Unvented attics/foam insulation in Houston? Is it possible? (Howe: how much, houses)

[behtypa]

So far I have only seen vented attics, those that have soffit vents underneath + baffles + ridge vents.

Now I came across the "energy efficient technology" of completely sealing the attic ceiling with a closed-cell spray-foam insulation (bye-bye vents!) that is a moisture retardant and a heat insulator.

The foam is supposedly of R6.6 per 1 inch of thickness. Which translates to R60(?) for 2x10 rafters, right?

Now, people, tell me:
- does this approach really work in our climate? Is it worth it?
- why it is not popular? At least I did not see any 1980-2000 houses with the foam so far.
- how much would it cost per sq ft or cub ft?
- Where does radiant barrier go to?

[tdhg566]

I have heard of this technology, but haven't seen it in real life nor have I had a chance to challenge a salesman about it. Personally, I would never own a house with an attic that didn't have ventilation. The more ventilation the better. How do you vent the extra moisture you get if the roof leaks? (and if you assume the roof will never leak, I have a bridge to sell you - ALL roofs leak at SOME point). Is there a guarantee that the closed system attic won't ever get hotter than a vented attic (and thereby radiate heat down into the house? I suspect this approach was developed by the foam insulation people.

I wonder why you couldn't use foam directly above the ceiling in place of loose-fill blown-in insulation.

[tdhg566]

But, I would very much like to read more about this. Please post links to this technology if you have them. Thanks in advance.

[SteveArmy]

I think the best solution goes like this : you have the frame of the roof then the roof itself - that is sloped upwards normally . you need another board(either plain or with insulation) under the frame. this effectively now is ducting right under your roof that will guide hot air to the highest part of the roof and be vented out. you can also employ fans to actively mobilize hot air and these fans will now operate more efficiently since its pulling hot air from the source of the heat

[behtypa]

Originally Posted by tdhg566

But, I would very much like to read more about this. Please post links to this technology if you have them. Thanks in advance.

Here is an analysis:
RR-1001: Moisture-Safe Unvented Wood Roof Systems — Building Science Information

[tdhg566]

Originally Posted by behtypa

Here is an analysis:
RR-1001: Moisture-Safe Unvented Wood Roof Systems — Building Science Information

Thank you. Read the paper. Essentially the strategy is to turn the attic into a cathedral ceiling and to condition the air within the attic. This allows the attic space to be used for climate controlled storage or living space (see introduction). But when the attic is used that way, you can't vent it using traditional means (e.g. soffit vents). So the paper is examining unvented solutions. However, the abstract (first page) says it all: humidity must be controlled.

This approach would be of great interest to anyone who wants to reclaim their attic space and use it for climate controlled storage or living space without building sealed rooms in the attic space. But for the rest of us who just need "an attic" and are willing to let outside air vent the attic of extra heat and humidity, I'm not sure of the value.

Another very important thing to consider: foam, or any other insulation, applied to the underside of the radiant barrier will significantly diminish the value of the barrier. A radiant barrier works best when there is air on the underside.

[rugby]

The unvented attic is conditioned from the air in the house.
We are in Lake Charles and have such a house. The exterior walls are closed cell foam and under the roof deck is open cell foam. Should a roof leak occur, the water would penetrate the open cell so you could see it!
Our electric bill is approx $100 per month, 3000 sqft 1 story house, steep roof- standing room attic which we use for storage. The attic temperature is close to main floor temperature. Additional benefits is sound proofing, structural integrity, wind resistance.
The cost to insulate $13,000. So I'm guessing that's why you don't see too many homes with unvented attics.
Unvented attics are actually recommended for Louisiana's, humid weather by the LSU AG online site, which is similar to Houston's!

[tdhg566]

Originally Posted by rugby

The unvented attic is conditioned from the air in the house.
We are in Lake Charles and have such a house....!

