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A homeowner preparing to install new flooring asked GreenBuildingAdvisor readers how to air-seal areas exposed after removing baseboards. The post describes gaps and loose concrete around a slab edge, plus questions about sealing a bonus room and second-floor walls; it does not provide a confirmed repair plan or answer.
A homeowner preparing to install new flooring has asked GreenBuildingAdvisor readers for advice on air-sealing exposed wall and floor junctions, after removing baseboards revealed gaps near a slab-on-grade foundation. The question also raises uncertainty about where to seal around a bonus room with knee-wall attics and whether second-floor baseplates need attention.
The homeowner said the house was built in 1993 in climate zone 4A and has slab-on-grade construction. With the baseboards removed, the homeowner saw gaps between the slab and foundation wall. In some places, the concrete near the slab edge was described as thin, cracked and loose, and appeared to sit over foam insulation. The post does not establish what the foam is or how extensive the gaps are.
The homeowner is considering removing loose concrete and using Sikaflex self-leveling concrete sealant, but presented that as a possible approach, not a completed repair or a recommendation from an expert. They asked how to address the perimeter gaps without damaging the slab or using an unsuitable material.
A second set of questions concerns an upstairs bonus room with knee-wall attics. The homeowner said the subfloor appears continuous, with a bottom plate resting on it, and asked whether air sealing should be done from the room or attic side. They also asked whether sealing should address both the plate-to-subfloor gap and the drywall-to-plate junction, and whether similar work is appropriate along the second-floor walls. The supplied source contains the homeowner’s questions but no verified answers or documented outcome.
Air Sealing Before New Flooring
Removing baseboards can expose joints that are difficult to reach once flooring and trim are installed. For this homeowner, the work presents a limited-access opportunity to inspect the wall-to-floor perimeter before the renovation proceeds. Whether these particular gaps allow meaningful air leakage, however, has not been measured in the source.
The distinction between an air leak and a concrete or insulation defect matters. A visible crack does not, by itself, establish the correct repair material or show whether the slab edge is structurally sound. Loose or crumbling concrete and foam at the perimeter may need closer inspection before sealant is applied. The post offers no assessment from a building professional, so its proposed product and removal approach should not be read as approved instructions.
The upstairs questions also point to a practical issue: the effective air-control boundary may not be obvious where a room meets an attic or an exterior wall. Sealing only a visible interior joint may not address a separate leakage path, while sealing in the wrong location can leave gaps behind finishes. For readers undertaking similar work, the key takeaway is to identify the intended boundary and the condition of the materials before choosing a sealant or closing the area.
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The House and Exposed Joints
The source is a homeowner question published by GreenBuildingAdvisor, rather than a report of a completed retrofit or a building-code ruling. The writer said baseboards had been removed in preparation for new flooring and that this was likely the only time the bottom-plate area would be accessible. The house was described as a 1993 slab-on-grade home in zone 4A.
For background, the homeowner cited a Matt Risinger video as the closest practical guidance they had found and said they had read Martin Holladay articles about air-sealing bonus rooms. They believed their room might differ from examples in those articles because its subfloor seemed continuous. Those references explain the homeowner’s research, but the source does not say either author inspected this house or endorsed a particular repair.
The question covers three separate locations: the slab-to-foundation edge on the main level, the bottom and drywall junctions around a bonus-room knee-wall attic, and bottom plates on the second floor. Each is a question about a specific assembly; the source does not establish that all three locations are leaking or require the same treatment.
“I was hoping to air seal wherever necessary.”
— The homeowner, in the GreenBuildingAdvisor question
Repair Details Still Unverified
The source does not provide measurements, photographs, a site inspection, or a professional diagnosis. It is not clear how large or continuous the slab-edge gaps are, whether the loose concrete is limited to a surface layer, or what material lies beneath it. The homeowner’s description of foam as “styrofoam” is an observation, not a confirmed material identification.
It is also unknown whether air leakage was tested at any of the locations, which air-control layers are present behind the finishes, or how the knee-wall attic and second-floor assemblies are built. The post does not establish whether the drywall-to-plate junction is open, whether the subfloor is continuous across relevant boundaries, or whether the suggested sealant is compatible with the actual gap and substrate.
No replies, final repair decision, permit or code determination, or post-renovation result are included in the supplied material. Readers should not treat the homeowner’s proposed concrete removal or sealant choice as a confirmed solution.
Inspection Before Trim Returns
The immediate next step for the homeowner is to identify the slab-edge materials and determine whether the loose concrete needs repair beyond air sealing before selecting a product. Because the source does not confirm the condition or suitable repair method, a qualified building professional or concrete contractor can inspect the perimeter if the damage is extensive, continues beneath the visible edge, or raises concerns about the slab.
For the bonus room and second-floor walls, the homeowner would need to establish where the air-control boundary runs and inspect the accessible joints before the new flooring and baseboards conceal them again. The source gives no confirmed work sequence or product recommendation. Any guidance from respondents would need to account for the house’s actual assemblies and local requirements; the outcome remains unreported.
Key Questions
What did the homeowner find after removing the baseboards?
The homeowner reported gaps between the slab and foundation wall, with some edge concrete described as thin, cracked and loose. The post does not include an independent inspection or measurements.
Did the homeowner use Sikaflex sealant?
No completed repair is reported. The homeowner said they were considering Sikaflex self-leveling concrete sealant after removing loose concrete, but the source does not confirm that this approach was suitable or carried out.
Where should the bonus-room knee-wall area be sealed?
The question asks whether work should be done from the room or attic side and whether both plate-to-subfloor and drywall-to-plate joints matter. The supplied source does not provide an answer or enough construction detail to determine the correct location.
Does the post say every second-floor bottom plate should be sealed?
No. The homeowner asks whether to seal the second-floor bottom plates, but no inspection or response confirms that those joints leak or require sealing.
Source: greenbuildingadvisor.com
