Is this a good plan for wood exterior siding?
I am residing my house located in Minneapolis, MN built in 1907. The wall assembly is — plaster/lathe, wood framing, building paper, wood board siding, and the old wood lap siding (which will be removed except for the soffit/crown trim at the eaves.) Before residing I will be blowing dense pac cellulose into the stud cavities. My house is a 1 ¾ story gabled configuration with ~10” overhangs. The exterior wall are highly exposed to the sun and weather.
From what I have gleaned from this site a drainscreen installation will maximize the longevity of the wood lap siding and paint. 3/8” gap is the recommended minimum gap. I plan to do this but the 3/8” furring will cause the new siding to furr out past the trim at the soffit which I don’t want to replace (and trim around 3 ornate windows at the tops of the gable ends.) I am wondering if there is a method or furring material that I can spec for my contractors to keep labor costs reasonable without sacrificing performance and durability. In case of cost issues would it be too risky to omit the drainscreen now that I am insulating the walls and reducing the sidings drying potential?
For the WRB I prefer felt paper as it seems to me a more environmentally benign product. My tendency is to spec #30 felt paper to error towards the safe side but this may become a cost issue. Any recommendations on how low a weight per 100’ felt paper is prudent to use? Are Grade D Building Papers any good?
At the butt joints of the siding and when the siding abuts the trim I hope to flash with non-corrosive metal flashing. This I also expect to be a cost issue. Is it sufficient to flash with and extra layer of the WRB, in this case felt paper? With good flashing at all joints is it true you don’t need to caulk?
Robert Riversong mentioned in a previous post the use of Exterior Solid Color Latex Stain as an alternative to paint. This seems to solve the only reservation I have with wood siding – scraping off the old paint. Would others second this recommendation? Could anyone name brands to help me with my research?
Lastly, from what I read on this site my residing project doesn’t seem to present an opportunity to establish an effective air barrier because this is best accomplished with rigid material such as plywood or drywall and the barrier would not be contiguous with the ceiling and floor plane. Does this mean I shouldn’t worry about choosing/detailing a WRB that would add to the air tightness of the house?
Thanks for any recommendations.
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About all I can reply to is the exterior stain. We have stained our exterior T1-11 siding exactly twice in 30 yrs, plus one more time on the south side that has a black deck right below it; that side gets HOT in the summer. We did a very minimal amount of sanding loose stuff, and, in fact, the first re-coat was strictly a change of color. This is in Fairbanks, AK, which although it gets pretty cold, it is not terribly hot/humid. H/H may affect the stain more than the cold. Don't recall the brand, but it was one of the usual "big names"; not sure if we used the same brand each time, either. Hope that helps. I will be doing the new house w/ the same product.
J Chestnut,
You're in a moderate rainfall zone and, if you're in the city, probably don't have a high exposure site. So a rain/drain screen is not necessary and certainly less important than maintaining the aesthetic integrity of the home. I have never used a rain/drainscreen, as I don't build in high rainfall zones. I backseal the siding with the same solid color stain I use for finish, as well as putting the first coat on the front before installation. Then I seal the cut end-grain with the same stain just prior to nailing up and brush on the second coat after each lift of siding is on, so there is no need to re-stage for finishing. This makes a very durable finishing system.
With plaster and wood lathe interior, board sheathing and cellulose insulation, you'll have a very breatheable wall and don't have to worry about its drying potential.
I would stay with the code-approved #15 felt, which is more vapor permeable than #30. If you use ASTM D226 #15 felt, it will weight 11.5 – 12.5 pounds per square and meet the code requirements for a weather resistant barrier.
You can also use felt gaskets under any door or window or corner trim that you're replacing as well as at butt joints of the lap siding. No metal is necessary. And, while felt won't meet today's strict air barrier standards, it's been used for more than a hundred years to help keep the wind and the rain from penetrating the walls.
J Chesnut,
I disagree with Robert's advice. Your decision to install new siding gives you a once-in-50-years opportunity to install a rainscreen. Research shows that even a 1/4-inch rainscreen (formed by vertical furring strips made by ripping 1/4-inch plywood) will have significant benefits. Not only will the rainscreen help your wall dry rapidly after it gets wet, but it will extend the longevity of the finish (stain or paint).
