Attic ventilation with spray foam insulation?

Submitted by shanedn t3_10kau80 in DIY

We purchased a home years ago and one of the big selling points is the attic was spray foamed under the roof decking. It's a bigger house than we're used to, so the utilities cost being quite higher wasn't a huge surprise. However, it took me a few years to notice that there are roof vents in the spaces that are spray foamed. Considering that the attic is essentially conditioned the same as the rest of the house, wouldn't venting be a major heat loss? If so, are there any major issues with caulking them completely shut and insulating the hell out of them?

Roughly 80% of the upper floor is vaulted ceiling, so no attic. This is mostly in knee well "attics"

Edit: attic space example: https://imgur.com/a/U5GcyLP

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nobamanomore t1_j5r6b9d wrote

I don’t want to punk out any individual people, but I can’t believe some of you answer when you have no idea what you’re talking about. Foaming a roof is completely different than any other type insulated home. You do not ventilate the attic at that point please learn some more before you try to give information that could harm this guy or his home.

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jinbtown t1_j5ptvii wrote

You do not want those vents in a hot roof type attic. It's part of conditioned space and you aren't insulated between the "warm" attic and "hot" (relatively speaking) house. If it's part of the thermal envelope it should not be vented. The point of the spray foam is to provide an air and moisture barrier.

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Traveling_Carpenter t1_j5py9es wrote

I wish people would stop saying attics or buildings need to breathe - it’s just not true. People need to breathe; building assemblies made of materials that can rot need to stay dry. One way to keep them dry is to give them space to dry into, and that is often achieved by venting. However, all vents need to be outboard of insulation (on the side that’s cold in winter). Any insulation on the outside of a vent is doing as much good for a house as it would do sitting on a rack at the lumber yard.

Attic vents are not for cooling; they are for venting moisture out of an attic space. Venting has roughly zero effect on the temperature inside an attic or on the temperature of a roof deck.

Old-timers (people who were around when insulation started to become common in the 1900s) came up with the notion that houses needed to breathe when paint started to fall off of the siding on walls that had recently been insulated. The issue was vapor pressure, not inability to breathe, but folks back then didn’t know any better. There’s been about a century of research on building science since then. Anyone interested in the topic can look at the decades of research done by Building Science Corp., or for a crash course, check out the recently published book, “Houses need to breathe - or do they?” Spoiler alert: I gave it away up top. (Edited to consolidate two comments in one for clarity)

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FBogg t1_j5pjall wrote

attic vents are primarily for heat to escape uninsulated attics. with spray foam at roof joists, attic is part of your whole house thermal envelope so open vents will hurt your energy performance. I wouldn't spray the vent, but putting up insulation board over the openings would help.

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Maplelongjohn t1_j5q378v wrote

Wow someone didn't have a plan at all there.

Those vents should be sealed up, a long with any other penetrationns up there.

However the roofing lifespan may suffer from a hot roof.

Back to someone not having a plan

Do you have an ERV/HRV?

If you want a tight envelope you can cause mold issues. An audit by energy company may be worth it.

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shanedn OP t1_j5qzie0 wrote

We do not have an ERV/HRV. Half of the house is pretty old and drafty, so it probably wouldn’t be critical immediately. But probably worth looking into.

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lovallo t1_j5s7wrr wrote

Wow, a lot of bad information here. You cant really go to school for home building so information gets passed down...

You want your thermal barrier and air barrier on the same surface. Previously that was the attic floor, now it is the attic ceiling.

The heat from the whole house is rising up through the vents, and that is pulling cold air in down at the low points.

You want to seal the vents. It might not be a bad idea to install a fan to the outside up there that can be sealed or a bathroom exhaust fan. Your house sounds unlikely to become too airtight, but if it did the answer is controllable mechanical ventilation.

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J3RAK33N t1_j5rgpi4 wrote

Look into MVHR as an option to ventilate the property. Will keep it well aired, prevent humidity build-up, and keep the heat in. If you seal up the existing vents without an alternate solution though you will have humidity issues as spray foam insulation is very good at sealing a property.

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carlbernsen t1_j5pll4u wrote

This sounds like a scam.
How much insulation is in the attic floor?
A cold loft has floor insulation and lots of ventilation to keep the moisture rising from the house below moving outside. There should be a gap along the top of cavity walls and a draught blowing through the loft.
A warm loft is insulated under the rafters with air moving around the timbers above the insulation.
Insulation under the tiles with air blowing around the open loft space defeats the object.
One advantage though, would be to reduce heat transfer through the roof in summer.

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shanedn OP t1_j5pn76o wrote

No insulation in the attic floor, except for a couple inches of 80yr old insulation where they added a second floor on top of the first floor and didn't put in the effort to remove it. Newer parts of the house you'll just see the ceiling drywall from the room below.

There is roughly 2-3" of spray foam under the roof decking/between the joists. Colorado front range for climate reference.

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seabornman t1_j5sa05o wrote

You do not want ventilation and that is not nearly enough spray foam to meet code in CO.

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ZealousidealPickle11 t1_j5pgzqc wrote

You generally want your attic to breath. Trapping all heat inside your attic isn't helping your house to breath. You want your living space well insulated, but do not fill your roof vents. They are there for a reason.

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shanedn OP t1_j5pi3yx wrote

Even with spray foam insulation under the roof deck? From everything google seems to say, you usually don't want ventilation:

https://www.google.com/search?q=spray+foam+insulation+attic+ventilation

However, I'm not the one who did the insulation or the venting, so I'm trying to find out if they broke the "rules" for a reason I can't think of.

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Electronic-Being7258 t1_j5qnoon wrote

I had a home that was insulated with a nonrigid foam. It was wonderful in the attic during all seasons. The attic becomes basically part of the interior of the home with comparable temperatures. No vents in the attic are necessary, but the HVAC system needs better humidity control and fresh air exchanger.

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nobamanomore t1_j5r6233 wrote

Please stop listening to these ignorant people that don’t know anything about spray foaming a roof almost all the information people are giving you is incorrect. Contact an experienced foam insulator in your area to come out and give you his opinion. I’m pretty sure I know the answers but I’m not going to speculate without seeing the entire house you need to make sure you don’t make any mistakes.

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Bldaz t1_j5pszdu wrote

The attic has to breath or it will get hotter, and so the main house. Vents low and vents high passive cooling. The foam just slows the progression

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nobamanomore t1_j5r5pti wrote

You have absolutely no idea what you’re talking about

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