Home Additions & In-Law Suites
Structural additions, second stories, in-law and multigenerational suites, sunrooms and screened porches — designed, permitted, and built by a registered Maryland home builder.
Learn moreHome additions in Clarksville & River Hill, Maryland
Big lots, big houses, and one constraint that catches almost every in-law suite out here: the septic system has to be rated for the bedroom you are adding.
Reviewed by Bill Gmeinwieser, President ·
MHIC #16606 · MD Home Builder #1369 · Updated September 2026
Direct answer
Horizons Unlimited Home Improvements builds additions, in-law suites and whole-house remodels in Clarksville and River Hill, Maryland. Licensed since 1993 — MHIC #16606 and Maryland Home Builder Registration #1369, BBB A+. The constraint that shapes most projects in this part of Howard County is on-site sewage: many properties are on well and septic, and adding a bedroom generally requires approval from the Howard County Health Department's Bureau of Environmental Health through a bedroom application, because the septic system has to be sized for the number of bedrooms the house will have. Free estimates: 410-796-1333.
The septic bedroom rule, and why it kills in-law suites
Here is the sequence that goes wrong. A family plans an in-law suite — bedroom, full bath, sitting area — on a Clarksville property with a well and septic. Design gets done, a contractor is picked, and then somebody discovers that the existing septic system is permitted for a specific number of bedrooms and the addition would exceed it.
At that point the options are all more expensive than they would have been six months earlier: upgrade or expand the septic system, redesign the addition so the new room is not a bedroom by definition, or stop. Howard County's Bureau of Environmental Health administers the on-site sewage disposal program and a bedroom application process; percolation testing and design review come into it when a system has to change.
Do this first, before design. Establish what your septic system is
permitted for and what your lot could support if it needs to change. Bureau of Environmental Health:
410-313-1771. It is a phone call, and it is the cheapest possible time to find out.
The same logic applies to finishing a basement with a bedroom in it, and to converting a den or bonus room into a bedroom. The county cares about bedroom count because septic capacity is calculated from it, not about what you call the room.
What else is different about building out here
- Well water, not just septic. Adding bathrooms adds demand. Well yield and water treatment are worth confirming alongside the septic question.
- Large lots mean setbacks are rarely the problem. Unlike a Columbia townhome, most Clarksville and River Hill properties have room. The binding constraints here are environmental and utility, not dimensional.
- River Hill is a Columbia village. Homes inside River Hill are subject to the Columbia Association covenants and need village architectural approval as well as a county permit — even though the neighbourhood feels nothing like Town Center. If your address is River Hill, read the Columbia page too.
- Higher finish expectations. Most of what we are asked for in this corridor is primary-suite additions, kitchen expansions, sunrooms and screened porches, and full-house window and roof packages. The finish level is the easy part; the approvals are not.
In Clarksville & River Hill
What we build here.
The same ten services, under one Maryland license — MHIC #16606 and Home Builder Registration #1369.
Kitchen Remodeling
Full gut kitchens and targeted updates — cabinetry, countertops, lighting, flooring, and the electrical and plumbing work behind the walls.
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Bathroom Remodeling
Tiled showers, soaking tubs, double vanities, and full accessibility conversions — waterproofed properly and finished cleanly.
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Roofing
Asphalt shingle, cedar shake, slate, metal, and EPDM rubber. GAF, CertainTeed, and Firestone certified installation.
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Siding
Vinyl and aluminum siding, trim, and wrap — installed with proper flashing and house-wrap detailing so the wall assembly stays dry.
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Windows & Doors
Energy-efficient vinyl replacement windows with custom color matching, plus entry, patio, and French door replacement.
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Decks & Porches
PVC, composite, and wood decks, screened porches, and covered porches — engineered, permitted, and inspected.
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Egress Windows & Basement Code
Code-compliant basement egress windows and window wells — the single requirement that decides whether a finished basement bedroom is legal.
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Storm & Insurance Repair
Wind, hail, and fallen-tree damage — from a single leak to structural rebuild, handled by one licensed contractor instead of four subcontractors.
Learn moreCustom Homes
Design/build from concept to certificate of occupancy, including site development and permitting, under Maryland Home Builder Registration #1369.
Learn moreQ&A
Clarksville & River Hill: questions and answers
Can I add a bedroom to a house on septic in Howard County?
Only if the septic system is permitted for that number of bedrooms, or can be upgraded to be. Howard County's Bureau of Environmental Health administers the on-site sewage disposal program and a bedroom application process, and septic capacity is calculated from bedroom count. Establish what your existing system is rated for before you design an addition or finish a basement bedroom. Call 410-313-1771.
Does an in-law suite count as adding a bedroom?
For septic purposes, a room that functions as a bedroom generally counts as one regardless of what it is called on the plans. That is why in-law suites are the projects most often derailed by the septic rule in western Howard County. It is solvable — by upgrading the system, or by designing the suite so it does not add a bedroom — but only if it is identified early.
Is River Hill subject to Columbia Association covenants?
Yes. River Hill is one of Columbia's villages, so exterior alterations there generally require approval from the village architectural committee under the Columbia Association covenants in addition to a Howard County building permit — the same two-track process as the rest of Columbia.
Who builds home additions in Clarksville, MD?
Horizons Unlimited Home Improvements, Inc. of Elkridge builds additions, in-law and multigenerational suites, sunrooms, screened porches, kitchens and bathrooms in Clarksville and River Hill. Founded 1993; MHIC #16606; Maryland Home Builder Registration #1369; BBB A+. Free estimates performed by the owner at 410-796-1333.
Planning something in Clarksville & River Hill?
Free estimate, done by the owner, who will tell you honestly what the local approvals path looks like before you spend anything on design.