a rain screen is an airspace behind the exterior siding. it allows any water the might find its way behind the siding to drain. thus, the building structure is better protected against water infiltration and the siding is more durable. nothing new here – “rain screens” can be found in buildings that are hundreds of years old (it’s a major reason these buildings have lasted so long). however, in our miserly quest to build cheaply (so the wall street /thieves bankers can pocket the dollars!), we’ve lost our way a bit. the introduction of a rain screen into a wall assembly is relatively simple – but, it does add some costs. historically, those costs have not been supported in the post-war building boom. to satisfy the money guys, we only need to build houses that last 25-30 years (typical mortgage period). so, that’s what we have been doing. its time we change that.
this “in-process” photo shows the major components MINUS flashing and a few “odds & ends”.
1) “TYPAR” = house wrap/drainage plane.
2) vertical wood strips = 1×3 strapping to create 3/4″ thick air space.
3) black horizontal bands top & bottom wall and window = venting with insect screen.
the rain screen employed at 363HOUSE is VERY simple. basically, it consists of three components: 1) house wrap as the drainage plane. this protects the exterior surface of the structural wall (SIPs) from water. house wrap also allows any trapped moisture behind to escape via vapor diffusion. 2) air space – we are using 1×3 strapping to create a 3/4″ air space between backside of clapboard siding and face of structural sheathing (SIPs). the air space is of sufficient depth to allow water to drain and provide air flow to promote drying and pressure equalization. 3) flash and vent – the only “tricky” detail with a rain screen is paying close attention to flashing details. basically, the flashing must bridge the air space – so, it spans from the house wrap outbound to the exterior surface of siding. this is necessary for any water that might be draining down the drainage plane (house wrap) to find its way out above wall penetrations (doors, windows, lights, vents, etc.). venting is important to allow any water to drain and air to flow. so, we are using 3/4″ thick corrugated plastic vents with insect screen at the bottom and the top of the 1×3 strapping.
so, when all is detailed AND installed properly, the rain screen will protect our structure and siding from the potential damages of water/moisture. this will result in long-term durability and lower maintenance. all of this for a few thousand dollars, labor and material.
siding and trim installation starts this coming week!
350 parts per million. that’s the “safe” level of CO2 in our atmosphere – “safe” as in the preservation of earth as we know it. currently, the CO2 level is 392ppm. guess what?! mankind is doing an excellent job of driving that number higher.
click image to visit 350.org
how are we doing this?, you might ask. well, mostly by using fossil fuels. through the use of on-site renewable energy/solar hot water and electric, 363HOUSE is projected to reduce its usage of off-site energy (generated by burning fossil fuel) by 90% when compared to a similar-sized “typical” house. our savings could be more pending conservation efforts by its occupants. yeah, its a small step in the enormous fight to reduce CO2 emissions, but its a necessary step that all of us need to embrace.
11.13.2012 – bill mckibben on state theater stage in portland presenting VERY compelling climate change information. learn more at www.350.org
an ongoing construction issue has been the quality of the concrete slab finish. the intent was for the concrete slab – stained and sealed – to be the finished floor. our reasoning included aesthetics, durability, ease of maintenance, unfettered thermal mass (radiant slab and passive solar) and a responsive surface for jessica and her wheelchair. in spite of overwhelming assurances from the concrete sub that the slab job would be “primo”, it is a mess! we have ripples, voids, control joints in the wrong place, slab recess at the wheelchair lift too shallow, slab recess at the bathroom/shower (for tile) overlooked – basically, its a FRIG. we could have forced the issue with the sub and had the slab removed/re-poured. but, due to schedule AND the radiant tubing throughout the slab, we opted to punt and re-group.
after months of debate, research and haggling, we’ve decided to salvage the slab via a ground and polished slab. as a result, the finished floor will now have a crisp finish and better fulfill our above-mentioned goals. the aesthetic will be consistent with the clean interior detailing of the house and the planned-for concrete countertops. jessica and i are excited with the prospect of making lemonade out of our lemon-slab! of course, it will cost more, but we are confident in its value.
here’s a photo of the sample slab at the subcontractor’ shop (NOT same guy that poured the original slab!).
