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6 Answers

How to properly insulate an unvented cathedral ceiling

In your recent "Musings of..." you refer to an unvented roof assembly as follows:

"The 2009 IRC (Section R806.4) allows unvented roof assemblies insulated with a combination of rigid foam insulation above the roof sheathing and air-permeable insulation in the rafter bays. (The 2009 IRC defines air-impermeable insulation as “an insulation having an air permeance equal to or less than 0.02 L/s-m² at 75 Pa pressure differential tested according to ASTM E 2178 or E 283.” Although spray foam insulation and rigid foam insulation can meet this standard, dense-packed cellulose cannot.)"

In Building Code Questions | Asked By Ralph Hill | Feb 29 12
3 Answers

SIP Roof

Moisture control and permiablity in CZ 4. A client is interested in a SIP roof as a retrofit for an older log home. Currently the plan is to strip the existing roof of asphalt and felt and repair as neede the existing osb. The build out calls for 1.) 30# felt 2.) 4-6" SIP panel nail board 3.) 30# felt 4.) High albedo standiing seam metal roof. Is the first layer of felt a potential moisture collection issue, would the system be better off without it?

In Green building techniques | Asked By Bruce Glanville | Feb 29 12
8 Answers

Fireplaces in Tight Houses

We are building a custom house with SIP walls and SPF roof. Manual ventilation will be installed. Plans were originally for a 2x6 enclosure and an unvented fireplace. The research I've done says unvented fireplaces in a tight enclosure are a bad idea but the client (my wife) doesn't like the look of an exterior chimney.
Is there a way to vent a fireplace unobtrusively? Or, can I get a way with unvented gas logs if I supply make up air?

In Green products and materials | Asked By Chris Baddorf | Mar 1 12
36 Answers

Stacking SIPs and nailbase for superinsulation

I have a passive house project in the Colorado Rockies and need heaps of insulation to make the numbers work (R-90 walls, R-120 roof). A local supplier has polyurethane SIPs that come in at R 6.66 /inch, however only to a dimension of 8.25" thick for approx R-50 for the 8" panel. I had thought about stacking nailbase SIP from the same manufacturer on top to achieve my R value, but my brain sounded alarm. There would be a layer of OSB that can't "breathe"-this seems bad.

In Energy efficiency and durability | Asked By Erik Lobeck | Feb 24 12
1 Answer

Cathedral ceiling rigid foam vents?

New construction -- having the attic trusses built with 18" top chord for insulation and baffles. Not totally sold on spray foam.

The question is: doesn't building vents with foam or using plastic vents that are sealed to the truss create an area of condensation (it shouldn't condensate with that much insulation)? Or at least, in the event it did get wet, doesn't give it the ability to dry to the outside?

The drywall inside will be sealed and there is only one roof penetration design for plumbing vent.

In Energy efficiency and durability | Asked By jeff ANDERSON | Feb 29 12
1 Answer

Site upgrades going on now

Hello all,
We are in the process of adding a couple of features to GBA and tweaking some of the styles. You will likely notice a few glitches as we move code from the development servers to the live server.

You can report problems here if you wish. We should have this first phase of upgrades complete sometime tomorrow, but you never really know how things will flow.

Thank you for your patience.


In General questions | Asked By Daniel Morrison | Feb 29 12
9 Answers

Are there efficient in-slab radiant systems that also cool?

A client is getting bids from HVAC contractors to design/install heating & cooling systems for a 3100 SF single-level home located in the high desert climate of southern Utah (think Alburqurque, NM). The bids are quite high, perhaps due to the fact everyone says the client will need TWO complete systems; one to heat, one to cool. The bids all specify in-slab boiler-fed hydronic radiant heating coupled with a standard forced air furnace with a conventional AC unit for cooling (and I guess back-up heat). A friend keeps saying: "Screw that!

In Mechanicals | Asked By Timothy Smith | Feb 28 12
4 Answers

Is this a durable roof assembly?

I am working on the details for the roofing assemblies of two houses which are modeled in the PHPP to meet the Passivhaus Standard. We are in the Sierra foothills of California.

For the roofs, I am planning on metal roofing, over 3/4 furring strips, over 2 layers of EPS with staggered and taped joints, over Grace Ice and Water shield on plywood roof decking. The rafter cavities are insulated with cellulose and the assembly will dry to the inside.

In Energy efficiency and durability | Asked By Mela Breen | Feb 28 12
1 Answer

Radon and Sub Slab Drainage

Asked this over at JLC, I am still interested in opinions on question and comments...

I am going to use the formadrain in a few weeks. I am going to use the interior formadrain for radon abatement (interior formadrain connected to a 4' PVC passive system to vent out the roof at first, then fan driven if the radon numbers come in high after the house is completed).

In General questions | Asked By Joseph Garten | Feb 29 12
15 Answers

What's wrong with this wall?

From inside out...
1/2" Drywall
2x4 framing
Diagonal T brace or let in 2x bracing
2" XPS caulked and taped (doubles as WRB)
Horizontal Furring strips
Extira Siding

2x4 framing w/ 2"XPS makes window bucks easy. Extira (exterior grade MDF) is the probable siding choice as the desired look is approx. 2'x4' panels, and smooth texture is preferred. Running the furring strips horizontally allows the panels to be fastened in a location the makes sense for the panels, as well as allowing some customization of panel size. What am I missing/overlooking

In Plans Review | Asked By Aaron Vander Meulen | Jan 3 12
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