HomeMy WebLinkAboutRe: exterior wall construction Torii Jacobs February 25, 1986
Building Inspector
City of Orono
1335 S. Brown Road
P.O.Box 66
Crystal Bay, Minnesota 55323
Re: Building Permit
265 0`_c. Crystal Bay Road North
Dear Tom:
This letter is written in response to our meeting on Friday,
February 21, 1986, concerning my proposed method of constructing
exterior walls on the first and second floors of the above
residence .
It is my intention to construct the exterior walls in
accordance with the working drawings attached. Under this method
of construction, the entire wall , including both stud walls,
vapor barrier , insulation, plates and sills , and exterior
sheething will be built on the floor before the wall is raised.
Before any such exterior walls are built, I would like to
call for an inspection so that the construction could be observed
for approval of the process.
One aspect of the wall construction we discussed in some
detail is the placement of the vapor barrier, as shown on the
plans which were submitted to the City with my original
application. Under this method of double wall construction, the
6-mil poly barrier will be placed on the exterior of the inside
stud wall . This will result in 3-5/8 inches of insulation to the
warm side of the barrier between the 2x4 studs . There would be
approximately eight (8) inches of insulation to the cold side of
the barrier . In addition, there will be plywood sheething and a
brick facade outside the wall .
The primary reason for this placement of the vapor barrier
is so that it will not be necessary to break the vapor barrier
for electrical and other utilities.
I have also enclosed certain authorities approving of this
vapor barrier placement -- as opposed to placing the poly
directly over the inside stud wall and directly under the drywall
or other finished wall .
Please let me know if this procedure is acceptable.
Si cerely,
A
jCott K. Goldsmith
L&y ? 5045) �3 y .7Jtb �(15`�1
96 WALLS -7�1U7P
a 6-mil polyethylene sheet installed on the outer surface J,
R-60 INSULATION of the inside wall.
INSULATION STOP One of the most noticeable, and sometimes objection- k
able, features of this wall design is the cantilevered outer
wall.An alternative is to set the outer wall back so that it is
either flush with the platform (Figure 7.20a) or cantile-
AIR'VAPOR BARRIER, vered only a few inches to accept exterior rigid foam
PLYWOOD foundation insulation (Figure 7.20b). Another alternative
NON-STRUCTURAis to use balloon-type framing for the outer wall, resting
STRUCTURAL L the studs on the foundation outside the latform Figure
INNER WALL OUTER WALL p ( g
t 7.20C).
BUILDING PAPER AND SIDING The Embedded Air/Vapor Barrier The primary rule
SHEATHING for or air/vap barriers is that the must be installed on the
AIR/VAPOR BARRIER y
R-11 FIBERGLASS INSULATION worm side of the insulation.
R-19 FIBERGLASS INSULATION However, the Saskatchewan double-stud walla ears
R-11 FIBERGLASS INSULATION pp
to violate this rule: the air/vapor barrier is near the middle
of the insulation (Figure 7.19). Despite this apparent de-
parture from recommended practice, the Canadians have x�
3/8"PLYWOOD not reported any problems. Why?According to Canadian
TREATED PLYW ODNDATION WALL researchers,the embedded air/vapor barrier will cause no
AIR/VAPOR BARRIER moisture problems as long as the insulation on the Cold
R-11 F.G.INSULATION ii side of the barrier has twice the R-value of the insulation
R-11 FIBERGLASS INSULATION on the warm side. In other words, the air/vapor or barrier
R-19 FIBERGLASS INSULATION p 4 t
d
z"RIGID INSULATION may be safely placed one-third of the way into the insula- ;•F 1
tion from the warm (heated) side. ,
_ Does this technique—called the !,-1 rule—actually
MOISTURE /z"RIGID FIBERGLASS work? It would seem to in theory. Consider the following
BARRIER DRAINAGE LAYER interesting parallel between a Saskatchewan-type double
wall with embedded air/vapor barrier and a double-
2"RIGID
lazed window (Figure 7.21). '
INSULATION g ( g
The wall has three layers of 3.5-inch (R-11) fiberglass
Figure 7.19 Section of the "Saskatchewan"-type double batts with the vapor barrier installed between the middle
wall. and inner batts. 66 percent of the R-value is outside the
vapor barrier.
