Section 408.30420. Ventilation.

 Sections 1203.1, 1203.2 and 1607.1 are amended and 1203.2.2 and table

1203.2.2 are added to the code to read as follows:

                             General. Buildings shall be provided with natural ventilation in accordance with section 1203.4 or with mechanical ventilation in accordance with the Michigan mechanical code.

                               Attic spaces. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each separate space by ventilation openings protected against the entrance of rain and snow. Blocking and bridging shall be arranged so as not to interfere with the movement of air. An airspace of not less than 1 inch (25 mm) shall be provided between the insulation and the roof sheathing. The net free ventilating area shall not be less than 1/150 of the area of the space ventilated.

Exceptions:

1.    The net free cross-ventilation area may be reduced to 1/300 provided that not less than 50% and not more than 80% of the required ventilating area provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet (914 mm) above eave or cornice vents with the balance of the required ventilation provided by eave or cornice vents.

2.    The net free cross-ventilation area may be reduced to 1/300 where a

Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.

3.      Attic ventilation shall not be required when in climate zones 5A through 7, as defined in chapter 13, sufficient insulation is installed to maintain the monthly average temperature of the condensing surface above 45 degrees Fahrenheit (7 degrees Celsius). The condensing surface is defined as either the structural roof deck or the interior surface of an air-impermeable insulation applied in direct contact with the underside or interior of the structural roof deck. For calculation purposes, an interior temperature of 68 degrees Fahrenheit (20 degrees Celsius) is assumed. The exterior temperature is assumed to be the monthly average outside temperature, or when the conditions outlined in section

              are met.

1203.2.2 Unvented attic and unvented enclosed rafter assemblies. Unvented attic assemblies (spaces between the ceiling joists of the top story and the roof rafters) and unvented enclosed rafter assemblies (spaces between ceilings that are applied directly to the underside of roof framing members [rafters] and the structural roof sheathing at the top of the roof framing members [rafters]) shall be permitted if all the following conditions are met:

1.       The unvented attic space is completely contained within the building thermal envelope.

2.     No interior Class I vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed rafter assembly.

3.     Where wood shingles or shakes are used, a minimum ¼-inch (6 mm) vented air space separates the shingles or shakes and the roofing underlayment above the structural sheathing.

4.    In climate zones 5A, 6A, and 7, any air-impermeable insulation shall be a class II vapor retarder, or shall have a class III vapor coating or covering in direct contact with the underside of the insulation.

5.    Either items 5.1, 5.2, or 5.3 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing.

5.1.     Air-impermeable insulation only. Insulation shall be applied in direct contact with the underside of the structural roof sheathing.

5.2.       Air-permeable insulation only. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing as specified in table 1203.2.2 for condensation control.

5.3.    Air-impermeable and air-permeable insulation. The air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing as specified in Table 1203.2.2 for condensation control. The air-permeable insulation shall be installed directly under the air-impermeable insulation.

5.4       Where preformed insulation board is used as the air-impermeable insulation layer, it shall be sealed at the perimeter of each individual sheet interior surface to form a continuous layer.

Table 1203.2.2

INSULATION FOR CONDENSATION CONTROL

a. 

CLIMATE ZONE	MINIMUM RIGID BOARD ON AIR- IMPERMEABLE INSULATION R-VALUESa
5A	R-20
6A	R-25
7	R-30

 

 

Contributes to but does not supersede the requirements in chapter

13

TABLE 1607.1

MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS, Lo, AND MINIMUM CONCENTRATED LIVE LOADSg

Occupancy or use	Uniform (psf)	CONCENTRATED (lbs.)
1.  Apartments (see residential)	−	−
2.  Access floor systems Office use Computer use	50 100	2,000 2,000
3. Armories and drill rooms	150m	−
4.  Assembly areas Fixed seats (fastened to floor)	60m

Follow spot, projections and control rooms Lobbies Movable seats Stage floors Platforms (assembly) Other assembly areas	50 100m 100m 150m 100m 100m	−
5.  Balconies and decksh	Same as occupancy served	−
6.  Catwalks	40	300
7. Cornices	60	−
8.  Corridors First floor Other floors	100 Same as occupancy served except as indicated	−
9.  Dining rooms and restaurants	100m	−
10.  Dwellings (see residential)	−	−
11.  Elevator machine room grating (on area of 2 inches by 2 inches)	−	300
12.  Finish light floor plate construction (on area of 1 inch by 1 inch)	−	200
13.  Fire escapes	100	−
On single-family only	40
14. Garages (passenger vehicles only) Trucks and buses	40m                                           Note a See Section 1607.7
15.  Handrails, guards and grab bars	See Section 1607.8
16. Helipads	See Section 1607.6
17.  Hospitals	80	1,000
Corridors above first floor
Operating rooms, laboratories	60	1,000
Patient rooms	40	1,000
18.  Hotels (see residential)	−	−
19.  Libraries Corridors above first floor Reading rooms Stack rooms	80 60 150b, m	1,000 1,000 1,000
20.  Manufacturing Heavy Light	250m 125m	3,000 2,000
21.  Marquees	75	−
22.  Office buildings Corridors above first floor File and computer rooms shall be designed for heavier loads based on anticipated occupancy	80    −	2,000    −

