Correct plywood for making walkway in attic?

[AcidWater]

Want to make a 2' walkway so I don't have to balance on the joists when I inspect my attic.
Could create some storage space as well.
5/8" thick enough?
What sort of spec do I need, for least cost but not going to degrade?

Oh, and is there any reason I can't lay fiberglass batting on top of it to keep the R value up? Walking on it once a year should be OK.

 

[Reach4]

5/8" thick enough?

1/2 plywood or OSB should be enough In my non-pro opinion. Plywood is lighter to carry, which is good.

I would not feel right about walking on the fiberglass, but for all I know, it could be ok. Some people extend the wood up on 2x2s across the rafters to clear insulation, but care would be needed to prevent that from slipping.

If you have fiberglass, take care to not let any particle get in your eyes.

 

[Sponsor]

 

[Dana]

If you weigh 300 lbs and the joists are 24" o.c. half-inch CDX isn't going to cut it. 23/32 OSB sub-flooring ripped to catwalk width should do it.

Walking on fiberglass is going to create performance-robbing compressions, and will move the batts creating even worse performance degradation when the edges no longer abut one another.

Using blown cellulose (preferred) instead of batts wouldn't have the edge to edge separation, but would still have the footstep compression problem. If you know what you want the final depth to be, set the bottom of the catwalk at that depth, using it as the local depth gauge.Install other depth marker at least every 5' in all directions and rake the cellulose level as you go.) Cellulose is far more air-retardent than fiberglass, and it's opaque to infra-red, unlike fiberglass where under a hot roof deck the fiberglass an inch below the top can be hotter than the attic air. Open blown cellulose is a fairly easy DIY, and most box-stores throw in a day's blower rental with a minimum purchase.

With ANY attic insulation project an all-important first step is to air seal the ceiling plane below at every electrical, plumbing, flue, and duct penetration. If conditioned air is seeping into the attic in winter it can condense it's moisture out in the cooler layers of the insulation sometimes to the point of dripping through onto the ceiling, but it also increases the moisture content of the wood in the attic. Are there any signs of condensation moisture damage or mold on the rafters/joists or roof sheathing? Air sealing prevents this, and also prevents the convective loss of heat out of the house. Cellulose will slow that convective loss by well over half compared to fiberglass, but nowhere near as well as doing a good job on the air sealing.

 

[AcidWater]

Attic already has fiberglass batts on top of a few inches of 1966 blown in stuff. In some areas I have 2 layers of batting that extend well over the joists. So the catwalk will compress one layer a bit. Tossing another roll on top of the catwalk can only help the R value; getting a bit torn by walking on it once or twice a year is not worth trying to raise the catwalk. And I would smack my head more often.

Yea, separate question posted about moisture damage. Have some black mostly at the eaves, but if its from winter ice damming or condensation I don't know. Also don't know if its an active situation - if it were from outside leaking in, it might have been solved when I put the second layer of shingles on the roof about 30 years ago.

So starting to think about when I might need to rip off both layers & re-roof. So at that point determining areas of degraded roof sheathing becomes part of the job & cost. Below freezing now & I can see some frost on the vertical fascia at the ends of the eaves (two foot overhang). Black around nail heads, but dunno if its the "new" nails or the first layer. Have to go look again. Some black areas higher up, maybe some white mold too.

Just got an estimate from a nationwide roof company & the cost is about 10% the value of the house, without knowing exactly how much sheathing would need to be replaced. They factor in 300 ft2, probably to put new sheathing across the eave end along with their venting system.

Good info on mold in attics:
https://inspectapedia.com/ventilation/Attic_Moisture_Mold.php

 

[Reach4]

a nationwide roof company

I think you should check out local roofers.

 

[AcidWater]

Also
https://inspectapedia.com/mold/Attic_Mold_Causes.php

https://inspectapedia.com/mold/Cosmetic_Black_Mold.php

 

[Dana]

It's fine to blow cellulose over the existing batts and blown fiberglass, which will fill-in any voids, and it's higher air-retardency will e the convective loss of performance that it otherwise has when there is no top-side air barrier. Seriously, it's a MUCH better solution than rolling some batts over the old stuff. The new batts aren't significantly more air retardent than the old batts (unless you use high density "cathedral ceiling" batts), they don't fill in any of the voids, and they aren't cheaper than cellulose.

And just as seriously, if the mold signature is even on the gable ends, there is chronic wintertime high humidity in the attic, almost certainly due to air leakage from the rooms below, and if there is visible frost on the gable facia it's an ongoing condition. If the air leak from conditioned space happens to be near the exterior wall the frost and mold may be heavier near the leak, but if the leaks or leaks are in the middle and distributed (say, a bunch of recessed light fixtures) it will be everywhere. With a flashlight you may be able to see liquid water or ice on roofing nail points more heavy above the air leaky areas.

The first order of business is chasing down and fixing all of the air leaks in the ceiling plane below, which may require moving some of the existing insulation to get at it.

 

[AcidWater]

When I wrote "gable" I meant "eaves." Corrected above. I think there is some black on the lower portion of the gables as well.
This is a 1966 house, it leaks.
Probably mainly from the interior wall/ceiling junction -- sideways into the wall cavity, which has lots of air gap in the fiberglass, then up.
Only ceiling openings are 2 bath fans & 3 can lights in bathrooms & 2 electrical penetrations for kitchen lights.

Improved attic ventilation is probably the biggest requirement. Like a ridge vent & eave vents.
And venting the bath fans outside, but we don't really use them in winter since we have a hard time keeping the house humid enough.
Maybe run the attic fan in the winter ???

Not planning on adding insulation, except on the catwalk to make up for compression of stuff below.
And blowing stuff would fill the 2' overhang of the eaves.

 

[Dana]

No, the biggest requirement is still air sealing. There are completely dry attics that have NO venting.

Having problems keeping the humidity up is also symptom of high air leakage rates.

Fiberglass doesn't slow down the air leaks especially low density R19s and R38s, or the low density blowing wools that were around prior to 2000 or so. Some of the newer blown fiberglass is much improved (eg AttiCat), but some are still pretty crummy from an air retardency point of view. But a more air-retardent insulation does not take the place of air sealing.

Installing purpose-made chutes for keeping the insulation from contacting the roof deck, and cobbling in dams to keep it from filling up the eaves is pretty standard practice.

If you add a ridge vent, be sure than it's no more than 40% of the total cross-sectional vent area, with the eave vents being no less than 60%. If the ridge vent area is bigger than the eave vent it depressurises the attic, which pulls more air in from your conditioned space.

The biggest bang/buck for heating energy conservation and comfort is a round of blower-door and infra-red guided air sealing. If you first go ahead and air seal all of the bigger or more obvious leaks before letting the pros have a crack at it it's even more fruitful. Shrugging it off as "it's a 52 year old house- it leaks" it just silly. I have a 95 year old house built with plank sheathing (much leakier than plywood, which was the most common sheathing in 1966), and (even without benefit of blower door) have reduced the air leakage to the point where low indoor humidity is never a problem, even when it's -5F outdoors. Between sealing up the leaks and retrofit insulation it's taken more than 25% off the heating energy use too.

Any energy that you save from putting batts on top of the catwalk pales in comparison to what even a modest (but serious) attempt at air sealing will deliver.