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Turning a Basement into an In-law Suite: Six Elements of Successful Conversions

comments (6) January 9th, 2011 in Blogs
Olitch Mike Litchfield, Blogger, book author, one of the first FHB editors

Two sets of 8-ft.-high French doors on the east wall of this basement in-law allow air, light and people to circulate freely. The taller the doors or windows, the farther light can penetrate. The three-point arch (a Roman favorite) creates a graceful transition between rooms. Design: Jon Larson, Jarvis Architects. From In-laws, Outlaws, and Granny Flats.
Before the basement of this bungalow was remodeled, badly located stairs and a carport blocked sunlight and limited access. From In-laws, Outlaws, and Granny Flats.
By repositioning the stairs, removing the carport, resurfacing the parking area and erecting a screen (which will be covered with vegetation), the architect created a sunny patio without sacrificing any parking spaces. Design: Jon Larson, Jarvis Architects. From In-laws, Outlaws, and Granny Flats. 
Setting two tiny sinks at an angle was a creative response to the tight spaces in this basement suite: there simply wasnt room for a single larger sink. Sometimes constraints produce elegant solutions. Design: Jon Larson, Jarvis Architects. From In-laws, Outlaws, and Granny Flats.
To enable occupants to exit quickly in case of a fire, building codes require a method of egress--escape--for sleeping rooms on every level of the house, including the basement. Codes specify the size of the egress: typically, at least 20 in. wide and and least 24 in. tall, with a combined net-clear opening of 5.7 sq.ft. From In-laws, Outlaws, and Granny Flats.
If the drainpipes of a basement in-law suite are below the city sewer main, youll need to pump wastes up to the main--by using a sewerage ejection pump or a macerating toilet unit, shown here. Macerating toilets sit atop the floor, so theres no need to cut a trench for pipes.
Two sets of 8-ft.-high French doors on the east wall of this basement in-law allow air, light and people to circulate freely. The taller the doors or windows, the farther light can penetrate. The three-point arch (a Roman favorite) creates a graceful transition between rooms. Design: Jon Larson, Jarvis Architects. From In-laws, Outlaws, and Granny Flats.Click To Enlarge

Two sets of 8-ft.-high French doors on the east wall of this basement in-law allow air, light and people to circulate freely. The taller the doors or windows, the farther light can penetrate. The three-point arch (a Roman favorite) creates a graceful transition between rooms. Design: Jon Larson, Jarvis Architects. From In-laws, Outlaws, and Granny Flats.

Photo: Muffy Kibbey


Converting a basement can be one of the most cost-effective ways to create an in-law unit. Correctly done, it is also one of the least expensive to heat and cool, because temperatures will be moderated, to a degree, by the basement's contact with the earth. The crux of a successful conversion is how un-basement-like you make it feel. In other words, it depends on how much sunlight, fresh air, comfort, and ceiling height you can get into the space. Below are six common conditions you may encounter when converting a basement into an in-law unit and what to do about each.


1. Remediate excessive moisture 

Although moisture can appear as condensation on the inside of basement walls and isn't a difficult thing to resolve, serious water problems have their source outside the basement. Thus, inexpensive interior "fixes" such as sump pumps or dehumidifiers will mitigate seasonal dampness to a degree, but living spaces may still smell musty and be plagued by mold. Increasing sunlight and ventilation is always welcome, but to keep moisture from entering, you'll need a solution that stops water before it gets through the basement walls.


By far the cheapest remedy-universally recommended by how-to books and ignored by homeowners-is to keep gutters and downspouts clear so they can direct water away from the foundation. Sloping the ground away from the house also helps, as does trimming back vegetation that hinders air circulation. Beyond that, cures get costly, such as installing perimeter drains around the house to remove the water or adding French drains uphill to intercept it. If you have running streams nearby, high ground-water levels, or if you live in a flood-prone district, developing the basement simply may not be viable.


SIDEBAR: A better way to insulate a basement

To retain conditioned air and prevent condensation on cool, below-grade basement walls, builders usually install 2-in.-thick rigid insulation over the foundation walls, erect a 2x4 stud wall on the inside, and then install drywall. That 6-in.-thick assembly eats up precious space. For that reason, companies such as and Owens Corning offer modular finishing systems that combine insulation, water-resistant panels, and the like. Installed by licensed professionals, such systems tend to be proprietary and pricey.


