Basement subfloor help needed
Hello,
Have an 1964 split-level home in zone 5a, Colorado. It’s had many remodels/conversions/additions. We’ve had the home 1.5 years, and are remodeling the lower level ~4′ below grade level, — primarily area W of the Breezeway. We’re finding it challenging selecting flooring and slab insulation.
I’ve read many posts here, and have read many referenced articles, including the FHB articles “The Stay-Dry, No Mold…”, “Floor that can survive…”, “Build risk-free finished…” as well as Martin’s articles on Fixing wet basements, Finishing a basement floor, etc.
Issue: Flooring type selection and insulation with minor moisture evidence
Drawing: See below.
Comments:
– Slab heights vary – see image with slabs A, B, C
– Foundation walls are not above grade, some closer than others. Brick extends below grade, and re-grading is not a practical option.
– A couple spots where some mold is present, though nothing tremendous for area last remodeled 30 years ago. See *’s on attached image
– A few areas where rotting has occurred to base of fiberboard between studs and brick – not too scary, given it’s been that way probably 30+ years.
– Multiple slabs at varying heights – no insulation under these
– Where drywall was glued to foundation wall, some white minerals
– Pulled out 10 year old carpet – no mustiness to it
– repaired failed cove joint in N/S walls of inside breezeway – had mustiness/earthiness, bug infiltration, and some evidence of moisture on the N side. After repair, mustiness/earthiness went away in that room, but then mustiness appeared in NE bedroom… there may be some joint to repair in the foundation joint between slabs B&C, versus it being a direct moisture issue.
– Home is on a unique lot up hill of a large farm unlined irrigation ditch off a major seasonal creek. Runs 6 weeks during the summer – maybe 6′ deep and 6′ wide. Downhill neighbors have had some historic water issues.
– Soil drains very well – 65% Sand, 13% Silt, 22% clay (Sandy Clay Loam)
– About 1 yr ago, put down rubber gym flooring tiles in breezeway, directly on slab.They have developed some mold underneath them, though it’s not clear if this is from moisture from mopping the joints or condensation, as the room can be very cool, but heat up rapidly during the summer day or warm spring day.
– Even with the major area flooding a few years ago, supposedly this home had no bulk water infiltration, but the garage/breezeway exit are technically below the top of the irrigation ditch, which filled at that time.
Questions:
1. Is the approach with 1″ EPS topped with 1/2″ plywood held with tapcons, topped with 1/2″ plywood offset, topped by engineered hardwood or LVT (or similar) valid for my situation? Referring to areas West of the Breezeway, only.
2. It’s not clear from the writings on the topic if it’s OK to frame before putting down the EPS and plywood. I’m assuming so. Should edges be sealed?
3. Between slab A & B, there is about a 1″ drop. Any issues just adding 2″ of EPS here to level things out?
4. Recommendations for transitions into lower areas, such as the utility room (already tiled)?
5. If there is a bulk water infiltration (pipe breaks, etc), I assume the entire subfloor needs to get ripped out?
6. If putting carpet back down, any recommendations?
7. If anyone knows of someone knowledgable offering a pay based service for this and related insulation challenges, please let me know.
Sorry for all the wordiness – complex topic!
Thanks in advance!
Rossn
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Replies
Rossn,
Q. "Is the approach with 1 inch EPS topped with 1/2 inch plywood held with tapcons, topped with 1/2 inch plywood offset, topped by engineered hardwood or LVT (or similar) valid for my situation?"
A. That approach should work, as long as you are sure that there are no water entry problems. If I were you, I would probably install a layer of polyethylene between the concrete slab and the EPS.
Q. "It's not clear from the writings on the topic if it's OK to frame before putting down the EPS and plywood. I'm assuming so. Should edges be sealed?"
A. Are you talking about framing the partitions? I'm not sure what you mean by "OK to frame." If I were doing this work, I would frame walls and partitions after the floor insulation and subfloor was installed.
Q. "Between slab A & B, there is about a 1 inch drop. Any issues just adding 2 inches of EPS here to level things out?"
A. No issues.
Q. "Recommendations for transitions into lower areas, such as the utility room (already tiled)?"
A. I don't understand your question. Certainly, changes in floor level that measure only 1 or 2 inches are tripping hazards -- so if that's what you are talking about, keeping your finish flooring level is desirable.
Q. "If there is a bulk water infiltration (pipe breaks, etc), I assume the entire subfloor needs to get ripped out?"
A. The answer depends on the volume of water. If you have 1 quart of water, your subfloor should be fine. If you have 100 gallons of water, probably not, unless you notice the leak immediately and stop the water flow.
Q. "If putting carpet back down, any recommendations?"
A. Make sure that carpeting only goes down in areas that have a continuous horizontal layer of rigid foam under the carpeting.
Thanks for taking your time to respond to my questions, Martin -- greatly appreciated!
I feel confident there isn't a bulk water issue in these areas, possibly a moist foundation for certain times.
Would it be reasonable to frame the walls and partitions before putting down the EPS and plywood? While I understand this house has never suffered from a flood, with the driveway going beneath the irrigation ditch, there is the chance of that 1000 year flood, and the thought of having to pull out all framing due to a flood just makes things less bearable to think about. And, there's always the chance of a pipe leaking... had an icemaker line burst once.
Unfortunately, I'd end up with minimally 3 areas (utility room (tiled), entering the garage, and one grade-level door) where I'd not have the subfloor and therefore a 2-3" drop/rise.
How does this approach work with tile over the top, say in a lower level bathroom?
Rossn,
Q. "Would it be reasonable to frame the walls and partitions before putting down the EPS and plywood?"
A. Obviously, it's your house, and you can do it that way if you want. But if it were my house, I'd install the EPS and subfloor first, as I already explained in my last answer. If you ignore my advice, you should at least install a strip of EPS under the bottom plates of your partitions to keep the bottom plates isolated from the damp concrete.
Q. "Unfortunately, I'd end up with minimally 3 areas (utility room (tiled), entering the garage, and one grade-level door) where I'd not have the subfloor and therefore a 2-3" drop/rise. How does this approach work with tile over the top, say in a lower level bathroom?"
A. I'm not sure what you mean by "how does this approach work?" You'll end up with either (a) a custom-made ramp at the threshold, or (b) a riser that amounts to a tripping hazard -- that's how it will work.
Thanks, Martin. I was referring to if there are any issues with tile over this type of a subfloor, in terms of stability.
Rossn,
The standard recommendation (when installing ceramic tile over 1/2 inch plywood subflooring) is to install a layer of 1/2 inch plywood underlayment above the subflooring. For more information, see this Fine Homebuilding video: How to Prep a Plywood Subfloor for Tile.