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elbartee 02-19-2008 01:47 PM

Which is better? (Non-vented roof construction with indoor pool)
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Hi, all. I'm new to the forum and at the beginning of building a new home after 1yr+ design phase. Currently finalizing structural plans and have to make decisions about roof construction. The 2 options on the table are:

1. The designer, recommended gluelams to accommodate our choice of Insulated Roof Panels (SIPs). The gluelams would be exposed under the cathedral ceiling which will be finished with TnG pine.
2. The builder, who will do the log structure and roof, is recommending an alternative roof construction to save us some money. 14" BCIs (as spec'ed for the clearspan by Boise Cascade) would be topped with OSB and TnG pine finish material on the underside with paper insulation blown in.

IceShield and single will be the same with either option and we're thinking of adding a radiant barrier.
Don't recall the R-values just now, but with BCIs and paper its about 15+ higher than the SIPs.

With either option, the roof will not be vented as part of it covers in indoor pool room so we'll go with a shingle manufacturers that will warranty (Elk or Certainteed).
The indoor pool room will also have waterproof membrane under finished ceiling material (likely cedar).

My main question is about the actual construction with BCIs.
This method is about 1/2 the cost of Gluelams and SIPs, but is it also half as sound structurally or will only be trouble-free for half the time?

Attached pic of cross-section. Its basically 2 big shed roofs with a clerestory separating them.

acorn construction 02-19-2008 03:53 PM

roof decking.
There are several companies that make a self venting roof panel. usually a 2"insulation board with 3/4" air passages that are secured to wood decking. We used it on a Church 10yr ago that had major Ice Dam problems. Stopped the killer Ice. So we had intake and exaust venting buildt in. Be careful to not have to many Vapor barriers. And I hope you havc people have the room completely separate.

Ed the Roofer 02-19-2008 06:20 PM

Atlas Insulation makes vented polyisocyanurate insulation with an attached osb board decking adhered to the top.

Real quick edit: I found a JM spec for a similar product.

2nd Edit: Here is a link to the Atlas version of Cross Vent Insulation.

The rest of your question has too many unknown intangibles to properly answer at this time and will require more research by me.


elbartee 02-19-2008 07:13 PM

Thanks, Acorn.
The only redundant vapor barrier will be in the pool room to trap all the water in the pool room where it will be remediated with an air handling system as specified by a pro.

The radiant barrier, I guess would be another vapor barrier and it would be applied under roof decking so perhaps I need to rethink that part.

HVAC will be in a basement-level mechanical room separated from living space by the garage.

Interesting idea about the self-venting roof panel, I'll have to check into that.

Ed the Roofer 02-19-2008 07:27 PM

It is a little on the expensive side, but if moisture permeated the exterior of the decking, at least it has the opportunity to flow with a properly designed continuous intake ventilation and exhaust ridge ventilation system.


PKHI 02-19-2008 07:31 PM

Ed would this be in your opinion a good place to use sleepers and have a second roof deck to achieve ventilation?

elbartee 02-19-2008 07:31 PM

Thanks, Ed. I wish I would've known of this forum back when I first began researching SIPs.
To prevent moisture issues associated with the indoor pool I understand a hot roof (not vented) is best.

If you have a minute, will you list the intangibles so I might clarify for all. Tried to be comprehensive in my question without writing a novel, and it sounds like there's some detail I should add. Thanks again!

Ed the Roofer 02-19-2008 07:34 PM

Nothing in particular, as the Hot Roof scenario is relatively new and not long term field tested yet.

By the way, check out the shingle manufacturers warranty limitations again. The last I checked, the unvented, or hot roof had a reduced down to a 10 year limit on materials from Certainteed.


elbartee 02-19-2008 08:02 PM

That's what we're thinking now for preventing ice dams.
The last replies on this thread about venting got us to thinking about venting and the concern of ice dams.
Since the indoor pool requires the roof to be sealed (not vented) we're looking at applying roofing over the top as you describe.

At the same time there's the concern of water vapor from the interior migrating into the roof and forming a sheet of ice in the underside of the roof deck.

A hot roof with sleepers, OSB, then finished roof might be just the solution.?.?.?

elbartee 02-19-2008 08:08 PM

Ed, thanks for the heads up on warranty. I saw you mention that on another thread--definitely will weigh in the decision. What do you think of this improvement suggested by PKHI?
With that added, the roof would look like this from the outside in:
ice shield
vapor barrier
radiant barrier
14" BCIs filled in with damp spray paper insulation
TnG pine

PKHI 02-19-2008 08:34 PM

The only reason I mentioned it is we sided a pool addition that was done with scissor trusses and the engineer spec'd filling the truss space with spray foam, and adding sleepers to get vent space.

FWIW I too have seen what happens to shingles that are on non vented roofs, they tend to get yucky pretty fast.

Ed the Roofer 02-19-2008 11:40 PM

I am either having a brain cramp, or am not familiar with the acronym BCI, which obviously means insulation for the last "I".

From what I read, but without practical hands on experience to fall back on, the spray on closed cell insulation eliminates the necessity for ventilation.

If you need me to, I can post this question on another forum where several members are much more experienced with that technology, but it may take a few days for the responses.


elbartee 02-20-2008 09:32 AM

Thanks, Ed. A BCI is a wood I-joist. That's what we'd use for rafters, filling in with damp spray recycled paper insulation (from my research, its also called cellulose fiber insulation, the same as what you're referring to).

The BCI's are really what opened the issue for us as I'm not sure of the durability of the wood I-Joists (BCIs). And the BCIs will be replacing Glulams on our plan.

So 2-fold:
1. Seems like we're getting to the bottom of the venting issue: build hot roof with a cold roof over it, basically.
2. Will my roof be strong and solid for many many years to come, constructed this way on top of BCIs rather than Glulams? Its a log house and the builder tells me the roof basically ties the structure together.

Thanks you all for your advise on this. Its been really helpful this far!!

Ed the Roofer 02-20-2008 11:13 AM

I have posted a link to this topic thread in a forum hoping to get noticed by an expert in this field, whos knowledge about this is much more extensive than mine, and whos years in the field and expertice is highly revered by myself and many other fellow posting members on an inspection site.


ncgrogan 02-20-2008 11:40 AM

Where are you located at? Location makes a big difference as to which direction your moisture drive comes from most of the year. It changes from winter to summer. with winter usually having the biggest temp. differential. I would do a hygrothemal analysis on your system using WUFI or a similar program. Convential wisdom I don't think will take you very far in this situation.

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