Tuesday, July 3, 2012

Closing Up

Yours truly: ridge workin
Well its been a tough 8 day stretch, but the house is almost fully framed in and we got the temporary roofing installed - so now the whole place is a LOT more waterproof than before. Hopefully we'll keep at least a few of the wisconsin storms from floodin' the basement from now on. 

the house on friday - ready to get closed up

This past weekend and first of this week was all about closing up: gettin' the roof waterproof and sheathing the walls. 

Sheathing the Lake-Side walls
The walls on this house are very different than a traditionally framed home - and not just because of the super insulation and the air sealing. In addition to being made of two 2x4 studs walls 12" apart and filled with blown cellulose insulation, the walls are framed sort of the 'reverse' of most double-stud walls. Most use the 'exterior' 2x4 wall as the primary wall - carrying the loads and doing most of the work. We chose to make the 'interior' wall our primary load-bearing wall. This frees us up to over-insulate all the window headers as well as the rim-joists at the sill and the roof eave connections and make an almost totally thermal-bridge free construction assembly. 
Typical Roof Eave-to-Wall Detail: note the Over-Insulated rafter ends and Rim-Joist
In addition to this sort of 'inside-out' double stud wall - we've chosen to use fireproof Glass-Mat sheathing on the exterior of the home and utilize 1x4 diagonal bracing for all our shear requirements. What this means in practice is that instead of plywood or OSB wrapping the walls of our house - we have bright green sheetrock!

(the wall is actually very similar to one that 475 showed in their blog a little while back here)

USG Securock sheathing. Awesome Green color too.

We went with USG securock glass-mat sheathing. It is 5/8" thick and is classified as Type X. Since the last cabin burned down in a small forest-fire, the owners were very excited about this fireproof quality. In addition, it has a Perm rating of 26 (for 5/8") which means it will be a very vapor-open exterior sheathing, which is important as it will let our walls dry towards the outside if any moisture does work its way into the wall cavity. 

Close-up of the Glass Mat sheathing exterior coating

You can see in the close-up here, it is basically standard gypsum core with a funny waxy, fibrous coating on the outside, instead of the normal drywall paper we're all used to. It went up very well - its heavy of course, but the guys got the whole main house sheathed very quickly. 

But at the same time - it was all up in the air for the roof-crew. The 12/12 pitch on this roof is just about as steep as they get, and while 30' above ground doesn't sound too bad when you say it: it sure feels high when your up there!

Roof sheathing going up - Lull style.
John - installing rafters

The roof detail is very similar to our ground floor detail: the whole idea was to avoid as much thermal bridging as we could, and to keep as much of the material warm and dry to increase durability over the long term. So we used our 'outside' wall to cover the rim-joist which would normally be on the exterior of the house. This allows us to fully cover it with insulation. the detail here is a little more complicated because of the sloped top-plate and the precision to which everything needs to be cut and built. But all in all it worked out great.

Typical roof eave detail

One interesting thing to note in these drawings (from a few months ago) is the extra foam insulation we had planned to add to the top of the sheathing. However, after working with our consulting engineer, the NYC firm Baukraft, they taught us that this wouldn't work at all and would actually lead to a serious potential for condensation to occur on our roof sheathing (a definite no-no). The reason for this is that if you want to put a vapor-closed insulation (like foam) on the outside of the house it needs to be AT LEAST thick enough to keep the sheathing above the dew-point, otherwise any moisture vapor in the wall cavity will condense there. Given the wisconsin climate and the thickness of the rest of our ceiling, we figured this would need to be way too much insulation for our assembly and would lead to more trouble than its worth. So . . . no extra insulation. 

Jason, installing Rim board on the ends of the rafters - note the 'exterior' wall with the sloped top-plate

The finished detail - the roof sheathing ties the two wall layers together here and 'caps' the insulated wall cavity

Carrie, spider-man style


me, finishing up the north ridge

For the exterior waterproofing we decided, like for the air-sealing, to try out the Pro-Clima system on this house. That meant we used the Solitex Mento 1000 3-layer wrap instead of regular tar-paper or something like a tyvek house-wrap. (thanks again to 475 High Performance Building Supply for their help in spec'ing this product and install details!) This membrane is used as a sub-roof waterproofing, as well as the waterproof layer below our final rain-screen facade (more on that later).

The Solitex is another super-engineered wrapper, with a very high vapor permeability rating to, again, make sure to let our walls dry to the outside. Inaddition it is SUPER durable - and held up incredibly well to us walking and siting on it. Its also like 1/3 the weight to tar-paper and very 'grippy' which made the roofing a lot easier than with a traditional product. We decided not to tape our seams or nail-holes, these will all be getting covered by battens later so we can save some time and tape that way.

Jason lying down Solitex. Nice big 5' rolls cover a lot of ground fast.
The Solitex Mento 1000 - we are using the 3-layer version here

Zoom of the Solitex: its more like a shirt or some sort of fabric than a paper or wrapper. 
Delaminating the 3 layers

The 3 Layer Solitex is made of a top layer of water-resistant polypropylene microfiber which covers the middle layer and protects from abrasion and UV damage. The middle layer is a stretchy, plastic-y film they call a 'Specialist Film' - this is the water-proof yet vapor open layer. Then underneath is a reinforcement layer again made of polypropylene. Very cool product and real easy to use. In terms of price / SF and ease of install - it don't think it really matches like, lets say a Huber Zip sheathing (12-16 perms) or something like that.  But I still like it a lot and for a roll membrane it's certainly the nicest one I've worked with. It's also applicable for a true rain-screen facade where the Zip is not - so that is one big reason we decided to go with it on this house.

But for now its a few days of R+R for the holiday, then right back to it.