hardiplank over exsisting 3/4 siding… vapor barrier ??? furring strips ??? etc…

i am residing 2 sides of a house in san fransisco… im going with preprimed hardiplank. i will apply one finish coat on saw horses, and one final finish coat, once installed…
my first thought was tyvek followed by 1/4″ ext ply furring strips… and maybe that is the way to go.
the house itself, is comfortable year round. it as has no noticible drafts, and has no mold issues… it breathes well… the climate here is very mild… house was built approx 1940’s… anotherwords it functions very well as it is. the siding is a 3/4′, probably redwood…and it lays flat…
so… ive been thinking (rarely a productive activity, often counterproductive)… why put any vapor/ water barrior on? it might actually create a problem… then i also thought, why fur it out ?, being an overlap siding… theres a channel for breathing. i slide houses(a portion/ small additions) maybe every 2 years, so its not my specialty, and i cant draw from previous jobs, where i had similar circumstances. so, i would very much appreciate your advice/ thoughts.
reason for residing, if your interested… siding now is in such bad shape, that the many layers of paint, would have to be completely stripped, very expensive, and with the lead base paint laws… i wouldnt do it… new paint job will last much, much longer… along with many other advantages that you all know
regardless, thank you for taking the time to read my post. .. and in advace thank you for any and all responses..
john
Replies
In San Francisco there's probably no great need to use housewrap. It would likely make the house a bit less drafty (you'd notice the difference, even if you don't think the house is "drafty" now), but in that climate you can tolerate a bit of a draft.
Note that housewrap is not a "vapor barrier", though -- all decent quality housewraps "breathe".
You likely want the furring because the existing siding will not be sufficiently flat without it, plus you'll likely end up with some "air nails" in the joints without it.
siding job san fran
thank you so much for your input. leaning toward a wrap and 1/4 ply...
john
Of course you will want to install a weather resistant barrier (wrb). Tyvek or similar serves that purpose. This allows for windows, doors, and other penetrations to be flashed effectively. Without the wrb one would have to rely on caulk... not a real good first choice.
The addition of 1/4" battens creates a rain screen. This is also a really good idea.
Read the Instructions?
The Hardie site has their detailed instructions for installing their products. Go look them up.
They like house wrap - which, btw, is not a 'vapor barrier.'
They "allow" the use of furring strips, but one detail remains important: They want the nails to go into the STUDS, not just the house sheathing. Not even if the house has 5/4 sheathing.
These deatails will come as a shock to all the 'just slap it up" and the "I've done it different forever" folks, but they are details Hardie insists on. That's why there are "certified" contractors. Read the 'fine print' of the warranty.
Do a little reading up on Tyvek and cedar or redwood siding to see how surfactants can affect housewraps.
If your redwood is encapsulated by paint, it may not be an issue. But it's something to at least be aware of. Short story? When wraps like Tyvek are in contact with woods like cedar and redwood, the extractives in those woods can case decayed performance in the housewrap. Again, bad things can be verted if the wood is primed/painted, etc, and it sounds like yours is.
I even remember problems with Tyvek behind fiber cement siding and cementitious stucco sidings, but I think it was with unprimed fiber-cement in direct contact with the housewrap. The alkali in the stucco or F-C would cause the housewrap to break down. They came up with a stucco-friendly version, "Stucco-Tyvek" or something like that. Some guys around here use that behind fiber-cement siding.
Others use tar paper.
So, no doom and gloom. Just a head's up.
siding job san fran
its been years since ive used breaktime... i hope everyone who has responded can read this... thank you so much for taking the time to respond to my posting. your input is greatly appreciated... im leaning towards a house wrap... yes, im aware that they breathe... i believe everything is permeable at the end of the day... and ill pretty much ignore the exsisting siding as far as calculating nail depth.. with 1/4" furring strip im at 1 1/2"...so im good...unless i go to 1/2" furring strips... still enough...
this forum is great... thanks again
john