Entry door - tongue and groove?

[Jason Ferris]

I am making a 1.75” thick entry door and wondering if a simple tongue and groove construction would be adequate. My plan is to use a dado set to cut a .5” wide, 1.5” deep groove in the stiles and rails, in which two 1/2” panels of Baltic Birch plywood will seat. I will make a 1.25” tongue on the ends of the three rails. I figure that because the groove will be a little deeper than normal, I’ll have lots of glue contact. I will also glue the panels in place because the plywood is stable.

I’d like to know if people think this method will stand the test of time. I was going to use loose tenons, but I don’t know why this would be stronger than a deep tongue and groove construction. Thanks.

[Peter Kelly]

Most Baltic birch isn’t made with waterproof adhesive so no, wouldn’t use that. The panels would buckle and warp pretty quickly.

Stub tenons also wouldn’t be adequate joinery for an entry door. Floating tenons would be the better choice.

[Jason Ferris]

Thanks. This door will be protected by a storm door, so I’m not too worried about water warping the plywood. I’m still curious as to why long stub tenons wouldn’t hold over time.

[lowell holmes]

I made my entrance door to replace one that had failed. It is solid stiles and rails. The insert panels are each two pieces that are 7/8" thick.
They are flat on one side and raised on the other. The flat panels are back to back with a piece of poly between the two panels. The raised
panel inserts on the original door split because of the exposure to the sun. The differential temperatures from outside to inside caused panels
to split. I also painted the flat panels. I made the door about 12 years ago and it still is has no issues.
I built several houses many years ago and had issues with purchased raised panels splitting in the Galveston County summer sun.
There is no plywood in the door. The door is made of fir.

[John TenEyck]

I think your approach will work fine. I'd use epoxy to glue it up. With all the glued surface area it will never come apart. If you use Titebond, use TB II, not TB III. TB III looses substantial strength when it gets hot, enough that it can fail in your application.

John

[Mark Bolton]

I have taken apart numerous PVA joints with a heat gun. You dont mention the rail and stile material. The storm door (unless well vented) amplifies your problems by a factor of 10 at the least and perhaps more if the opening will ever see direct sunlight. Perhaps if its vented storm door, in full shade, under a large overhang, and in a temperate climate, maybe. A storm door may protect you from wind driven rain but it still doesnt eliminate a moisture gradient and it most definitely can kill you if the sun hits the door.

You dont see baltic birch in a lot of door construction.

A 1.5" will likely hold if joinery is good and good adhesive.

[Jason Ferris]

I appreciate these replies. Mark: the door is west facing on a city block, so it will get afternoon sun only. Re: the storm door, Can you explain what you mean when you talk about the moisture gradient? I assumed the storm door would offer protection from rain, not make things worse.

[Mark Bolton]

A storm door even in short periods of sunlight, unless extremely well vented, can create a massive heat trap against the face of a wood (or any) door. The moisture gradient has nothing to do with rain. It has to do with the fact that the outside relative humidity as compared to the interior relative humidity WILL be drastically different throughout the seasons. It doesnt matter if you have a storm door or not. Even if your door sees no liquid water from rain, it more than likely WILL be wetter on the exterior face in the summer than it will in the interior (air conditioning). It may be wetter on the interior in the winter and drier on the exterior due to humidification.

Those differences in moisture are what will bite you. Dry on one face, wet on the other.

Again, you dont mention what your frame material or construction is to be. Solid wood? Stave core? Ladder? LVL?

I dont disagree that in the right location and the right climate any solid material with a ply panel could work. You dont state your climate region, or what your rail and stile material is intended to be. At least to me there are a lot more factors to consider beyond baltic birch panels and 1.5" tenons whether they be loose or true.

Just my $0.012545

[Jason Ferris]

The rails and stiles are laminated 4/4 birch hardwood. The location is Philadelphia PA. I can remove the storm door and apply a marine varnish if that would work better.

A storm door even in short periods of sunlight, unless extremely well vented, can create a massive heat trap against the face of a wood (or any) door. The moisture gradient has nothing to do with rain. It has to do with the fact that the outside relative humidity as compared to the interior relative humidity WILL be drastically different throughout the seasons. It doesnt matter if you have a storm door or not. Even if your door sees no liquid water from rain, it more than likely WILL be wetter on the exterior face in the summer than it will in the interior (air conditioning). It may be wetter on the interior in the winter and drier on the exterior due to humidification.

Those differences in moisture are what will bite you. Dry on one face, wet on the other.

Again, you dont mention what your frame material or construction is to be. Solid wood? Stave core? Ladder? LVL?

I dont disagree that in the right location and the right climate any solid material with a ply panel could work. You dont state your climate region, or what your rail and stile material is intended to be. At least to me there are a lot more factors to consider beyond baltic birch panels and 1.5" tenons whether they be loose or true.

Just my $0.012545

[John TenEyck]

I have to agree with Mark, if you get any direct sun on the door. Direct sun + storm door = problems for the wooden door behind it. You would be far better off w/o the storm door. Even without direct sun you should at least vent the storm door.

If the door is going to get direct sun you need a really good finish. Marine varnish is sort of OK, but takes forever to harden. You will get much better longevity with a 2K Poly. Target Coatings EM-9300 Polycarbonate finish is very good, too, with fewer health concerns.

John

[Jason Ferris]

This is really helpful, thanks everyone.

[Peter Kelly]

I’m still curious as to why long stub tenons wouldn’t hold over time.

Nowhere near enough glue surface. Exterior doors take lots of abuse from weather and usage.

[John TenEyck]

Nowhere near enough glue surface. Exterior doors take lots of abuse from weather and usage.

A 1.25" long tenon would hardly be called stub. And if the panels are just as deep, and also are glued, you have a combined surface area that far exceeds a typical M&T door, and many times more than that if you think about doweled doors, which have proven themselves over many decades.

To the OP, rather than Baltic birch plywood you might want to consider MDO if it's going to be painted. It paints great and is exterior rated.

John

[Peter Quinn]

I don't like exterior doors with no mechanical connection between rails and stiles. A stub tenon is not a mechanical connection, even a deep one. I'd rather cut the stub tenons/panel grooves to 5/8" depth and use dowels or preferably loose tenons, better glue surface. Some BB is water resistant, check with your supplier. If not the MDO is a good call. Birch is not a species with any natural rot resistance so your counting 100% on the finish, consider an epoxy sealer like Jamestown's Total Boat or Smiths CPS. I wouldn't be quick to "value engineer" a door for my own house, the little extra time spent over the life time of the door makes it worth using best practices.