Spray foam attic with A/C ducting

[cashcropper]

An insulation company I was getting a bid from recommended if we spray foam against the decking of our roof and sealing off the attic we should have an A/C duct blowing into attic to prevent humidity. Ive never heard of this. Anyone else hear of this?

[Pineywoods]

I've never heard of that but the attic should have soffit vents and ridge vent as well as either an attic fan or whirly birds to move air inside that space.

[ShoootLow]

Adding cold air would actually increase humidity I think.

[cashcropper]

Normally foamed attics have no soffits or ridge vents but thanks.

[CabezaBlanca]

An insulation company I was getting a bid from recommended if we spray foam against the decking of our roof and sealing off the attic we should have an A/C duct blowing into attic to prevent humidity. Ive never heard of this. Anyone else hear of this?

A friend of mine just purchased a brand new home and has exactly what you described above. It's the craziest thing I've seen on a new house.

[txoutdoorsman24]

I've never heard of that but the attic should have soffit vents and ridge vent as well as either an attic fan or whirly birds to move air inside that space.

That is true but when you have the insulation added to your attic, those vents are closed. The vents are used in the normal attic set up.

[txoutdoorsman24]

An insulation company I was getting a bid from recommended if we spray foam against the decking of our roof and sealing off the attic we should have an A/C duct blowing into attic to prevent humidity. Ive never heard of this. Anyone else hear of this?

No, never have heard that before. I have sold/recommended the insulation to lots of customers in Austin and never worried about venting conditioned air into the attic. Worked in many that had it and it was the best feeling attics ever.

[kae006]

the attic should have soffit vents and ridge vent as well as either an attic fan

One or the other, not both

[randal]

Following, building house now..

[mfarmer]

A foamed attic should not have soffit or any vents.

Traditional (blown) insulated attics have vents.

I wouldn't recommend an a/c vent cooling the attic.

[Pineywoods]

That is true but when you have the insulation added to your attic, those vents are closed. The vents are used in the normal attic set up.

I gotcha.. guess I'm unfamiliar with this. If it's air tight it makes sense to have an a/c vent blowing up there

[8mpg]

So there are a couple ways to skin a cat when it comes to attic insulation.
1. conventional blown in insulation with soffit vents and roof vents. You want good air movement throughout the attic. Continuous soffit vents are now very popular as often there is not enough soffit venting.
2. Spray foam the rafters with a sealed attic. This creates a semi-conditioned space. You want the attic tight as possible so you have no airflow from outside. While I dont personally believe in putting a duct into the attic to cool the attic (conditioned space) some people do this. Semi-conditioned spaces bring the ducting into a much more habitable space. This is my recommendation
3. Spray foamed attic floor with a vented attic. This minimizes the amount of spray foam product used. Adds insulation to the ducting and air sealing. I dont like this idea because changing ducting, storage in the attic, etc becomes an issue. This could save 15-20% on the spray foam costs though (not worth it).

If anything, I would put a small return in the attic. This will pull the possibly moist air (not sure why it would be) and let the a/c dehumidify it and blow that air into the house. I follow a Matt Risinger on Youtube who is a builder in Austin that focuses on building science and he recommends a semi-conditioned space.

[Giddings_TX]

I agree with 8mpg. I just had this done in the house I am building. We went with the spray foam in the rafters and no vent in the attic. I was told this semi-conditioned space will be somewhat close to the conditioned space temperature (maybe 10-15 degrees different). I would assume the benefit of the vent in the attic is (potentially) circulating more air which may help reduce the chance of humidity and as a result mold.

[double bogey]

In other parts of the country they go with the sealed attic thing. They think we are crazy putting our ac duct outside, which is where it is in a vented attic.

[bloodtrailer28]

No way in hell I would be paying to blow cold air in my attic!