Insulation and Thermal Bridging

Look closely at this picture. Do you know what caused the ‘stripes’? 
The building trade is full of exciting experiences such as watching paint dry, reading the Building Code, and talking about insulation. Flash new bathrooms and kitchens are much more exciting to consider when planning a renovation, but the choice to add insulation could serve you after the latest trends in cooking and bathing areas have passed. Fashions come and go, but human comfort is constant.
For most of the last half century, New Zealanders have looked at renovation as a way to improve the look of their homes rather than to enhance energy performance. While that perspective is slowly changing, there has been a renewed push for warmer, dryer homes from various health agencies. When compared against the costs of health care and lost productivity, the price of insulation is often considered low. This is why Sharon Duff at the WRPHO is doing great work acquiring funds for insulating ceilings and floors across our region.
Yet in many Kiwi’s minds, it’s still hard to justify spending part of a renovation budget on something stuffed in walls and ceilings that is rarely, if ever, seen. That notion of invisibility, however, is only skin deep. Let me explain.
Take our insulated walls. Well, please don’t actually take them, we’re using them at the moment. I’ll rephrase that: Take a look at the picture of one of our insulated walls. Notice anything that slightly resembles a wonky gridiron field?
Dry areas are where the studs are. 
If I have done my job as an amateur photographer, you’ll see a series of alternating vertical wet and dry ‘stripes’. No, the photo is not altered, nor did I take a rag to the wall. The pattern is the result of a phenomenon called “thermal bridging.” Where the wall is dry, heat from our home is conducting through the timber studs, and where the wall is wet, insulation between the studs has slowed the flow of heat. The studs act as “bridges” because they convey heat across the wall faster than the insulation. What seemed invisible becomes visible on a cool, winter morning.
Thermal bridging also occurs when insulation is placed between ceiling joists, as is normally done. As an alternative, we installed our ceiling batts across (perpendicular to) the joists. We also chose a thicker batt (higher R-value) than required by code. The combination of a thicker batt installed across the joists has resulted in a high performance ceiling at little additional cost.
Rafter to rafter insulation prevents thermal bridging. 
This strategy runs to the core of eco-thrifty design thinking: spend a little and save a lot. Regular readers of this column will know I emphasize the concept of payback period: the amount of time it takes energy savings to pay for the additional installation costs. We embrace payback periods of one to ten years, which represent 7% to 100% annual return. What bank is offering those terms at the moment?
Our money is, quite literally, earning us more stuffed in the walls and ceiling than in any bank in the country.
Want to learn more?
• Warm, Dry, Healthy Homes. Monday, 2nd September, 5:30-6:30 pm. Gonville Café Library, Abbot St. Wanganui. Free
• Understanding Your Power Bill. Tuesday, 3rd September, 5:30-6:30 pm. Gonville Café Library, Abbot St. Wanganui. Free
• Ask a Solar Question. Thursday, 5th September, 7-9 pm. Quaker Meeting House. 256 Wicksteed St. Wanganui. $20. Registration essential. Ring CES – 345 4717

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