Door sill detail for concrete slab on grade
Problem statement – new construction, slab on grade with R10 slab edge insulation – How to install entry door with extended Endura sill
In the attached detail I’m showing a concept I think will work. Does it?
When placing the concrete for the slab on grade we would have a 2″ deep recess where the door goes. A pressure treated 2×10 trimmed to fit, would go down over the concrete. This will result in a final recess depth of 1/2″. Since we’re using EPDM elsewhere on the project we can cut a strip of it as a sill pan, going down the face of the 2x and slab edge insulation below, covering the flat part of the 2x, and then up the remaining 1/2″ to the finish concrete level. At the jambs on either end we can carry the EPDM up the framing and sheathing an additional 3″ to lap under the WRB.
Any issues here?
I haven’t sloped the actual EPDM surface, in order to have a flat surface providing full support to the door sill. The door is well sheltered under an overhang, but I’d like this to be a solution I can use on projects where I don’t have that shelter.
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Looks pretty good to me. With sill pans it's important for the corners where horizontal changes to vertical to be protected, so I would choose a thinner, more flexible, self-adhered material if it's available. Most rot I've seen at doors is at the lower corners. But if you're used to working with EPDM, use a thin version (0.04" in the US) and can seal the corners, and you adhere it to the surfaces, it should work.
I prefer to have more distance from the floor to the door leaf; most people in the US, from what I've seen anyway, have a small rug inside entry doors and it sucks when a door too close to the floor prohibits that. I generally aim for 1/2"-3/4" clearance in case people want to use thick door mats.
Door manufacturers usually require full support under the sill, which prevents having good drainage. Some high-performance builders risk the warranty and install a sloped sub-sill, then the sill pan, then closely spaced shims.
If the porch slab is floating--not connected to the house foundation--there is risk of it settling, which is hard to fix. I would consider running thick rebar "pins" from the porch slab into the house slab to prevent settling. If there is risk of the slab heaving with frost I would not do that.
Thanks, Michael. Lots of good material in there, especially the tip on using a thinner EPDM. Are there other sturdy membranes you would recommend instead? I had thought of the EPDM because we're going to have some thick stuff on hand any for a section of low-slope roof.
I'll keep the floor mat idea in mind. I was trying to minimize the threshold height to approach something like an ADA sill but using a standard sill. But it's not a requirement here, just a preference. The external slab edge insulation certainly complicates matters.
Thick (0.060") EPDM is just more challenging to work with than materials made for the job, because of the thickness, the necessity for separate adhesive and the corners. You can use EPDM flashing tape and sealant at the corners but they build up in thickness which would prevent your sill from sitting flat.
A fluid-applied membrane would be ideal, or Zip Stretch tape, or Tyvek Flexwrap.
Before those were readily available I made my own from Vycor or Protectowrap, with "bow ties" cut out for the corners.
Before that I soldered my own copper pans and then tried heavy-gauge aluminum but technology has fortunately moved beyond those!
This was one of the very first blog posts on this site: https://www.greenbuildingadvisor.com/article/dont-let-this-happen-to-you
Why wouldn’t you just make a buck on the exterior with the wood and sit the door on concrete? Seems like it’s a lot more likely to rot out with what you show
Or alternatively use thermal buck
I'll look into thermal buck. I had assumed a foam based product might not be the most durable solution under a door sill. For a window it makes sense, but a door sill takes much more of a beating. You've got people doing things like rolling furniture and appliances in and out on dollies and heavy usage like that.
Setting the door directly on the concrete seems to have 2 disadvantages. The concrete is more of a thermal bridge than the wood. Also, connecting the door sill to its supporting surface seems easier if it's wood than concrete.
Then there is the question of where the jambs meet the floor. With only a 1/2" recess in the slab there is no opportunity to lap the wall WRB over the drainage surface below. Of course I could put a metal sill pan over the concrete. That would just be doing the same thing as the EPDM.
I'm not arguing against your suggestion. I'm just saying I don't see how it offers an advantage. If a pressure treated sill is going to "rot out", then every pressure treated sill plate in every North American home built on a concrete slab is currently rotting out.
But maybe I've got it all wrong.
Are you saying you are going to screw through your sill pan and mechanically fasten to the substrate? As for most sill plates, they are not surrounded on all sides by vapor barriers and on one side by a pourous material that wicks water. And they are mostly not under a weak point like a door. If you are worried about weight it seems like a piece one treated wood on exterior of concrete to support would just as if not stronger.
I would just much rather have concrete under my sill (and pan) than wood.
Thanks. It's my understanding the door sill does need to be connected to the surface below. I suppose it can be anchored directly into the slab. I just thought it might be easier to attach into a wood sill. But certainly having just concrete would be more durable.
Then it's just a matter of protecting the top of the slab edge insulation. For that a bit of pressure treated wood should be fine. I'll consider that.
I had thought to do the EPDM sill pan first because we're using it already elsewhere and second because we wouldn't have to have a carefully fabricated metal sill pan custom fit to the opening. Cutting EPDM to fit would be simple.
Kinda defeats the purpose of you sill pan doesn’t it? Most nice thresholds don’t require fastening to substrate. Even if a door manufacturer recommended it I would still not do it and instead use something like silicone dabs to adhere it.
I’m not sure I totally understand why you can’t use your epdm pan if it was concrete, it would be the exact same shape as your first drawing just would be concrete instead of wood under it…