Air Changes in Attic

[Sushmit Shreyans]

I am simulating a vented residential attic with closed cell foam insulation sprayed on the OSB sheathing. How and where should I simulate the attic ventilation?
I have used an Air Layer (50 mm) and applied a constant ACH of 5 to it. Is this the right way to do this?
Where should this Air Layer be located- after ccSPF layer or sandwiched between OSB and ccSPF?

[GCS]

Sushmit,

please give more details about your construction and boundry conditions, e.g. where is your building, where do you want to place the ventilated airspace, etc. You are saying you have SPF against the OSB, but also talk about an airspace. Where is that airspace?

BTW, WUFI 4.2 only allows cavity ventilation with exterior air!

Christoph

[Sushmit Shreyans]

Hi

I am trying to model a vented attic of the roof in Florida. The attic has been retrofitted with ccSPF for strength and insulation. I want to model the vented condition in the attic.
The exterior is the roof surface which is exposed to atmosphere and interior surface is in the attic which is unconditioned. There are soffit and ridge vents in the roof which maintain the ventilation in the attic. Essentially there is circulation of external air inside this system.
The roof consists of asphalt shingles, underlayment, OSB sheathing and 1 in. layer of closed cell spray applied polyurethane foam (ccSPF) sprayed on the underside of the OSB.
My main concern is how to introduce ventilation in the system.

Is there any other version of WUFI which is capable of doing this and how can I get that?

Thanks
Sushmit

[GCS]

I am trying to model a vented attic of the roof in Florida. The attic has been retrofitted with ccSPF for strength and insulation. I want to model the vented condition in the attic.

I'm still uncertain, are you investigating or designing. i.e. has this already been built or are you trying to determine how best to built it??

The exterior is the roof surface which is exposed to atmosphere and interior surface is in the attic which is unconditioned. There are soffit and ridge vents in the roof which maintain the ventilation in the attic. Essentially there is circulation of external air inside this system.

For the exterior condition you typically use the weather files provided in WUFI or your own, for the interior side, if its just an attic, I would probably use a low moisture sine curve if that would represent the condition.

The roof consists of asphalt shingles, underlayment, OSB sheathing and 1 in. layer of closed cell spray applied polyurethane foam (ccSPF) sprayed on the underside of the OSB.
My main concern is how to introduce ventilation in the system.

Again the question is investigation vs design. If it is built, is the SPF installed already?

Is there any other version of WUFI which is capable of doing this and how can I get that?

WUFI 4.2 should be able to model this situation as you described it.
Christoph

[Sushmit Shreyans]

ccSPF has already been installed in a test house. The test house is an occupied residential 1 story house in Gainesville, FL with a vented attic.
We are monitoring the temperature and relative humidity both in exterior and interior of the house and attic.
Based on how good we are able to model and compare the experimental and WUFI results, we would possibly design other roof systems.
In another experiment, leaks are going to be introduced on the roof surface to simulate a wind driven rain. We need to determine an optimum amount of water to be introduced on the surface. We will be running several different cases in WUFI (to determine water content and drying times of sheathing) before we actually start spraying on the roof surface.