On renovations and other non-new construction, the potential for hidden problems (read: costs) is always there. This holds particularly true in renovating your siding, where you never know what condition your substrate is in. Does this mean you should avoid the issue altogether? No. As they say: Kill the monster while it’s small, before it has the chance to become a full grown problem.
Replacing old Siding
You may be looking at EIFS for a multitude of reasons; saving money on your heating bill, damaged siding, or you may just be looking for a more modern look. A good portion of homes built in the 70s, 80s and even 90s used unattractive and incorrectly installed vinyl or board and batten siding. These days, not only is the siding considered retro and shows signs of aging, but in most cases it wasn’t properly sealed and may be covering serious rot and mold. The fact is you don’t know if the subdivision builder slapped the walls together as quickly and cheaply as possible, at a time comparable to medieval age in terms of knowledge about weather resistance.
Stucco Substrate Condition
In replacing your siding with stucco, you will be forced to take a good look at your substrate and it’s suitability for synthetic stucco siding. Any instance of mold or rot will need to be replaced before the trowel-applied weather barrier can be applied. The substrate is required to be free of surface contamination, including (not not limited to); dirt, form release agents, efflorescence, oil, chalkiness, and cracks greater than 1mm. Even in situations where the substrate is fine, it may not be approved to have EIFS applied over it. EIMA defines a suitable substrate as: “gypsum sheathing in compliance with ASTM C 1396 (formerly C 79), glass-mat gypsum sheating in compliance with ASTM C 1177 (Dens-Glass Gold® or BPB GlassRoc), and gypsum fiber panels in compliance with ASTM C1278 (Fiberock® Brand, Aqua Tough™)” and certain manufacturers such as Durabond have products for exterior grade plywood (which also acts as lateral bracing). Felt paper or building wrap is no longer recommended because it requires mechanical attachment, which penetrates the weather barrier, allowing moisture in. Certain substrates such as exterior-grade drywall (gypsum sheating) may also require lateral bracing between studs. Lateral bracing is used to prevent excessive horizontal movement and assist in absorbing wind loads transferred to it from the stucco wall. When in doubt, you may want to have an engineer look at your walls so as to avoid having your siding crack down the road. A final note is that most EIFS manufacturers require less than 1/4″ deflection per 60″ span (L/240) — a feat that a good portion of construction projects wouldn’t meet if measured.
Retrofiting Stucco with Brick and CMU
With brick and CMU (concrete masonry units), your sheating and cladding may not need to be touched at all. Brick contains an air gap between itself and the substrate — usually covered in a building wrap. This means that while you may need to level the brick face with basecoat to properly adhere the styrofoam, you need not worry about replacing the substrate, adding a drainage layer or the stucco causing moisture problems. Along the same lines, CMU construction can not rot or support mold growth and usually acts as a partial weather barrier (note: they usually have poly installed between the masonry and interior drywall.) In this case, the styrofoam may be applied directly to the CMU. Even on brick and masonry, it is a good idea to to have the drainage channel to prevent water from becoming trapped behind the EIFS cladding; and they still need to comply with sheating requirements (free of dirt, form release agents, efflorescence, oil, chalkiness, and cracks greater than 1mm.)
It’s important to realize that whatever is currently on your house will have an impact on how any siding replacement proceeds, and stucco is no exception. It is a good idea to have some extra money budgeted and an agreement with you stucco contractor as to what will happen in the event you run into unsuitable substrate. Stucco Contractors rarely do sheating replacement and you will likely need to find a general renovation contractor to do this before they can proceed. You will also need to have a large bin on site to dispose of your old sheating and substrate, or specify this as part of your general contractor’s job. In the case of applying stucco directly over brick or masonry, you may even be able to save some money because there’s one less layer to be applied.