I have an old barn that I’d like to fix up for a workshop. I was planning to sheath the frame with plywood or SIPs, then reattach the old vertical board siding. However, I’m concerned that water might get in between the old siding and the new plywood or OSB, causing both to rot. (The siding is not at all waterproof, what with knot holes, cracks, and gaps between boards.) My understanding is that wood can get wet without rotting as long as it is allowed to dry out again later. The old siding has been exposed to air on both sides, and so has lasted 100 years. But now it will only be exposed on one side. I would hate to lose the boards that give this barn so much character. (I would also hate to lose the new plywood or OSB...)

Is it okay to just nail the old siding directly over the plywood? Would housewrap help to protect either the old siding or the new plywood? Should I use furring strips? If the furring strips were installed horizontally, it seems that they would form pockets to hold water. The strips could also be installed vertically, like a board-and-batten wall, with the battens on the inside. This would form little vertical air passages, which should allow air to circulate behind the siding. But this might also make little chimneys, which could cause a fire to spread quickly up the wall, if a fire were to ever start.

What’s your recommendation? Surely I’m not the first one to come across this problem. Any help that you could give me would be greatly appreciated.

Thank you very much.

--Bruce Brittain

Greetings...

I'm a rookie at this, so...

I agree that horizontal firring strips would be a bad approach for the reason you stated.

I don't think house wrap is the right approach. It is intened to reduce air infiltration into the building. It would not make a very good drain plane.

I would not attach the vertical siding directly to the plywood/sips. Instead, I would use commercially available "drain plane" between the siding and the plywood/sips. This material will hold the siding slightly away from the plywood/sips for drainage.

Considering the sising is far from water tight, I'd be tempted to consider treated plywood or treated plywood on the exterior of the sips.

Hope this helps.

Joel

Just some thoughts here:

Firstly, the House Wrap idea is a good one from several perspectives. It is a "membrane" that stops draughts, is water resistant, is water immpermeable, etc. Use it underneath regardless of the method you use to re-install the siding.

Secondly, about the fastening of the siding: I would be very tempted to strap the panels horizontally after applying the house wrap. The space behind the siding will keep the wood dry even if water leaks back there through the knot holes, etc. It is the reccomended method here in rainy British Columbia. The Prov Building Code requires the "drain and vent space" under wood siding, I believe. For any of you fortunate to have viewed or visited the Eagle' Eye Restaurant at the top of the Ski Hill during the Kicking Horse Bridge Project in 2001, that method was used to attach the siding up there. And drying out is critical above the treeline, since the hot season is so short.

Also, if the furring strips are well attached to the panels, I think nailing the siding to the furring strips would be a better method than nailing it to the exterior sheathing of the panels.

Another thing to consider would be to wrap the barn, attach the horizontal Furring strips, hang "black paper" vertically over top of the furring strips, then attach the siding. The Black paper is (relatively) inexpensive and would conceal any of the house wrap from showing through the defects in the siding AND provide one more layer of water / wind resistance??? It could be the light "tar paper" or the heavy "roof felt".

Thre is a newer variant of "black paper" that is 6 feet wide and made of non-woven synthetics backed by waterproof membrane. I believe it goes by the name of RoofGuardII or something like that. We have used it under standing seam roofing and the nice part is that it is quite light but reasonbly strong. Given half the number of seams, perhaps there is water vapor issues to consider but it sure is nicer to work with.

Bruce...

I would be very interested in what is determined to be the best approach to your siding.

Perhaps a call to the SIP supplier?

My concern with house wrap and horizontal nailers is potentially trapping water. My sense of logic, which has failed me many a time, is that you need a drain plane that includes air space between the it and the siding.

Please post what you come up with.

Joel

The purpose of the outer layer of black paper (or perhaps the other product suggested above) would be to keep the water from reaching the Horizontal nailers. Even if water reaches this area, it would vent into the airspace and be gone soon enough.

You state "The siding is not at all waterproof, what with knot holes, cracks, and gaps between boards.". I would assume then, that these defects, knotholes, etc would allow enough air circulation and/or air access to dry the backside of the siding.

The outer layer of black paper would also hide the sips or nailers from view.

Hello Bruce,

I'll throw in my two cents. I'm fond of tar paper and I'm convinced it's a much better solution than Tyvek, particularly where you don't have a lot of moisture coming through, as you do in conventional framing from all those fiberglas batts. Synthetics don't hold up to UV as well as tar paper, with all the knot holes.

And for what it's worth, I heard of a fellow putting board and batten with horizontal furring strips beneath that had been run across a table saw every foot with a 1/4" X 1/4" dado to increase air flow. Seems like you might accomplish the same in less time with a router, laying all your batts on the flat and buzzing four feet at a time or so.

Good for you for trying keep the old boards.

Zach

You need only borrow an old idea, and add a few new ones to make good use of your vertical boarding.

Many barns hereabouts (and they’re always better for it + it is part of how they survive after the boarding begins to fail) were boarded with a thin vertical batten against the frame beneath the butt joints – commonly known as reverse board an batten or RB&B – this provides that “drain plane” Joel was speaking of, but more importantly, it separates the sometimes wet and leaking boarding from the frame allowing everything to readily dry after a rain.

I commonly enclose barns with this method and have come to add only one improvement, this by attaching a hunk of “Roll Vent” betwixt the battens against the sills,
this void would historically tend to fill with hay and chaff and spiderwebs, all the stuff of everyday, and these accumulations would sometimes act as a sponge, retard evaporation and hold moisture against the sill. I remove the breathable fabric cover from the roll vent, cut it to the full size of the space between the battens, then refold the fabric over the ends of the matrix top and bottom, this to keep bugs from dragging their stuff up into the void and to keep gravity and time from clogging it from above.

Add some type of high tech building fabric (overlapped from above to shed water) and I would not be unwilling to reuse even somewhat used up boarding.

Be your best

Hi All:

Here is my 2 cents worth on this problem.
I agree one has to approach this problem with caution, and I might say a solution that is not in any text book. These are the type of problems restoration architects deal with, because they are mixing new methods with old ones, and plywood under old looking siding is done all the time on restored older homes.

I would install vertical furring (1 by 4") every 36 inches under the horizontal (1" by 3") strapping applied every 24".
This is much the same as the method of applying wood lathe on the inside of historical homes before the rooms were plastered.
This should allow breathable space to vent any moisture that might get behind the vertical siding

NH

Hi all,

Sounds like a lot of good ideas here, and maybe a couple of bad ones?

One thing that should be looked at is the difference between how plywood without an attached foam panel (SIPs) and the two types of available foam panels would react to being used to enclose a conditioned space. If you choose plywood and attempt to attach foam panels or other types of insulation, you run a pretty high risk of condensation in the walls due to conditioned air meeting ambient air behind the siding. The same holds true with panels that are not sealed correctly at all the connections and penetrations (doors, windows etc.).

There is also the issue of EPS vs. urethane panel performance relative to vapor drive as a result of permeability. EPS panels are permeable (air will move through them slowly) and as such should be allowed to breath behind the siding. Urethane panels are not permeable so this subject is irrelevant.

We have had pretty good luck with using vertical lattice strips hammer stapled to the OSB @ 12" O.C. and horizontal 1x3 firring applied over them for the siding. We vent top and bottom and use Cobra roll-a-vent as Will suggests to keep yellow jackets fom moving in. You might want to staple a chunk to the back of the siding where knot holes are for the same reason.

Good luck with keeping your barn useful!

Rudy