How to put rigid foam over brick then stucco the foam
RMHvthukqE
| Posted in Energy Efficiency and Durability on
I have a house in El Paso Texas that has a brick exterior. I would like to put 2″ of rigid foam over the brick then stucco the foam. How should this be done? What type of stucco is best? I do not want to put the insulation on the inside of the house because it is a small house and it would take up too much room. The house has zero insulation. The house was built in the late 20’s. What questions should I ask a company that would be putting on the foam?
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Replies
Joan,
Any EIFS contractor should be able to help you. (EIFS is a siding system consisting of synthetic stucco over rigid foam.)
Here's a question to ask: what's the maximum thickness of foam you can provide? To get an R-13 wall, you'll want 2 1/2 or 3 inches of XPS, or almost 4 inches of EPS. More is better.
And if you are on this site, I assume you know about "Deep Energy Retrofits" and the Passive House movement (or at least would be open to looking into it). I would strongly consider working with a Passive House consultant, or an energy modeler who can help you make return on investment calculations, while you are at this opportunity point, where there is so much potential.
In response to Matt's post I'm going to stick my neck out and say that a Passive House consultant would have little to offer in your situation, Joan. PassivHaus technology is well understood in northern temperate European climates, also in the northern US and Canada, but to this point it is primarily a heating climate technology that has not been fully proven for climates where a/c costs can be significant. By all means hire an energy modeler if one is available locally but otherwise unless you have the very deep pockets for a deep energy retrofit or want to be at the bleeding edge of PassivHaus development for your area, stick with Martin's very sensible advice. Keep it simple.
If this is a brick cavity wall then adding insulation around the exterior might not be effective. Is there a frame wall at the interior, or is it solid brick?
Thomas, the walls are 2 bricks thick ( 8~9") with a variable one inch cavity between. The inside of the house is a cement or plaster over the inner stack of bricks. An electrical up grade put wire runs on the outside with holes leading to added interior wall receptacles. The plan is to glue 2" of sheet foam (XPS) over the wires and the exterior brick. The building contractor is not concerned about the bumpy brick, the shielded wires and some brick joints that have eroded a bit more than 1/2" . This looks like a big foam attachment problem. What happens to the air cavities that will be created between the foam and brick? What do you think about foil faced sheets? Foam over bumpy brick ! Thanks
Joan, rigid board insulation over a bumpy surface isn't a great idea. If outside air can circulate past the insulation in a gap, thermal value is compromised. That applies to any space between brick and insulation, and the cavity between two wythes of brick. Insulating the outside is a good idea but you really need either spray foam or blown fiber insulation, to deal with the irregular surface.
The next question is how thick of a wall you can live with. Basically you can set vertical furring strips exterior of the wall and support them with long screws, then attach cladding over the furring with insulation in the middle. Closed cell polyurethane would be a high performance insulation that needs fewer inches of thickness, but it's expensive and not especially green as a material. With a greater thickness you could use cellulose. This would need exterior sheathing over the furring to contain it. The window openings would also need to be rebuilt.
If you're going to sandwich the wiring in between the masonry and the foam, you should definitely check with your local building department to be sure they'd sign-off on such an assembly. If they're okay with it, then you should also think about future service access since you wouldn't be able to to just "open a wall" from the inside to get to the wiring if needed. If the wiring isn't already sheathed in rigid conduit, I would certainly consider doing this before enclosing it. Then it would probably make sense to run extra lengths of empty conduit at parallel locations if you needed to upgrade or add electrical or data-com wiring in the future. You should also look at using wide-sweep fittings to make it easier to get fish tape through them at a later time.
Also, when considering a retrofit outstation strategy, you want to be mindful of how the added depth may affect your roofing overhangs. I know that it's fairly common in TX architecture to have fairly sizable overhangs for shading, but if yours aren't already 12 or more inches on all sides, you might want to factor that into your decision process.
Joan, If you're still on this website, could you share how this turned out? I am looking at a similar situation for my own home. Thanks.