No, you do not caulk the sheathing but the horizontal seam should be blocked and nailed off to achieve full perimeter nailing.

 

It would not hurt to cover the seams with tape before installing housewrap.

 

Wrong gap to worry about; http://www.buildingscience.com/docu....com/documents/insights/bsi-038-mind-the-gap-eh/?searchterm=foam board in walls

Gary

 

caulking joints

IF you are not going to use spray foam insulation I would highly recommend caulking such a gap. Granted you do need blocking to seam your sheathing together four feet in from each corner. Fiberglass insulation does not stop air flow. This means that if air can enter the wall the insulation is virtually useless. It has no ability to stop cold from passing through the wall unless it is sealed on all six sides. Once this is accomplished it is fairly effective. I would recommend caulking as many gaps and joints as you can. It really doesn't take that long.

 

do not caulk the exterior sheathing.. not only will you be creating a vapor barrier on the outside of the house which reduces the framings ability to breathe to the outside but it will also reduce the sheathings ability to swell if it does take on moisture which will cause it to buckle

wall sheathing is expected to have a minimum gap of 1/8", some inspectors have been known to expect a 1" gap where the framers had to go around and cut that size gap after the fact

 

Every thing i have been learning as of lately has been steered me in the direction of sealing up all the gaps. The school of thought that I have come to agree with teaches that moisture tends to ride in on air through gaps in the structure and wood is not a vapor barrier. This means the more you seal the wall the drying it will remain and filling the gaps does not turn the wall into a vapor barrier. I have had many building inspectors encourage sealing the wall and have not had any who had a problem with it. Here is a site I found that mentions a few such things http://www.co.monterey.ca.us/buildi...lation Certificates/2008_CF-6R-ENV-20-HERS-BuildingEnvelopeLeakageTestRev07.pdf. Here is some info for requirements on habitat for humanity houses http://www.builditsolar.com/Projects/Conservation/opcaulk.pdf. I have been to several classes and seminars that all teach what I have mentioned and the building codes are all getting on board with it. What code book is it that requires these large uncaulked gaps in the structure?

 

interesting Hart,you don't feel using an air barrier to be sufficient?

 

I am not sure that I know what you are asking? All of the components together are the air barrier. Its about limiting air exchange which requires a lot of different techniques through the entire building process. Some of it has to do with where you are. I live in northern IL and it get cold. I learn more from Wisconsin which is just an hour away and they are way ahead of there time. If you are in a more moderate climate some of these techniques may be overkill.

 

i meant a taped wrb,which would be considered an air barrier

 

I think that helps but there is a specific way that house paper has to be installed to stop air and I have never seen any one install it that way. The bottom of the paper is almost never addressed and then thousands of holes are put in the paper to attach it and the siding. I think this is important but not the answer.

 

i agree,thanks for the discussion:thumbsup:

 

Caulk the exterior plywood (don't use OSB unless it is THE BEST stuff made), but caulk it w/ flexible caulking between the studs and it. Leave the gap for the ply to move if it has to, and tape over the gap. That way, you get the air sealing you need and the gap that some people say you need.

 

Hart, your first link addressed caulking between "conditioned and unconditioned" areas, not uncod. to uncod. as in sheathing gaps. The second link caulked sheathing gaps, contrary to OSB info- "Moisture protection" and "Reminder" - when paint/stain is fine for treating field-cut edges, but leave the required 1/8" gap all around the sheathing for expansion/contraction. You don't want material in the gap: http://www.ewpa.com/Archive/2006/aug/Paper_266.pdf

Much better to stop the air leaks to the wall; from the inside- at the drywall; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/
and from the outside; caulk the sheathing/studs/plates joint from inside the cavity before insulation.

Gary

 

GBR. I agree with all of the info in the articles you linked. I do not agree that you stop the air at the drywall. The drywall is where you stop the warm moist air from the inside of the home from entering the wall not the cold outside air from entering the home. Why would you allow cold air into the wall cavity from the outside putting the cold air right on the back side of the drywall. Stop the air before it can get into the wall and let the insulation have a chance to do its job. On the topic of allowing a gap for the plywood. I would never build a wall that had a 1/8"gap that was not spiting on framing. If i was not going to install framing for it to split on I would prefer to see a caulked gap then an open gap. If you build with dry lumber and keep the air out you reduce the moister content of the lumber in the structure keeping it from swelling. In the instance it did swell it is the result of an actual leak and in that instance having an open gap in the walls or a caulked gap will not make a difference. I would actually think it would be better if it was caulked so the water didn't get to the gap and get in the vulnerable edge of the plywood. The water might drain down the entire wall. Keep in mind in the real world plywood never has an 1/8" gap all the way around it for obvious reasons. That can be protocol all day long and it never happens and every builder and every inspector knows that.

