Replies

1. 
   Randy_Williams | Jul 02, 2025 06:42am | #1

   Hi Harry,
   It sounds like you have a good opportunity to drastically improve the performance of your home. Changing windows from a single to two panes will more than double the insulation value, but only for the area the window takes in the wall. Adding insulation to the wall and attic will be a bigger contributor to energy cost savings and comfort. The tricky part with any renovation is to make sure to get the details right. If your walls leak a little water into them every time it rains, adding insulation may be detrimental. Slowing the movement of air moving through the building assemblies is also more important than insulating. There is an order of importance to follow when renovating, we call this order the control layers:

   1. Bulk water management, or the water control layer, is the most important. If things in your walls or roof get wet, adding insulation will slow the drying and possibly be more harmful to your home.
   2. Air sealing should be completed before adding any insulation. This is called the air control layer. Air sealing is easier if there isn't any insulation in the way. If you are removing your stucco cladding, there is a way to make your exterior sheathing an air barrier.
   3. Insulation is arguably the third most important control layer, called the thermal control layer.
   4. The final control layer is vapor. Managing water vapor in a way that we keep in out of areas where it can be harmful, or give it a pathway to leave an area if it does get into one of those areas. If you've effectively detailed the other three control layers, vapor is usually well controlled. In your case, if you have a dirt floor crawlspace, you'll want to install a vapor retarder on the ground and seal it to the walls and any penetrations. Also, manage humidity inside the home.

   There are whole books written about your seemingly simple questions, but here are a couple blog posts that may help:
   The Four Control Layers of a Wall - GreenBuildingAdvisor
   Webinar: Walls That Work–An Intro to the Four Control Layers - GreenBuildingAdvisor

   Good luck with your project!

2. 
   walta100 | Jul 02, 2025 03:53pm | #2

   1. I’m getting them changed to double pane windows. How much improvement should I expect?

   Unless the old windows are literally falling apart or have Aluminum frames you will not live long enough to recover the cost of the windows in fuel savings. My wild guess is at best you might save 12% on your energy bill.

   2. My contractor is removing the stucco and there’s no insulation in the outer walls. Should I get insulation in between the open studs? What type of insulation should I put in?

   Is the old stucco in such poor condition that replacement is the only option?

   If so, why did you chouse ignore the problem so long and allow it to get to this point?

   If the stucco is salvageable, I would have cellulose insulation blown into the wall and blower door directed air sealing done.

   Avoid foam insulation as is the most expensive, least green and riskiest way to buy an R of insulation. Pick the lowest cost per R offered likely cellulose.

   3. Should I put in attic fans to help with the heat? Should I put in a powered / unpowered fan? What kind of fan would be a good choice?

   I do not think attic fans will lower your energy bills in fact they will likely increase them. The fan depressurizes the attic it will suck the conditioned air from your home making your AC work harder. Note the fans will be incapable of moving enough air to make a meaningful change in the attics temp. If the hot attic bothers you fill the attic with R60 of cheap fluffy insulation. The attic is not vented for summer heat it is vented to expel moisture in the winter.

   Walta

3. 
   jollygreenshortguy | Jul 03, 2025 02:23am | #3

   I lived and worked in the SF Bay Area for decades. I'm no longer in the region.

   As you will find if more people answer, you have an overwhelming number of options for how to proceed (as well as a wide range of opinions about the best approach). Both answers #1 and #2 above offer good points. I'll suggest more. Which path you follow depends largely on the specifics of your house. You would really benefit from a local house designer with expertise. Unfortunately you cannot rely on the contractor to provide either the expertise or the unbiased advice.

   Regarding the walls, if you really don't NEED to remove the stucco you will save yourself $$$ simply by insulating the walls as Walta suggests. This can be done from inside but will require patching the drywall afterward. However if the stucco must go this is a good chance to deal with any existing moisture damage to the framing, as well as doing seismic upgrades. In that case you would benefit from doing continuous exterior insulation before installing your new siding.

   Regarding exterior insulation, the key to success is having a plan that also includes the installation of the doors and windows. Probably the most cost effective approach is to use 1 1/2" of EPS foam, applied over your existing sheathing. The EPS can be taped to serve as your WRB (water resisting barrier). This taping will need to integrate with your door/window installations. In San Jose you may be able to get away with no gapped rainscreen but I wouldn't advise it. So if you're finishing with stucco you'll need a system that provides a rainscreen. Or if you're going to wood/cement siding you will apply furring strips over the insulation.

   If you do exterior insulation do the blown cellulose suggested by Walta as well.

   Doors & Windows - Buy the most reliable you can afford. Remember, the cost of labor is the same whether you install a junk window or a high quality one. So try to put that labor cost into the best window you can afford. One way to save a little is to use fixed windows wherever possible. The installation is as or more important than the windows themselves. How they're installed needs to be planned carefully to integrate with your wall WRB. This is critical for avoiding problems with leaks in the future.

   There is a large array of resources here on GBA, including other Q&A strings and a big library of details. If you haven't joined, please consider joining for 1 year and exploring the detail library. This will be especially useful with regard to window installations.

   Roof - are you re-roofing? If so, then you can access the eaves. When it comes to attic insulation, the difficult spot is the eaves. You need to provide a way to ventilate the eaves. Baffles between the rafters is the typical approach and easy to implement if you are re-roofing and can get at your roof framing from above. A vented roof allows you to insulate the attic to a high level very affordably, simply using "fluffy stuff", cellulose or fiberglass loose fill insulation. If you do a vented attic DON'T put mechanical systems and ductwork up there.

   Are you in a wildfire zone? If so then you may not be allowed to do the ventilated roof system I just described. In wildfire zones you need to do an UNvented attic, which requires a very different approach to insulation. There are too many specifics to be able to describe your best option here.

   Unvented attics have the advantage of enabling you to use the attic space for mechanical units and ductwork.

   I encourage you to post a few photos of your house and come back with more questions.