Some homeowners have been disappointed with the performance of stain, and end up painting; if that happens during the next few decades, you certainly want a rainscreen gap behind your siding.
Asphalt felt will work fine — personally I prefer #30 asphalt felt, since the heavier weight of the #30 more closely approximates the old "15-pound" felts. (Today's #15 felts are far lighter than the 15-pound felts of the past.) But taped Tyvek or Typar will provide a better air barrier.
Thanks so much for quick responses. This forum is really impressive on both the quality and quantity of contributions. These responses don't necessarily make my decisions easier as I hoped but I am definitely better informed and more confident.
Robert thanks for going into detail on your application method for the exterior stain. I have read that it dries fast and care must be taken so the color is even throughout the application.
I'm finding now that my local contractors are working mostly with finger-jointed paulownia (polonia?) wood coming out of China for beveled siding. I'm planning to use FSC certified siding - the local supplier carries Inland Red Cedar from Idaho. However I'm curious how well finger-jointed products are holding up in the field if anyone can comment on that. Thanks again.
Perhaps Martin might offer links to the research which demonstrates significant advantages to a rainscreen.
Since there is no accepted definition of rainscreen and no accepted research methodology by which to test them, there is much confusion and misinformation about the value of what is often mis-labeled a rainscreen.
Many authorities limit the use of the term "rainscreen" to a fully pressure-equalized cladding system, which is almost never used in residential construction. A more accurate term for what passes as rainscreens is a drain screen or drained cavity system, which relies on gravity drainage. A fully vented cavity system uses convection as well as bulk drainage. But there are unintended consequences to such systems.
For one, they create a fire channel and increase the risk of fire extension, particularly in wildfire zones. If they are vented into or near the soffit, they can introduce moisture as well as fire to the roof/attic cavity.
The HUD Best Practices Guide for Moisture Resistant Homes suggests determining which cladding system to use - sealed face, secondary WRB, drained cavity or vented cavity - according to a combination of factors, including amount of rainfall, site exposure levels to wind, height of house, amount of roof overhang and moisture index (wetting potential vs drying potential).
Their conclusion is that it's only with the most severe exposure levels that a vented rainscreen offers significant benefits. I concur. In moderate rainfall zones on a moderately shielded site with good overhangs, a secondary weather barrier and back-sealed siding performs as well or better than a rainscreen system in which can be far more challenging to integrate flashings, weather-resistant barriers and air barriers.
Rainscreens, like self-adhering membranes, polymeric housewraps and above-grade foam insulations, are overhyped and overused and rarely necessary.
I love the once in 50 years opportunity comment but in relation to energy efficiency. It has become apparent that one to energy efficiency is sealing the building envelope and thereby reducing the the no. of air changes per hour. On March 10th Harold Orr made a presentation to SESCI-NAC (see http://www.solaralberta.ca/seminars.php for powerpoint slides) about a 4 plex that he retrofitted in Regina, SK. He stripped the stucco and building paper, wrapped the house with a poly vapor barrier, and added an non structural outer wall made of 2 x 4s 4 feet on center which he hung from the eaves (problem for you) and supported it with metal straps (slide 17) - shaped like short hockey sticks but with flat bottom instead of a blade. This enabled him to add R42 insulation which he covered with tyvec, OSB & stucco. Costs are detailed on slides 40, 41 & 42 although he estimated for vinyl siding instead of stucco. In prairies he doesn't believe in need for a windscreen and finds that it is better to stuff the space with insulation to stop cold air from cycling.
He also treated the low sloped roof like a vaulted ceiling with too space for adequate space for insulation so he stripped the asphalt shingles that were in need of replacing, wrapped it with a poly vapor barrier, built it up with crisscrossed 2 - 2 x 6s and a 2 x 4, added R52 insulation, tyvec (?), OSB and metal roofing. He reduced the air changes from 11+ to 1.97 ACH at 50 Pascals.