 

I just wen back and looked at my links. I think you need to rethink what you said about the situation we are looking at being unconditioned to unconditioned. That would be an attic or an unheated garage. The inside of the wall does not count as an unconditioned space. It is the barrier between the conditioned and unconditioned space and the link I posted is calling for the gap to be caulked or foamed.

 

any building inspector ive ever had alwaysa looks for the 1/8" gap in the plywood or osb. its expected here as per building code and per the manufacturers specs. the do not want hte gap caulked its supposed to be open.. the installation of a air barrier is what stops air movement. the air barrier can be either type 2 foam or house wrap (tyvek, typar). i know carpenters that have installed sheathing tight toghether only to be made by the inspector to either remove and reinstall it or cut a gap in it. when it does get wet it swells and buckles. in a perfect world situation the framing will never get wet but unfortunately that sorta thing doesnt happern.. new homes get rained and snowed on during the courese of construction

gbr's link is directly from a national site which states building codes.. yours im not so sure of.. regional codes do change though.. regarding habitat for humanitys practices they try to do things to the best of their ability however they are limited by the skill of the volunteers plus the more often than not the local building authorities are very very easy on them when it comes to inspection time do to the nature of the organization, i am very well aware of them as i am a build leader for the local h4h, ive come on site after being away for a few days to see things done which passed inspection which never would in a real inspection

 

I cant imagine any inspector requiring an 1/8 gap all the way around. You would have to adjust your layout quite a lot to make this work as well as transfer the 1/8 gap to the drywall installation. You would have to run your drywall the same direction as the plywood. There are benefits standing the osb up but that is not how you want to install the drywall.

 

There are benefits standing the osb up but that is not how you want to install the drywall.

Hart: I have heard this: Residential, stand drywall up. Commercial, lay it horizontally. What is there to gain by having it horizontal? To me, that just ensures that you will have an unsupported joint to deal w/. (or do you automatically put blocking there anyway?) Then, too, what do you do w/ 9.5' high walls if you lay the drywall horizontally? Thanks.

 

I too, have seen framers have to cut gaps in roof sheathing after inspections. That link was from OSB of Canada.
OSB is sized with a gap, no need to allow for it when laying-out framing. http://www.apawood.org/pablog/index.cfm/2006/5/15/Tips-for-avoiding-panel-buckling

Gary

 

Go here: http://www.gp.com/build/product.aspx?pid=5849

Scroll to the bottom of page, click on "Installation"

Choose to download; "APA guide- WALLS" (the first one)

Fig. #13- sheathing 1/8" gaps all around.

Next to fig. 20 (last one)- The ink stamps for "sheathing" all say "sized for spacing" on them.

Gary

 

ive also seen inspectors make guys go around each piece of sheathing with a saw

but i don't think the caulk negates or affects the purpose of the gap in any way

but a carefully done wrb can be as effective regarding the 1/8'' gap imo

 

standing up osb when sheathing walls will fail inspection here anyway.. every sheet is clearly stamped with which way it should be installed.being horizontally.. every inspector knows to look for the arrows running perpindicular to the framing.

standing up drywall is a commercial method, in residential is run horizontally.. so to reduce the number of joints and it makes for one joint at waist level for the taper to mud.. not 1000 vertical joints every 4'

as for adjusting the framing for the gap ??????????? every house ive ever framed we snap a chalkline 48 1/4" up from the bottom plate and install the sheathing to that.. the next row gets spaced by the thickness of a hand spike.. and so on.. when sheathing a roof both h clips and tongue and groove are made so to create the gap between the sheets

i seriously believe your overthinking this

 

standing up osb when sheathing walls will fail inspection here anyway.. every sheet is clearly stamped with which way it should be installed.being horizontally.. every inspector knows to look for the arrows running perpindicular to the framing.

The advantage of installing OSB vertically is that every edge has a nailing surface. That significantly adds to the shear strength of the wall. Installing it horizontally requires installing solid blocking if you are to achieve the same shear strength (6" nail spacing on the edges). All that blocking bumps up material and labor costs. I don't think orientation alone affects the design strength of the wall. Now, roofs are a different matter...

That said...what works for one local building jurisdiction may not work for another.

 

Kirk: ah so. a 4' high seam is much easier to tape. i assume that requires blocking under it so you don't have a joint floating across 22.5"??? and what about a 9.5' ceiling? two horizontal joints? thanks.

 

That said...what works for one local building jurisdiction may not work for another.

True , no blocking at all where I'm from installing sheathing horizontally.

 

you sure don't have the amount of nails in a sheet if you install structural sheathing horizontally. how that affects racking resistance i don't know. maybe two sheets nailed to the same stud (vertical installation) are a weak link. i'll have to ask the engineer about this when we chat later.

 

Fourth time in last two years; http://www.apawood.org/pablog/index.../1/Help-Desk-Question-Should-Wall-Sheathing-be-Installed-Horizontal-or-Vertical

Gary