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Plywood flooring in Attic and Insulation

T

Turin39789

Lifer
The attic in our new to us 1956 home has a decent amount of insulation. The joists are 2x8, and there are two rooms in the attic with hip walls. We'd like to throw some plywood in the remaining attic space to use for storage, right now one section has a loose insulation about halfway up the joists, the other side has rolled r19 pink stuff along the joists, sometimes over the top of it.

I'd like to just get some plywood in there now, but I'm worried that it will decrease the effectiveness of the insulation we do have. I also need to figure otu if I'm going to raise the plywood an inch or so for the wires to run across the joists or if we're going to drill holes and re pull the wires.

Any advice?
 
Thanks for the help guys.

Brick Cape Cod 1 and 1/2 story home.


Rolled around in the insulation today. There are no soffit vents on the house, actually no soffit. So two large triangle gable vents at the ends of the main ridgeline and a round one halfway up the attic space on a front facing extension.

It appears that there are fiberglass batts on the sides of knee walls and pushed up into the area above part of the top of the finished area upstairs. There were a few spaces where the insulation was not stuffed into the upper cavity, and I started to add some here but I'm thinking they need to stay open to allow air to get up into the peak area between the two gable end vents.

I'm going to try to use 2x4s as furring to place on top of the 2x6 joists leaving me with 9 inches of space to blow in cellulose insulation below the plywood I will be adding to the attic. I'll probably just be adding 4-5 sheets of plywood leaving most of the space empty but giving us enough room to stash the christmas crap and old boxes of junk.

I noticed that on the half of our front wall where our roofed porch is, there appears to be no top plate to that wall. I can see the wall cavity, and through it to the area inside the porch roof. I'm tempted to check out the electrical in that area and make sure there are good boxes behind the outlets and then spraying some cellulose down into that area and then adding a top plate. Right now that front wall, and probably many more don't have insulation at all. Right now where the wall meets the joists, there were paper bags to keep the original mineral wool insulation from falling into the walls.

The attic doesn't appear to have ideal ventilation, but the roof has been on for a good long time and it doesn't appear to be suffering. My concern right now is to try to improve or at least not screw up the ventilation anymore than it currently is. Also to get the electric cleaned up and checked out(thats what brothers are for) as right now the outlets upstairs in the kneewalls are exposed without boxes, and I need to get that cleaned up before the insulation goes in.

I thought this was supposed to be a simple project?
 
For the plywood, use at least 5/8 TiG. For ventilation between the roof joists, they make plastic panels with corrugated air vents that are put in place before installing insulation over them.
 
I would try to avoid compressing insulation. If you want it for easier movement inside the attic I find crawling using two broom sticks works well, and eye the joist location by looking at the above rafter, as they are nailed to the joists so you know you'll be on the joists when you put your knee/hands down. This becomes trickier as the layers of insulation increase.
 
Turin39789 said:
The attic in our new to us 1956 home has a decent amount of insulation. The joists are 2x8, and there are two rooms in the attic with hip walls. We'd like to throw some plywood in the remaining attic space to use for storage, right now one section has a loose insulation about halfway up the joists, the other side has rolled r19 pink stuff along the joists, sometimes over the top of it.

I'd like to just get some plywood in there now, but I'm worried that it will decrease the effectiveness of the insulation we do have. I also need to figure otu if I'm going to raise the plywood an inch or so for the wires to run across the joists or if we're going to drill holes and re pull the wires.

Any advice?
Click to expand...

If you drill holes in joists, don't drill any in the middle 1/3 of the span.
 
Don't add a top plate there, it was not needed then and it would serve no purpose now.
cut some batts into 1 foot chunks and tuck those in to insulate that area. If you changed your mind after blowing in stuff over the porch you'd have a fun time getting wire back in there.
 
RedSquirrel said:
I would try to avoid compressing insulation. If you want it for easier movement inside the attic I find crawling using two broom sticks works well, and eye the joist location by looking at the above rafter, as they are nailed to the joists so you know you'll be on the joists when you put your knee/hands down. This becomes trickier as the layers of insulation increase.
Click to expand...

The goal is to raise the plywood so that it is not compressing the insulation, also to use it as storage space and not just for movement. The joists will wind up covered by the new insulation, so I am tempted to add more wood as a walkway for any future work, but I don't think I will go overboard.

Ozoned said:
If you drill holes in joists, don't drill any in the middle 1/3 of the span.
Click to expand...