J
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157 L
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aQ
Q
_ 19
A. OUTER WALL FLUSH WITH PLATFORM B.OUTER WALL CANTILEVERED TO ACCEPT C. MODIFIED BALLOON FRAMING OF
EXTERIOR FOUNDATION INSULATION OUTER WALL
Figure 7.20 Double-wall variations at first floor joist area.
DESI N AND CONSTRUCTION DETAILS 97
The double-glazed window has a total R-value of 1.84, Dou le-Wall Assembly Sequence The double
composed of the inner and outer air films, the air space wall i prefabricated into a single unit on the platform,
between the panes, and the glass itself. The inner surface then )ted into place and fastened as with conventional
of the window is a vapor barrier. The inner air film (R- single stud wall construction.
.68) is inside the vapor barrier, while the rest of the win- Th sequence is as follows (Figure 7.22):
dow (R-1.16) is outside the vapor barrier. As with the 1. he inner wall is framed on the platform.
1 double wall,about two-thirds of the R-value is outside the 2. he air/vapor barrier is stapled to the outer surface
vapor barrier. f the inner wall.
Theoretically, the temperature of the inner glass win- 3. Structural sheathing is applied over the air/vapor
dow surface should be almost exactly the same as the barrier.
temperature of the air/vapor barrier in the wall. More- 4. he outer wall is framed on top of the inner wall.
over, moisture condensation on the window should be 5. Temporary spacers (either 3.5- or 5.5-inch) are
just about identical to moisture condensation on the air/ laced between the walls.
vapor barrier in the wall. Therefore, by observing mois- 6. -inch plywood top and bottom plates are installed.
ture condensation on the window, we can deduce the 7. a insulation can now be installed in the central
amount of condensation in the wall. Ovity and the outer stud cavities. Or it can be in-
Common experience has shown that double-glazed stalled from the outside, later, after the wall is
windows do not exhibit severe moisture condensation erected.
problems unless the indoor humidity is excessively high. 8. The wall is tipped up into place.
The 3-1 rule would, by extension, work for double-stud Note:The assembled wall is heavy, so it should be fabri-
walls as well, cated ip position for tilting into place. Once up, it is very
One of the reasons the H embedded air/vapor barrier stable and strong.
rule can be relied on is that moisture problems do not Fortwo-story construction, the sequence continues as
happen overnight;they take a while to develop. Consider follows,(Figure 7.23):
a climate in which the 99 percent winter design tempera- 9. 3-foot wide strip of 6-mil polyethylene air/vapor
ture is say, -1WE In an average winter,the temperature b mer is attached and sealed to the top of the first
falls below -10°F. for only 22 to 54 hours, occurring as fl r wall air/vapor barrier. This strip is then placed
2-or 3-hour periods on 10 or 20 days during the winter. o er the top of the wall. The air/vapor barrier must
This isn't enough time for moisture condensation to b protected here with roofing paper or other suit-
cause a real problem. a le material to prevent damage when the second-
There is one important exception to the J-3 mile. In hot fl or joists are slid up for installation.
tub or pool enclosures, greenhouses,or any space where 10. a second floor joists and floor are then installed
the relative humidity is constantly 70 or 80 percent, the o er the inner wall.
air/vapor barrier should be installed on the winter-warm, 11. a air/vapor barrier is then brought up around the
inner surface of the insulation. jo st header and onto the floor.
R-VALUE R-VALUE
EXTERIOR AIR FILM 0.17 EXTERIOR AIR FILM 0.17
SIDING 0.50 GLASS 0.04
31/z"FIBERGLASS BATT 11.00 AIRSPACE 0.91
31/2"FIBERGLASS BATT 11.00 GLASS 0.04 OUTSIDEV.B.
