When moving from a 3/4" hardwood floor to a thinner product such as engineered or laminate which is usually 8mm or 12mm, do you typically want to offset the lower profile of the new product by installing an additional layer on the sub-floor in order to bring the level up snug under existing door frames, etc?

Quick calculations show 12mm to be a little less than 1/2" so it seems like I'd be able to layer 1/4" sheets of plywood directly on top of the existing 3/4" plywood sub-floor so that by the time I add any underlay and then the new product on top I should be at the same height as the old hardwood.

Am I thinking about this in the wrong way? I don't want to re-frame all my door casings to be lower just to avoid gaps between the bottoms and the floor and obviously slapping quarter round on the bottom of the jamb / casings is not feasible so raising the sub-floor seems to be the best option to me.

Thanks in advance for your answers / help. Glad to have found this site - I've used Stack Overflow for years as a software developer and it looks like there are just as many knowledgable, helpful folks over here.

  • 3
    Welcome. This is really a matter of opinion and project circumstances. There's no typical, partly because solid hardwood is rarely removed--it's usually refinished. Do what makes sense in your case.
    – isherwood
    Aug 26 '20 at 13:38
  • I don't think anyone will notice gaps between door casings and the floor. Aug 26 '20 at 14:13

Do what you can live with. If it means laying down 1/4" underlayment everywhere, do it. Especially if the floor has issues, whether minor or major, that an additional layer of underlayment will assist in correcting. Do straight edge the floor beforehand to make sure it is within the install guidelines for flatness.

When I changed the flooring in the house we have now, there were 4 different types of flooring on a slab on grade. Glued down 3/4 X 2 1/4" maple, 3/4" x 3 1/4" "floating" T&G maple, not glued or anything like that, carpet and click lock laminate. I installed vinyl click lock that was only 3/16" thick in its place. Gaps at the trim where the flooring was pulled up, to look at the gaps left over was more than I chose to live with. I used a gauge block and oscillating saw to cut all the trim bottoms the same, and set small pieces (about 7/8") of matching trim carefully in place with wood glue buttered on both cut faces to hold it there. There was only one door jamb that was an atrocity, and from another door jamb that was demoed, I cut a portion to fit under the recut jamb to fill it in. It all blended in rather nicely. Much better than the gaps. More economical too.

  • Thanks for the comments, Jack. I'll give the technique you used a try and see if I can fill the space under the door jambs with some matching trim blocks and make it look professional. Will be a heck of a lot easier than adding to the sub-floor throughout. Aug 28 '20 at 13:16
  • When I was cutting the existing trim, I used a piece of 1X4, in my case so I could set the oscillation blade flat across the top of the gauge block, allowing me to make a square cut in but directions. Then I set my powered miter box up with a mark to mass cut blocks that fit the cut. I did notice some fit loose, some tight. I made very lightly tapered shims to draw the glued blocks in place to the bottom of the original trim
    – Jack
    Aug 28 '20 at 14:02

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