How do you appraise an in-law suite?

A reader’s question about appraising homes with an in-law suite

in-law suiteI was recently asked a question by real estate agent Tammy Anderson about how appraisers might appraise an in-law suite. She was specifically curious about whether a second kitchen and entrance might cause trouble in the valuation. If you have any further questions about an in-law suite or would like to submit your own question, leave a comment below or message me.

In-law suite defined

An in-law suite is not uncommon in homes and can go by various other names, such as mother-in-law suite, granny flat, or it can even be used as a teen apartment. On a side note, there is an older area of Birmingham with homes that have what is known as a carriage house, which is an apartment over a detached garage. Most of the time an in-law suite will have a sleeping and living area, a simple kitchen, a bathroom, and a separate entrance. There are different types of in-law suites as well that can include an apartment over a garage, a finished basement, an add-on to the main house, and an attic conversion.

An important thing to remember if you are going to build an in-law suite is to check with local zoning ordinances. There can also be certain fire guidelines you must follow for an additional kitchen in the home. If you do not get approval with your local building department then it could cause you problems down the road whenever the home is appraised or when you go to sell.

Considerations when appraising a home with an in-law suite

From an appraisal perspective, there are various things that we consider whenever appraising a home with an in-law suite. These are also things that you as a homeowner should be aware of so that you get maximum value for your home and the best return on your investment. By the way, there are no negative consequences with having a separate entrance.

You will get the most value for the finished area in your house when it is above grade and contiguous to other finished areas. Any finished areas that are below grade, such as in a basement, will not typically contribute to the overall value of the home as much as those areas that are above grade.

If you have any finished areas that you access by leaving the main home this will contribute less value. An examplein-law suite considerations of this would be an apartment over a detached garage or an apartment over an attached garage that you must access by going through an unfinished area of the home. Some apartments over attached garages are accessed by going through the garage or by an outside entrance.

When we appraise an in-law suite the two types that typically get the most value, but can also cost the most are those that are either an add on to the above grade area of the main house or are attic conversions. The attic conversion is probably the most costly because you must make sure the foundation is adequate for the addition.

The least costly in-law suite to build is the type where you finish off an unfinished area that is already under roof. As I previously stated, whenever these areas are part of the above grade area of the house you will get maximum value for the money you spend on the conversion.

So now that you are aware of the different types of in-law suites and how they contribute to value let’s look at how they are handled in an appraisal.

It’s all about the comps

Value is measured best whenever there are more similar properties to compare the subject property to. The more truly comparable properties you have the more accurate the appraisal will be. If you have a one of a kind property and there are no other sales to compare it to then it becomes difficult for the appraiser to measure the effect on the value that the in-law suite has.

It will depend on the area you are located in as to which type of in-law suites are most common and therefore the ones that will have the most comps. In the Birmingham, AL area I find that the most common type of in-law suite is the one located in the basement of a home. Because they are common there will be more sales to compare it to and the value arrived at will be more dependable and accurate.

As I noted, the trouble in appraising a home with an in-law suite comes when there are no other properties to compare it to. If you are planning to add an in-law suite to your home the best thing for you to do would be to find out what is common in the area and copy that. You will have more potential buyers should you decide to sell and there will be plenty of comps.


Do you have any other questions about homes with an in-law suite? If so leave a comment below or if you would like your question featured in a future blog post, let me know. As always, thanks for reading.

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  1. Hi Tom,
    I have a detached garage I renovated last year for my mom to stay in. It is 480 sq ft and has a half kitchen with fridge and microwave (no stove), bathroom w shower, large closet and W/D hook ups. There are two separate entrances, one door goes to backyard, and one door exits out to carport. There are really no comps in our area, being by the lake with all ages of houses. How would it be calculated to add value?

    • Sometimes there may not be any recent sales, however, if you are able to look back in time over the last several years you may be able to find a home that sold with a similar feature. You can then compare that sale at that time to other homes to see what the added value was. Another approach may be to look for more recent sales in other areas that may give you an idea as to how much value it added. I find that sometimes people tend to stay within close proximity to the subject but it would be okay to look further away just to get an idea of how buyers react to this type of improvement. Hope this helps in some way, good luck.

