Case Study: Floor Insulation for Antoinette – How We Solved a Sagging Floor

When Antoinette called us at RH Insulation, she was worried about her floor. She told us the floor under the window near the outside wall felt like it was sagging, and there was a “give” under her feet. She asked us to come take a look and figure out what was happening.

Our First Look

As soon as we arrived, we knew there was a problem. When we removed the skirting board, we could see the floor had a lot more movement than it should. Antoinette agreed to let us take up a section of the laminate floor, as well as the plywood underneath, so we could inspect the joists supporting the floor.

That’s when we found the real issue, the support joist had completely rotted away. Even though these joists were only installed four years earlier, they were already ruined.

The old contractor hadn’t used treated wood or any wood preservative, and, to make things worse, they’d blocked up the air vent. This trapped all the damp, moist air under the floor and allowed Wet Rot to eat right through the joists.

The manufacturing stamp on the wood showed they were just four years old.  The damp smell was awful.

Our Plan of Action

We explained everything we found to Antoinette and her family. She wanted a safe, lasting solution, not a quick fix. Here’s what we did:

1. First, we removed all the old, weak joists. The room had a low tassel wall as support, but it had no breaks for airflow, which was part of the problem in the first place. So, we took down the wall so air could move freely under the floor.
2. Airflow is really important for stopping wet and dry rot. Instead of blocking the air, which leads to problems, we isolated the living area using special breathable damp-proof membranes, breathable insulation, and breathable airtight membranes. This keeps the room comfortable while letting the space underneath “breathe.”
3. We upgraded the joists to much stronger 9” by 2” timber, Hung these with special joist hangers so they wouldn’t just sit on a wood wall-plate and risk more problems later.
4. We added another vent at the side of the house to allow air to cross under the floor, making sure moisture couldn’t get trapped again.
5. We carefully unblocked the old vent and, since it was between the joists, made a special duct to make sure air could get beneath the floor as it should.
6. Antoinette wanted to keep her old laminate floor because it ran through both the sitting room and the living room, giving a nice open feel. We took time to number every single board, cut them out one at a time, and stored them safely until our work was done.
7. When putting the floor back down, we had to start from the opposite side of the room and carefully stitch the boards back into the existing floor. It took time and patience, but the end result was a floor that looked just like it did before we started—only now it was safe and solid.