Thank you for the explanation. Very interesting. Did your house come built this way, or did you specifically contract/request that the builder use this technique? When you say your electric bills are $100/month, is that summer months, or year round average? And do you have gas heat, or a heat pump, and is your dryer gas or electric? (just curious how long it might take to reclaim the $13,000). Thanks

[behtypa]

Originally Posted by tdhg566

Thank you. Read the paper. Essentially the strategy is to turn the attic into a cathedral ceiling and to condition the air within the attic. This allows the attic space to be used for climate controlled storage or living space (see introduction).

Correct. "Seal the attic, add foam insulation and add an air conditioning too".

Originally Posted by tdhg566

But when the attic is used that way, you can't vent it using traditional means (e.g. soffit vents). So the paper is examining unvented solutions. However, the abstract (first page) says it all: humidity must be controlled.

Not using soffit vents concerns me too. Actually, I don't mind sealing them. But would this affect the roof (namely, OSB/plywood boards and shingles)?? Help me with more research, because so far I could not find an answer.

Here is an example of discussion:
TreeHugger Forums • View topic - Cost of spray foam insulation (http://forums.treehugger.com/viewtopic.php?f=1&t=11145&start=45 - broken link)

Originally Posted by tdhg566

This approach would be of great interest to anyone who wants to reclaim their attic space and use it for climate controlled storage or living space without building sealed rooms in the attic space. But for the rest of us who just need "an attic" and are willing to let outside air vent the attic of extra heat and humidity, I'm not sure of the value.

I would put it this way:

1.I don't use attic for storage, but I recognize that it is extremely hot right now, and not well insulated, and the A/C unit is trying to make a cool air in the middle of +110F. Which add more load and stress to the unit = it works too hard and will not last long enough.
2. I also recognize that either way I will have to spend money on insulation. Either it is an additional (fromR19 to R60) attic floor insulation. Or it is a roof insulation. In any case I have to do it. So it is just a question of a "most effective way" and "most economical way".

Originally Posted by tdhg566

Another very important thing to consider: foam, or any other insulation, applied to the underside of the radiant barrier will significantly diminish the value of the barrier. A radiant barrier works best when there is air on the underside.

The traditional approach is to loose-fill the attic floor. Not good. Because R60 would be a thickness of around 22 inches. 22inches?!! There would not be a space left for walking up-right in the attic! And I worry about it because one day my AC and heater would need to be serviced!

The new approach is the seal everything and remove the soffit vents. I am OK with that, but besides insulation, an A/C would need to be redirected to condition the attic too.

The only thing I don't yet understand is how much the under-the-roof ventilation through soffits is critical? Can it be painlessly removed if the attic is conditioned??

Help me to find the answer.

[behtypa]

Let's talk about the pros and cons of the spray foam insulation:

Pros:
- closed-cell foam works as insulator (R6 per each 1in of thickness, then a little less), a moisture barrier and (some types) as a fire retardant. They are also claimed to be a partial radiant barrier - it needs to be verified.
- it seals every cavity of the surface. It is very adhesive. Nothing can beat that.

Cons:
- it is expensive compared to more traditional methods (loose fill, fiberglass). 1 board foot of surface (1 feet x1 feet of surface x 1 inch of thickness) costs from $2 + labor (also about $2) = $4 for a bd foot. This translates to around at least of $4000-6000 for 1000 sq ft (depending on a contractor) for just 1 inch thick insulation. A joist-full (2x10 joist completely filled with foam) insulation would cost $20,000 if not more.

Pros are still better than cons. Besides, I read many comments that 1-2 inch (R6-12) thickness is enough to seal the nicks and crannies. And the remaining insulation can be added with a fiberglass which is cheaper. This should save much money.

The second thing that will save money is a DYI approach. A spray foam is sold in large bottles, 200-600 board feet of coverage area. (Tiger Foam) for example. A 600 bd ft bottle with a hose and applicator spray costs around $600.

Why not Buy it, put an overall, respirator, goggles, rubber gloves and do it yourself? If it is as easy as it sounds, I don't see the reason to pay an extra $1000-4000 to someone that can do it as well as me.