Changing a Vented Attic to an Unvented Attic?

We had an energy audit a few weeks ago and they recommended looking into putting more insulation into the attic. We had an insulation company that they recommended come out last week and they suggested sealing off the attic and making it non-vented. They would spray 7" of open cell Polyurethane Spray Foam between the rafters to seal the attic to the outside. Has anyone ever had this retrofitted to their house, and if so, what was your experience?

Some of my concerns:
- Our roof is original, and around 22-23 years old. The foam would be sprayed on the sheathing, so when the roof needs replacing in the next 10 years, I think it could complicate that process.
- From what I've read, the spray foam can be damaged when replacing the roof
- We are in CT, and experience temperature swings from roughly -10F to 100F over the course of a year
- Water leaks can be more difficult to observe/trace because of the spray foam

Sealing off the attic isn't cheap, but there are rebates which would allow us to recoup 40% of the cost within a few months, and 0% financing for a good portion of the cost. From running the numbers, it seems like the payback for the foam based on lower energy costs would be roughly 3-7 years (my estimate is the higher #, their numbers say 3-4 years).

I've all but decided to pass on it until after we re-roof a few years down the road (and I can do more research), but I'm curious what the hive thinks of this...

Thanks!

Replace your shingles, then do the foam...... I had the largest savings replacing my furnace/ AC. How old/ efficient is your heat/ AC system?

This sounds like very bad advice, unless the attic is a living space.

Furnace is also original (22 to 23 years old) and efficiency is in the high 70s (new models can be in the low to mid 90s). We're likely going to kill two birds with one stone by replacing the furnace with a more efficient one, but wanted to understand all of our options before deciding. A/C system is about 3 years old, so hopefully we shouldn't have to worry about that one for a while.

The house actually did very well in the energy audit, after their sealing improvements for the doors/windows, we were sitting on the minimum suggested value. Any lower, and the house would have not had the recommended amout of ventilation.

Our attic is not living space right now, it just provides some minimal storage.

Thanks for all the feedback!

I don't think you want to do that. It sounds like a recipe for mold and ice dams.

You may want to consider laying some more insulation down on the attic floor, but I wouldn't want to do anything on the underside of the roof.

This message comes to you from across the river.

That's the way they recommend doing it nowadays and it can save you a ton of money if done right. It's called cocooning.

1st you have to use the right foam. The softer foam (don't know the official name) can mask leaks because it can become water logged which can allow the wood sheathing to rot. The harder foam (read that more expensive foam) doesn't do that.

Usually when you do this you have to also add an outside air intake for your AC. It doesn't take all the air from the outside, just a portion. Or at least that's what all the AC guys told me when I was building my house.

It's also called a hot roof system - if you do a google search on that term a bunch of information pops up.

If you seal up a house really well, you probably need to add an air-to-air heat exchanger to exchange fresh outside air with stale inside air.

Here's an alternative and it's DIY.

I set my house up for the cocoon system, but when the foam guys came out to blow it they'd doubled the price. Not just one company, but all 3.

They all told me that if they'd have given me the proper bid in the first place I'd have never designed it for foam it so they underbid knowing I'd be stuck and have to pay it when the price came. NOT ME!

I'd had a funny little feeling and so I'd designed to allow room for more blown cellulose. But I didn't get the radiant barrier decking because you're not supposed to put that on if you're adding foam. That's bugged me.

I've recently begun my own cocooning process, and of course I waited till it turned hot.

I'm in the process of putting 3/4" hard foam sheet with radiant barrier on the underside of my roof joists. (R5 + radiant barrier) The area between the foam and the roofline will be vented. I put in 5' stringers to form a plenum chamber right at the peak.

The attic will be sealed pretty well and the air will flow between the joists up to the plenum chamber where my powered exhaust fans will exit the hot air.

I've been adding some passive roof vents at the ends of the long runs of the plenum today. The idea is that when the fan is on it will pull the cooler air from the ends of the plenum.

My AC is already set up for outside air so I'm cool there (pun intended).

I've worked on the underlying stud/plenum chamber & eave venting for some time now and have only just begun much foam layment. A whole back I did put some foam up in a relatively inaccessible area of the roof and that section of the attic is noticeably cooler than all the others.

This is more for my own piece of mind and maybe a selling enticement since I've got 5100 Square feet and my heating/cooling & water bills (I'm on a well so my electricity bill includes the cost of my water) has only topped $200 a couple of times.

In reply to carguy123:

Can you shoot a couple of pictures of this. It sounds like a good idea for a retrofit. I'd be interested in looking at what you are doing.

Sure, I can't post them because the forum won't let you post pics unless you post them elsewhere first, but I'll send some direct to you.

While it's not super cheap, it is something you can do at your own pace. I've been working on it for a couple of years. Not very hard of course, but still, whenever I've had a few moments or a little money I've worked on it some.

Toyman I sent you a PM

Replied, thanks.

90% of the time it will void your roof shingle warranty (although I think they are full of it)

It's not a single issue. You will increase the volume of conditioned space, and may need make up AIG for your gas fired appliances.

Though it is a modern technique, it's not that practical in most retrofits. The reality is that you can't seal up the rest of the house tight enough to make it a good overall system.

Draft sealing is the #1 payoff. After that, swap out AC unit for a more efficient one. Then comes draft sealing the ductwork, then increasing the insulation (without moving the envelope).

Moving the envelope is pretty far down the list

SVreX wrote: 90% of the time it will void your roof shingle warranty (although I think they are full of it) Moving the envelope is pretty far down the list

Apparently that's only an issue on the cheaper shingles as every shingle I looked at when I built 5 years ago said they were good for a foam insulated roof right on the package.

When you already have the other issues taken care of the envelope is the logical choice plus moving the envelope does a bit of the sealing for you.

You dramatically lower the amount of heat moving from the attic back down into the house as well and put your AC equipment in a much more friendly atmosphere which makes your equipment more effective all by itself.

But yes, do all the cheap easy things first - always.

Thanks for all the input, guys. Additional insulation on the attic floor is another option, they proposed, but I think there's some easier stuff I can tackle like installing a laddermate (I installed one at old house and loved it), and building a box around the whole house fan.

If we really want to get aggressive, we can look into upgrading to a new furnace....

WTF is an energy audit?

I remember always being told the foam insulation backing on the roof always led to "softer"/weaker shingles in the hot summer months......could be wrong though.