Replacing termite-damaged foam board
bconway52
| Posted in General Questions on
Hi everyone,
I’m renovating my parents’ basement due to termite damage, and I’m hoping to get feedback on the best replacement strategy for the damaged foam board insulation—especially given that I have to work from the inside of the wall due to intact brick veneer.
Background:
- House is a 1996 two-story home with brick veneer over 2×6 wood-framed walls.
- Location: northeast Georgia, IECC Climate Zone 3A
- Exterior basement walls were originally insulated with 1/2″ Dow Styrofoam blue rigid foam board (used as sheathing) with fiberglass batts on the interior side.
- The foam board was not taped or sealed at the seams and had several large gaps between panels and large holes where penetrations were made.
- Multiple sections of the foam are damaged and/or removed, and I will likely have to replace it entirely from the interior, since the brick veneer is staying.
My current plan (inspired by a Matt Risinger retrofit detail):
- Clean up the back side of the brick veneer (removing mortar droppings). Install some retrofit brick ties from the interior. Place weep holes as appropriate since there are none.
- Install Delta-Dry drainage and ventilation mat (vs MTI SureCavity) against the back of the brick maintain a proper drainage and air gap for the brick veneer. Once the excess mortar is cleaned up there will be a little over 1” space between the framing and brick.
- Install Delta Vent S (or another WRB) inward of Delta Dry, air-sealed and taped to the stud bays.
- Fill each stud bay with mineral wool batt insulation.
- Install drywall as the final interior finish.
My questions:
- Does this assembly make sense for an interior-side retrofit under brick veneer, particularly from a moisture management and air control perspective?
- Is Delta Vent S the right WRB here, or would a different perm rating be better? I’ve read some posts suggesting a target perm around 1 for WRBs behind brick veneer.
- Would rigid foam board (EPS/XPS) be viable as an alternative to the Delta combo if properly sealed/taped—especially considering termite risks? Caveat is taping would be done from inside…not sure how that would effect the properties and durability of the tape vs using a sealant.
- Any thoughts on using a particle barrier like TRM or 16-grit sand at the base of the brick veneer cavity to help deter future termite intrusion? I’m also planning on applying Boracare to the new framing and have already done an exterior perimeter termite treatment with Termidor SC.
Thanks in advance for any guidance—trying to get this right before I begin insulating and closing up walls again.
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Replies
As you've already figured out, you're trying to do something very difficult and success of any approach will hardly be guaranteed. That said, I can offer the following feedback:
First, you haven't mentioned how much (if any) structural termite damage is present and whether you are replacing any structural members. If more than just cosmetic damage, one option would be to temporarily build an interior wall to support the floors above and to remove the entire current exterior framing. While this sounds extreme, it would give you the ability to use full sheets of materials and even do a reasonably good job of taping for air & water tightness. In a job like this, labor costs easily outstrip material costs. You also didn't mention whether or not there are any signs of water intrusion into either the cavity or the studspace. If so, this absolutely has to be addressed at the top. I would go so far as to spray the walls with a hose above the terrace/balcony structure. Turn on all of the exhaust appliances to induce some negative pressure and spend as long as an hour, wetting the entire wall and terrace floor. If you have no water coming into the basement level, that's great and you can proceed. Addressing some of your numbered questions:
1. Yes. Clean the mortar. Brick ties will be necessary, but will make this job much harder. This is not a very tall veneer, so I would go with as large a spacing as possible. Depending on the ties and the rigidity of the restraint at the top of the wall, I would be tempted to go with a single row of ties midway up the wall every other stud. There are also ties that can be installed from the outside after the veneer is complete and these might be a good option in your case, just so you can get your sheet goods properly installed.
2. You can probably skip the Delta Dry or another similar material. These are used to stop mortar from clogging the vent cavity during installation of the brick. Drainage and ventilation are sort of secondary functions.
3. Delta vent S is a good WRB and would be fine for the application, as would others. With such a sheltered wall in your climate, drying to both sides would be nice to have.
4. Mineral wool batts would work fine, as would unfaced fiberglass batts. Again, drying to both sides is good.
5. I always recommend moisture-resistant drywall in basement applications. There are many options here, from treated paper facings to fiberglass mats. Decide what you can afford, but the extra moisture and mold protection is worthwhile.
You ask about using foam insulation again. The foam doesn't increase the risk of termite infestation or the damage they do. The termites were already there and would probably have found the house sooner or later, and would have probably done the same amount of damage. The foam is just a highway for them, and an open cavity is just as much of a highway. Treating the exterior with Termidor and the interior wood with Boracare is as good a combination as you will find. You could use pesticide treated foam insulation but I'm not sure it buys much of an improvement in your application. I would consider attaching the foam to the back of the brick with dollops of adhesive and taping the seams with a high-quality tape like the ones offered by 3M, Siga and others. The edges are going to be the difficult part here, all around the perimeter. This is obviously far easier with the interior studs removed. The small cavity created by the surface roughness and the dollops of adhesive provides plenty of space for drainage. IMVHO, Ventilation of brick cavities is oversold as a performance thing, and your cavity won't vent much at all unless you can vent into the joist cavities of the terrace above without causing other issues. The same is sort of true for weep holes. Weeps don't do any good unless they sitting on well-installed through-wall flashings. It won't hurt to drill weep holes at the base of your wall, but it won't help much either. I would still do it just to provide some possible improvement. Yes, glued and taped XPS foam can act as your water, air, and vapor management layer.
One thing that seems to be missing in your walls is diagonal bracing. With that little earthquake last week, people are once again realizing that seismic concerns are real even for the eastern part of the country. And wind loading is also a legitimate concern. Your walls as built have no shear bracing and plain XPS does not provide any shear value. The easiest way to retrofit bracing would be to install diagonal strapping on the interior of the stud wall. Best practice would have the sill plate of the wall bolted down to the footings and the metal strapping connected to the sill plate. Alternately, some of the fiberglawss faced gypsum boards may be shear rated. I know the exterior ones (Dense Glass) are, but I'm not sure about interior ones right now. Worth taking a look.