Looking for a basement contractor in Mountainside, NJ? Describe your project once and up to three basement contractors who work in Mountainside and Union County get back to you with a quote. It's free and there is no obligation.
Mountainside is home to about 7,228 people (2024 Census Bureau estimate), a growing community (+2.9% since 2020). With 1,809 people per sq mi, it is a suburban area. Full basements are common here and often the cheapest way to add living space.
Mountainside at a glance
- Population (Census Bureau estimate, 2024)
- 7,228 (+2.9% since 2020)
- Rank in New Jersey
- 156th of 323 cities and towns
- Land area
- 4.0 sq mi
- Population density
- 1,809 people per sq mi (suburban)
- Type
- Borough (Mountainside borough)
- Main county
- Union County
What to check before hiring in Mountainside
- Moisture first: waterproof before finishing.
- Egress: in New Jersey, a basement bedroom needs an escape opening.
- Radon: test before you finish.
- Price drivers: size, bathroom, ceiling height, finishes and egress.
Useful official resources
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ICC: International Code Council
Official information and guidance.
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EPA: radon
Official information and guidance.
Services available in Mountainside
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Basement finishing
Framing, insulation, electrical, drywall and flooring of a basement, with permit.
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Basement bathroom or rental unit
Bathroom, kitchenette or legal basement unit with egress and plumbing.
Frequently asked questions in Mountainside
How much does basement finishing cost in Mountainside, NJ?
It depends on size, bathroom and finishes. Describe your basement: contractors who serve Mountainside reply with a quote.
How long does it take?
Often several weeks.
Can I rent it out?
Only if local rules allow an accessory unit; check zoning.
Which basement contractors will contact me?
Up to three independent basement contractors who serve Mountainside and the surrounding area, chosen for the service you need. Your details are shared only with your consent.
Source: U.S. Census Bureau, Population Estimates Program (Vintage 2024) and Gazetteer Files (public domain), imported on 10/31/2026. Figures describe the incorporated place or county as published; they are shown for information only.