How old is your house? Different eras had different building techniques. If that insulation got wet, I would not "stuff it between joists" until it is completely dry.

Check if your local utility offers an "energy audit". IIRC, ours was either free, or $100, that was refunded after we did a certain amount of "energy saving" changes.

If they do offer this, they should be able to advise you on having your attic "air sealed".

It is usually a fairly reasonable cost, and I think it cut our heating & cooling costs by 20 -25%.

As with any home improvement, you need to know what other changes should be completed before or during this project.

You can't stop the roof tin condensation by adding insulation to the attic floor. You need to use condensation control on the tin. Three products will control condensation, house wrap with taped seams, reflective bubble insulation, and Pro-Therm Condensation Blanket or equivalent but the last option is very expensive.

Would the bubble wrap go on the bottom of the trusses or between them on the purlins?

Thanks Hallett. As of right now I have two windows open on the gable ends of the house, so I guess I'm trying to keep the attic outside the envelope. It's gonna be hard to completely seal it off as we have a staircase for the access. I priced out getting spray foam and it was very expensive and if we ever need to replace the roof the foam would make it a nightmare. It's just a storage space which is why I wondered if foamboard on the floor would help.

Hi, Brian,

Your problem is (obviously) related to the amount of moisture in your attic. There are a couple of ways to deal with it. You may find you need to implement more than one.

First, make sure your attic has adequate ventilation. A combination of soffit and ridge vents with sufficient open area to meet code requirements is usually all you'll need. You can increase the ventilation, but it won't always solve the problem you're experiencing.

To reduce moisture at the source, make sure you have appropriately sized bath vent fans exhausted to the exterior (never into an attic, basement or crawl space) and run them during and for 20-30 minutes after a shower. Check to ensure your clothes dryer exhaust vent is properly connected and free of obstructions (e.g., lint build up) so the dryer exhausts to the exterior. Make sure to use a range/cooktop vent hood which exhausts to the exterior whenever the range or cooktop is in use. If you're using a humidifier, I'd suggest you discontinue using it at least until attic moisture levels are no longer an issue.

Rather than insulate under the roof deck, I suggest you air seal the ceiling directly below the attic. That will reduce the pathways for moisture to enter your attic from the living area. The easy way to air seal the ceiling is to apply a layer of spray foam insulation on the attic side of the ceiling--- especially at any piping or wiring penetrations. It doesn't need to be a thick layer since you're only looking for it to air seal the ceiling. If you have recessed lights, you may need to use rigid foam to create enclosures for them and then seal the enclosures with spray foam. Once you've air sealed the ceiling, add insulation on top of the foam to attain the required R-value for your climate zone.