. But if he really does have 2x4s, and depending on the angle of the roof, there probably wont be enough space to fully sister the 2x12 in there. The ends would have to be trimmed at an angle to sit down there nicely, which would work fine. Just something to be aware of.
 

Wharf Rat

Ooomph Ooomph
VIP
Birch and Oak in 3/4" will likely be more of a cabinet grade plywood and cost more. The regular old stuff is either pine or fir, I dont remember.
Thx. Seems like Lowe's only has birch or Oak in 3/4 at my location. Will look elsewhere.

I hate HD.
 

synonymous

Better than you.
VIP
Birch and Oak in 3/4" will likely be more of a cabinet grade plywood and cost more. The regular old stuff is either pine or fir, I dont remember.
They also use a different glue in them. They are more pliable than T&G flooring plywood. I used it for my wainstcoating, but moreso that it was paint grade.
 

synonymous

Better than you.
VIP
HD is junque. Unfortunately, Lowes is like 4 times the distance or more away. Lowes costs more as well, but I make the trip for certain items.
 

Wharf Rat

Ooomph Ooomph
VIP
HD is junque. Unfortunately, Lowes is like 4 times the distance or more away. Lowes costs more as well, but I make the trip for certain items.
Sometimes it actually costs less. Usually they have decent sales around me.

Picked up 6 arbor vitae for like $30 a piece there, big ones. They were around $44 @ the homie depot.
 

Wharf Rat

Ooomph Ooomph
VIP
Well it doesn't look like 2 X 2 furring strips are going to be big enough. Here are some pics to show you what I am dealing with here. Taken last night.



Pull Down





Once up there, view towards rear of house. Plywood is just sitting on insulation now.








Looking toward side of house









Looking towards front of house...I was not going to touch this part.





What do y'all think I should do with this as far as spacing the floor up so that it's not sitting on insulation?
 
Top