How To Measure Replacement Windows

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Measure Replacement Windows

Learn the important steps to measure replacement windows

With the continued drag on the economy I see a longer, continued focus on renovation work. One of the most common renovation jobs we receive are replacing old drafty windows, but I’ve seen many windows not fit because of a lack of knowledge on how to measure replacement windows.

Frankly, it’s not that surprising if you’ve spent the better part of your career installing new construction windows. After all, replacement windows are entirely different and there is a different approach to measure replacement windows.

There are three main steps you need to follow when you measure replacement windows: (1) measure width (2) measure height (3) unit depth. If you’d like to learn how to measure replacement windows then read my in-depth article on the topic. Don’t forget to follow all the current local lead paint laws as well.

With the economy continuing to show signs of a slow rebound it’s likely more and more new home construction builders will have to continue or start doing more remodeling work. We certainly are seeing an increase in window replacements, kitchen and bath renovations and weatherization projects like insulation and HVAC upgrades. Make sure you have the skills needed to tackle these projects.

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Todd Fratzel is the editor of Tool Box Buzz and president of Front Steps Media, LLC, a web-based media company focused on the home improvement and construction industries. He’s also... Read more

10 comments on “How To Measure Replacement Windows

  1. Jeff

    great topic Todd, this is a mystery to many people. even the window reps. though in some situations the r.o is much larger and you can see it until the old window is out

      1. Kimber

        Well, I do like wood windows, they are more compatible with many of the Historic Buildings we work on, but good ones are pricey. I am a big fan of fiberglass, it is much sturdier than vinyl and more attractive. I first installed Marvin Integrity Wood/ Fiberglass on a job 15 years ago and ended up using them throughout our house. I was very happy when they came out with all fiberglass units- these are our first choice for windows in wet locations like showers. There are other manufacturers who have picked up on fiberglass: Andersen Renwal- they use their own installers, won’t sell direct to us and their wood element is a thin veneer not solid like Marvin: Pella has all fiberglass but not the quality. There are some very high performance fiberglass windows available as well, a friend of ours used Alpen/Serious windows with Heat Mirror glass on a monastery project. They have very impressive U values but are a little clunky looking.
        So fiberglass is far superior than vinyl performance wise and just a tad more expensive than a top quality vinyl window.
        If you install lesser vinyl windows, somebody will need to replace within 20 years.

        1. Joe Sainz

          Good comment Kimber – Thanks. I’m right with you on the fiberglass over vinyl – and I just bought a house that needs all the 20 year old vinyls replaced. I’ll be using your post to get my replacements.

  2. Kimber

    This is a good topic Todd, I have replaced many windows over the years, there are options to consider for different situations. We do a lot of older homes with double-hung windows and complex trim. An insert replacement works well for these if the frame and sill are in good shape and are reasonably square. If sills need a little help we often carefully clad them with paintlok sheetmetal.The beauty of insert systems is that existing interior and exterior trim are left intact.
    There are options for inserts as well. Sash kits made up of side tracks and sashes andshould work as well as a new window if properly installed. It is important to measure existing sill slope so the new sash can be made to fit.
    Slim jamb inserts are just what the sound like, a complete unit with slim jambs. They are a little faster to install than sash kits and a little more forgiving. They do cost a little more and require new stop moulding to be thicker than the old ones.
    Some folks will use vinyl windows as inserts, I think this is a mistake. We replace many vinyl windows and they don’t seem to last long and they certainly do not belong in an old house.
    We do whole unit replacements as well,sometimes as part of a remodel sometimes because bad windows have failed. I can’t understand why folks would choose to replace a bad window with another one that is not likely to last a reasonable-at least 50 years- length of time.

  3. Marc

    I have come across replacing windows with the sashes and jam liners only. You have to make sure that the sill is level. Otherwise the lower sash won’t seal well. I’ve had to make a wedge the width of the sill and the thickness for what it is out Of level. So the lower sash seals. Then cover the wedge with a piece of aluminum.

  4. Kimber

    It is not so much how level the sill is but how square it is to the sides, if the whole opening is tilted but still square it will seal. Many window have shifted over time so that they are a parallelogram, the sides are plumb and the sill and header are out of level. Take that into account when measuring the height. Correct the sill by fabricating paintlok sheetmetal sill cladding. Istall the cladding level with shims and sealant, the old sill is protected, the lower sash seals. Top sash may require a tapered insert to help it seal.

  5. Eric Haubert

    This is an interesting topic. An even better discussion that follows. I understand people have a lots of difference in opinion about vinyl replacement windows(windowchoice.ca/window-tips/why-do-most-homeowners-prefer-vinyl-windows ). But for me it was always a good option. I don’t know anything about replacing windows myself. I used a window company services. For past ten years, my house is having vinyl windows. Very little maintenance required, was very cheap when i installed it, energy efficient i would say. May be there will variations in all these factors for each company. But that doesn’t mean the entire thing is bad. Choosing the best company may be thing everyone should take care of.

  6. Robert

    Hello Kimber,
    I’m not sure if you’re still taking questions on this topic but I’ll find out.
    I have an older house that has the wood Windows and need to replace a few of them. It appears that you’re having us leave the inner cabling section still in the walls and the new window fits inside the old framing. Is this correct? If so, then I’ll actually end up with a smaller glass pane than we currently have, correct? If I didn’t want to lose glass dimension, how difficult would that become? I’m good with my hands if that’s helpful.
    Thanks for your help,

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