I often hear, glass block “vents give you great air flow”, or so my customers tell me that “Joe” down the street told them.
Now I’ll be honest — if you want vents, I will sell them to you, but not because you need them and as long as we’re being honest, not because they’re beneficial.
I sell them because my competitors sell them and because some people were convinced by a friend who believes they understand everything they know about glass block windows, that they need vents. But there is one valid reason where you should put in a vent.
Building Codes Often Require Bathrooms To Have Vents
For bathroom windows, most municipal codes require you to have a vent if you do not have a ventilation fan in the bathroom.
The Great Security Myth
Vents for glass block windows are made out of vinyl — a type of plastic. Depending on the company you choose, these are either mortared, caulked or glued into your pre-fabricated glass block window. If you’re doing it for security, ask yourself what is more secure, mortar or plastic?
If you put a plastic vent into even a mortared glass block window, the weakest part will be the plastic. Once that is knocked out, the strength of the entire unit is compromised.
The cross-ventilation myth
Understand this — your vent will likely take the place of two 6 inch x 6 inch blocks. That means the opening will be 6″x12″. Realistically you lose about a half inch for the mortar and the frame tends to take up about an inch on each side so that’s 2-1/2″ lost per side to framing alone. That now means your open air space is about 4-1/2″ x 9-1/2″. For perspective of how big that is, draw out a rectangle that size on a piece of paper.
Now you have the the vent which tilts in and partially obstructs the remaining opening. Now draw a line across roughly the lower 1/3rd of the remaining opening on your piece of paper. That line should be about the width of the vent, which when opened, obscures about 1″ of visible light space.
Having done the above calculations and penciled out the diagram explained above, are you happy with that amount of ventilation?
- Yes: You’ve made an educated decision understanding the pros and the cons and putting in basement vents are likely the right decision for you.
- No: You may want to consider putting in a regular window that opens, giving you superior air flow for the space available.