Insulation help--

[matouse3]

I am planning to build a 32x40 garage, gambrel trusses with a bonus room in the second story. I also plan to have radiant floor heat in the slab and in the joists to the bonus room. I live in Mid-Michigan.

My question is what is the best way to insulate. I would like to spray foam a portion of the building (roof/ceiling) and conserve costs by going with batting on the walls. I am having 2x6 construction on the walls which will give me some extra room there.

Is spray foaming the roof deck and not venting the building the way to go? Or should I vent and insulate around the bonus room and the ceiling of the first floor? I have read that this can cause some moisture problems and that applying the spray foam to the roof deck is the way to go as it provides a moisture barrier and insulated directly from the outside temps, but will create a larger space to heat?

As always, your suggestions/experience is appreciated.

Thanks

 

[rsa]

My first thought is an unvented roof using an appropriate thickness of rigid insulation above the roof deck and appropriate non-foam insulation below the deck. Look at Option 2 in this A Crash Course in Roof Venting article.

Depending on exactly where you are in mid-Michigan, you'd need R-20 or R-25 above the deck (around 4" of polyiso, give or take), and an appropriate amount and type below the roof to achieve the total amount of insulation required by code (R-38 in south mid-Michigan, R-49 in north mid-Michigan). Heck, you could *completely* fill the second floor volumes outside your bonus room with insulation like cellulose. Even if you don't, depending on the geometry of your gambrel, the second floor volume outside your room could be minimal.

IIWM, I'd also research ice damming with whatever approach you favor. You could execute a vented roof with the venting above the roof deck, with or without exterior insulation.

I have my reservations about encasing the roof deck in closed cell spray foam. It doesn't normally address thermal bridging issues, hides leaks and make repairs difficult. I think it's best advantage is its air-sealing properties. Many respected professionals favor it though. It's sort of a magic bullet. One of them, Michael Chandler, is an editor over at GBA (see last paragraph below), designer and builder. Check out his article in Fine Homebulding.

Do you have a dimensional diagram of your gambrel trusses? I'm guessing your standard gambrel trusses won't have much depth—at the top plate, where the roof changes pitches and above the bonus room—to install insulation and or venting. You could ask about trusses with an energy heel. Trusses with a smaller bonus room, but more room for insulation where the roof changes pitches and above the bonus room. Trusses with deeper top chords.

Why don't you register and ask your question over at greenbuildingadvisor.com? This sort of thing is right in their wheelhouse and the answers come from professionals.

Stewart

 

[matouse3]

Thanks for the links, very helpful.

 

[rsa]

Thanks for the links, very helpful.

You're welcome. You might find directed searches at greenbuildingadvisor.com and buildingscience.com helpful. A gambrel has insulation challenges in common with cathedral ceilings, cap cod homes, story and a half homes, etc, so don't limit your searches to gambrels. Example seaches, cathedral site:buildingscience.com and insulating cathedral site:greenbuildingadvisor.com.

I'm in the planning stage too. It's been an eye-opener to me how important it is to consider insulation, air sealing, etc before construction starts.

 

[stevefasano]

removed due to

 

[matouse3]

Thanks, I have looked at that site. It holds some concern for me since it is referring to areas of high heat (Fl, TX) and also that it is from the installer/manufacturer.
I live in Mid-Michigan and have some concerns that not venting could be an issue in the summer as I won't be running any AC in my garage. Perhaps this isn't an issue, but I'm not sure.

 

[Teken]

http://www.advancedinsulationinc.com/newconstruction/sprayfoam/default.htm

What are peoples opinion about *un-vented* roofs?? This is not only uncommon but ground breaking if this is allowed to continue.

In one of the video's it is indicated that this *un Vented* attic roof is not recommended for cold climates.

How is this different from those regions like Arizona where it is hot??

Teken . . .

 

[matouse3]

Teken,

I can't understand what you are trying to say?

Please explain. Your quoting has me confused as to what you said and what you are quotes others as having said.

Thanks.

