Guide to Custom Trim Molding Installation

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Custom Trim Molding Installation How-to

One of the last projects done in new home construction and renovation is the installation of trim packages.  Although many contractors can install trim well, there is a difference between installing trim and creating a full trim package to match the house.  Anyone can cut miters on a saw or use an oscillating multi-tool for fine cuts, but only an experienced few can put together a trim package to complement the design of the house.

Selecting Your Molding

When selecting your molding, there are a few important things every trim installer needs to consider.  First, you need to know which trim styles complement each other well.  You also need to know the quality of the MDF (medium density fiberboard). When picking the molding for your next project, make sure you use moldings with a high quality MDF and profiles that are consistent between pieces to guarantee a clean miter joint.

Traditional vs. Modern Trim

Traditional trim usually consists of flat stock and with smaller moldings added to create a custom look. You can create shadow lines and add depth to the molding profile by varying the thickness of the molding components.  The two main types of traditional trim are Mission and Craftsman style.

Mission style uses only flat stock and each piece has different dimensions. It is used for Boston headers, chair rails and baseboards.

Trim Molding Installation - Traditional Mission Style

Traditional Mission Style
Image from inspirationgreen.com

Craftsman style uses a combination of flat stock and small moldings.  It is used for built-up casing, Boston headers, crown moldings and baseboards.

Trim Molding Installation - Traditional Craftsman Style - familyhandyman

Traditional Craftsman Style
Image from familyhandyman.com

Modern trim is usually is a three-piece casing detail for windows and doors.  It has two side legs and a header.  It is mitered so the profile will wrap around the jamb. The baseboard is a single piece of molding that is installed after the floors are finished.

Trim Molding Installation - Modern Style

Modern Style
Image from nuhomedesign.com

Custom Trim Packages

Custom trim packages consist of stock moldings, standard flat stock, and custom flat stock and custom trim profiles.  The custom flat stock and custom trim profiles can be cut on your router table. When you combine these elements you create trim that is original and unique for each house.  To help with the design of your custom trim installation, you can use construction design software.

Even though selecting the right combination of trim moldings is important, there is another piece that is more important.  The most important part of crafting a custom trim package is ensuring correct proportions in order for the trim to be aesthetically pleasing.  Too often in mass produced homes and apartment buildings the builder throws together different moldings to make the trim attractive, but it’s the small things that matter, and if you get the proportions right the eye will be automatically drawn to the trim.

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Trim Installation Proportions

Casing to Baseboard Ratio

Trim Molding Installation - Case Molding & Baseboard

Baseboards should always be at least two inches taller than the case molding is wide.  For example, if you’re using a 2-3/4″ casing you should be using a 5-1/2″ tall baseboard. The baseboard should also be 1/8″ thinner than the casing to create a reveal when the baseboard and casing meet.  If you don’t do this your baseboard will be flush with face of the casing and you will have to make a chamfer cut on the end of the baseboard to create a shadow line at the joint.  If you don’t want to make the baseboard 1/8” thinner, you can use base blocks (also known as plinth blocks).  Base blocks should be thicker than the casing and taller than the baseboard. For example, if your casing is 3/4″ thick the base block should be 1″ thick. If a baseboard is 5-1/2″ tall, the base block needs to be between six and seven inches tall. This will create a reveal on the base block.  If the baseboard and base block are flush, the paint will crack over time as the house settles.

Boston Header to Side Casing Ratio

Trim Molding Installation - Boston Header

The header should be two inches taller than the width of the casing. You can do this by using flat stock that’s slightly wider than the casing and then add a bullnose detail to either the bottom or top of the flat stock.  As mentioned in creating the baseboard to casing ratio, you can use a flat stock that’s thicker than the casing so to create a reveal.  A discussion on Boston header designs is so extensive that it would require its own article – I will write one in the future with some sketches I have created.

Chair Rail Height

Trim Molding Installation - Chair Rail - doncodesigns

Image from doncodesigns.com

When you install a chair rail, it’s important to make sure the height is perfect.  If the chair rail is too high, you can confuse the eye into thinking the walls are shorter than they really are. Most homes have eight foot ceilings and more luxurious homes might even have nine and ten foot ceilings. The rule-of-thumb is to install the chair rail at one-third the ceiling height.  For example, an eight foot ceiling you should have a chair rail 32 inches high and a nine foot ceiling at 36 inches.

Crown Molding

Trim Molding Installation - Crown Molding

Trim installers have fewer guidelines to follow when it comes to crown molding.  You can let your creativity fly as long as it doesn’t become so elaborate that it starts to creep down the wall and interfere with window trims. As you start looking at profiles for crown molding you will find that there aren’t many options available.

Photos are from Jeff Kirk and Robert Risley, owner of Fit`n`Finish Carpentry in New Jersey.

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Jeff Kirk is a Red Seal journeyman carpenter in Halifax, Nova Scotia. He completed a 4-1/2 year apprenticeship in 2008. His work has been focused on high end residential renovation and custom new home construction… Read more

13 comments on “Guide to Custom Trim Molding Installation

  1. Dan

    Great article Jeff! I like all the guidelines you have laid out for proportions of different trim pieces and how they should come together.

  2. Charles

    Very good points Jeff. I like to do restoration work so I use plinths and rosettes a lot. Also the height of chair rail or even a wall paper border can really confuse the eye when it comes to ceiling height. I also find that color can have an effect on a room size, too dark of a color below a chair rail can really make a room look “narrow”

  3. Jeff Post author

    your right charles. more often than not we go with a light color below the chair rail even more so if its a full on panelling detail

  4. Forrest Bonner

    Very interesting article, but I wonder why there were no ‘rule of thumb’ for the width of crown moulding vs. room size?

  5. Jeff Post author

    there isn’t too much selection for different crown sizes.. small crown is only about 2 ” which typically gets used for custom boston headers.. the 5 1/2″ crown which has a 3 1/8″ lie is standard.. the rare occasion youll see something bigger

  6. Jenny

    Jeff, would these same baseboard/casing guidelines apply in a modern or contemporary home? I thought I read somewhere for modern they should be smaller than in a traditional home? Would like your opinion on this. Thanks

  7. Jeff Post author

    depending on the budget lower end modern homes will get colonial casing and baseboard, which are typically 2 3/4 wide casing and 4″ base, where as the higher end ones will get a simple flatstock for both but with a 3 1/2″ casing and 5 1/2 or 6″ base.. it just depends on what the architect has spec’d or the homeowner is looking for

  8. Sam

    Very nice. I really enjoy trim work and it’s nice to learn so of the theory behind it.

    If I wanted to learn more about trim theory, is there a resource you could point me to?

  9. Eric Levine

    Hi Jeff (or whoever can answer my question)

    I really like the colors in the second photo from the top with the caption “Traditional Craftsman Style.” Can you tell me the brand name and style name and/or number of the both the gold color below and the lighter yellow above the molding about 3/4 of the way up the wall?

    If it was a custom color mix perhaps I can get it re-created if you have any details

    I would be most appreciative. Thanks for any help you can give.


    Eric Levine

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