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Condensation & Ventilation
Condensation
Condensation occurs when warm moist air contacts cold surfaces. The amount of condensation depends on temperature differences and dew point.Warm air has the ability to hold more moisture than cold air. When this warmer air contacts cold surfaces in your pole barn, condensation forms since the air loses its ability to retain as much moisture.
A literal example of this is that 45° air can hold 1/3 the water vapor that 75° air can. Condensation problems are more extreme in areas where temperatures frequently drop to 35° and lower for long periods.
Everyone has heard of relative humidity. If its 70° outside and the relative humidity is 50%, that means that the air contains 50% of the moisture it can hold (at that temperature).
Condensation Control
Vapor barriers are used to resist vapor penetration from the moisture source. Insulation, a vapor barrier, and proper ventilation are all crucial elements of condensation control, especially in areas where condensation problems are prevalent.Vapor barriers are installed on the warm side of the insulation. In most locations this is the inside surface of the insulation. Some southern areas with hot humid climates install the vapor barrier on the outside surface of the insulation.
Vapor barriers are really only vapor retarding materials. Vapor pressure is what drives water vapor through a vapor barrier. Vapor pressure changes with temperature and humidity.
If vapor pressure gets too high in your barn any vapor barrier will cease to work, regardless of the material used or how carefully you seal it up. (See comments about pouring your slab after your building is finished below). That is why it takes a combination of insulation, ventilation, and vapor barriers to properly solve difficult condensation problems.
The facing material of vapor barriers are rated using a scale called 'perm'. The lower perm value means a better vapor barrier facing. Any facing material with a perm greater than 1.0 is not considered a vapor barrier. As an example, FSK (foil/scrim/kraft) has a perm rating of 0.02
Ventilation
Ventilation is a necessary ingredient to aid in condensation control. The amount of ventilation required varies based upon the utilization of the building.For farm buildings, ventilation helps keep odor to a minimum and removes carbon dioxide for optimum animal health. Since a single dairy cow can produce 11.5 pounds of water vapor per day exhaust type ventilation is necessary for control of their environment.
Typical garages can get by with vented soffit and vented ridge in most applications. Many soffit vents are combo units consisting of alternating solid and vented pieces which provide much less air flow than fully vented soffit does.
The airflow of ridge vents are not created equal either. Econo-vents flow much less air than their more expensive counterparts. So, vented soffit and vented ridge are not all created equal.
Man Made Condensation Problems
It is common practice to pour a slab after a pole barn is erected using the grade boards as forms. In the winter months propane fired heaters are used to heat the building to provide an adequate environment to cure the concrete.This creates enough water vapor to penetrate any vapor barrier and create condensation problems for even a properly installed and ventilated pole barn. Once this condition occurs it takes months to evaporate the water out of the building. The migration of this water vapor through the vapor barrier will soak your insulation and ruin it forever. Here are some facts:
• Compressed Insulation Loses R Value
• Wet Insulation Permanently Loses R Value
• Insulation Requires Air Gaps From Adjacent Materials
• Condensation Creates Mold & Damages Building Materials
How Often Does Your Region Reach Dew Point?
Dew point Temperature Table
|
Relative Humidity %
|
|||||||||||||||||||
|
0
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
50
|
55
|
60
|
65
|
70
|
75
|
80
|
85
|
90
|
95
|
|
|
5
|
|||||||||||||||||||
|
10
|
9
|
9
|
|||||||||||||||||
|
15
|
9
|
9
|
9
|
12
|
12
|
15
|
|||||||||||||
|
20
|
9
|
9
|
12
|
12
|
15
|
15
|
17
|
17
|
20
|
||||||||||
|
25
|
9
|
12
|
12
|
15
|
15
|
17
|
20
|
20
|
22
|
23
|
23
|
||||||||
|
30
|
9
|
12
|
12
|
15
|
17
|
20
|
22
|
23
|
23
|
25
|
27
|
28
|
29
|
||||||
|
35
|
9
|
12
|
15
|
17
|
20
|
22
|
23
|
25
|
27
|
28
|
29
|
31
|
32
|
33
|
|||||
|
40
|
9
|
12
|
17
|
20
|
22
|
23
|
27
|
28
|
29
|
31
|
33
|
35
|
36
|
37
|
39
|
||||
|
45
|
9
|
15
|
17
|
22
|
23
|
27
|
28
|
31
|
32
|
35
|
36
|
38
|
39
|
41
|
42
|
44
|
|||
|
50
|
12
|
17
|
22
|
25
|
28
|
29
|
32
|
35
|
37
|
39
|
40
|
42
|
44
|
46
|
48
|
48
|
|||
|
° F
|
55
|
12
|
17
|
22
|
25
|
28
|
31
|
35
|
37
|
39
|
41
|
43
|
46
|
48
|
49
|
51
|
52
|
53
|
|
|
60
|
15
|
20
|
25
|
29
|
32
|
36
|
38
|
41
|
44
|
46
|
48
|
51
|
52
|
54
|
55
|
57
|
59
|
||
|
65
|
9
|
17
|
23
|
29
|
33
|
37
|
40
|
43
|
46
|
48
|
51
|
53
|
55
|
57
|
59
|
60
|
62
|
63
|
|
|
70
|
12
|
22
|
25
|
32
|
37
|
41
|
45
|
48
|
51
|
53
|
55
|
58
|
60
|
61
|
63
|
65
|
67
|
68
|
|
|
75
|
17
|
25
|
32
|
37
|
41
|
46
|
49
|
52
|
55
|
58
|
60
|
62
|
64
|
67
|
68
|
70
|
72
|
73
|
|
|
80
|
20
|
25
|
36
|
41
|
46
|
50
|
53
|
56
|
60
|
62
|
65
|
67
|
69
|
71
|
73
|
75
|
77
|
78
|
|
|
85
|
23
|
32
|
39
|
45
|
50
|
55
|
58
|
61
|
64
|
67
|
70
|
72
|
74
|
76
|
78
|
80
|
82
|
83
|
|
|
90
|
27
|
36
|
43
|
50
|
55
|
59
|
62
|
66
|
69
|
72
|
74
|
77
|
79
|
81
|
83
|
85
|
87
|
88
|
|
|
95
|
31
|
40
|
48
|
54
|
59
|
63
|
67
|
70
|
73
|
76
|
79
|
81
|
84
|
86
|
88
|
90
|
92
|
93
|
|
|
100
|
33
|
44
|
52
|
58
|
63
|
68
|
71
|
75
|
78
|
81
|
84
|
86
|
88
|
91
|
93
|
94
|
96
|
98
|
|
|
105
|
37
|
48
|
56
|
62
|
67
|
72
|
76
|
79
|
83
|
86
|
88
|
91
|
93
|
95
|
89
|
100
|
102
|
103
|
|
|
110
|
41
|
52
|
60
|
66
|
72
|
76
|
80
|
84
|
87
|
90
|
93
|
95
|
98
|
100
|
102
|
104
|
106
|
108
|
|
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