Benefits of Spray Foam Insulation & Attic Ventilation Requirements
Hey everyone. Today, we’re going to talk about attic ventilation. If you’re building a custom home, ADU, or remodeling your entire house and gutting the entire thing, you’re going to be required by the city, or the county, to draw up a set of plans and include attic ventilation. Attic ventilation is calculated in relation to the actual square footage of the structure.
How to Calculate Attic Ventilation
Let’s say you have a 2,000 square foot home with a 500 square foot garage. The structure totals 2,500 square feet of area. This amount must be divided by 150, which gives us a total of 16.67 square feet of Net Free air ventilation that we need for that attic space. The Net Free air will be achieved by installing roof ventilation such as O’Hagin roof vents, dormer vents, or Gable in-vents on the gables.
Standard Roof Ventilation
Adding roof ventilation is a standard method of building where you install your insulation at the ceiling level of the home, leaving the attic as unconditioned space. Doing this in wildfire areas totally changes what is required. Often, we use Brandguard vents because they have baffles in them, which really reduce the Net Free air ventilation area that you get from each vent.
How to Calculate the Vent Itself
Let’s say you had a 14-inch by 24-inch gable end vent, this nets 336 square inches. We can then divide that by 144, to get 2.33 square feet of Net Free area per each individual vent. That 2.33 square feet goes against the total 16.67 square feet needed. We can make up the additional footage by subtracting 2.33 from the 16.67, and that would give you the combined total needed from the other gable vents, high roof vents, and low roof ventilation.
Wildfire Attic Ventilation Requirements
With modern day wildfire requirements, baffled vents, such as Brandguard or O’Hagin vents, help mitigate embers from blowing directly into your attic, but they also greatly reduce that Net Free area. For one O’Hagin vent that you put on the roof, you may only get a half of one square foot of ventilation from that specific vent. Gable end vents may get a little bit more, but not much.
How to Prevent Fire Threats in Attics
Having to meet these requirements of the ventilation could result in 20, 40, even 50 holes cut in your roof plus your gable end vents as well. The roofers must cut out all these holes, like Swiss cheese, to put these vents in. Composition shingles don’t always look that great with this method, and although you can blend tile a little bit better, it’s still not the best look. Additionally, it still leaves a potential penetration point for any embers to enter the attic that just might happen to get through the baffles. These are the most critical points where a fire could breach and get into your home with driving winds. Fire threats are what we’re trying to avoid.
How Spray Foam Insulation Works
With all that said, we can eliminate these attic vents by using spray foam insulation. If you go to our YouTube channel on 2021, March 30th episode, and you can see this being installed. The concept uses expandable spray foam that is shot up against the roof sheeting all the way down to the plate line on top of the exterior walls. That creates an envelope typically at about an R-38 value, which is a common requirement for that installation in the San Diego area. It equates to about 10 and a half inches thick.
How to Get Rid of Attic Ventilation Requirement
From the top of the wall down, we’ll then do either batt insulation, or you can elect to do spray foam on the walls as well, but that’s not required to get rid of the ventilation requirement. To remove the attic ventilation requirement, the spray foam is only needed from the walls down to the plate line, and on the entire gable end walls. Gables are typically five and a half inches thick, which equates to roughly R-21 spray foam.
Semi-Conditioned Attic Space
Now that we have eliminated any requirement as far as attic ventilation, they consider the space between the top of your drywalled ceiling up to your roof sheeting to be a semi-conditioned attic space. This also relieves the load on your HVAC systems which are typically installed up in the attic above the ceiling. These air handlers usually include your furnace and your air conditioning condenser.
Benefits of Spray Foam Insulation
When you get that attic space conditioned with a spray foam, it takes the load off that system which normally runs extra due to trapped unconditioned air. Often the HVAC company can downsize the tonnage on the HVAC system, which saves a little bit of money and even reduces the physical size of the system. The efficiency also helps bring down your utility bills because you’re not having all this cold air or hot air exposed to either cold or hot air in the attic. So, spray foam has a couple of different benefits. It helps lower the utility bill and protect from wildfires too. I did not mention this earlier but having spray foam really minimizes the radiation of solar heat, so your home does not require as much cooling during the summertime and that’s huge. Spray foam really helps keep that building at a consistent temperature inside, as well as taking the load off that system like we talked about, about downsizing that HVAC system.
Other Helpful Resources
I hope that was helpful and that you learned a little bit more about why spray foam could benefit you when you’re building a home, an ADU, or possibly doing a whole house remodel. If you’d like more information or access to other resources please view our website or YouTube channel. Thanks for your time and have a great rest of your day.