Homeowners determined to do their own basement conversions might want to look into the Insofast system ( Insofast insulation panels are 2 ft. by 4 ft. by 2-in.-thick expanded polystyrene (EPS) whose edges interlock so you can assemble wall sections on the ground, tilt them up and adhere them to foundation walls using foam-board adhesive. Panels' backsides have vertical channels for moisture drainage and horizontal ones that you can feed electrical wiring through-later, if need be. On the panels' front sides are integral fastening strips that you can screw paperless drywall panels directly to, so you don't need to frame stud walls. the finished, insulated assembly is only 21⁄2 in. thick.


2. Create sufficient headroom 

For most codes, 7-ft. 6-in. finished ceilings are the minimum. If that's not what you have, you must either raise the house or lower the basement floor. Either approach is a big undertaking. Lowering the floor typically involves supporting the house, removing an existing slab, excavating, and augmenting or replacing all or part of the foundation and drainage system. Raising a house is a big project, too, but, in general, it's the better strategy because it creates more height for windows, and thus allows more natural light to enter  the space. If you also must replace a failing foundation (which requires supporting the house), then your choice is even clearer: Up she goes.


3. Provide access and egress (escape) 

Two types of access can be difficult to provide in a basement in-law: emergency egress and entry. Some provision for emergency egress is required by code, and can be provided by a door that leads directly to the garage, or by a window that's large enough and low enough to crawl out of. Codes generally specify a maximum window-sill height of 44 in. above the floor, although a 32-in. sill height seems more reasonable if there are kids or elders present.


An in-law unit's entry, on the other hand, could be through the house above although, ideally, it should be an exterior door to maximize privacy for you and your tenant. If you have a large home, however, the door to the basement may be buried deep in the middle of the house. And your basement may have few or no windows.


4. Correct foundation problems 

If your foundation is failing and must be replaced, that's a great opportunity to create or upgrade a basement in-law. A structural engineer can assess the foundation and design its upgrade, but some common signs of foundation failure include large (1⁄2 in. or wider) vertical cracks through the foundation, foundation walls bowing in, sinking foundation corners, and flooring in the rooms above that crowns above a girder.


If your house is on a sloping lot, there's an interesting upside to enlarging the space under the house. The downhill face of a basement unit will be aboveground so on that side, you can create a whole wall of windows. You may need to scoop out a lot of earth, build a retaining wall, and augment the foundation-all big undertakings-but the in-law unit that results will be sunny, spacious, and very un-basement-like. The house in the first four photos (above) was built on one side of a gully: thus, while the west wall of the basement was cut into the hill and windowless, its east side was gloriously tall and open--perfect for a bank of French doors.


5. Maximize natural light

On a sloping lot, a good design can deliver abundant natural light into the unit. But if a basement is buried under the house and is, say, two-thirds underground, natural light will be hard to come by. Frequently, homeowners add window wells. You can also try an interior solution such as sacrificing part of a closet upstairs to run a light tube to the roof. Your choice of artificial lighting matters, too: warm- fluorescent bulbs or dimmable halogen lighting can impart hues that are more natural. Lastly, if you share your yard or create a patio where tenants can catch some sun, those rays will help them lose the subterranean blues.


6. Flush up when the basement's below sewer connections

Most of the time, wastes flow freely out of a house via downward-sloped drains. All it takes is gravity. If, however, you have a basement unit whose drainpipes are below the city sewer main, you'll need to pump wastes up to the main. This can be achieved by using a sewage ejection pump or a macerating toilet unit.


Sewage ejection pumps can be used with standard toilets. If the floor is concrete, you must first cut a slot in it and then excavate a trench large enough to accommodate drainpipes and a sewage-holding tank. (You can rent concrete-cutting saws but it's a miserable task for an amateur; hire a concrete-cutting specialist instead.) In the bottom of the tank is a pump that propels sewage up to the sewer main, via a 2-in. or 3-in. discharge pipe rising from the top of the tank.


A macerating toilet unit sits atop the floor and there's no need to cut a trench. The sewage goes directly from the toilet into a chamber whose cutting blades shred or grind the solids into a slurry that can be ejected through a much smaller discharge pipe-typically 3⁄4 in. Macerating units cost more, but, once you factor in labor, they're competitively priced. Macerating units are less widely known, however, so check with building authorities to be sure these toilets are approved for your locale.


Create Your Own In-Law!

