Caulking plates and inside corners
One of the great things about my schooling is that it taught me how to think, not what to think.
In new construction the insulation contractor comes in and automatically caulks all the exterior bottom plates to the subfloor and caulks the inside corners of at all the exterior walls. Funny how you accept things when you don’t do them yourself.
So recently on a small addition I do all the insulation myself. Don’t even think about caulking bottom plates and inside corners. Inspector comes along points out my ommision. “You will have to caulk the plates and inside corners before I can give you the ok to cover”, he says.
Fine, I’ll caulk it. My pneumatic Cox gun works great for this I’m thinking.
WAIT A MINUTE! Why am I doing this? This was obviously thought up by someone (with too much time) who thought air was going to get in thru the two pieces of 2x. Ok, I can accept the fact that air might get in between the the plate and subfloor, or the two 2×6’s at the exterior corner, but by that rationale EVERY DOUBLED UP 2X6 INCLUDING CRIPPLES AND KING STUD TRIMMER COMBOS ON THE EXTERIOR WALL SHOULD BE CAULKED.
Think about it! If it is so important to caulk plates and inside corners, then all doubled up material on exterior wall assemblies should be caulked.
Anyone out there caulking the king stud trimmer combo?, I doubt it.
So why should we caulk exterior corners and bottom plates?
(Shudders at the fact that my local inspector will be telling me to caulk the doubled up 2x on the exterior walls next year)
Ps. air can pass thru batt insulation as well, guess we’ll have to find a way to caulk stud bays too. Forget the half inch caulk, forteen seven is the new school of caulking gaps.
Replies
funny thing is those areas (bottom plate,inside corners) of exterior walls all have overlapped sheathing and housewrap (on homes we frame). gonna be awfully hard for air to pass that.
Sounds like a bad deal dude, but in the past ive learned, better to get along with the man, he can make it alot worse.
Woods favorite carpenter
Edited 12/7/2009 5:32 am ET by MattSwanger
lefthanded,
Those joints usually align with seams in sheet sheathing so they are more vulnerable to drafts than other places where 2-by's are laminated.
Maybe you should also caulk a long horizontal line about four feet up from the subfloor.
Ron
Where are you? I know that you are not doing this, but if you google air tight drywall they show details about where to caulk to prevent air leakage. Just wondering what energy code jurisdiction you are under.John
I'm in Seattle. Pretty mild climate.
Actually the places I've mentioned rarely line up with seams in the plywood. We are in a seismic zone so wall sheathing overlaps the rim. The inside corners get sheathed (on the outside of course) after both walls are stood so the sheathing overlaps both walls.
I guess nobody got my lame attempt at humor. Fourteen Seven is 14 7/16"- lenth we cut blocking . I was implying that you would have to caulk the horizontal seam with caulk rated to span 14 inches.
Edited 12/7/2009 7:22 pm ET by left handed hammer
LHH. Our insulation contractors caulk everything: doubles, triples, headers, sills, sill plates, corners... all of it. Framing shrinks, and all our houses are subject to blower door tests. It's way easier to seal framing than it is to seal a trimmed out house.
We do have to remind the caulkers, though, that gobs on the faces of the framing aren't part of the deal.
Speaking as a DYI'er, in predominantly heating climate, I seal the poly vapor barrier at the corners and top and bottom plates. This acts as an air barrier, but the bead of caulking is needed at the plate to floor joint. Inside corners would be lapped with the vapor barrier and less of an issue in my mind.
Edited 12/7/2009 12:03 pm ET by Muteability
Left handed,
It sounds like you haven't had the pleasure of walking around a house during a blower-door test. If you do, you'll soon discover that the areas you describe are indeed sources of air leakage.
And yes, here in Vermont, many contractors do caulk all double studs. I recently watched the work being performed by a spray-foam contractor.
How is that Cox air powered caulking gun? Is it the larger 29oz one, if so I am thinking of buying one and wondered what your opinion was.
thanks
John
This is standard brainwashed eco-warrior idiocy. It's like when they push so hard for heating/cooling the attic space where a furnace is located. They can understand the 3rd grade level logic of making the furnace work a little easier, yet can't get anywhere near the 4th grade level fact that you are now working the machine more to heat extra space that you weren't heating before. It took how many years before JLC ran an article a couple months ago finally admitting that when they actually studied it, it came out as a net-energy loss. It's rabid and mindless nitpicking.
And that's coming from someone who's been vegan the last 10 years.
Do you know what JLC issue that was in?
yet can't get anywhere near the 4th grade level fact that you are now working the machine more to heat extra space that you weren't heating before.
Well by the time that you get to the 6th grade you will find that this is controlled by science and no what some one thinks is "logic".
That fact is that only energy that it takes to heat SPACE is the very, very minor amount of energy needed to bring the air to the desired temperature. And a Slightly more, but very little, to warm up the interior space surfaces. After that it takes ZERO energy to "heat" SPACE.
What the furnace has to do is to replace the heat that leaves through the surfaces by air leakage and transfer through the building materials and insulation.
Now the typical ceiling has a large number of penetration that are hard to do a good job of sealing and they are a major source of heat loss. Now going to a conditioned attic space does elimination those losses and the penetrations in the roof are much much less. And the increase in surface area is small, depending on how style of the roof.
And all of this is regardless of where the HVAC system and duct work is located at.
Read for yourself- Journal of Light Construction - July 2009 pages 15 and 16 under "Sealed Crawlspace Testings Sheds Light on Energy Performance".
And I even went to the trouble of copy and pasting a piece of an article on it for you that I found online.
"While moisture reduction was consistent, energy
savings varied with climate, insulation and duct
placement.
In Flagstaff, researchers monitored energy use
throughout a single heating season. While the homes
with insulated floors used 20 percent less natural gas
than the controls, those with insulated foundation walls
used 53 percent more.
This seemed counterintuitive; ducts are a notorious source of heat loss. With
all the Flagstaff homes’ ductwork in the crawl space, one would expect better
performance from the warmer, wall-insulated crawl spaces. But according to
Cyrus Dastur, the Advanced Energy building scientist who directed the research,
those homes’ lack of floor insulation let heat radiate from the first floor to the
crawl space, robbing more heat from the house than was saved by keeping the
ductwork warm.
The research makes it evident that in cold climates, it’s better to insulate the floor
above the closed crawl space than to insulate the foundation walls.
Baton Rouge results also varied, ranging from a 6 percent savings to a 29 percent
penalty. Here, homeowner behavior and the location of insulation and ductwork
appears to have caused significant variation. While Advanced Energy plans more
monitoring to quantify the impact of occupants in the home, duct placement had
an unmistakable effect."
As I said, energy was lost due to the fact they were heating an unecessarily bigger space.