Ready your envelope – Part 1 is an overview of the role of a tight building envelope.
Finally, let’s consider pressure differences.
Why it matters: With pressure differences, air and everything it carries (heat, moisture, contaminants) is moving from higher pressure to the lower pressure.
- Tighter buildings resist the movement because air leakage requires a pressure difference AND a pathway (like an actual hole or an unsealed penetration).
📢 Repeat after me for review
👉 Hot moves to cold
👉 Wet moves to dry
👉 High pressure moves to low pressure
🔬 Zoom in: 3 factors can create pressure differences —> wind, stack effect and mechanical systems (like your HVAC or large vent hood)
⛏️ Dig deeper with this great explainer by Dr. Allison Bailes.
Here’s one example you might relate to:
If you have a bedroom door that tends to close when your AC kicks on, the AC is creating negative pressure in that room.
- The attic above that bedroom is now at a higher pressure —> and the air, moisture and pollutants in the attic will try to move into the bedroom through any leaks. 😬
✅ For your Smart Homeowner list
- Start observing your home with this idea in mind.
- Do you feel cold drafts in the winter?
- If you have a two-story house, is your second story always hotter in the summer?