Your insulation is rotting. You just can't see it.

We pulled the insulation out of a home in Onetangi last month.

What came out looked nothing like what went in.

The batts were compressed, discoloured, and damp to the touch. Under the floor doing almost nothing while the owners wondered why their power bills kept climbing and their home felt cold.

We see this problem endlessly on Waiheke Island. New build or retrofit fiberglass insulation that looks great in a pamphlet but looks terrible in a house within five years, if that. Sagging, compressed, damp and never drying out. Simply not the suitable solution to our coastal and often humid and damp conditions.

What fiberglass actually does when it gets wet

Fiberglass insulation works by trapping millions of tiny air pockets between glass fibres. That trapped air is what slows heat transfer, that is: its slows how fast your house gets cold in winter. Kind of like your insulated water bottle or insulated coffee thermos.

When moisture gets in (and on Waiheke, moisture always seems gets in) those air pockets collapse. The batt collapses, and/or breaks apart. Water is not a good insulator, nor is it being trapped good for your home.

We're not just talking about floods either, the humidity that rolls in off the Hauraki Gulf every single day. That salt breaze, humid summer days, damp winter mornings. A lot of homes on Waiheke lack the ability to ventilate that damp out, which is an other problem. While the home waits to dry in the meantime, those batts are being given a beating and they might not bounce back.

The sagging problem nobody talks about

Even in drier conditions, fiberglass has a structural integrity problem. Over time, gravity wins. The batts compress and sag downward, leaving gaps at the top of the wall cavity, uninsulated cold spots that act like open windows to the outside air.

You can't see this happening, the wall looks fine. The insulation is technically still there but the warmth is escaping through gaps you don't even know exist.

Under the floor this is even worse. Batts quickly sag over strapping, break apart in the slightest breeze, and end up littering the crawl space with what remains of them. Very soon a "insulated" underfloor is a fluffy itchy mess.

If your home is more than 8–10 years old and has fiberglass insulation, there's a very good chance this is already happening.

Why we use polyester, and why it's a better fit for this island

Polyester insulation doesn't trap air the same way fiberglass does, it holds its structure.

The fibres don't compress when wet, they don't sag over time. Heck I've pulled a polyester batt out of a wall after 15 years and it looks like the day it went in. Maybe a little dirty but besides that still bouncy as ever!

For homes on Waiheke, the endurance of all building products makes all the difference.

But there's another (controversial) reason we recommend it, especially to families with young children or health-conscious homeowners: polyester contains significantly fewer additives than other insulation products. No binders, no resins, no chemical treatments. Just heat.

Yes its a plastic product, but as my health conscious friends tell me: the less numbers and letters on the ingredient list: the better!

Island homes need island thinking

Waiheke isn't like everywhere else: The lifestyle is different, the architecture is different, and the climate is different.

Our homes deal with conditions that a lot of spec builds don't anticipate. The damp valleys, the coastal sea air, the overflowing gutters, the funky soil. We need tailored solutions, not one size fits all.

We're not saying fiberglass is always bad. In a dry, well-ventilated, controlled environment it performs adequately.

But that's not what we get a lot of the time on Waiheke. And if you've never had someone pull back your wall lining and actually look at the state of your insulation, there's a decent chance you're living in a home that's working much harder than it should be to keep you warm.

We are passionate about getting it right, and improving our methods and the advice we give. We'd love to have a chat about how we can help improve your plans for your property!