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Deep energy retrofit strategies for uninsulated brick home in Phoenix

I'm looking to perform a deep energy retrofit on my 1947 brick home in Phoenix, AZ, and was hoping to get some feedback from the forum about the most cost-effective and beneficial strategies. The exterior walls are exposed double-wythe brick with 3/4" plaster on the interior. The windows are the original leaky, single-pane, steel casements. The attic is vented with R-38 on the ceiling, and the majority of the ductwork is exposed to the high attic temps.

In Phoenix, homes of this vintage are considered historic, so I am unable to cover up the original exposed brick on the exterior. The windows are a hot button as well, but I may be able to swap those out if I can maintain the original aesthetic. My thoughts include replacement windows, a layer of rigid insulation on the interior side of the walls, maybe open-cell spray foam on the underside of the roof deck to create a conditioned attic, replacement A/C, duct sealing, etc.

Any comments or thoughts are welcome. Phoenix receives very little rain, but I am a little concerned about insulating/air sealing the interior side of the previously un-insulated brick wall. Does anyone know if this will cause any unintended condensation or vapor drive issues?

Thanks in advance.

Asked by Nathan Morey
Posted Fri, 01/25/2013 - 15:13

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3 Answers

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Nathan,
In your climate, it should be safe to insulate the interior of a multi-wythe brick building. But beware of thermal bridging: if you are going to insulate the interior of your brick walls, you have to be consistent, all around the building. Insulating just one or two walls won't help much.

In your climate, replacing windows makes sense. Pay close attention to the SHGC of the glazing you choose. You want a low SHGC, especially on the east and west sides of the building.

You'll definitely want to create a sealed, conditioned attic. More information here: Creating a Conditioned Attic.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 01/25/2013 - 15:42

2.
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With any type of brick it's useful to leave a cavity between the brick & any interior insulation even in Phoenix. In most places 1.5" would be the minimum but in Phoenix you can probably cut that in half. Using vertical 1x furring 16" o.c. screwed to the masonry would allow you mount foil-faced polyiso held in place with lateral 1x furring through screwed to the cavity furring, on which the wallboard could be mounted. In this climate (and very few others) the foil-facers provide a real performance enhancement for cutting down peak cooling loads on walls that get direct sun. (Foil facers are relatively easy to air-seal using FSK tape too.) Whatever the chosen thickness, using two layers of iso seams-staggered sealing all seams with FSK tape, and all edges with can-foam or closed cell spray foam works.

A double-layer of 1" would be R12 nominally, but would perform better than R15 on the hot sunny-side walls, and would outperform a 2x4 studwall with R15 rock-wool butted up against the interior brick by a large margin at the same wall thickness. At 3" iso it would outperform a 2x6 interior studwall solution. In your climate a rationale for wall-R greater than that doesn't really exist.

See table 2, p10 of this document:

http://www.buildingscience.com/documents/reports/rr-1005-building-americ...

Phoenix is in zone 2, and a 3" layer of continuous polyiso is R18 nominal, a bit less with the thermal bridging of the screws, etc, but still pretty good. It'll do slightly better than that during the cooling season, somewhat less at the wintertime low temps. I'd stop there unless you have specific PassiveHouse or NetZeroEnergy considerations in mind. Even 2" can be pretty good, spending the difference in cost on better windows.

Roofing materials/finishes can also make a huge difference in cooling loads even with a conditioned attic if you're allowed to use CRRC rated "cool roof"materials (see http://www.coolroofs.org/ ), but if it's a tile/masonry roof it's not worth changing- concentrate on the interior. Roofs and glazing type are far more critical than wall R once the walls are at R12 or better.

Answered by Dana Dorsett
Posted Fri, 01/25/2013 - 17:47

3.
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Dana,
You wrote, "With any type of brick it's useful to leave a cavity between the brick & any interior insulation even in Phoenix."

Not true! For insulating the interior of a multi-wythe brick building in a cold climate, that wouldn't work. You have to use spray foam directly against the brick. To find out why, read Insulating Old Brick Buildings.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 01/25/2013 - 18:02

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