Exterior Wall Sheathing In B.C., Canada?

wallmaxx

I live 4 miles south of Canada. Being a dual-citizen I often take work in Vancouver (remodel mostly). The exterior wall sheathing requirements up there are different than anywhere I have framed (Houston, TX; Columbus, GA; Clarksville and Memphis, TN and now NW Washington state.) I would like to hear some of your opinions and thoughts.

The current residential codes require that the heated living space be completely wrapped in a 6 mil plastic envelope that lies immediately under the sheetrock. The framers run a 16” wide strip on top of the top plates that touch insulated space and all exterior “t” intersections. Then the insulator applies the final plastic over all his insulation.

The common explanation is to not allow the warm moist “inside air” to permeate through into the insulation space – hit the colder outside air – condense – soak in – and promote rot.

Now comes the strange part. In Langley and Delta, exterior plywood shall be applied horizontally (I’ve been told it’s stronger to apply it sideways)

And, the next row of plywood shall leave a gap of ½” to ¾ between the rows as a vapor release measure.

Also, all cavities above and below windows / doors must have holes drilled to provide adequate outside ventilation. This leaves you with a 1/2" to 3/4" gap running the entire length of the exterior of your house. With no edge blocking...defeats the whole shear concept.


Then, following your plywood nailing inspection you can cover the walls with 30 minute paper or housewrap.

Does anyone else do this anywhere else?

kpatrix

It wouldn't work here in Houston, obviously.

But I wonder how does moisture escape the house. A steamy hot shower produces lots of vapor. Where does this go if it is blocked from passing thru the wall cavity.

Built in dehumidifiers or maybe leave a window open so that cool winter air can suck it up ?

If the house retains humididty, won't all the wood inside the house, like trim and furniture absorb it, or at least the drywall. Sounds like soon you're gonna need to leave a sweat screed between the poly and drywall as well as siding and WRB.

The poly detail is good, I just wonder if it would be better to leave some airspace and weep screeds between it and the drywall.

Zoltar

Yeah we do it the way you explained in calgary alberta. As far as the horizontal sheathing goes, the osb sheets are made tobe layed horizontaly. The strength axis runs the long on the sheets. I have seen ,lately, some builders applying the sheets vertically, mostly 9ft sheets on 9ft walls. I know in Japan you must run sheets vertically. Earthquakes and such.

wallmaxx

The horizontal strength axis only applies if is to be walked on as in flooring. Then, yes, I concur. As far as shear strength, the plywood is the same strength running vertical or horizontal, as it resists movement in the 1/2" thick plane. (As long as the top and bottom plates are all connected to the same plywood with the proper nailing pattern.)

Make sense?

Tsar

Hi,

I live in Victoria just across the water and yes, you've got it all right.

Most of these new codes have come up in the wake of the nasty leaky condo problem we've discovered in the last 10 years. Essentially we like our houses to breathe, the reason behind this is that due to the weather we get (lots and lots of rain) we are making the admission that whatever siding product we are applying will eventually fail. A totally sealed house will trap that moisture and then you've got problems. The gap in the plywood sheathing and the holes drilled out beneath the windows are all to let moisture escape.

As I said above we've had a lot of problems with moisture and everyone around here scared out of their wits about producing a house that leaks. The costs for re mediating in just downtown Vancouver is running into the billions.

Just be glad you're not siding on this west coast...
30mil Paper X 2 layers
Rainscreen (3/4 PT ply on running on every stud in the house)
Sometimes another layer of paper (depeding on how close you are to the water)
Hardie
Caulk and all the rest.

Trimwerx

30 minute paper?

Chris Johnson

Ontario's rules are very simalair, that is why we use ventilation, I recommend HRV's, ERV's or TRV's, depending on your area. We built the houses so air tight we needed a way to get fresh air in and stale air out

__________________
Chris

GregS

Every summer in Ontario the new home owners complain that they have leaks in their basement when it's just humidity forming.

Builders are supposed to tell them to leave the master bath exhaust fan on all the time and put a dehumidifier in the basement. I'd say 50% of the people actually get a dehumidifier.. too many people buying new houses who don't know how to 'work them'.

wallmaxx

30 minute is similar to 30 lb but one is more for vapor control and the other is made to stop all moisture - tar composition I guess.

I prefer the Dow Weather-Mate house wrap.


In WA state we use a timer set whole house fan. Every 4 hours all the air in the house is changed out. Now if you get smart and install an A/C then that changes - but I am no A/C expert.

I just find it funny that just 4 miles from my house, the framer's in Canada are required to install their plywood sheeting 90 degrees rotated from here in WA. The code here does not state vertical or horizontal application. Now, if you are building shear walls, then all edges must be nailed as prescribed. Horizontal would create a whole bunch of blocking in between studs to satisfy that code.

NorumConst

I frame in BC and any shear walls add so much extra time to build a wall and since you completely block any kind of venting, you have to drill 2 holes in each cavity between studs. It would be so much nicer and easier to run the sheets vetically.