Seal gap between felt paper and interior wall stud cavity?
Hi there,
I’m currently remodeling a house in Austin, and while I have the walls opened up from the interior, I wanted to know whether or not to caulk or use spray foam as a way to fill in the gaps between the sheathing material and the stud walls. In portions of the house there is felt paper for the areas with wood siding, and other areas there is thermo-ply for the brick walls.
My concerns have more to do with pest prevention more than energy efficiency and air tightness. Specifically I want to do something about the gaps between these sheathing materials and the bottom sill plate – I can see evidence of dirt from ant mounds and termites, and dead weeds that have found their way in in years past. For the areas with thermo-ply, there is also a layer of black plastic sheeting sandwiched between the thermo-ply and the bottom portion of the stud frame. Blow-in cellulose will be the insulation material.
Thanks for any help,
Charlie
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Replies
Charlie,
Your instinct is correct. Air sealing efforts have multiple benefits, and pest entry prevention is one of them.
So go ahead and air seal. Typically, small cracks can be sealed with caulk, and larger cracks can be sealed with canned spray foam.
Of course, there is no guarantee that mice won't chew through cured spray foam. But air sealing efforts always help.
Hi Martin,
Thank you for your prompt reply. Do I need to take into account any kind of expansion or moisture issues? I'm leaning more towards the foam because in some areas the materials are fairly loose, where the the black plastic/thermo-ply pull away from the studs and there isn't much contact.
I'll keep that in mind about the mice, thankfully there hasn't been an issue with them in the past, if memory serves me well.
Charlie,
Q. "Do I need to take into account any kind of expansion or moisture issues?"
A. A high quality caulk should be flexible enough to handle normal expansion and contraction issues -- better in most cases than cured spray foam (although using spray foam to seal gaps is obviously a good idea, even if the spray foam isn't particularly flexible).
Every builder should consider moisture issues. The first question to ask is, "Am I seeing any signs of moisture accumulation or damage?"
If the answer to that question is yes, then the second question to ask is, "What is the source of the moisture?"
Martin,
I’ll keep that in mind when choosing caulks and spray foam then.
As far as the moisture question, there were roof leaks in the past, and thus an issue with termites. It’s difficult to tell if there were other moisture issues on top of that. In about 5-10 areas spread throughout the house, the bottom portion of the thermo-ply has either been chewed away or disentigrated, which I take it to mean there must be moisture building up in those areas, but I’m not sure of the cause.
But I just wanted to make sure that by filling in the seams I originally posted about, I wouldn’t be contributing to a moisture buildup somewhere down the line.
Charlie,
The causes of the damaged Thermoply need to be investigated.
Is there splashback on the bricks?
Is the grade too high?
Does the exterior grade slope toward the house?
Are the weep holes at the base of the brick veneer clogged?
In some cases there are walls that were partially brick and siding, and thermo-ply was the sole backing material. The siding in these areas is in a poor state, which I think can explain the damaged t-ply at least under those conditions. [first 2 photos]. We will be replacing the siding and gutters later in the year, which hopefully will take care a lot of moisture issues.
The grade looks a few inches too high in some areas, but even where I can see the full foundation slab, I’m still seeing holes in the t-ply. The weep holes look okay now, but could have been clogged by ant mounds at some point. There are splash back issues causing siding to rot, but no t-ply in these areas, and the felt paper looks in good condition.
The grade does not appear to be sloping towards the house.
The third photo is of damaged t-ply which doesn’t seem to be explained by some of the suggestions, and I’m not seeing mounds of dirt. Where I’m seeing mounds of dirt, I’m assuming the damaged t-ply is due to the ants/clogging of weep holes.
If the windows were not properly sealed, could water be collecting at the bottom of these studs and be causing the damage to the t-ply? [fourth photo, hole in both black plastic and t-ply]
Thank you again for all your help so far.
Instead of using thermo-ply to replace to damaged sections (and because there might still be moisture issues), could I use extruded polystyrene instead? I'm wondering if it will be too thick to slide in between the brick an the bottom plate. If it does fit, could I just wedge it between the undamaged t-ply and the studs?
Charlie,
I hesitate to provide advice over the internet for your problem. A site visit would be necessary to figure out why you are getting rot.
The usual order of business would be:
1. Determine the source of the moisture that caused the rot.
2. Remedy the problem that allowed the moisture to accumulate.
3. Remove all rotten components and install new materials.
In general, the ThermoPly should be fastened directly to the exterior side of the studs and bottom plate, so I'm not sure why you are thinking of "wedging it [the XPS] between the undamaged t-ply and the studs."
I understand that a physical assessment would be better. Who would I consult with to check on those issues, a building inspector? As of now, I'm still thinking the issues are related to deteriorated siding, windows that don't have much in terms of flashing, and perhaps old ant mounds. Both siding and windows will have to be replaced later in the year, or early next year, but in the meantime, we're trying to close up all the walls in order to move back in within the next two months. Originally I was planning to replace the rotted t-ply with new t-ply, but then started wondering if XPS or some other material that could withstand water could be a better option.
By wedging it, I meant some kind of adaptation of an approach to a flood-proof wall assembly as proposed by the Building Science Corporation [first attached image]
https://buildingscience.com/documents/building-science-insights/bsi-101-rebuilding-houston
where the xps is installed in a shingle-like fashion. There, the foam runs along the complete height of the wall, but in our case, we wanted to know if it would be possible to use the existing t-ply, cut just above the deteriorated portions, and insert the foam just underneath the t-ply, using adhesive or a flashing tape to secure the foam. [second image attached]
I'm not looking to flood-proof the wall, but until we can address the moisture issues, I was hoping there be a solution that could serve as a better moisture barrier or drainage plane while we have access to these areas. I can also use some flashing tape on the bottom plate if that would help (and fill in the gaps/seams with caulk/foam like originally discussed). I know it's a bit backwards, but our timeline and budget are slightly out of sync right now.
Charlie,
You need to find a local contractor who is experienced at diagnosing and fixing water-entry problems in walls. I wish there was a magic way to tell the good contractors from the idiots, but unfortunately there isn't. It's tough. Get advice from local people you trust.
If you are working from the exterior, you can use any type of sheathing you want. Certainly plywood is more durable than ThermoPly. In Austin, you can safely use thin rigid foam for your sheathing, as long as you don't install so much rigid foam that the walls are imperfectly braced.
If you are working from the interior (where you have brick veneer), your options for repairing sheathing rot are more limited, and you may have to try something like the approach suggested by Building Science Corp.