Using existing siding as rainscreen
New here and hopeful an expert can offer some opinions.
I have a 1930 home I am renovating and adding a new addition adjacent to the existing structure. The home has original wood clapboard siding nailed directly to studs – no sheathing. With aluminum siding over. The interior surface of exterior walls are 3/4″ tongue and groove sheathing. It has blown-in rock wool insulation. I plan to remove the aluminum siding and install 1/2″ ply, a draining housewrap and Hardie siding. My question is would it be better to leave the original wood siding (walls are pretty straight and good shape) and install the 1/2″ ply sheathing over, or strip the siding to the studs and re-sheath. One opinion is to leave the wood siding creating an airspace for moisture control. The other is to strip to the studs, remove the rock wool, re-insulate (foam, fiberglass?) and sheath from the studs. Opinions around here are about 50/50. What do the experts say? The images of the project are here. http://misadventuresinremodeling.wordpress.com/
Thanks for any help. This is a great resource.
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Replies
Curt,
Engineers like to see the sheathing installed directly against the studs, for bracing (racking resistance). The code-specified (or engineer-specified) nailing schedules for attaching sheathing assume that the sheathing is directly attached to the studs. If there is intervening clapboard, the final wall assembly might not be as strong.
That said, your house has survived for 80 years without any sheathing, so anything you add is only improving the situation. From a moisture-management perspective, I don't see any disadvantages to leaving the clapboard in place, as long as you come up with an air sealing plan at the perimeter of the sheathing sheets as well as the sheathing seams.
Curt,
You have the best opportunity to install plywood, taped Tyvek, 2" taped rigid foam for thermal bridging and condensation control, rain screen and cement siding. It’ll pay back pretty quickly. If you want to re-insulate the wall cavity, I would use dense packed cellulose.
Martin, Thanks for the quick response. The house is actually completely sheathed with 3/4" - just on the inside. I suppose that takes care of the racking issue. The draining housewrap would be taped at seams and caulked at perimeters.
Armando - thanks as well. Are you saying strip the original wood siding to the studs? I am only worried about the wall thickness using exterior foam, I have new casement windows installed and this siding / room addition thing was an afterthought. I did put azek trim around the windows that is removable, so I could fabricate a new window trim profile. The would make my windows 'innies' instead of flush, but that could be accomplished.
It might make sense to install 2x furring over the existing siding through-screwed to the studs and apply a ~1" nominal flash of closed cell foam between the furring, leaving a rough 1/2" rainscreen gap between the foam and the siding.
Foaming the exterior would both air-seal the wall, add a nominal ~R4 to the whole-wall R, and provide a weather-resistant surface- the cc foam itself. Take a little care foaming the bottom & top edges of the wall to ensure it's a complete air seal, to avoid air leaking into the air-permeable rock-wool in the stud bays.
Thanks Dana - that is an interesting solution. My concern is the additional wall thickness, but the concept seems plausible. We are in zone 4 and winters are fairly mild.
I would treat the existing siding as sheathing. Fur with 1"x2"@16"o.c. Attach the Hardi to the furring. Done.