SHEATHING 0.80 OUTSID V.B. °
AIR/VAPOR BARRIER -0- '
31/z"FIBERGLASS BATT 11.00 VAPOR BARRIER -0-
GYPSUM BOARD 0.45 INTERIOR AIR FILM 0.68 INSIDEV.B.
INTERIOR AIR FILM 0.68 INSIDE B. %
ILI TOTAL 3 - % TOTAL 1.84 0.68-37
DOUBLE WALL WITH EMBEDDED AIR/VAPOR BARRIER DOUBLE-GLAZED WINDOW
Figure 7.21 Comparison of air/vapor barrier location in "Saskatchewan" double wall and
double-glazed window.
f ti
'j
98 WALLS
STEPS 1,2,3 INNER WALL IS FRAMED ON STE 19 AIR/VAPOR BARRIER STRIP IS ATTACHED,
PLATFORM,AIRNAPOR BARRIER;IS SEALED,AND COVERED WITH
STAPLED ON,THEN SHEATHING IS TAR PAPER
APPLIED
441,
r "
4 OUTER WALL IS FRAMED ON 10,11 SECOND FLOOR IS FRAMED,
TOP OF INNER WALL LEAVING SPACE FOR JOIST HEADER r
INSULATION,AND THE AIR/VAPOR
BARRIER IS WRAPPED ONTO FLOOR. '
KW
I
.';
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12 SECOND STORY WALL IS FRAMED, a
5,6,7 OUTER WALL IS SPACED 31/2"-51/2" SEE STEPS 1-7
FROM INNER WALL AND TOP AND BOTTOM
PLYWOOD PLATES ARE APPLIED.
MM-
i.
13
WALL ASSEMBLY IS TILTED INTO
POSITION AND RIGID INSULATION IS
WALL ASSEMBLY IS TILTED INTO APPLIED TO JOIST HEADER
POSITION,AND AIRNAPOR BARRIER IS
SEALED AND STAPLED
r
Figure 7 23 Double-wall construction sequence—
Figure 7.22 Double-wall construction sequence—first story. second st)ry.
y7.
��1 i�!�i o►,� ��7�u5y�T�o� ( int
' f-F®��r C7 C()��t�G.U� C��� Ems•) ��
THE 1/3-2/3 RULE
Some of the wall systems developed and tested in Canada use two layers of
insulation (strapped wall and double wall) ith the air/vapor barrier positioned
between the two layers (Figure 3-6b). This is OK as long as at least two thirds
of the insulation (R-value) is outside the air7vapor barrier. With twice as much
R-value outside the air vapor barrier as inside, the barrier should never gel
cold enough to cause moisture condensation. This technique has been used in
climates with 12,000 degree days without pr blems.
One exception to the 1/3-2/3 rule would be in spaces with very. high indoor
relative humidity, such as swimming pool enclosures or hot-tub rooms. In those
applications, one should position the air/vapor barrier on the inner surface of
the wall.
The air/vapor barrier should never be installed on the-outside of the
insulation as in Figure 3-6c. (A possible exception is in very hot humid
climates.)
Double Vapor Barriers
There has been considerable concern re{ ently about the inadvertent
installation of a double vapor barrier on the inside and outside of walls'.in
superinsulated houses. Exterior foam sheat' ing, for example; forms a vapor-
barrier on the outside of a wall. Theoreti ally, this should cause moisture
condensation problems, but field investiga ions have shown no evidence of damage
or degradation of insulation. Although.fur her research is necessary in this
area, current thinking is that exterior fo m sheathing is an acceptable
practice. The best insurance against any mQisture problems is a carefully
installed, well sealed air/vapor barrier on the interior surface of the
insulation.
