[Yakker0117]

My attic has blown in insulation. It is old and only about 6" thick. Much of it is settled. The floor in the attic is tongue and groove boards. Is it ok to put 2" rigid foam over the floor boards and the cover that with plywood?? Will the rigid foam cause moisture problems below? Should the foam be foil backed? Foil on top or bottom???
Thanks.

 

[Windows on Wash]

Doesn't work that wall as you are hard pressed to get it sealed and you are basically moving the insulation plane up. Moisture will still leak into that space and given the lack of ability to dry through the foam (most foams of a substantial enough R-Value that are available big box stores won't be that permeable). If you use foil faces, it is basically non permeable at that point.

If you could make that surface the air barrier, easier said than done, that might work but you would really need some thick foam there for sufficient R-value.

What are you trying to do with the space and if storage is the goal, is it rated for that?

 

[Yakker0117]

There is insufficient insulation in the ceiling of the top floor. As a result the up stairs is cold in winter. The attic is used for storage and there is no concern about the attic environment.

 

[Bud9051]

Hi Yakker and welcome to the forum. WoW is correct and the question as what you want up there is important.

Your problem is the T&G floor up there and doubtful the ceiling (attic floor) was well air sealed. as air leaks into that space it carries moisture. Currently, that moisture is probably drying through the wood floor. Adding substantial rigid insulation and another layer of flooring gives any moisture no place to go.

There are ways to get another floor up there with more insulation, but not by just adding above the current floor.

Bud

 

[joecaption]

With no location and no idea what your plans are on that second floor hard to say what to do.
Most attics where never even intended for living space of even storage.
What the size of the joist and the free spans?

 

[Yakker0117]

The space is used as storage. Nothing is going to change in that regard. I am only trying to add more insulation. The joists are 2x6 and they are covered with tongue and groove flooring.

 

[Yakker0117]

The space is used as storage. Nothing is going to change in that regard. I am only trying to add more insulation. The joists are 2x6 and they are covered with tongue and groove flooring. The second floor is bedrooms.

 

[joecaption]

We still have no idea where you are.
Here a bare minumum idea of what insulation you need.
That T & G needs to go.
https://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

 

[Yakker0117]

I am in southern ny. My question is this: can I safely use rigid foam on the attic floor without worring about moisture builing up in the ceiling below?

 

[Bud9051]

@yakker "can I safely use rigid foam on the attic floor without worrying about moisture building up in the ceiling below" NO!!!

As I said, there is moisture passing through the drywall and all of the leaks from the heated space into that attic, currently much is entering below the T&G and managing to dissipate into the attic air. If you add a thick layer of rigid plus a layer of plywood, it will be difficult for that moisture to exit that confined space.

Your priorities are, reduce the heat loss in those bedrooms to make them warmer (and that may not all be due to the ceiling) and maintain some storage space in the attic.

First, do a heat loss evaluation for those rooms. You will see what improvement an additional 6" of insulation will give you. Does the T&G cover the entire attic floor or just the center area. If you were add insulation to all of the exposed insulation and leave the T&G where it is you would be reducing the heat loss. If you dug through the currently exposed and did the required air sealing the improvement would be even more. Related link below.
https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/TBC_Guide_062507.pdf

Bud

 

[Yakker0117]

THANK YOU! This is exactly what I was looking for.