I know I might be poking a hornets nest, but here goes;
We have a 100+ year old farmhouse type victorian, and due to a hail storm last summer, I have to replace the vinyl siding now in place. We have decided to use prefinished fiber cement as the house with fiber cement one block to the west sustained no damage and ours was total loss on 2 sides.
We have remodeled and restored this house mostly from the inside out, replacing bad plaster and lath with drywall, upgrading and installing the systems (windows, electric, insulation, etc..) as we went.
The siding we put on about 8 years ago over original board sheathing after stripping off old masonite 10″ lap. Thing is, we used fiberglass batts to insulate (which I would not do now) the interior, with poly as an interior vb and housewrap under the vinyl. As such, I believe the R value of the fiberglass is diminished by air movement through the small gaps in the siding, and the rather constant wind we endure here. The wrap we used is a woven type ( small flat strips of plastic woven like burlap) as opposed to a spun type, and I tested a sample I had over an open window and could feel the air movement.
My thoughts are that I should put something under the new fiber cement that would stop air infiltration. Would it be advisable to use something akin to a fanfold foam and screw down strapping over it to allow for firm fastening and provide a drainage plane, and also providing a thermal break. Or would it be better to attach strapping directly to the sheathing, put sheet foam between and spray foam any gaps (seems more problematic for sealing, but a firmer attachment and perhaps I could use thicker foam).
Or am I fooling myself to think I could gain any appreciable benefit, and just go with a better type of wrap or felt.
I know that if I do build out, that I will need to make changes for corner boards, window trim, etc…, but we want to restore what original elements we can and are prepared to do so. Thanks in advance.
Replies
If the added insulation value of the foam is important to you,and you dont mind building out your trim, then I would go that route. 1" of blue or pink board (R5)will increase the r value of your wall quite a bit.
Others WILL disagree with me but I wouldnt worry about the "vapor" barrier on both sides of your wall as long as you pay good attention to weatherproofing at windows/trim etc. (think flashings etc. ,not caulk)
If you dont want to bother with the buildout, I'd probably use felt. The fiber cement is probably at least a 50 year product, felt is time-tested..Not always sure about housewrap.
I really would like to up the R-factor, since I don't think I'm getting full benefit out of the fiberglass now, and I don't mind working with the trim elements. I have quite a lot of building/remodeling experience, so I am comfortable with all the flashing considerations as well.
But it seems to me that the greatest benefit is just stopping air infiltration. I know the extra R's would be helpful, but the thicker I go, the more complex it all seems. I am also concerned about keeping the waves out as best I can, thats why I am thinking about the two ways of putting up the foam. I just know I haven't done the FC before and any suggestions as to what to do underneath are really helpful.
I'm a fan of Tyvek-type wraps. However, to really work well, they need to be installed properly, i.e. prior to the doors & windows. Depending on what style of windows you have, you may still be able to do this with some, er, "creative" flashing and sealing. That said, tarpaper will probably work just as well, tho' will still require proper flashing and sealing around openings.
You may also wish to consider installing a rain shield/drainage plane behind the siding. This may help with the water sealing problems that can develop since it would create a better drainage path for anything that does get behind the siding. Like this stuff: http://www.benjaminobdyke.com/visitor/product/key/homeSlickerPlus (Note: I've not used this brand -- it's just the first on I found via Google.) Kinda kills two birds with one membrane.
FWIW, I like FC siding, for what it is, but I pretty much hate the way the fake wood-textured ones look. If it's gonna be fake, it may as well look like itself, and not try (poorly) to look like something else. I prefer the smooth FC siding and I've learned to love the reduced shadow lines, etc. ;-)
Mike Hennessy
Pittsburgh, PA
The idea of a drainage plane appeals to me. After 8+ years I'm a bit concerned about what I'll find when I peel off the vinyl, the old sheathing was in great shape for its age before, but was better protected from moisture from out to in before as well. How much seperation does one need for an effective rainscreen, and whats the best way to build one? The product you pointed me to is interesting, I'll give that some thought as well.
You can either use a drainage plane product, in which case the added thickness is minimal, or use 1/2" or 3/4" firring. I've never used the former, but it seems like a good idea.
Mike HennessyPittsburgh, PA
BQ
FC over foam is slightly problematic for waviness. Your house is really old, however so waviness is going to be a problem regardless.
If you do a rain screen detail with 3/4 build out, you may be able to eliminate some waviness with string and shim method.
Foam between nailers seems inefficient for labor and long term results and effectiveness. FWIW
That's sort of what I thought as well. I thought I'd rip plywood into strips for the strapping, then shimming and screwing them over full sheets of foam to level out as best I could. What works in my favor is that the house is made up of fairly short wall lengths before some element breaks up the run, so waviness is less likely to show.
I'm not disagreeing with you, but just curious why you feel that foam under fiber cement is a problem for waviness?
I have very little experience with fiber cement, but havent found foam to cause that problem under vinyl siding as long as the foam was 1" or at least 3/4". Thinner foam doesn't seem to lay as flat though.
Good observation. Vinyl over foam is easy. Vinyl floats, it is not nailed tight (it should not be anyway).
FC is going to telegraph the topography of an uneven or pliable surface. FC nailed with a gun or hand nailed will pull snug to its underlayment.
I sided a lake house a couple of years ago where the framer and some helper rats of the GC had applied the foam board. Basically just shlepped over everything hoping to "level" out the poor substrate.
I had never applied FC over Foam at this point and I soon learned why, as the waviness telegraphed. The client screamed about the shoddiness of our workmanship while I stood there knowing it was the GC's cutting of corners that established the structure I had to work with.
I had to go back and cut nails and shim in several places. I vowed to never apply FC over foamboard if I had the choice.