Can I add rolls of unfaced insulation to increase the R value of my attic insulation?

Question

I live in a two story home that is approximately 150 years old. The attic floor is constructed with large beams and old wood planks laid across the complete surface area, rendering the attic useful for storage. The space is not that large, maybe 26'x 16.' The previous owner of the home removed the center floor boards and just shoved encapsulated insulation the length of each bay. This came no where near filling up the bays in both width and depth. Obviously the upstairs was noticeably chilly.

Last fall I had new siding and new main roof installed on the house. At that time I had a ridge vent installed as well as soffit vents on the front run of the main roof (unable to do them at the rear of the house because the main roof meets a flat roof). Due to the nature of the floor construction in the attic we could not install baffles so we ended up drilling multiple holes in the wood floor in order allow some air circulation.

Moving forward, last January I had a company open up the center few planks of the attic floor and remove the old insulation and blow in cellulose. To keep the soffits up front clear, they inserted fiberglass at the end of the bays. Even though the bays are not deep, maybe 6-7 inches, I noticed a drastic improvement in the warmth of the upstairs even though the R-Value of the cellulose is not that high do to the size of the bays. I also noticed my moisture issue in the attic was gone.

My question is, to achieve a higher R-Value, (I live in New Jersey) could I lay down unfaced rolls in the attic to get the R-value up to where it needs to be? I do use the attic for storage, not packed full, just two rows of plastic containers. If I stacked the containers to open up more floor space and then laid down R-30 unfaced rolls, would there need to be anything I should consider before doing it?

Answer 1

Yes you can. Every bit helps, though you can eventually reach a point of diminishing returns. You're not there yet :)

I would leave the floor boards to avoid compressing the cellulose. I don't need to tell you to maintain a ventilation path from the soffit vents, but it's worth mentioning. I would also consider building a storage platform for both containers and on which to walk (crawl?) so the ceiling can be fully insulated even under the storage area.

Answer 2

I would frame up another floor to walk. 2x6 or 2x8 24" on centers with some plywood on top will stop you from walking and storing stuff on the new insulation. A 4' path in the middle would probably be enough.

Answer 3

I would recommend removing the existing floor boards and frame a new floor on top of the existing joists before adding any more insulation. Small pockets of air between the floorboards and your cellulose insulation can trap moisture and cause the wood to rot at an increased rate and can increase the likelihood of mold. Something to keep in mind is that when you add or remove insulation from your attic, you will be changing the thermal characteristics of the attic. For example, if you increase your attic's insulation, you will therefore lower the attic temperature in the winter, but you will also increase the attic temperature in the summer. Attics can reach extreme temperatures on excess of 120° F in the summer, even when properly ventilated, and this fluctuation can greatly contribute to moisture and mold problems.