looking for advice and the best practice for board and battens that will stay flat. All too often I see boards curling and warping shortly after install.
We are located in VT and will be using softwood.
Our last approach was to use KD TNG 8″ pine boards. They seem to hold up to stability, but are a real pain to work.
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Replies
Install dry boards, keep them as narrow as possible, install them so the curve of the grain faces in, use only 2 nails par purlin. If you're going to paint do so before you install the battens then paint again.
Paint both sides, or dip them in sealer before installing.
Hi Cotton,
Most importantly, the siding needs to be kept as dry as possible. If this is siding going on your home, then I would recommend including an air space between the sheathing and siding. This could be a HomeSlicker type product. This will allow the vertical boards to dry more evenly/faster after getting wet. Another idea that may help keep the wider "boards" flat would be to install them as "reverse board and batten" or "board on bat". The narrow battens get nailed hard to the sheathing then the boards lap onto the batten and get nailed towards the outside edge of the board, but NOT INTO the batten. This will also create the airspace behind the wider boards. As others have mentioned, let the boards dry as long as possible. I have seen rough pine boards from the lumber yard start at 12" wide and shrink to 11 1/2" in a few weeks after being nailled up vertical as shed siding.
Use fiber cement cedar grain type for your 8" nomianl siding and then w.r cedar for your narrow battens.
Priming or sealing all 6 sides of each board and some sort of rainscreen detail are important. Boards warp for a variety of reasons, but one of the most common is a difference in the moisture content of the front and the back of the board. Wet wood expands, dry wood shrinks, and the board cups. Sealing all the sides evens out moisture absorption and evaporation, helping to keep the boards flat. Likewise, a rainscreen helps to prevent moisture buildup behind the siding.
It's a little late to be
It's a little late to be contributing to this post, but FWIW.
A number of years ago, I did a rough sawn cedar 1'x12 board w/ 1x2 battens. I made three 3/8" deep saw kerfs on the back of the 1x12. Never had any problems.
Board and batt siding can look great, but with all the vertical joints, if your building takes much direct weather I don't think it's very practical. But, if you can keep water off your siding with adequate roof overhangs or maybe if the building is sheltered from the wind somehow, you still need to plan ahead a little if you expect the siding to last 200 years.
First off, in most climates, wood moves with seasonal humidity fluctuations. Especially siding. You can try to fight that movement, or you can allow for it as you build. Flat sawn boards, or boards with heartwood or wood from the outer rings of the log move more than quarter sawn boards. So in the long run it pays to invest in the better boards.
Secondly, the framing of the exterior wall should include horizontal backing no more than 24" o.c. to nail the boards, but more importantly the batts to. If your building wasn't framed that way and is already sheathed, you might consider adding a rain screen which will enhance the durability of the siding anyways.
Thirdly, when you apply the boards, use only one nail/24". I have read people say they put that single nail close to one edge then cover it with the batt, but I learned to center that nail in the board allowing movement each way away from it and have had good luck this way over the years. But the main thing is, using two nails will increase splitting if you securely nail into framing because when the wood shrinks it can't move from where you nailed it so it will crack in the center and shrink towards the nails. Using a single nail allows the edges of the board to slide back and forth behind the batts away from that single nail.
As for cupping, that's why you need all that horizontal backing, so your batts, which are carefully nailed so that the nail passes BETWEEN the edges of the boards are far more secure than if you only nailed them to the sheathing - even with ring shank nails I'm sure you can see how much better this is. And as I mentioned earlier, those batts are critical in the long run for sealing out wind and water and helping control cupping of the boards.
Detailing at corner boards and around windows and doors should allow for movement also - rabbits and various flashings are critical to that end.
Okay, I'm sure you are rolling your eyes by now thinking "how anal can one carpenter be?". But there are not many more important things than exterior trim details if you expect your building to last.