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Insulating a 1929 craftsman bunglow in San Diego

The exterior walls have no insulation, vapor retarder or barrier. Is an exterior barrier/retarder required when insulating walls? If so, what products are available that doesn't require removal of siding to install?

Asked by patrick owen
Posted Mon, 03/24/2014 - 02:59
Edited Mon, 03/24/2014 - 05:33


11 Answers

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When building a new home with wood-framed walls, builders are always required to include a water-resistive barrier (WRB). For more information, see All About Water-Resistive Barriers.

Most building inspectors don't require such a barrier when an older house is being renovated, because it is hard to retrofit such a barrier without removing the siding. However, in all cases it's a good idea to check with your local building department to understand what your local inspector requires.

Before suggesting the best way to proceed, it would be good to know what type of siding you have (for example, clapboard or stucco), what type of sheathing, if any (for example, plywood or board sheathing), and whether or not there is any type of paper between these two layers (for example, rosin paper, asphalt felt, or building paper).

In your climate, you don't need an interior vapor barrier.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 03/24/2014 - 05:38
Edited Mon, 03/24/2014 - 05:44.

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Bungalows typically have deep roof overhangs which reduces the amount of rain-wetting of the exterior. In 1929 it wasn't common to install flashing in the rough-framing around windows either, but a deep eave/rake overhangs dramatically reduce the risks that might otherwise be associated with insulating around those windows.

Most of these homes can be dense-packed with cellulose (3.0lbs/cubic-foot minimum in your climate) or new-school fiberglass blowing wools (1.8lbs minimum), which tightens up air flow through the wall assemblies considerably. It's usually done from the exterior by popping off a section of siding, drilling a single 2-2.5" hole through the sheathing to accommodate a dense-packing hose, and the siding section is replaced or re-installed.

Some installers will just drill through the siding and pound in a plug to be trimmed flush, but there can be cosmetic issues with that approach.

I personally dense-packed most of my 1923 craftsman by drilling up from the bottom plate of the studwall from the basement (prior to insulating the foundation), which left only the shorter cavities above windows & doors to be dealt with in another manner.

Answered by Dana Dorsett
Posted Mon, 03/24/2014 - 12:11

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thanks for the two answers so far. Here's some more details on siding. Walls are cover with red cedar clapboards. no flashing around windows and no water barrier was originally installed. i am planning on using recycled blue jean insulation for the project. Sounds like i may not need to provide a barrier, but was wondering if there are any products that could be used to provide the water barrier. Spray-on that could be installed in the cavity prior to insulating? Just to be on the safe side.

Answered by patrick owen
Posted Mon, 03/24/2014 - 16:35

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We're getting closer. Now we need information on the sheathing. I'm guessing either:
1. No sheathing, or
2. Board sheathing.

If your 1929 bungalow was ever re-sided, there are other possibilities, including:
4. Plywood sheathing, or
5. OSB sheathing.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 03/24/2014 - 16:40

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Sorry for not including that info. There is no sheathing . Thanks for the help.

Answered by patrick owen
Posted Mon, 03/24/2014 - 16:50

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Clapboards nailed directly to studs, no sheathing is a problematic assembly to insulate. (Are you sure it doesn't have at least 1x planking or ship-lap sheathing under the clapboards? That's an assembly more often seen in 18th century houses in New England or 19th century desert south west than in maritime CA.)

If you insulate the insulation blocks back-side ventilation of the siding and there is no capillary break between the clapboards & insulation- the exterior paint will blister & peel without much prompting, and there is potential for moisture to migrate inward on the studs.

In addition to Martin's options 4 & 5 you could just leave the clapboards on, dense-pack the cavities, then put 2x furring on the exterior (over the existing siding) through screwed to the studs and apply 1-1.5" of closed cell polyurethane between the furring, leaving a gap between the sprayed foam and the siding to back-ventilate any new siding. Closed cell foam is weather/water resistant, and at 1" would add another R6 to the center-cavity R. You'd have to figure out what to do around the windows, but if you have 18" + overhangs it needn't be a full-flashing & re-mounting of the windows kind of deal.

Blown cotton from scrap denim would be fine, but only if you did a serious weather resistant barrier on the exterior. If you do it with a housewrap and forego the inch of spray foam you're probably better off with 1.8lb fiberglass, since it dries more quickly from bulk water incursions.

Answered by Dana Dorsett
Posted Mon, 03/24/2014 - 18:32

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Thanks Dana. to clarify a couple of thing please note: the blue jean insulation are batts, not blown in as i have the walls opened up. Also i believe that the siding is reffered to as "lap siding. it is rabbeted on the bottom so each piece over laps the previous. i hope i didn't miss lead you by reffering it to clapboard. not sure if those make any diference to your answer, but i thouht i'd check. Thanks again for your help.

Answered by patrick owen
Posted Tue, 03/25/2014 - 03:49

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Numbers 4 and 5 on my list were not suggested options for Patrick to consider; they were guesses concerning Patrick's existing sheathing. Patrick answered that #1 on my list was the actual situation.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 03/25/2014 - 05:51

Helpful? 0

There are at least two different ways to insulate stud bays on homes without any wall sheathing. Both methods create an air gap between the back of the siding and the insulation.

1. You can cut strips of a plastic mesh product like Home Slicker or Cedar Breather, and install these against the back of the siding, followed by some type of air barrier material (for example, strips of housewrap or rectangles of rigid foam). Unless you are insulating with spray foam insulation, this approach requires fussy air sealing in each stud bay.

2. You can install vertical 1"x1" sticks in the corners of each stud bay, against the back side of the siding, to create an air gap, and then install rectangles of rigid foam. This approach also requries fussy air sealing in each stud bay.

For more information, see Cut-and-Cobble Insulation.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 03/25/2014 - 05:59

Helpful? 0

Ship-lap siding has the same issues as clapboards when applied directly to the studs without sheathing, and is slightly MORE susceptible than clapboards when installed over sheathing, since there is less air between the siding & sheathing to act as a capillary break.

Martin's options in response #9 are really about all you get, though there are variations in the materials that you can use. In your climate I'd be inclined to use cut-up 2" wide strips of 3/4"-1" rigid EPS foam rather than 1x1 wood for the spacers between air-barrier & siding, (unfaced only, so the contact zone with the siding can still dry) and 1" foil-faced rigid polyiso for the air-barrier, reducing the total cavity depth by 2", then sealing all edges with can-foam. Since you have the interior stripped, take the time to caulk the seam between doubled-up top plates of the studwall with acoustic sealant caulk, as well as caulking the bottom plate to the floor/sub-floor.

Any way you do it means standard batts won't have the proper thickness, and may be difficult to split or compress denim batts sufficiently (I've never dealt with them, don't have a great feel for just how springy they are.) If you have full-dimension 2x4s (as opposed to standard milled 1.5" x 3.5" versions) Batts would have neither the correct depth or thickness anyway, which requires a lot more detailing to get the near-perfect fit they need to perform. Blown insulation and open cell spray polyurethane doesn't have theses issues, and it may be both cheaper and easier to staple in 10mm Obdyke Rainslicker (tm) and spray half-pound polyurethane directly onto the mesh than a cut'n'cobble + fiber (blown or batt) solution.

Answered by Dana Dorsett
Posted Tue, 03/25/2014 - 12:01

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Thanks for all your help. I really appreciated findng both of you with considerable knowledge on the subject. If y6ou like I can forward some photos as I proceed with the project so you can see how it goes. Thanks again


Answered by patrick owen
Posted Tue, 03/25/2014 - 15:49

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