 

[rsa]

Thanks, I have looked at that site. It holds some concern for me since it is referring to areas of high heat (Fl, TX) and also that it is from the installer/manufacturer.

That site recommends insulating ceilings/attics to R-21. Code in Texas is at least R-30. That's the same marketing that Icynene uses:

It’s OK to Skimp On Insulation, Icynene Says A manufacturer of open-cell spray foam advises building officials to approve insulation that doesn’t meet minimum R-value requirements

While energy experts often advise builders to exceed minimum code requirements for insulation, Icynene Incorporated, a manufacturer of open-cell spray polyurethane foam, is swimming against the tide. Surprisingly, Icynene is trying to convince builders to install less insulation than the code requires.

Icynene’s bizarre campaign against thick insulation is the second controversial move by the Canadian company. Last year, Icynene ruffled energy experts’ feathers by waging a spirited (and successful) lobbying campaign to defeat a widely supported effort (the so-called “Thirty Percent Solution”) to raise the stringency of insulation requirements in the International Residential Code.

The motive for Icynene’s current effort — let’s call it the “it’s OK to skimp” campaign — appears to be economic. The company has apparently decided that the only way Icynene can compete with less-expensive types of insulation (like cellulose) is to convince builders that they can get away with less insulation than code books require.

For the rest of the article, click here.

 

[Teken]

Teken,

I can't understand what you are trying to say?

Please explain. Your quoting has me confused as to what you said and what you are quotes others as having said.

Thanks.

The vendor states that they insulate under the roof sheathing using *un vented* roofs.

This is not common in North America . . . Air circulation is paramount to ensure hot / cold air is allowed to circulate and vent off.

In the same video the vendor states that they do NOT recommend using a un vented system while applying the spray foam in colder climates.

There is over 100 years of building practices which illustrates why a roof needs to be vented. I am trying to grasp the pros and cons of what they are saying by using a un vented roof system.

Teken . . .

 

[matouse3]

I understand that its not common, but that doesn't necessarily mean that its incorrect.
Its much more expensive to spray that much rigid foam to the roof,and since cost is the main driver for most construction decisions (unfortunately) this is likely why it is uncommon.
Fiberglass insulation performs terribly compared to other options, but its still used on a regular basis because its cheap and anyone can install.

I'm still trying to wrap my head around this concept and make the best decision. As always- your input is appreciated

Some interesting reads:

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

http://docserver.nrca.net/pdfs/technical/7877.pdf

http://www.jlconline.com/cgi-local/...e.storefront/4eba876409c7b7ac271a0a323cb406e3

 

[rsa]

I am trying to grasp the pros and cons of what they are saying by using a un vented roof system.

Start with Unvented Roof Assemblies for All Climates. The site the article is from, Building Science, has much more information on Unvented Roof Assemblies. Also try Vented or Unvented Attic? GBA is also flush with unvented attic information.

If the articles don't mention it, the complex roof shapes of today are almost impossible to vent well. One reason vented roofs are prevalent:

For 20% of the effort, it gets us to 80% of optimal performance, and it works in hot climates, in mixed climates, the Arctic, the Antarctic, the Amazonian rain forest — it works absolutely everywhere. The value proposition of a vented attic, meaning the money that you invest in building one of them — it’s hard to argue with the benefits.

For the rest of the article, click here.

 

[rsa]

Some interesting reads http://www.jlconline.com/cgi-local/...e.storefront/4eba876409c7b7ac271a0a323cb406e3

The Journal of Light Construction is a great site. Their article on concrete garage floors turned me into a subscriber.

 

[Teken]

Start with Unvented Roof Assemblies for All Climates. The site the article is from, Building Science, has much more information on Unvented Roof Assemblies. Also try Vented or Unvented Attic? GBA is also flush with unvented attic information.

If the articles don't mention it, the complex roof shapes of today are almost impossible to vent well. One reason vented roofs are prevalent:For the rest of the article, click here.

RSA,

As always I thank you . . .

Teken . . .

 

[matouse3]

Thanks so much. My afternoon just filled up with reading!!!!

Keep it coming if you think of anything else!