Lobbies and first-floor corridors Offices	100 50	2,000 2,000
23. Penal institutions Cell blocks Corridors	40 100	−
24.  Recreational uses: Bowling alleys, poolrooms and similar uses Dance halls and ballrooms Gymnasiums Reviewing stands, grandstands and bleachers Stadiums and arenas with fixed seats (fastened to floor)	75m 100m 100m 100c, m 60c, m	−
25.  Residential One- and two-family dwellings Uninhabitable attics without storagei Uninhabitable attics with storagej, k Habitable attics and sleeping areask All other areas Hotels and multifamily dwellings Private rooms and corridors serving them Public roomsm and corridors serving them	10 20 30 40     40   100	−
26. Roofs All roof surfaces subject to main- tenance workers Awnings and canopies: Fabric construction supported by a skeleton structure All other construction Ordinary flat, pitched, and curved roofs (that are not occupiable) Where primary roof members are exposed to a work floor, at single panel point of lower chord of roof trusses or any point along primary structural members supporting roofs: Over manufacturing, storage ware- houses, and repair garages All other primary roof members Occupiable roofs: Roof gardens	5 nonreducible 20 20                        100	300                              2,000 300

Assembly areas All other similar areas	100m Note 1	Note 1
27.  Schools	40	1,000
Classrooms
Corridors above first floor	80	1,000
First-floor corridors	100	1,000
28. Scuttles, skylight ribs and accessible ceilings	−	200
29.  Sidewalks, vehicular drive ways and yards, subject to trucking	250d, m	8,000c
30.  Stairs and exits	40	300f
One- and two-family dwellings
All other	100	300f
31.  Storage warehouses (shall be designed for heavier loads if required for anticipated storage) Heavy Light	250m 125m	−
32. Stores Retail First floor Upper floors Wholesale, all floors	100 75 125m	1,000 1,000 1,000
33.  Vehicle barriers	See Section 1607.8.3
34.  Walkways and elevated platforms (other than exitways)	60	−
35.  Yards and terraces, pedestrians	100m	−

 

 

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2,

1 square foot = 0.0929 m2,

1 pound per square foot = 0.0479 kN/m2, 1 pound = 0.004448 kN, 1 pound per cubic foot = 16 kg/m3.

a.     Floors in garages or portions of buildings used for the storage of motor vehicles shall be designed for the uniformly distributed live loads of Table 1607.1 or the following concentrated loads: (1) for garages restricted to passenger vehicles accommodating not  more than nine passengers, 3,000 pounds acting on an area of 4.5 inches by 4.5 inches; (2) for mechanical parking structures without slab or deck that are used for

storing passenger vehicles only, 2,250 pounds per wheel.

b.    The loading applies to stack room floors that support nonmobile, double-faced library book stacks, subject to the following limitations:

1.   The nominal bookstack unit height shall not exceed 90 inches;

2.    The nominal shelf depth shall not exceed 12 inches for each face; and

3.   Parallel rows of double-faced book stacks shall be separated by aisles not less than 36 inches wide.

c.    Design in accordance with ICC 300.

d.    Other uniform loads in accordance with an approved method containing provisions

for truck loadings shall also be considered where appropriate.

e.    The concentrated wheel load shall be applied on an area of 4.5 inches by 4.5 inches.

f.    The minimum concentrated load on stair treads shall be applied on an area of 2 inches by       2 inches.   This load need not be assumed to act concurrently with the uniform load.

g.    Where snow loads occur that are in excess of the design conditions, the structure

shall be designed to support the loads due to the increased loads caused by drift buildup or a snow design determined by the building official (see Section 1608).

h.    See Section 1604.8.3 for decks attached to exterior walls.

i.     This live load need not be assumed to act concurrently with any other live load requirements.

j.     The live load need only be applied to those portions of the joists or truss bottom chords where both of the following conditions are met:

i. The attic area is accessible from an opening not less than 20 inches in width by 30 inches in length that is located where the clear height in the attic is a minimum of 30 inches; and

ii.     The slopes of the joists or truss bottom chords are no greater than two units vertical in 12        units horizontal.

The remaining portions of the joists or truss bottom chords shall be designed for uniformly distributed concurrent live load of not less than 10 lb./ft2.

k.Attic spaces served by stairways other than the pull-down type shall be designed to support the minimum live load specified for habitable attics and sleeping rooms.

l.     Areas of occupiable roofs, other than roof gardens and assembly areas, shall be designed  for appropriate loads as approved by the building official.                    Unoccupied

landscaped areas of roofs shall be designed in accordance with Section 1607.12.3.

m. Live load reduction is not permitted unless specific exceptions of Section 1607.10 apply.

History: 1979 AC; 1981 AACS; 2010 AACS; 2014 AACS.