Requirements for Fire and Sound Resistane: Permeance of Materials, Degree Days a
Requirements for Fire and Sound Resistane: Permeance of Materials, Degree Days and Ventilation
Topic 2 – Requirements for Fire and Sound Resistance; Permeance of Materials, Degree Days, and Ventilation
Fire Resistance
Many buildings are constructed to prevent the spread of fire from one portion of a building to the next. Walls, openings, and floor systems are designed with a specific fire rating which is designated by hours of fire resistance. The NBC specifies wall assemblies and their fire resistance ratings:
***In table <IP_ADDRESS>-A of the NBC, find the minimum assembly allowed to achieve a 1-hour fire rating in a non-loadbearing wall constructed of a single row of wood framing.
Sound Transmission Loss
Transmission loss is a term that describes the number of decibels lost as sound is transmitted through a wall or floor system. The greater the value, the more effective a structure is at reducing the amount of sound that is transmitted through it. The amount of airborne sound that is able to transmit through walls is directly affected by materials and methods the structure is composed of. When sound waves hit a structure, some of them are reflected back or absorbed into the materials. Others find their way through cracks and holes.
To quantify a structures transmission loss, a Sound Transmission Class (STC) rating is assigned. The greater the STC rating, the better a structure is at reducing sound transmission. STC ratings are given with a number value which represents the reduction in decibels. For example, a wall with an STC rating of 40 would reduce a sound from 85 decibels to 45 decibels.
The primary factors that will influence a walls STC rating is the materials it is constructed with. Construction methods such as dividing a wall into independent layers and staggering the studs will also increase its STC rating. Additional methods can also be used:
The part of the wall most likely to transmit sound is the openings. Airtight installation of windows is essential in sound control. Solid core doors equipped with gaskets at the jambs and auto-bottoms will produce a higher sound transmission loss than a hollow core door.
Vapour Permeance
Materials that are meant to restrict the transmission of water vapour are rated in terms of their permeance. The lower the perm rating of a material, the better vapour barrier it is. For example, 6 mil poly has a permeance rating of 0.06 whereas drywall with 2 coats of oil-based paint has a permeance rating of 91-172. As the 6 mil poly has a lower rating, it is a much better vapour barrier.
Degree Days
Degree days is a tabulation of data which is used to express the severity of an area’s climate. For each day that falls below 18°C, an average between the high and low is taken and the difference from 18°C is calculated and added to the total degree days for that year. For example:
Let’s say on April 8, Regina experienced a high of 15°C and a low of 3°C. The average temperature for that day would be = 9°. If we w