  2. Alicia Mac says

    Hi Tom,

    Our home is definitely unique. We built our home in 2017 to accommodate my in-laws within the roofline of our ranch home to meet the VA housing requirements. The laundry room is accessible via the attached garage. The in-law suite is adjoining the main house via the laundry room. The in-law suite is 976 sq ft. Featuring a full kitchen, bedroom suite, living and dining areas. The kitchen boast a stand-alone island, pantry, water osmosis system, Whirlpool appliances to include range, side by side refrigerator, microwave, and dishwasher. The bedroom suite includes a walk in closet and bathroom with dual vanities, 5×5 shower with dual shower heads, and water closet. The total square footage of our home is 3261. We have a salt water pool and detached spa. Due to the unique floor plan, how would you suggest we price our house?

    • If the laundry room and in-law suite are accessible from the finished area within the house then you can include all of the square footage together, however, if you must pass through the unfinished area then you cannot include the in-law suite. This does not mean it does not add to the value, however, these area’s contribution to the overall value of the entire property may be less.

      • Alicia Mac says

        Hi Tom,

        Thank you for your insight. The in-law suite is finished and attached to the main home via the laundry room via L-shaped design. We had been advised to charge more per square foot. As an appraiser, would increasing the price by $15 per sq foot be advisable?
        Thank you in advance for your insight.
        Very Respectfully,

        • The thing about price per square foot is that the larger a house is the less the price per square foot is. It is the law of diminishing returns. It is never a good idea to randomly assign a price per square foot. I would get an appraisal to see how your home compares to others that are similar in size. It is better to bracket the physical characteristics of the home, including square footage when picking comparables. Tha will give you a more accurate indication of value.

  3. Hi Tom,
    I was wondering if adding the in-law suite with living space, bedroom and bath with be acceptable and get the same return? My father does not need an additional full kitchen but would add creature comforts such as mini fridge and microwave in an area that would look like a “kitchen” do you still feel this would could maximize our investment? We are in Charlotte, NC

    • Generally speaking, adding square footage will be the best way to increase the value of your home. Keep in mind what is typical square footage for the area so that you do not overbuild. If the addition keeps you within the ranges for bedroom/bath count and square footage for the area then you should be good, however, if you go over these norms then the investment will most likely not give you as much bang for your buck, but will add some value.

  4. Maria Willis says

    I have an in law suite, its above my 4 car garage ,
    You can only enter it from inside the garage. I have put a door that leads to that space. Then there’s another door that leads to the wash room that goes into the house. Would the inlaw suite be consider in my GLA

    • I’m not sure if I quite understand the layout you are explaining. If you must go through non-living or non-heated and cooled areas then most likely it will not be included in GLA but will still get some contributory value.

    • Peter Murdza says

      Hi Tom:

      I am happy to see your discussion of in-law apartments. We live In Hanover NH and are downsizing but in no rush whatsoever to sell our house. We have lived in the house, which has a basement apartment (accessory dwelling unit), for twenty-five years and have been able to rent it every month but one. We are very close to Dartmouth and have been able to rent to undergrad, medical students, hospital interns, etc. We currently get $1200 per month for a 1000 square foot apartment; because of a recent ordinance change we could even get more by renting to two people. We had an appraisal done for a change in our home equity loan two years ago but the appraiser was only able to find comparables without an such an ADU (Hanover is a small town) and we got little credit for the income value. I have talked to several appraisers and their response has been that once you use an income approach it affects the valuation of the entire property and they would end up valuing it as a two-family house, with a lower overall amount. Do you have any problem with using comparables for our part of the house and an income approach for the apartment? If we were to use the income approach for the apartment, do you have any thoughts on a capitalization rate? (I will also be sending this email separately to Gary Kristensen who had thoughts on this issue.) Thank you very much for any help.

      • You really cannot just do an income approach for the apartment and a sales comparison approach for the owner-occupied portion of the home. I would not have any idea of what a capitalization rate for your area would be. If the rental market in your area is good due to the availability of college tenants the income approach may provide a higher indication of value but if not then it would probably be best to just look at the additional living area as a teenage apartment or in-law quarters.