THE JOIST HEADER PROBLEM
The most troublesome spot when desigi�g and installing the air/vapor -
barrier
ir/vaporbarrier is at the floor joists. How does one make an effective airtight seal
between floors. One approach is to terminate the air/vapor barriers at the
joists, then install panels made of rigid foam insulation between all joists,
sealing the panels to the joists and floor above. When properly done, this is a
satisfactory method, but it is very time consuming. Each panel must be precut,
set in place and sealed.
T3-7 - THE FLOOR HEADER PROBLEM - NEVER!
The best method for continuing the air/vapor barrier between floors is to
wrap it around the floor headers, but it is very important to avoid runnin .the
air/vapor barrier outside the insulation. figure 3-7 shows one of the worst
mistakes that can be made in a superinsula ed house. Unfortunately, this error,
or some variation of it, is quite common and has even been shown in
superinsulation construction guides. Never do it. If the air/vapor barrier is to
run around the joists, then it must be insulated on the outside.
T3-8 - A PROPER AIR/VAPOR BARRIER INSTALLATION AT JOISTS
Figure 3-6 shows a good air/vapor design. This house has 2 x 6 walls on the
first floor and 2 x 4 standoff walls in the basement. The air/vapor barrier is
run around the joist header and is sealed tD the barrier of the walls above and
3-4
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r 32.10
U.B.C.STIINDARM 1982 E
* �:� UNIFORMBUILDINQ CODE STANDARD N0.32.10
Mc P k4r
SLATESHIN®LES
Based on Standard Specification C406-57T of the American
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Society for Testing and Materials Be!
kZ See Section 3203(c)2 and(d)3 C,Uniform Building Code
Scop
See.32.11.This standard covers natural slate shingles as commonly used ao' Scope
�rl 4�, sloping roofs and also square or rectangular tiles for flat roof coverings. Sec.
¢ Grades shingle
c See.32.1002.Three grades are covered,based on the length of service than ar+
thickne
be expected,as follows: aad spc
�D
Def nP
' SERVICE PERIOD
(Years) Sec.
v t 5!rued
Grade SI. 75 to 100 CRC
GradeSZ .................................... 40 to 75or..
lip
Grade S3 .................................... 20 to 40 tion of
71
inns ft
Physical Requirements inches
5 b. See.32.1005.The slate shall conform to the requirements for modulus of M - DIA
oz
f - sure,absorption and depth of softening prescribed in Table No.32-10-A. pamlle
.. .. Nall Holes slap
4 Y rx L S FEA
—
i � ate s ng : or scoping roo7s shall
1 be rttachme punched or drilloM . —the hi —
v�� k �� for two nails properly loco
ted for 3-inch fiend lap.
ja �,-ire-
TABLE NO.3210-4—PHYSICAL REQUIREMENTS Orin ar
DESIGNATION OF 13V ME At}300TION SOFTNENAt� FLA
ACROSS THE AR 1 a hor
tMsattMlNn t�arcenO (Mailmum tact
+ nngsa
x x Glade Si... ... 9(N%1 0M 0.002 SHI
V"Mx rz Grade SE....._... 9000 1138 0.008 SQ1
IN
Grade S3 . ... 906
0 0.45 0.014 Of IOC
weathc
Tot
3 - - whiske
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Imperfections
Sec.32.1005.(a)Curvature.The curvature of shingles shall not exceed%inchim WA
12 inches.Curved slate shall be sheared and punched so it can be laid with the t fid`
} vex sidenp. Osney
_ (b)Knots or Knttris.These terms refer to rounded defects which affea do See.
smoothness of split.They are not objectionable on the exposed portion of the to heart"
face but on usher parts they may prevent as close contact of shingles as desist npl:
Shingles having knots or knurls on the lower face or covered portions may be reg (b)t
jetted if the protuberances project more than'/„inch beyond the split surface.
Mum
(c)Ribbaas.Grades S and S shall be free from soft ribbons and Grade Ss shtl , in use.
d
be free of soft ribbons 9(;bol nail holes. iDg,ar
z� + 4 1010
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