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Question DetailsAsked on 2/19/2017

floor sill splicing need when sills are sitting on concrete block

joining two floor sills over concrete block is splicing of sills required are can we just butt sills together

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2 Answers



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Answered 3 years ago by Member Services


If you HAVE to use two pieces, I certainly would - otherwise you risk having the ends split or bulge up and cause a barrier to free door movement.

If you actually mean the sill (the bottom piece of the door frame) there is no reason to splice that - use a full-length piece of wood or metal as applicable. I would not splice because that is just asking for a high spot in the sill and possible splitting of the ends of the sill, which will then bow the threashold and affect the free opening of the door and probably lead to door bottom seal being shredded. Normally the sill would come with the door unit in one piece anyway, so I really don't see why this is an issue unless you are replacing and existing rotting sill. (BTW - if replacing or installing an unfinished unit I strongly recommend using pressure-treated material - basically ALL pieces of wood in contact with block or concrete should be treated.

Splicing would be a last resort - because the splicing is going to promote splitting at the ends - minimum 8 inch lap splice would be best choice if you have to splice.

Also - over concrete block the sill should be fastened down at least every foot (I use 6" maximum spacing), so typically those top blocks (unless there is a cap block) have to be grouted full in at least the top 6 inches or so to provide a material for the anchor screws to go into. (You can use expansive foam to provide filling lower down in the cells to prevent the grout from filling the cells all the way to the footer, which is bad from an energy standpoint if not needed for anchoring/strength).


If you actually meant the threshhold (which fastens down on top of the sill strip and forms the rain runoff lip and dripedge over the sill and commonly contains as least part of the door bottom seal):

Metal threshhold strip comes up to 8 feet long so that would avoid splicing. Wood door threshold typically comes in 36", 42", 48". and 73" lengths so should be able to do that in one piece too. Pieces to 8 feet available at specialty wood supply distributors and millwork supply shops, occasionally at home improvement stores - or buy square edge stock of desired wood type and plane/sand to desired profile.

Answered 3 years ago by LCD

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