  5. Ashlea Chance says

    Hi, Tom. We have thoroughly enjoy reading through your blog posts, and we greatly appreciate the information you have shared. We purchased a farm (house, land, multiple barns) a year ago, and we have been making steady improvements. The previous owners used a 1200 sqft structure as room/board for their hired hands. It provided menial value on our original purchase appraisal as it was in no way fit to be considered living area (no a/c, concrete floors, unfinished sheetrock). We understand that once we remodel and finish the structure that it will not be valued as highly per sqft as our primary residence on the property, but will it have any value at all? We are trying to determine if it would be better to invest our funds into other projects based on the rate of return. The structure will include a full commercial kitchen, living area, washer/dryer, and full bathroom upon completion. We’d also be interested in scheduling an appointment to discuss the best options for investing in our property if that is available. We live about an hour North of Birmingham.

    • You are correct about the area not contributing as much as the main residence. Finishing off area that is part of the main residence such as basement or attic space would give you a better return on the money spent. I’m not sure if I cover the area you speak of that is an hour north of Birmingham. What county is it in?

  6. Jen McMurray says

    Hi Tom
    I own a property with an in law suite that has only a separate entrance but is above grade and attached to the main house. I just had an appraisal done for a refinance and was surprised that it didn’t count in the total square footage and was only given value at cost ($88/sqft) vs market value ($280/ sqft). My area has plenty of such suites. Needless to say I was shocked to have it only valued at cost. Is this typical? I hate to think the value for resale is that low. Any insight appreciated.

    • ANSI standards state that if you have to go through either unfinished area or through the outside to get to another living area then it cannot be included in the main gross living area GLA. This does not mean that it is not given value or that it does not contribute value. The amount of value will depend on what is indicated by the sales. If there are plenty of sales as you suggest then the appraiser should be able to determine how much value the in-law suite contributes. It’s hard to say where I’m at how much value this feature provides. Some things to consider is whether any of the comps had this feature. The figure you give of $280/sqft may be for the main GLA of the house whereas the in-law suite may not contribute as much.

  7. A good friend is building a cottage on my property to live in. How would you recommend we value her interest in the increased value of the property? We are trying to determine When we sell down the road, what % of the sales price should she get? Any suggestions?

  8. Nice site,Thank you.

  9. Thank you for the post Tom. I had a similar question this week from an agent friend. My response is that all three approaches to value are usually applicable to accessory units. If everyone is doing it, the value could be equal to or greater than cost and if few are doing it then the value could be equal to or less than cost (minus physical depreciation of course). If people are buying the units for extra income, it can help to estimate what it could rent for and then estimate a capitalization rate. Finally, it is important to find comparable sales with a similar accessory unit. Ideally those would directly compare to the subject and could be used in the sales grid, but they could also somewhat compare and be used to pair up and support an adjustment. Then reconcile.

    • Great points, Gary. I find it certain areas of my market that the in-law suite is more for family members and not renters. In another area of town, closer to the university, the income approach would be very relevant since they are rented out most of the time.

  10. john snyder says

    I have one now with interior and exterior access. 4k square footage total. The In-law suite is on first floor, constructed that way. Do you give extra for the in-law suite? its already counted in above grade square footage but most of market does not need a mother in law suite with exra walls and with no in-law comps that are similar …how to adjust up or down?

    • The value of the in-law suite is based on what typical buyers are willing to pay for it. If there is not a market for this type of home in your market area then there probably will not be any additional value given for the in-law suite. Ideally you would be able to find other sales with this type of floor plan, however if there are none then that should tell you that it is really not very important to buyers. The in-law suite will probably cost more to build but cost is not always a good indicator of value.

  11. Nice Tom. In your market is an in-law suite the same thing as an accessory dwelling unit? I’m curious to hear if there is any distinction. The use of “in-law” as it’s used above to me suggests it’s really something meant for family living in the house rather than a rental.

    • Great question, Ryan. Yes, the in-law suite is the same as an accessory dwelling unit as long they are independent of the main unit. This means that it will typically have a kitchen and a bath.


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