Clapboard Joinery

Here you'll find a wide range of discussions on old-house topics.

Moderators: oldhouse, TinaB, Don M, Schag

Post Reply
Posts: 4733
Joined: Tue Jun 28, 2005 9:50 am
Location: Northeast

Clapboard Joinery

Post by lrkrgrrl »

At the NH Old House and Barn Expo, Himself noticed on one of the slide shows that it looked like clapboards on one restoration project had a sort of scarf on them....he thought it odd, but it was just a quick slide flash...

In the vendor's hall, one of the several establishments offering quartersawn claboards had a sample of an old piece of siding for display and comparison (ironically, shedding chunks of old lead booth to the nice girl from the lead safety project...)...that had those same long scarf cuts, so instead of boards meeting with butt joints, they overlapped.

Does anyone have any opinions or experience with this sort of joinery on exterior clapboards? Is it a weird regional thing? is it better or worse than butt joints? Himself's question regarded the comparative virtues of the larger cut surfaces of the scarf joint vs. the butt joint: which is more resistant to water as it runs down the side of the house?

I know a glued scarf joint is stronger than a glued butt joint, but these joints would just lap over. And who cuts the boards that way? The mill? The 12 year old apprentice? The journeyman or master? It sure would make a heck of a lot more work to do by hand.

Please discuss...fact, fiction, and reasoned conjecture welcomed. :lol:
"Oh, Time, Strength, Cash, and Patience!"
(H. Melville, Moby Dick, Ch. 32)

Posts: 1688
Joined: Fri Feb 23, 2007 12:28 am
Location: Brooklyn, NY

Post by BrooklynRowHouse »

In traditional joinery a scarph joint is usually intended to make a joint less visible if/when the wood shrinks. In exterior construction, it also plays a role in the case of the wood swelling due to moisture. Instead of forcing two butt joints together, which could lead to cracking and mashed joints (technical term :wink:) the wedge of a scarph cut would force one board to ride up over the other.

Scarph joints usually have a 1:8 ratio to the thickness of the lumber, i.e. nominal 3/4" lumber would have a joint 24/4" long, or 6". The angle is far too steep for a miter saw so it's usually done with a jig and a table saw. Here's a link:

Posts: 2189
Joined: Sat Sep 30, 2006 10:12 am
Location: WV

Post by Sombreuil_Mongrel »

It's called a skived joint, or a feather joint. The wood is tapered to zero thickness over two or three inches along its _thickness_. (A scarf joint does kinda the same thing along the width) The reason it was used for siding is that it continues to shed water, unlike a butt joint, which opens the framing to the weather. It fell out of use when tar paper came into use. Small strips of same underlay all of the butt joints allowing water that enters to drain out rather than assail the framing.
To skive (v.) means to taper at the edges; it is a technique from leather working.

Posts: 1
Joined: Mon Dec 07, 2020 12:38 pm

Re: Clapboard Joinery

Post by restoreframes »

I happened onto this as I was trying to find a faster way to cut these wonderful early joints (formerly we did them with a drawknife and block plane).
I am replacing many of the quarter sawn pine clapboards we installed 25 years ago. The reason: sapwood. Most of the companies/mills selling the “traditional”quarter sawn claps DO NOT cut out the sapwood. It rots with a dismaying speed.

Post Reply