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Question DetailsAsked on 8/14/2017

Cottage outer walls is constructed soley of 1/2 log siding. Can I side over with T-1 11. There is no 2x4 construct

This cottage in upper Michigan was constructed in the 40s and as stated has no 2x4 construction but is solely raised with 2x8 tounge and groove 1/2 log siding The siding has rotted at the bottom up to 4" in places so we plan to cut out the rotted logs and replace with a 2x6 board where needed. Then we will put a 1x8 board all around the bottom perimeter of the cabin. From that point we would like to cover the log siding completely with T-1 11. How should we prepare the existing log walls to accept the siding and because we are installing new windows; how should the flashing be installed?

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No framing at all - just the halflog T&G ? That does not sound at all stable, especially if in snow country. Of course, cost aside, my recommendation would be to put in proper framing, remove the T&G (possibly put up for sale if most is in good condition), then housewrap and the T1-11 like for new construction - though without interior finish and insulation in the walls would behave as a totally uninsulated house.

BTW - if 2x8 I would guess this is quarter-log siding (4 curved-face pieces cut out of a tree, leaving a dimensional lumber remnant after they are cut off) - because true half-log (full semicircle piece on the outside rather than about a 1/6 circle arc on each piece) would normally be more like 4-8 inches thick at the edges.

Also - don't know how you are going to remove bottom rotted board(s) without collapsing the house, or how they are going to be stable without T&G (would be very hard to get T&G into that location, though doable with several people with one backing up the other side as new piece is hammered in with heavy rubber mallet or backing baord and hand sledge), and hammering in a tight fitting T&G might risk knocking the whole wall inwards/outwards and causing instability. An iffy thing trying to replace bottom board with that sort of house-of-cards construction, though I guess doing short sections with adjacent jacks or blocking holding the wall up during the removal and replacement of short pieces might work. If doing that I would T&G the ends to provide more stability of the short pieces and install them, then drive the longitudinal T&G together with long-life acrylic latex caulk (stains less than silicone if it oozes out) in the end grooves.

Personally, assuming a major rebuild is not in the cards for this cottage, I would be looking at framing up an interior wall framing with 2x4's or flat-faced posts or such - whatever would provide structure and somethjing to fasten the T&G to from outside before putting the new siding on.

If you do put T1-11 on the outside over the log siding, I would use firring strips to fir out from the siding, then put housewrap (Tyvek Housewrap or Drainwrap) over that, then the T1-11. The firring out (vertically oriented at proposed T1-11 nailing lines) provides an airgap (screen T&B to keep insects out) in between the two wood layers to prevent wood-to-wood rot issues, where condensation and moisture tends to accumulate. Firring out, using an 8 foot level, also provides the opportunity to provide a planar surface for the T1-11 to be fastened to, otherwise it will look ripply and wavy because of the uneven log surfaces and variable diameter of the logs. Takes a LOT of time and a properly aligned sweeping laser level to locally rasp or grind away a bit of log or shim to provide a planar surface to nail to.

Certainly bottom replacement board should be ground-contact treated wood (even if not in direct ground contact).

And make sure ground level is low enough to prevent wetting of the wood.

Not sure why you want the 1x8 (presumably trim board) around the bottom - that again brings in the double-layer wood rot issue. Also, the T1-11 should hang down below the bottom siding boards then dripedge flashing there so water can't wick in under the T1-11 to the half-round siding and rot them again. IF you put a bottom sill piece of 1x8 (whcih should also be pressure-treated, which you would have to do yourself - not an availale size in pressure treated) unless it was totally covered with metal dripedge flashing (a custom piece or maybe a very wide dripedge designed as base flashing over foundation wall insulation, for instance), the water coming down the T1-11 would saturate it (and run in at the top joint) and cause base rot again. Best to run the T1-11 down to drop the runoff free below the half-round - which might require a bit of ground level reduction because there should be 3-4 inches from ground to wood - more like 8-12 in termite country, in which case the wide base metal flashing might be in order. Depends on what you have for foundation.

BTW - look up how to handle any horizontal T1-11 joints - best to use long enough sheets to avoid end joints (available in 8,9, and 10' lengths in areas where it is in common use), but if you hcve to have joints be sure to put in dripedge flashing under the joint lap board, otherwise water easily gets in under the lab board and behind the lower sheet. And caulk grooves in the T1-11 at the top of the lap board fully full, but NOT the underside ones so any water can drain out. Top-beveling the lap board 15-20 degrees before installation is also a nice higher-end touch to promote drainage and prevent water from sitting on top of it and soaking in.

On windows - flash per normal window practice if possible (full rough opening flashing) if you are doing new windows, and I recommend ones manufactured with brickmold to overlie the T1-11.

Otherwise if leaving existing doors/windows in, normal window ice and water shield overlap over the housewrap, then properly installed (top over lower pieces) normal window flashing under the T1-11 to the window, and full top and sides (NOT bottom) caulking at the joint. Windows will almost certainly need a brickmold or frame extension (waterproof glue or caulk at the window frame too) installed to bring the frame forward to lie in front of the T1-11. A rabetted design which overlies the T1-11 is what I like instead of the side flashing - the brickmold overlying and caulked to the T1-11, then the edge contact bead caulked. But either wey, proper ice and water shield top, sides, and bottom - with the bottom leading to free air under the sill to drain if any water gets in there.

Answered 3 years ago by LCD

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