Sjellonlund, Denmark – floor lowering and underpinning as a partial contract
A case with a clear handover: demolition, excavation and underpinning were completed professionally before the client continued the floor build-up.
Denmark · SjellonlundUnderpinning & foundation strengthening · BASEMENTATLAS
Cracks in basement walls
Cracks in basement walls. Start by documenting crack width and pattern, load-bearing support and stability and changes after rain. The purpose is to understand the building condition and constraints before choosing products, finishes or a work sequence.
Short answer
Cracks in basement walls. Direction, width, location and change over time are more informative than the presence of a crack alone. Different patterns can point to shrinkage, settlement or structural movement. Excavation, wall openings, crack repair and floor lowering can change load paths. Cosmetic repair is unsafe if movement or loss of support is still active.
Assessment
Cracks in basement walls
Foundation work is controlled by load paths and sequence. Existing footing depth, soil and groundwater conditions, crack patterns and the size of each working section can change what is safe to excavate or underpin.
1crack width and pattern2load-bearing support and stability3changes after rain4existing foundation depth
Technical checkpoints
Document these points before comparing solutions.
1crack width and pattern
2load-bearing support and stability
3changes after rain
4existing foundation depth
BASEMENTATLAS · Problem finder
Diagnostic signals
Direction, width, location and change over time are more informative than the presence of a crack alone. Different patterns can point to shrinkage, settlement or structural movement.
CheckPhotograph with a scale, mark the ends, record width and date, and monitor whether the crack changes before choosing a repair method.
Excavation, wall openings, crack repair and floor lowering can change load paths. Cosmetic repair is unsafe if movement or loss of support is still active.
CheckIdentify load-bearing walls, columns, foundations and temporary support needs before removing soil, masonry or structural material.
A change after rainfall points toward rainwater, surface drainage, wall penetration or drainage capacity rather than a purely indoor humidity problem.
CheckCompare the same area before rain, during prolonged rain and 12–24 hours afterwards. Also photograph gutters, downpipes, paving and ground slope outside.
The relationship between planned excavation and existing foundation depth governs whether underpinning, staged excavation or a different floor solution is required.
CheckDo not assume foundation depth. Confirm it from drawings, trial pits or professional investigation before lowering the floor.
What to document first
Photograph the whole area and close-ups; note approximate building age, wall/floor construction, outside ground level and when the symptom changes. If water is involved, record whether it follows heavy rain, snowmelt, showering or is present continuously.
What changes the decision
The decision changes with moisture source, structural condition, available height, drainage level, intended room use and whether the work affects load-bearing construction. Treat a product choice as the final step, not the first.
Common mistakes to avoid
Avoid sealing over an unexplained wet surface, building organic stud walls against a damp masonry wall, or starting finish work before drainage, structure and services are coordinated.
Structural, electrical, plumbing, geotechnical and health-critical work can require qualified professionals and local approvals.
Red flags
Rapidly growing cracks, active water, structural movement, sewage backflow or extensive mould deserve a more cautious assessment before finishes continue.
Cost factors
Cost changes with access, excavation depth, structural work, drainage levels, services, disposal and the finish standard. Compare scope before comparing price.
Next steps
Document the condition first, identify the likely source, compare relevant methods and only then decide the work sequence.
Follow-up
After the work, record visible condition, odour, humidity and any new water after roughly 3, 6 and 12 months. Long-term follow-up is more useful than a result measured the next day.
Problem guide
Relevant guides
Construction profiles
Comparisons
Problem scenarios
Checklists
Relevant real cases
Amager, Denmark – excavation, sectional underpinning and complete basement renovation
A first-party case showing excavation and numbered underpinning stages under an existing house, followed by a complete basement rebuild.
Denmark · AmagerBASEMENT ATLAS
Evidence basis
This page combines structured basement knowledge with sources relevant to the topic. Practical project experience does not replace regulations, structural design or licensed professional advice.
1 technical/authority sourcesUpdated 2026-08-30
BASEMENTATLAS · Evidence & moderation
Evidence & moderation
Frequently asked questions
Can this usually be solved from the inside?
Sometimes, but not always. External water pressure, drainage defects or structural movement may require work outside or in the construction itself.
What should I include in a BasementAtlas question?
Country, approximate building year, city/postcode area, photos inside and outside, timing, what has been tried and the result you want.
When should a professional be involved?
When foundations, load-bearing construction, excavation depth, electricity, plumbing, sewer backflow, geotechnics, hazardous materials or health-critical mould are involved.
BASEMENT ATLAS
Continue in the same topic
Related guides, problems, checklists, cases and technical terms from the same knowledge area.
GuideBasement contractor scope and handover→GuideBasement underpinning→GuideCrack injection in basement walls→ProblemCracks or movement→ProblemLow basement / lower the floor→ScenarioA basement crack is getting wider→ScenarioCracks appear after basement excavation→ChecklistChecklist: Monitoring basement cracks→ChecklistUnderpinning planning checklist→CaseAmager, Denmark – excavation, sectional underpinning and complete basement renovation→