I had to replicate this set of garage doors as it is in a conservation area of Southampton so aesthetically the same although the construction method employed differs from the original.
One of the issues that arise from traditional board faced doors often using TGV is that the boards will move substantially during periods of dry sunny weather and equally move during periods of wet weather. This process of expansion and contraction can be seen on virtually every board faced gate and door . The tell tell sign often being the exposure of the tongue (the T ) which leaves an unpainted or unstained vertical line which is the case with contraction or pinched boards with expansion and the forces involved in the pinching means that boards come away from the frame behind.
Even if this movement is not so visually apparent the process eventually results in the fastenings working loose. This being the case with these doors along with rot to the bottom third. So to overcome this I went down the route of laying the frame onto 18mm Marine Grade plywood which is pretty well bullet proof when it comes to movement and future rot issues. This method is often employed on board ships and larger vessels where a TGV boarding effect is desired often on dog houses and the forward facing section of wheel houses without having to deal with movement issues which would be
exaggerated in a marine environment.
It’s my opinion that as we move into a time of climate change and chaos with extreme heat and colossal amounts of rain over a very short period ( As I write this post stair rod rain is happening outside) all new exterior joinery needs to be future proofed against such extremes and often the methods adopted in the marine industry need to be employed on land. A bog standard gate or set of garage doors from one of the large retail chains no longer will be adequate for the job in hand and will literally fall apart over a period of several years not decades.
The process of laying the frame onto the plywood starts with cutting the sheet of ply to the size of the gate. Then the frame with halving joints is manufactured and glued onto the back of the board. The glue used is an exterior grade adhesive with a lifetime guarantee against chemical breakdown due to moisture. The ‘sandwich’ is then cleaned up and housings cut for the locks etc. The face of the garage doors is now marine ply and the back of the garage door the frame from Joinery Grade Redwood. You could go even further with this and use Acoya instead of Redwood which I have written about here and then you would have a set of doors that would last almost forever. The effect of a V joint to mimic traditional TGV can be machined out on the face of the Marine Ply but in this case battens were fixed onto the face. Finally the doors are hung using 600mm strap hinges . The only deviation from the original was that I used 3 hinges for each door as the weight of the new doors are that much more. The battens are machined to a D profile and are fixed to the face using Stainless Steel screws.