I'm listening - whats the story there? I was thinking about just coming in at an angle with some screws to attach the platform to the joists. Alternatly I was thinking about finding those metal connecters(I don't know the name) that would put a nail or screw horizontally into the joists and another set horizontally into the 2x4's.
 
ozoned was referring to drilling holes through the joists for the electrical wiring. a 3/4" hole in the wrong place can significantly reduce the strength of the member.
I'd rip some furring and nail or screw it down, with breaks in it for the wires. Blow in any additional insulation and toss in your planking. That is definitely more KISS than pulling wires out of boxes to re-do them.
The golden rule of home projects is, you touch it plan on replacing ALL of it. Better to leave it alone😉
 
skyking said:
ozoned was referring to drilling holes through the joists for the electrical wiring. a 3/4" hole in the wrong place can significantly reduce the strength of the member.
I'd rip some furring and nail or screw it down, with breaks in it for the wires. Blow in any additional insulation and toss in your planking. That is definitely more KISS than pulling wires out of boxes to re-do them.
The golden rule of home projects is, you touch it plan on replacing ALL of it. Better to leave it alone😉
Click to expand...

Yeah I try to watch out where I put my holes when doing electrical, data, etc. My rule of thumb is keep electrical in the middle of the joists and data just below using eye screws and strapping. If an electrical wire needs to go perpendicular I look around if there is existing holes I can reuse and use those.
 
RedSquirrel said:
Yeah I try to watch out where I put my holes when doing electrical, data, etc. My rule of thumb is keep electrical in the middle of the joists and data just below using eye screws and strapping. If an electrical wire needs to go perpendicular I look around if there is existing holes I can reuse and use those.
Click to expand...

Gotcha. No holes in the joists as of now, planning on leaving the wires above the joists by using a few lengths of 2x4 screwed to the top of the joists to raise the plywood and leave plenty of space for wires to run. Planning on building a border around the plywood a few inches tall to keep the insulation from drifting onto it and to keep any boxes from slipping off the edge.
 
Expose wiring using BX, conduit, tray, or simply tack the wiring/data since it is only a storage space.
 
iGas said:
Expose wiring using BX, conduit, tray, or simply tack the wiring/data since it is only a storage space.
Click to expand...

It's currently in a metal spiral sheath I don't recognize, but again no boxes on the outlets and I noticed one of them have old wires with cloth wrap going to them.

Thankfully my brother is an electrician, usually commercial but I'm going to drag him over next weekend to clean it up. Want to get that work done before I go spraying insulation above the joists.

Now officially using ATOT as my blog/project record/scratchpad. Currently 67-70 downstairs, 62 upstairs in the living space, 42 in the attic and 31 outside. Thank you $1.50 lowes thermostat with a sunflower print.
 
I need to blow insulation into the attic over my garage then lay plywood down for storage. My dammed 2 car garage is so full I can't get a single car into it...much of it is my wife's x-mas stuff...

Time for another huge garage sale...
 
Where do you live? Here in Michigan R49 is the standard now for attic insulation. Loose fill cellulose would need 15 inches to get that.

You'll need good ventilation to keep the insulation from becoming damp. The only way to do that is with some sort of air intake. The cheapest way is installing a drip edge to the roof that has accomidation for air intake. However, a backed up gutter and water will pour into your attic. The better way is with a vent under the second course of shingles. This requires re-shingling that course. It's not as cheap and there will be a difference in shade to that course.

EDIT: btw that plywood will actually add to the insulation as long as you don't compress the old insulation.
 
I did something similar in our attic just for storage. As it wasn't for heavy use I just added some high to the joists by ripping 2x4s down the middle and screwing them on top of the joists. I could leave gaps where the wires ran as I never planned to chage any of the existing wire. I laid batts down #.5 ' unfaced on top of the existing stuff and that brought it up to the hieght I had. I laid down plywood and it has been good enought for storage and the extra batting has helped. There is a lot of moisture that evaoprates out from time to time and so everytrhing we store I try to put in totes. Between the lack of heat and the softette and end vents there is a lot of temp and humiduty changes.
 
Squisher said:
Where do you live? Here in Michigan R49 is the standard now for attic insulation. Loose fill cellulose would need 15 inches to get that.

You'll need good ventilation to keep the insulation from becoming damp. The only way to do that is with some sort of air intake. The cheapest way is installing a drip edge to the roof that has accomidation for air intake. However, a backed up gutter and water will pour into your attic. The better way is with a vent under the second course of shingles. This requires re-shingling that course. It's not as cheap and there will be a difference in shade to that course.

EDIT: btw that plywood will actually add to the insulation as long as you don't compress the old insulation.
Click to expand...
New vents can be cut into the roof with out the need to re roofing. Vent can also be install in the soffit, or gable ends.
 
iGas said:
New vents can be cut into the roof with out the need to re roofing. Vent can also be install in the soffit, or gable ends.
Click to expand...

I assume you're talking about eyebrow vents. The ones I was talking about go under a course of shingles. You have to peel back the shingles and run a circular saw through the decking to cut a 1" channel. I doubt many shingles will survive this peeling.

http://www.airvent.com/homeowner/products/intake-theedge.shtml

Like I said, he could install a drip edge vent, but they can have problems with water infiltration.

http://www.airvent.com/homeowner/products/intake-ventedDE.shtml
 
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