If you're interested in second units, please check out my recent book, Outlaws and Granny Flats: Your Guide to Turning One House into Two Homes. The Library Journal named it one of the 10 Best Design Books for 2011. You can get an e-book version on Apple's iTunes Store, or on the Taunton Press Store. You can also preview In-laws, Outlaws' lush color photos at 


If you will be renovating your home (or perhaps creating an in-law suite), there's no better companion than Renovation 4th Edition, (November, 2012). Its 614 pages, 1,000 photos and 250 detailed illustrations cover home renovation from start to finish and  contain lifetimes of practical, field-tested techniques that professional builders shared with me over a 40-year period.

© Michael Litchfield 2012

posted in: Blogs, basement conversion, basement in-law suite, basement dwelling unit, basement in-law unit

Comments (6)

DennisMarshall DennisMarshall writes: Many people own homes with basements and this is inexpensive to finished it out, since it has already walls, flooring, ceiling and converting it to more space for your family. But it should also be equip with necessary amenities like heater that will serve as comfort to stay in during winter months for your family.
Posted: 5:31 am on May 27th

DennisMarshall DennisMarshall writes: You could actually turn that space into something to make money. If your house is in the city you can convert that basement into a profitable rental apartment. But don't go too crazy finishing it off with high-end finishes and expensive flooring.
Posted: 5:42 am on May 26th

pujari pujari writes: Nice article about the basement conversion, we really love it.

penninepreservations Basement conversion Company
Posted: 12:18 pm on May 19th

Horsham_Architect Horsham_Architect writes: Important issues:
1) Many communities require a zoning variance if the in-law suite has a kitchen.
If no kitchen, the stairs must be readily negotiatable. Many homes have STEEPER stairs to the basement or cellar, and they are often NARROWER, making a lift not
a practical alternative.
2) Some communities prohibit using CELLAR space for sleeping. Many use the word basement carelessly - a basement has over 50% of its wall area ABOVE grade, as in basement garden apartments. Most houses have CELLARS, which have more than 50% below grade.
3) The International Residential Code, which now covers MOST of the country, allows 7' ceilings. WHile 7'-6" or taller is far more desirable, I would rather have that than spend the equivalent of a Mercedes Benz raising a house a few inches with all the liabilities that entails.
4) Many insurance policies severely limit damage to finished subterranean spaces.
5) Those wells which look great in summer when filled with snow and ice could make exiting out of them pretty dicey.
6) The garage conversion still solves the light and moisture issues, can be readily accessible for walkers and wheelchairs,and allows the in-laws to better be integrated into the family.
7) Where permitted, the Medi-Cottage modular self-contained suite allows for those with significant medical issues to be close to you. We can adapt those ideas into many garages where zoning prohibits a separate structure.
Posted: 2:41 pm on January 17th

Olitch Olitch writes: Renosteinke's dour take on basement suites is not without merit but he's using a sledge to drive a finish nail. Yes, if you build a house on a flood plain, you are asking for trouble and few remedies will do much good. But the vast majority of houses with basements are not built on flood plains and the brief excerpt above is intended for them. NOTE: Since the original posting, I added a sidebar on insulating a basement, partly in response to Renostenke's gripe that the article didn't have enough meat to it.

In fact, this "blog" on converting a basement is an excerpt from a very substantial book (In-laws, Outlaws, and Granny Flats) that features five handsome basement conversions among its 30 case histories. As my intent is to sell books rather than give them away piecemeal on the internet, this excerpt is just a taste, not a meal.

Posted: 12:05 pm on January 16th

renosteinke renosteinke writes: A varying opinion was voiced to me by the local State Feam Insurance agent: Basements are NOT meant to be finished or lived in."

This was said in the context of a flood claim; the house was 15 years old, in great shape, was not in a flood zone, and had never before had a flood. Oops.

Face it: Moisture happens. Whether from above the slab, under the slab, or through the window ... it happens. Sooner or later, there WILL be a water problem.

Ordinary construction methods will only serve to maximize the amount of damage that follows. Yet, even a 'perfect' job can become an issue at sale time ... where the unpermitted work only serves to highlight the zoning violation that the 'apartment' created. Oops.

Whether on "Holmes" or "Income Property," HGTV is chock full of basement babies that matured into golems. Kind of takes the luster off puff pieces like this one!
Posted: 6:10 pm on January 12th

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