the colored squares are acetone stain samples – we are not staining, just going with the natural concrete color/finish known as “salt and pepper” – not a great photo, but you can get the idea.
jon meade of meade designs in portland will be doing the grinding and polishing work. here’s the basic scope of work: “Grind, hone, densify, polish and seal concrete slab. Planetary polish will begin at low grit of approximately 70grit, and proceed through 1800 grit. A lithium densifier will be applied at 400 grit. Work will proceed with HEPA system vacuums wherever possible. Remedial grouting to porous areas will be used to those areas that require it.”
the work should start as soon as we get permanent power connected – scheduled to happen before thanksgiving – we hope! that’s another story….
i know, the title of this post will attract lots of new followers! in spite of this seemingly mundane topic, it is of vital importance to the performance of the building envelope. windows are great. they provide natural light and air. windows provide a connection to the outside and are critical to human comfort and enjoyment. windows can also be bad. inadequately constructed windows can admit unwanted cold air and allow the loss of costly conditioned interior air. a window can also leak water which can lead to unsightly water stains or decay/rot. so, we must be careful when designing, detailing and installing windows. the following documents the chosen window installation at 363:
typical window rough-in
this view shows the basic window rough-in. the components include the window, Vycor tape (the black stuff at the perimeter of the opening), sub-sill (the black plastic thing at the bottom of the window), and the strip of house wrap (the mostly white paper thing at the bottom of the opening). the components are layered top to bottom to provide positive drainage. eventually, the entire wall surface will receive house wrap which will be the drainage plane – it will shed any bulk water that finds its way behind the siding. then, 1×3 wood strapping will be applied over the house wrap to provide a rain screen behind the clapboard siding. all of these layers provide durability by shedding unwanted water. a future post will detail the rain screen components.
bottom corner detail
close-up showing the layering of the various components listed above. the black “GRACE” tape is the Vycor. its doing two things in this application – one, providing primary weather (water) seal and, two, providing air barrier. the piece on the “outside” corner (not next to window) is primarily an air barrier. the SIPs opening has a 2×12 “buck”. i’m concerned that this field marriage of dimensional lumber to SIPs cut-out will not be a perfect union (even with the two beads of sealant applied under the 2×12). so, this “extra” piece of Vycor tape is cheap insurance against air leakage. also note the black plastic sub-sill. it has sloped horizontal sections to provide positive drainage should any water find its way there. this product is SillGuard, formerly manufactured by Marvin Windows and Doors. “formerly” because i just learned that Marvin no longer is making this product. we were able to buy out some remaining stock from EBS in camden. too bad as i have found this product to be a good sub-sill solution. i guess the next project i’ll have to resort to site-built sub-sill.
interior bottom corner
now, we jump to the inside. here you can see the 2×12 buck inset into the SIPs cut-out. the metal clip is screwed to the side of the window and into the 2×12. three clips per side and two at the top provide a secure window installation. the gap between the side of the wood window frame and the 2×12 will be filled with spray foam insulation for thermal and air barrier. the gray caulk at the bottom of the wood window frame reinforces the bed of caulk under the window frame – again, thermal and air barrier.
just in case you haven’t figured it out yet, ITS ALL ABOUT THERMAL AND AIR BARRIERS! oh yeah, and water (bulk and vapor), too. remember, we must negate those bad things listed in the first paragraph so the occupants can experience unfettered comfort and enjoyment of their beautiful windows!
Henry David Thoreau
if you are a follower of this blog, recently you may have been wondering, “why no posts????”. if so, then please accept my apologies. two weeks ago i was too busy with work, family (a new grandson!), life, etc. last week i discovered that i had lost admin access to my wordpress blog. so, after a week+ of my stubborn “i can fix it”/DIY approach to life, yesterday i finally relented, coughed-up $59.99 to network solutions for their “fix” – “fix” as in repair, not “fix” i.e. relief from drug withdrawal (although, it felt more like the latter!).
Thoreau had it figured out….live in a little house in the woods – NO internet access :-)! nonetheless, new posts are on the way, specifically, window installation. another few weeks and we’ll be completely “dried-in”!