Hi all
we have been asked by a friend to make an exterior wood door and frame for their house, our question is how should we be dealing with a solid wood door in central north america due to the extreme cold faced during winter. should this door have some sort of foam core or will solid walnut be suitable on its own ?
the door will be a horizontal TGV plank look.
We have made multiple exterior doors over the years but none since moving to north america.

What do you mean by "plank look"? Does TGV mean tongue and v groove? A v groove will be a horrible water trap.

the TGV does mean tongue and v groove
this door will have no water on it as there is an 8' overhang
we are more concerned about the cold bridge when it is -18 to -40 outside
the horizontal plank will have no issue being a moisture trap provided the tongue is facing up.

Dan,

There have been discussions, on this site, about this type door so, you could do a search on the knowledge base section.

Personally, I would make a stile and rail sub frame, fill between the frame with rigid foam and clad the outsides.

Two concerns I would have. One, how are you going to control seasonal movement of the faces. Two, if the v-groove runs from edge to edge on the door what is the detail where the v-groove closes against the weather stripping.

Again, personally, I would stay away from that type of door. In that climate, or any, I would recommend a solid wood door with frame and panel construction. If you really want insulation, make the door 2 1/4" thick and insulate between the panels,

We have made many doors with a method similar to what GW describes. You can search Woodweb for discussions of 'ladder core' doors and plank doors.

We make a 3/4" center core that is mortise and tenon stiles and rails, with several cross rails. Hence the term ladder core, since it looks a bit like a ladder. We then can add 3/4" planks that are T&G v-grooved to each face of the core. Rigid foam is used to fill the voids in the core.

In your case, I would run 2-3 vertical rails between the stiles so it will not look like a ladder, but the meat is still there to fasten your faces to.

As for dealing with wood movement in the faces, a v-joint T&G will have a bit of 'crush zone' in it along the edges. Keep the planks narrow, and leave about .040" between the planks at the joint. The idea is to let each board move in its own place, like flooring. They should be glued to the ladder core. We like a vacuum bag for this.

As for -40F, I might consider making the door 3" thick - or thicker, and sourcing hardware first. I know Rocky Mountain can adapt to 3". Glue will still work fine, hinges should be heavy duty ball bearing 5x5 or similar. I would try to use a wood sill to keep from transmitting cold in, heat out.

Also, Joe Calhoun at Cascade Millwork in Colorado makes a European style door that has a double rabbet system with better weather stripping than the usual single rabbet exterior door. That may be better suited to the extremes you deal with.

We build a lot of plank doors. They weather better than panel doors. Thicker is better. I do not like to make North American type non rebated doors thicker than 2 1/4" or so. Thicker than this the bevel edge gets large and not much purchase with the gasket. It is possible to make a flush rebated door using butt hinges and conventional mortise locks.

Here is a 78mm thick Fir (3 1/16") Euro door ready for foam insulation. And a conventional US door in rustic walnut at 2 1/4" thick.

View higher quality, full size image (968 X 1296)

View higher quality, full size image (968 X 1296)

View higher quality, full size image (1224 X 1632)

Thanks for the detailed response Guys.
The search turned up some good information.
I am still a little unsure on the complete weather stripping seal I did install some exterior doors that incorporated a mole hair seal around the edges of the door itself so we might add something like this.

David: when you say that you use vacuum bagging to get a good glue up to the boards is there a system that you can recommend or can I make my own ?
we have looked at some home made equipment for making some curved work with veneers. but had no idea if shop made Vacuum system would be good enough to secure planks.

Joe: Those are some good looking doors
do you have a source for a traditional mortise lock ?
I have not seen any since being in Canada, only on really old doors.
Can I ask you what you are using for a weather strip on the sill and frame ?

Our vacuum equipment is all from Daryl Keil of Vacuum Pressing Systems. Durable and reliable, with lots of support from the company. Vacuum bags will press with about 14lbs per square inch - not a lot on a point load, but quite a bit over the surface of a door. We always face and edge our materials on a joiner to get dead flat and straight stock.

The v-joints will present a problem with the current normal weatherstrip on the edge of the frame rabbet. You will need to augment or change to an edge sealing material. Or add a solid 1/2" perimeter at the edges of the door. We used to see a lot of spring bronze here - the type that is nailed to the jamb rabbet face - but that would be barely marginal at the extreme cold you get.

https://www.vacupress.com/